Chapter 3 – Factors Influencing Ecosystem Integrity · the landscape and modifies its character....

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Chapter 3

Chapter 3 – Factors InfluencingEcosystem Integrity

Ecosystems are not defined so much by the objects they contain as bythe processes that regulate them.

— Christensen et al. 1989

Key Questions• What are the primary natural

processes and human activities thatdrive change in the composition,structure, and extent of southernCalifornia mountain and foothillecosystems?

• How are those processes andactivities currently affecting thelandscape and what can bedetermined regarding the naturalrange of variability?

• What current trends are apparent andwhat threats or opportunities arepresented by them?

This chapter considers the primary pro-cesses and activities that modify ecologicalcommunities in the mountains and foothills.These include (1) natural disturbance pro-cesses such as fire, flood, drought, andoutbreaks of insects or disease; (2) human usesof the land for development, resources, andrecreation; and (3) the spread (often uninten-tionally) of new elements such as air pollutionand non-native plants and animals.

Each of these “change agents” acts uponthe landscape and modifies its character. Topersist over time, plant and animal speciesmust continually be able to survive, reproduce,or recolonize as the landscape changes. Thusthe disturbance processes that shape local eco-systems are as important to understand as thephysical components of those ecosystems.

Since disturbance and climatic variabilityare inherent components of natural systems,all species have adaptations to survive in achanging world. Yet, their ability to respond

to change is not limitless and some organismsare clearly more adaptable than others. In gen-eral, the complete assemblage of native plantsand animals is most likely to be maintainedwhen environmental conditions remain withintheir natural historic range. Thus we need todevelop an understanding of what the historicor natural ranges of variability are for variousecological processes. These serve as the refer-ence conditions to which present dayconditions can be compared. The closer cur-rent conditions are to reference conditions, thegreater our confidence that all the ecologicalcomponents will continue to persist (for de-tailed description of the “reference variability”concept see Manley et al. 1995). This is thebasis for the “coarse-filter” approach to con-servation described in chapter 2.

In our analysis, we first asked the assess-ment task group to identify and describe thekey interactions between landscape elementsand the change agents (e.g., ecological pro-cesses or human activities) currently shapingthem. Then we examined those interactions,using the best available information on refer-ence conditions to assess how today’s dynamicscompare with the historic range of variability.Of particular interest is how the current man-agement of natural processes (e.g., firesuppression or streamflow regulation) has af-fected the species and habitats that evolvedunder the influence of those processes.

The element/process interactions identi-fied by the assessment task group aresummarized in the following sections. A sepa-rate matrix was developed for each of the sixlarge-scale vegetation mosaics described in

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chapter 2. The matrices were used to clarifythe effects of different activities and prioritizethose having the biggest impact on speciesconservation and ecosystem integrity. We be-lieve this information will be useful when thetime comes to formally describe desired con-ditions and management priorities. Whatfollows is a description of the primary changeagents and how they influence ecosystems.

The Influence of FireExperience has taught us that we cannotprevent fire. In my opinion, it is better tohave a fire every year, which burns off a ...small area, than to go several years ... andhave a big one denuding the whole watershedat once.

— William Mulholland, 1908

Fire is a primary agent of change in veg-etation patterns across the southern Californialandscape. The distribution, composition, andstructure of almost all plant communities inthis region are influenced by fire, and as thequote above illustrates, prominent southernCalifornians have long recognized its impor-tance and offered opinions on how it shouldbe managed.

The significance of fire in shaping south-ern California wildlands is reflected in a largebody of scientific research on the subject. It isnot by coincidence that the Forest Service re-search station in southern California is theForest Fire Laboratory and, as the name im-plies, is largely devoted to fire research. Yet,even with the extensive scientific attentiongiven this subject there are widely divergentopinions among researchers regarding historicpatterns of fire frequency, size, and intensity(Zedler 1995). This uncertainty can largely beattributed to the inherent difficulties associ-ated with studying a phenomenon that affectslarge areas, recurs sporadically over time in-tervals that range from a few years to severalhundred, and whose individual events varywidely in extent and severity.

Fire history information provides valuableinsights, but the sources suffer from being (1)

anecdotal (e.g., accounts of a few early inhab-itants); (2) incomplete and less reliable thefurther back in time you go (e.g., officialrecords of past fires); or (3) based on indirectinformation that is subject to varying inter-pretations (e.g., fire scar analyses, vegetationpatterns observed in old aerial photographs,and patterns observed in nearby areas wherefire suppression is less of a factor). Unfortu-nately, this body of evidence does not provideclear, unequivocal answers; thus, there will al-ways be different interpretations of how thingsused to be.

In this assessment we examined varioustheories and supporting evidence on howtoday’s fire regime may differ from historicconditions and what is relevant about thosechanges. We focused primarily on factors in-fluencing the persistence of native ecologicalcommunities and how today’s conditions com-pare with what is known about the naturalrange of variability. In this section we presentsome of the local fire history data, describekey concerns, and try to identify where thereis strong scientific consensus and where thereis not.

Has the Fire Regime Changed?There is little argument that the fire re-

gime in southern California has changed ashuman populations have grown and fire sup-pression practices have become increasinglyeffective. Even assuming that Native Ameri-cans actively burned, there are many moreignitions today with the combination of hu-man- and lightning-caused starts, and thoseignitions are more concentrated along the in-terface between urban development andwildlands. However, most of those ignitionsare quickly suppressed unless conditions areconducive for rapid fire spread. Most acres nowburn in human-caused fires (Davis andMichaelsen 1995; Conard and Weise 1998),presumably because these fires can arise at anytime and thus have the greatest chance of ig-niting vegetation during key periods whenconditions are prime for fire spread (e.g., dur-ing extended heat waves or when “Santa Ana”

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Chapter 3or “sundowner” conditions bring high tem-peratures, ultra-low humidity, and high winds).

It is reported that 10 percent of the firesin southern California wildlands account forover 75 percent of the area burned (Strauss etal. 1989; Keeley et al. 1999). Thus, most ar-eas currently burn in large fires. It is unclearwhether this is a natural, historic pattern oran artifact of fire suppression. Keeley et al.(1999) analyzed fire history records and foundthat this pattern dates back to at least 1910.However, we have no way of knowing if it wasthe pattern prior to the arrival of Europeans.

Most of the vegetation that burns in south-ern California is chaparral, which is wellknown for its tendency to go from being dif-ficult to burn under moderate conditions toexploding into a fire storm under extreme con-ditions (P.H. Zedler, Univ. of Wisconsin, inlitt. 1998). Thus, chaparral has characteristicsthat make it naturally susceptible to large fires.However, it also seems evident that fires intoday’s environment are able to grow signifi-cantly in size only when weather and fuelmoisture conditions are severe enough to limitthe effectiveness of suppression actions. A re-sulting hypothesis is that active suppressionhas changed the fire regime such that fires arenow less frequent but likely to be larger in sizeand more severe in intensity.

Support for this hypothesis is found incomparisons of fire patterns in southern Cali-fornia with those in northern Baja California,Mexico, where fires are generally not sup-pressed (Minnich 1983; Chou et al. 1993).In a detailed comparison of 1920 to 1970 firepatterns in San Diego County and northernBaja based on examination of aerial photo-graphs, Minnich (1989) found a similarnumber of acres burned, but the fires in SanDiego County were significantly fewer andlarger. The vegetation patterns on each side ofthe border were strikingly different, with chap-arral habitats in northern Baja exhibiting amuch more diverse and fine-grained age-classmosaic (Minnich 1989). Minnich attributedthis difference primarily to fire suppression northof the border and lack of suppression south of it.

Studies looking solely at southern Califor-nia fire history records do not support thehypothesis that fires have become fewer andlarger. Using fire perimeter maps that extendback roughly ninety years, Conard and Weise(1998), Weise et al. (in press), and Keeley etal. (1999) did not find statistically significantincreases in average fire size over the recordedtime period. Keeley et al. (1999) also foundthat most southern California counties havehad a statistically significant increase in thenumber of reported fires per decade. Theseauthors conclude that large fires, usuallyfanned by fall Santa Ana weather conditions,have always been a dominant component ofsouthern California’s fire regime and this hasnot been changed by fire suppression activi-ties. Moritz (1997) came to a similarconclusion in a statistical analysis of Los Pa-dres National Forest fire history data, but hedid detect a significant decline in the frequencyof small fires. It is suggested that suppressonmay actually be helping maintain somethingapproximating the historic fire regime by neu-tralizing the large increase in human-causedignitions (Conard and Weise 1998; Keeley etal. 1999).

It is likely that these differing findings andinterpretations each have some merit. It is un-doubtedly true that large fires occurredhistorically; there is evidence of such fires inold charcoal deposits (Byrne et al. 1977), andthe combination of extensive chaparral veg-etation and extreme southern Californiaweather conditions is conducive to suchevents. It also seems highly probable that firesuppression has helped offset the impact of alarge increase in the number of fire ignitions.But there is also compelling evidence that sup-pression effectively narrows the range ofconditions under which fires are allowed toconsume vegetation and that the direction ofthis narrowing is likely to result in an increasein the proportion of high-severity fires. Dem-onstrating such a change is difficult becausethere is little quantitative information on theseverity or intensity of historic fires.

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Fire Issues in Foothill HabitatsThere are two primary concerns regard-

ing the current fire regime’s effect on foothillhabitats. First, overly frequent fires in coastalsage and buckwheat scrub can result in thedegradation of these habitat types. Short in-tervals between fires (i.e., less than ten years)can lead to pronounced declines in shrub coverand concurrent increases in herbaceous cover,particularly non-native annual grasses(O’Leary 1990; Zedler et al. 1983). This tendsto be a self-perpetuating shift, because denseannual grass cover hinders shrub re-establish-ment (Minnich and Dezzani 1998) andincreases the habitat’s flammability, making itmore prone to frequent fires (D’Antonio andVitousek 1992). Degradation of coastal sageand buckwheat scrub has been widespreadin the “front country” foothills where firesalong the urban interface have been frequent(table 3.2).

There is particular concern about the deg-radation of coastal sage scrub because its extenthas already declined by almost 80 percent dueto development in the coastal basins and it isthe primary habitat for the California gnat-catcher and other imperiled species (Westman1981; Davis et al. 1994; Beyers and Wirtz

Historically, fires appear to have burnedunder a wide range of environmental condi-tions, exhibiting erratic smolder-and-runbehavior patterns as weather and fuel condi-tions changed. Unsuppressed, some fireswould continue for months until extinguishedby rain or lack of fuel. The landscape wouldexperience smoldering burns, punctuated of-ten by short-duration, high-intensityafternoon runs and occasionally by large con-flagrations (Minnich 1987b; Minnich 1988).Today (and for at least the last fifty years),smoldering fires are actively suppressed andmost are quickly extinguished, thereby signifi-cantly reducing opportunities forshort-duration runs. Thus, by effectively re-ducing the other burn patterns, suppressionhas seemingly increased the likelihood thatwhen an area burns, it will do so in a rela-tively fast-moving, high-severity fire.

There does not appear to be much changein the average return interval of chaparral fires.There is general consensus among experts that(1) natural fire-return intervals in chaparralwere probably in the range of fifty to eightyyears and (2) current fire-return patterns inchaparral appear to be either within or nearthis range across most of the landscape(Minnich 1995; Zedler 1995; Conard andWeise 1998). Fire frequency appears to havesignificantly increased only in ignition-proneareas near the urban interface, usually wherethere are high proportions of scrub (i.e., thin-stemmed, semi-woody shrubs) and grassvegetation that facilitate rapid fire spread (fig3.1).

It is in montane conifer forests where thedisappearence of smolder-and-run fires ap-pears to have markedly decreased firefrequency. Fire-scar studies suggest that un-derstory fires were historically common inconifer forests, with average return intervalsof fifteen to thirty years (McBride and Lavin1976). However, over the last seventy years,fires have been rare in southern Californiamontane conifer forests, particularly in inte-rior forest habitats away from the chaparralinterface (fig 3.1). This is probably due to a

high level of suppression effectiveness in theconifer belt. Ignitions in the forest are notprone to rapid fire spread and thus are quicklyextinguished. In addition, firefighters havebeen largely effective at keeping fires that comeup out of the chaparral from moving into themontane conifer forest interior.

It is important to understand how the fireregime has changed and how those changesare affecting ecological communities. Yet, indensely populated southern California thereis little likelihood that we can adopt a policywhere wildfires are allowed to smolder and runat will. There are too many lives, structures,and resources that would be put at risk by sucha strategy. Consequently, we are better servedby focusing our attention on specific key is-sues pertaining to fire’s effect on the biota(table 3.1) and exploring the range of optionsavailable for addressing those specific issues.

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Chapter 3

Figure 3.1. Fire frequency patterns. Shows the number of times that different areas have burned over thelast century. Areas shown in white have no recorded incidence of fire. This is based on our fire historydatabase (see the “Information Sources” section of chapter 1 for more information on the fire data).

1997). Coastal sage is restricted to low eleva-tions (below 3,000 feet) and most of it occursnear the urban interface. The pervasive in-crease in non-native grass cover has increasedthe flammability of this vegetation type, suchthat it is often capable of reburning one ortwo years after a fire. Given these characteris-tics, increased management effort willprobably be needed to keep coastal sage fromburning at overly frequent intervals.

Existing management direction in south-ern California Forest Plans calls forshort-rotation burning to frequently rejuve-nate coastal sage scrub habitats (e.g.,

seventeen-year rotations on the ClevelandNational Forest and twelve-year rotations onthe Angeles National Forest) (Cleveland NF1986; Angeles NF 1987). The informationpresented above suggests that a different man-agement approach, which emphasizesretention of older stands of coastal scrub, maybe necessary to achieve desired conditions(table 3.3).

The second concern in the foothills is thetendency for very large fires (e.g., 10,000 acresor larger) in chaparral-dominated habitats.There have been a number of these large fires,

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particularly in the Los Padres National For-est, over the last several decades. Whether achange from historic conditions or not, a highincidence of large burns substantially reducesthe structural diversity of chaparral and scrubhabitats and causes high amounts of erosionand stream siltation. Large chaparral fires alsohave the propensity to be self-perpetuating,since they create a continuous block of single-age vegetation that becomes ready to burnagain at the same time.

An issue that is not of particular concernis the potential for chaparral stand senescenceor decadence due to the long-term absence offire. Formerly believed to be a problem, longfire-free intervals (i.e., seventy to one hundredyears) have been found in recent studies notto be detrimental to chaparral shrubs (Keeley1986; Zedler 1995). Many species, in fact,continue to produce new stems and even seed-lings during long fire-free intervals (Lloret andZedler 1991; Keeley 1992). The potential fornegative effects associated with overly frequent

Table 3.1. Key ecological issues that are influenced by the current fire regime.

Key IssuesHabitats/Species

Most AffectedEffects Associated

with Current Fire RegimeCurrent Trends and

Areas Most Affected

Overly frequenthabitat disturbance,leading to a shift incomposition andstructure of plantcommunities.

Overly infrequenthabitat disturbance,leading to a shift incomposition andstructure of plantcommunities.

Coastal sage scrub.Bigcone Douglas-firforests.Possibly pinyon-juniperwoodlands.

• Fires spread rapidly in coastalscrub and an abundance ofignitions along the urbaninterface can lead to frequentreburns.

• Chaparral fires areincreasingly carrying intobigcone Douglas-fir stands,which are very slow to recoverfrom stand-replacing fires. It isunclear if the situation is beingcaused by increased fireintensity or frequency or both.

• Coastal scrub in thefoothills is being convertedto annual grassland inmany areas.

• Extent of bigcone Douglas-fir has declined by 18% inSan Bernardino Mts. since1930s and is decliningelsewhere too.

• Recent large fires inpinyon-juniper woodlandsmay be related to increasedgrass cover in desert-sideareas.

Mixed conifer forest.Ponderosa pineforest.

Fires have been effectivelysuppressed in montane coniferforests, essentially eliminatingunderstory burns thathistorically occurred in theseforests. This increases the riskof stand-replacing crown fires,although such an event has yetto occur in this region.

• Mesic forests have hadsubstantial increases in thenumber of small diameter,understory trees.

• White fir and incense-cedarhave increased inabundance; ponderosa pineand black oak havedecreased.

fire appears to be a much greater threat tochaparral and scrub habitats.

Fire Issues in Lower MontaneHabitats

Recent fire frequencies in lower montanehabitats are similar to patterns in the foothills(table 3.4). This reflects the dominant influ-ence of chaparral in both the foothills andlower montane region. Studies suggest thatmost chaparral plant communities are adaptedto considerable variability in fire frequency andare not believed to be adversely affected bycurrent return intervals (Keeley 1986; Zedler1995).

The primary fire issue in lower montanehabitats is the apparent loss of bigcone Douglas-fir in stand-replacing wildfires. This problem hasnot been thoroughly studied; thus, there is un-certainty about the amount of loss incurred andthe reasons for it. Minnich (1999) states thatstand-replacement fires in the San BernardinoMountains have resulted in a net decline of 6,016

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Chapter 3

Values are the percent of area meeting the described condition

(a) Number of Fires

0 Fires 27% 17% 17% 16% 8% 14% 19% 26% 48% 25%

1 Fire occurrence 38% 33% 42% 35% 22% 43% 43% 41% 40% 39%

2 Fires 22% 27% 26% 24% 41% 26% 25% 21% 9% 22%

3 or more fires 13% 23% 15% 25% 29% 17% 13% 12% 3% 14%

(b) Year of Last Fire

1-19 years ago 16% 48% 37% 47% 26% 35% 22% 45% 10% 28%

20-39 years ago 26% 25% 17% 22% 54% 29% 17% 3% 16% 20%

40-59 years ago 20% 7% 3% 8% 6% 6% 23% 8% 19% 14%

60-90+ years ago 11% 3% 26% 7% 6% 16% 19% 18% 7% 13%

No recorded fires 27% 17% 17% 16% 8% 14% 19% 26% 48% 25%

540,499 229,344 62,297 72,200 156,603 208,903 637,922 468,623 162,586 2,538,976

Cleveland NF Los Padres NFAngeles NFSan Bernardino NF

SanDiego

Ranges

SantaAnaMts

SanJacinto

Mts

SanBernar-dino Mts

SanGabriel

Mts

CastaicRanges

S. LosPadresRanges

S. SantaLuciaRng

N. SantaLuciaRng

EntireFoothill

Zone

Acres of FoothillHabitat

Table 3.2. A look at recorded fire history patterns in foothill habitats by mountain range. (a) Shows thepercentage of the foothill landscape that has burned 0, 1, 2, or 3-plus times over approximately the lasteighty years. (b) Shows the percentage of the foothill landscape by categories of time elapsed since the last fire.

Coastal Sage Scrub: Fire-free intervals ofsufficient length (twenty-five years or more) toallow this vegetation type to reach structuralmaturity and remain there for an extended periodof time. This would promote increased shrub coverand provide higher quality habitat for at-riskspecies associated with coastal sage scrub (e.g.,

California gnatcatcher).

Table 3.3. Desired conditions for managing fire infoothill habitats of special concern.

acres of bigcone Douglas-fir or 18 percent of whatwas present in 1938.

Fires seldom start in bigcone Douglas-firstands but rather carry into them from thesurrounding chaparral (fig. 3.2). Thus, chap-arral fire dynamics strongly influence howthese forest patches are affected by fire. Theirdistribution in deep canyons and on steepnorth-facing slopes helps limit exposure to fire.A possible explanation for the recent frequencyof stand-replacing fires in bigcone Douglas-fir stands is an increase in the number ofhigh-intensity chaparral fires, which are morelikely to carry into forest patches. There is notadequate fire-intensity data to determine if thisis indeed the case. It is considered plausiblebecause of the current tendency for fires toescape rapid control only when conditions aresevere, and because urban interface ignitionsmay result in more base-of-the-mountain firesthat are prone to high-intensity runs up steeplower montane slopes.

One thing for certain is that bigcone Dou-glas-fir forests have been slow to recover fromcrown fires and many stands do not appear tobe recovering at all (Minnich 1978). Chapar-ral invades these sites and for many decadesthe new community will be more likely toreburn than the old one—until live oaks againattain tree stature and shade out the shrubs.Bigcone Douglas-firs are particularly slow to

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(a) Number of Fires

0 Fires 34% 24% 34% 18% 6% 30% 23% 4% 7% 19%

1 Fire occurrence 48% 56% 49% 40% 35% 52% 44% 7% 53% 44%

2 Fires 16% 16% 14% 30% 38% 17% 26% 68% 35% 28%

3 or more fires 2% 4% 3% 12% 21% 1% 7% 21% 5% 9%


1-19 years ago 15% 52% 11% 18% 21% 9% 21% 90% 19% 20%

20-39 years ago 13% 4% 19% 35% 40% 31% 17% 66% 30%

40-59 years ago 27% 17% 10% 23% 17% 14% 2% 3% 11%

60-90+ years ago 11% 3% 26% 6% 16% 16% 37% 6% 5% 20%

No recorded fires 34% 24% 34% 18% 6% 30% 23% 4% 7% 19%

Fire Issues in Montane ConiferHabitats

The widespread and prolonged absenceof fire is a concern in montane conifer forests(table 3.6). Fire-scar studies suggest that mod-erate intensity fires (i.e., hot enough to scarbut not kill most mature trees) historicallyoccurred every fifteen to thirty years (McBrideand Lavin 1976). However, over the last ninetyyears understory fires have been virtuallyeliminated from large areas, particularly ininterior forest areas. The result is denser standsand a dramatic increase in the number of un-derstory trees (Minnich et al. 1995). Theconcern is that this increase in stand densityand fuel loading makes the forests more sus-ceptible to large, stand-replacing crown fires(table 3.7).

Using data on precipitation, elevation,slope, stand density, and fire history, we de-veloped a model to predictively map areas atrisk to stand densification. Almost 30 percent


SanDiego

Ranges

SantaAnaMts

SanJacinto

Mts

SanBernar-dino Mts

SanGabriel

Mts

CastaicRanges

S. LosPadresRanges

S. SantaLuciaRng

N. SantaLuciaRng

Table 3.4. A look at recorded fire history patterns in lower montane habitats by mountain range. (a) Showsthe percentage of the lower montane landscape that has burned 0, 1, 2, or 3-plus times over approximatelythe last 90 years. (b) Shows the percentage of the lower montane landscape by categories of time elapsedsince the last fire.

Acres of LowerMontane Habitat

EntireLower

Montane

179,071 22,711 112,443 151,113 281,590 128,016 550,298 31,954 255,971 1,713,167

return when there are no surviving seed treesnearby (Weatherspoon et al. 1992).

Coulter pine forests also occur mainly inlower montane areas but do not appear to beas adversely affected by the current fire regime.Coulter pine regenerates extremely well afterfire (Vale 1979; Borchert 1985), but it requiresfire-free intervals of approximately sixty to sev-enty-five years for adequate seed crops todevelop (table 3.5). Thus, Coulter pine canbe negatively affected by frequent reburns orby extremely long intervals without fire. Thismay be a problem in localized areas (M.Borchert, Los Padres NF, pers. comm.), butoverall fire frequency in lower montane land-scapes does not appear to be outside thehistoric range of variability.

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Chapter 3

(108,500 acres) of mixed conifer and pinestands in the assessment area were predictedto be experiencing this problem (see fig. 2.17in chapter 2).

Over the last fifty years, there have beenvery few “forest” fires in southern California’smontane conifer region. Those that have oc-curred were either (1) driven primarily by steep

Figure 3.2 Bigcone Douglas-fir stands are at risk in high-intensity fires. This stand is located west ofColdbrook Campground on the Angeles National Forest. RICHARD HAWKINS

Bigcone Douglas-Fir/Canyon Live Oak: Minimaloccurrence of high-severity crown fires in theseforest stands. This is needed to maintain orincrease the distribution and extent of this foresttype which has recently been declining.

Coulter Pine: Fire return intervals ofapproximately 60 to 75 years are desired in thisforest type, which requires fire for regeneration. Atmaturity, stands should be fairly open (40% to 60%canopy closure) with trees reaching 20 inches

diameter at breast height (dbh).

Table 3.5. Desired conditions for managing fire inlower montane habitats of special concern.

terrain and extreme winds (e.g., the 1980Thunder Fire in the San Gabriel Mountains)(R. Hawkins, Cleveland NF, pers. comm.); or(2) took place in forest stands that were sur-rounded and interspersed with maturechaparral that facilitated the spread of high-intensity fires into them (e.g., the 1950Conejos and 1970 Laguna fires in theCuyamaca and Laguna mountains, the 1970Bear Fire in the San Bernardino Mountains).There seem to be few instances where the se-verity of these fires was attributed primarilyto increased fuel loads in overcrowded forests.

However, events in other areas give causefor concern. On the Boise National Forest inIdaho, many years of near-complete fire ex-clusion came to an abrupt end when a seriesof intense crown fires from 1986 to 1995 con-sumed 45 percent of the area’s ponderosa pineforest (Weiland 1996). The severity of thesefires was attributed to excessive fuel loadingresulting from the prolonged absence of fire.Similar large and unusually intense stand-replacing wildfires have occurred in recent

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(a) Number of Fires

0 Fires 45% 56% 78% 53% 32% 71% 66%

1 Fire occurrence 47% 31% 20% 31% 40% 27% 27%

2 Fires 8% 12% 2% 13% 27% 2% 6%

3 or more fires 1% 3% 1% 1%


1-19 years ago 12% 13% 21% 3% 2% 7%

20-39 years ago 5% 4% 7% 5% 36% 2% 5%

40-59 years ago 24% 18% 9% 12% 7% 4% 11%

60-90+ years ago 14% 9% 6% 9% 22% 21% 11%

No recorded fires 45% 56% 78% 53% 32% 71% 66%

49,467 0 55,749 202,112 105,681 1,748 96,544 0 0 511,301


SanDiego

Ranges

SantaAnaMts

SanJacinto

Mts

SanBernar-dino Mts

SanGabriel

Mts

CastaicRanges

S. LosPadresRanges

S. SantaLuciaRng

N. SantaLuciaRng

EntireMontaneConifer

Acres of MontaneConifer Habitat

Table 3.6. A look at recorded fire history patterns in montane conifer habitats by mountain range. (a) Showsthe percentage of the montane conifer landscape that has burned 0, 1, 2, or 3-plus times over approximatelythe last ninety years. (b) Shows the percentage of the montane conifer landscape by categories of timeelapsed since the last fire.

Fire Issues in Desert-MontaneHabitats

Fires have historically been infrequent insparsely vegetated desert-side habitats and, forthe most part, this continues to be the case(table 3.8). Proximity to urbanized areas ap-

years in the Sierra Nevada and the mountainsof northern Arizona.

At higher elevations, subalpine forestsdominated by lodgepole pine (Pinus contorta)typically do not carry fire well. In a study offire patterns in lodgepole pine forests of theSan Jacinto Mountains, lightning-caused firesoccurred every few years but were typicallysmall (less than 20 acres) and of low intensity(Sheppard and Lassoie 1998). This fire regimeappears to be within the natural range of vari-ability and not substantially influenced by firesuppression activities.

pears to be a significant factor in historic firefrequencies. A high occurrence of multiple fireson the desert side of the San Jacinto Moun-tains (table 3.8) appears to be concentrated inthe vicinity of Beaumont and Palm Springs(fig. 3.1). The most remote desert-montane ar-eas (i.e., the southern Los Padres ranges aroundMount Pinos and the extreme northeastern cor-ner of the San Bernardino Mountains) have hadvery little fire history (fig. 3.1).

Vegetation type is also a factor in fire-return intervals, with fires being more frequentin desert chaparral and scrub than in pinyon-juniper woodlands. The sparse understoriesand open canopies typical of pinyon-juniperwoodlands translate into long fire-free peri-ods. A study of these woodlands in the SanBernardino Mountains estimated that the av-erage fire-return interval was 480 years(Wangler and Minnich 1996). The authorsconcluded that twentieth-century fire suppres-sion has had little effect on this vegetation type.

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Chapter 3

Forest stands with understory species ratiosthat are similar to the current overstoryspecies composition. The emphasis is onarresting encroachment of shade-tolerant white firand incense-cedar and providing opportunities forpine and black oak regeneration.

Landscape patterns that are resilient to largecrown fires. Forest thickening and fuel continuityproblems must be addressed at a landscape scale(e.g., watersheds) to avoid large stand-replacingfires. Understory fires (or thinning) should occur ineach forest stand at twenty to forty year intervals.Some overstory kill during these events (2% to 4%of the stand) is desirable to create small openingsfor pine and oak regeneration. Under existingconditions, heavy fuels create a high potential forforest fires that kill a much larger fraction of theoverstory.

A continuous and well distributed supply oflarge trees. Large trees are both highlycharacteristic of pre-suppression forests and vitalto many wildlife species. They have declined innumber over the last fifty years and are threatened

further by stand thickening and crown fire risk.

Table 3.7. Desired conditions for managing ormimicking fire regimes in montane conifer forests.

Fire Management ConsiderationsOptions for managing fire or mimicking

its ecological function fall into three generalcategories: (1) prescribed burning where a fireis intentionally set under controlled condi-tions; (2) fuels treatments where vegetation ismanually or mechanically cut to reduce firehazard or mimick an effect that fire wouldhave; and (3) wildfire suppression strategies,which include confine-and-contain ap-proaches where an unplanned or naturalignition is allowed to burn within a predefinedcontainment area. The potential opportuni-ties and barriers associated with theseapproaches are summarized in table 3.10.

The defensible fuel profile is a fuels treat-ment option that is being consideredthroughout the western United States for re-ducing crown-fire hazards in conifer forests.A defensible fuel profile zone (DFPZ) is de-fined by Olson (1993) as a “low-density,low-fuel zone averaging 0.4 km (0.25 mi.) inwidth, located mostly along roads and de-signed to support suppression activities.”DFPZs can be likened to shaded fuel breaks,only on a larger scale. The focus of DFPZs isto break up fuel continuity over landscapes. Anetwork of DFPZs is expected to do severalthings: (1) reduce wildfire severity in treatedareas; (2) create broad zones where suppres-sion efforts can be conducted safely andeffectively; (3) effectively break up continuityof fuels; and 4) become anchor lines for fur-ther areawide fuel treatments.

According to Weatherspoon and Skinner(1996) and Olson (1993), DFPZs should beplaced primarily on ridges and upper southand west slopes. Where possible they shouldalso coincide with existing roads to simplifyconstruction and maintenance and to facili-tate their use by suppression forces. Thistreatment will result in a fairly open stand,which is dominated by large trees of fire-tolerant species. Post-treatment canopy closureis recommended to be no more than 40 per-cent. One of the key features of this is thegeneral openness and discontinuity of crownfuels (horizontal and vertical) to produce a very

However, Wangler and Minnich’s (1996)study looked at fire patterns up to 1983. Sincethat time, there have been several large fires inpinyon-juniper woodlands on the north endof the San Bernardino Mountains. This hasled to speculation that increases in non-native grass cover (e.g., cheatgrass), combinedwith increased ignition sources associated withthe rapidly growing human populations justnorth of the mountains (i.e., Hesperia, AppleValley, and Victorville) could be facilitatingfire spread in these woodlands. The hypoth-esis is that this problem would only be presentafter particularly wet winters, when grass coverreaches its peak. This issue needs further study.Pinyon woodlands are extremely slow to re-generate; thus, an acceleration in fire returnintervals would be of concern (table 3.9).

72


(a) Number of Fires

0 Fires 56% 32% 61% 43% 60% 83% 65%

1 Fire occurrence 38% 35% 28% 50% 35% 13% 26%

2 Fires 5% 20% 9% 6% 5% 4% 7%

3 or more fires 1% 14% 2% 1% 2%


1-19 years ago 8% 50% 22% 15% 12% 6% 15%

20-39 years ago 6% 1% 11% 17% 7% <1% 4%

40-59 years ago 29% 17% 4% 24% 4% 3% 11%

60-90+ years ago 1% 2% 1% 17% 8% 5%

No recorded fires 56% 32% 61% 43% 60% 83% 65%

78,406 0 110,135 134,468 88,560 61,092 418,145 0 0 1,713,167

Table 3.8. A look at recorded fire history patterns in desert-montane habitats by mountain range. (a) Showsthe percentage of the desert-montane landscape that has burned 0, 1, 2, or 3-plus times over approximatelythe last ninety years. (b) Shows the percentage of the desert-montane landscape by categories of timeelapsed since the last fire.

Pinyon-Juniper Woodlands: Long fire-freeintervals (one hundred to three hundred years) toallow this vegetation type to reach structuralmaturity and remain there for an extended periodof time. Pinyon-juniper woodlands recover very

slowly from crown fires.

Table 3.9. Desired conditions for managing fire indesert montane habitats of special concern.


SanDiego

Ranges

SantaAnaMts

SanJacinto

Mts

SanBernar-dino Mts

SanGabriel

Mts

CastaicRanges

S. LosPadresRanges

S. SantaLuciaRng

N. SantaLuciaRng

EntireDesertSide

Acres of Desert-Side Habitat

The Influence of Water:Hydrology, Regulation, andWithdrawal

The flow of water, both on the land sur-face and underneath it, is a powerful force inshaping landscape patterns and ecologicalcommunities (Dunne and Leopold 1978). Thedynamics of streamflows and the proximityof groundwater largely determine the extentand character of riparian, wetland, and aquatichabitats. Seasonality, volume, duration, andyear-to-year variability of streamflows allgreatly influence the structure and composi-tion of ecological communities found in thechannel and floodplain. Groundwater fluctua-tions have a similar effect on communitiesassociated with springs, seeps, and ephemeralwater bodies.

Southern California is an arid region wherethe human demand for fresh water greatly ex-ceeds the natural supply. Consequently, all of

low probability of sustained crown fire.Conard and Weise (1998) propose similar fuelmanagement zones in southern Californiachaparral habitats.

73

Chapter 3Table 3.10. Summary of the opportunities and barriers associated with the primary management toolsavailable for restoring or mimicking the role of fire on the landscape.

Prescribed Burning Fuel Treatments Wildfire “Confine & Contain”

Opportunities

TreatmentPotential(acres per year)

Effectiveness inand aroundDeveloped Areas

InstitutionalBarriers toImplementation

• Understory burns to thinforest stands.

• Chaparral burning tomanage fire frequencyand intensity.

• Selective timber harveststo thin the forest understory.

• Fuel breaks or defensiblefuel profiles to increaseability to control wildfires.

Confine and containstrategies allow unplannedignitions occurring underdesirable conditions to burnwithin defined containmentboundaries.

Moderate. Considerablepreparatory work is oftenrequired. Most efficient inareas far removed frombuildings.

Low. High cost per unitarea; requires accessiblelocations.

Moderate. Low cost per unitarea, but is feasible only inremote areas where life orproperty is not at risk.

Moderate. Only very lowintensity fires can usually beprescribed near developedareas.

High. Can be done in areaswhere burning is too risky.

Not an option neardeveloped areas; The riskof property damage is toohigh.

EnvironmentalBarriers toImplementation

• Complexities of keepingfire on the wildland side ofthe urban/wildlandinterface.

• In forests, high fuelbuildups now make itdifficult to underburn inmany stands.

• Air quality regulations limitwhen burning can bedone.

• Forest thinning is not costeffective on steep slopesor in areas that lack roadaccess.

• Fuel breaks requiremaintenance and can haveenvironmental impacts.

• Inadequate funding.Need authority to usesuppression money tofund this work.

• Lack of institutionalincentives to burn.

• Liability risks are a majordisincentive to burning.

• Lack of viable commercialmarkets for small-diametertrees.

• Inadequate funding. Needauthority to use suppressionmoney to fund fuelsreduction work.

• Need change in ForestPlan direction

• Requires change inattitudes towardssuppression — immediatecontrol is not always thedesired objective.

• Liability risks

• Limited to areas where therisk to life and property arevery low.

• Air quality considerationsmay also limit this option.

the major streams that originate in the moun-tains contain dams or diversions at some pointalong them. In addition, many small streamsand springs are dammed or diverted, both forwater supply and flood control. Subsurfacewaters are also heavily tapped. Yet this still doesnot come close to meeting the needs of theregion’s human population, so large quanti-ties of water are imported into the area fromnorthern California and the Colorado River.

The result is a dramatic reduction in theextent and distribution of native freshwaterhabitats in this region. Faber et al. (1989) es-

timate that 95 to 97 percent of riparian habi-tat in southern California floodplain areas hasbeen eliminated. In addition, much of whatremains must function under a highly modi-fied hydrologic regime with upstream damsregulating streamflows. Clearly no other land-scape feature has been so drastically altered byhuman activities as has freshwater habitat.

The presence of dams and diversions onmost of the region’s major streams (fig. 3.3)has greatly altered aquatic and riparianhabitats and reduced the capability of these

74

The Effect of Dams and WaterRelease Regimes

Dams destroy riparian habitat directly byinundation, but their greater effect (in terms

Figure 3.3. The locations of dams and diversions on central and south coast streams. Notice that themajority are concentrated in the foothills below 3,000 feet.

of miles of habitat degraded) is downstream.By retaining all or part of flood flows, or modi-fying the shape of the discharge curve, damstend to rob the drainage below of the hydrau-lic forces necessary to maintain a natural form.

Sweet (1992) illustrates the downstreameffect of dams by comparing the Santa YnezRiver below Gibraltar Dam (completed in1921) with Piru Creek below Pyramid Dam(completed in 1973). Most of the regulatedstreams within the assessment area resembleone of these two downstream patterns:

After 70 years, the affected sectionof the Santa Ynez River is characterizedby a near-total lack of sand and fine

habitats to support native species (table 3.11).However, the importance of these structuresin preserving domestic water supplies and con-trolling downstream flooding ensure thatmost, if not all, are here to stay. Recognizingthat their continued presence is necessary,there are important factors in the operationof major dams and diversions that significantlyaffect native habitats and species.

75

Chapter 3

Table 3.11. Key ecological issues that are influenced by water storage, control, and withdrawal.

gravel, and by a succession of very deepscour pools floored with boulders andmud. There are no sandy levees, onlycobble bars, and several oak terraces arebeing eroded as the channel moves lat-erally. Little if any arroyo toad habitatremains in the first 4 stream miles be-low the dam, and only marginal habitatbelow this as a consequence of the scar-city and small size of tributary canyonswhich can supply the sediment and flooddischarge needed to maintain the sys-tem.... Gibraltar Dam appears to haverendered the entirety of the downstreamlength of the Santa Ynez river on theLPNF uninhabitable for arroyo toads.

Pyramid Dam has been affectinglower Piru Creek for less than 20 years,and presents a somewhat different pic-

ture. As on the Santa Ynez River the sanddeposits are disappearing from the seg-ment between Frenchman Flat and thedam, and the creek has acquired a deepand boulder-filled channel. Unlike theSanta Ynez, large tributaries join PiruCreek within a few miles below Pyra-mid Dam and restore part of its sedimentload. There is a second difference in thatPyramid Dam releases 10-25 cfsthroughout the summer and early fall,resulting in the development of a verydense riparian corridor which is pro-tected from flood scouring. Thisvegetation effectively channelizes thecreek, and has transformed it into a habi-tat quite unsuitable for most native aquaticand riparian species. (Sweet 1992, pg 154)


Most Affected

Effects Associatedwith Water Storage,

Control and WithdrawalCurrent Trends andAreas Most Affected

Streams downstream ofreservoirs tend to be mostaffected.

Declines in habitatcapability caused bymajor changes in thevolume, duration,timing, and variabilityof stream flows.

Establishment andspread of invasive,non-native species.

Reductions insurface water flows.

Aquatic and riparianhabitats below damsand diversions.

Dams and diversionsdramatically alter flow regimes.Water releases below dams, ifthey occur at all, tend to beeither “high volume, shortduration,” or “continuous lowvolume,” neither of whichresemble historic patterns.Downstream transport ofsediment is also curtailed bydams, resulting in channeldowncutting over time.

Most large streams havebeen dammed or divertedfor many years and willremain so. Efforts areongoing in some areas toestablish release schedulesthat more closely mimichistoric flow regimes.

Aquatic andriparian species.

Reservoirs, both large andsmall, tend to be dominated bynon-native flora and fauna.These serve as points of spreadinto nearby native habitats.

• Wet meadows• Aquatic and riparianhabitats

Withdrawals of sub-surfacewater (i.e., spring- and ground-water extraction) can lower thewater table and reduceavailability at the surface.

The popularity of bottledmountain spring water isleading to an increase inextractions, particularly onprivate lands in themountains.

76

The Influence of Invasive,Non-Native Species

The spread of non-native species that dis-place, prey upon, or otherwise harm nativespecies is a major problem in both aquatic andterrestrial habitats. Alternately referred to as“exotic,” “alien,” or “non-indigenous” species,the alarming consequences of their invasionon the capability of habitats to support nativespecies is becoming increasingly recognized(Dudley and Collins 1995; Quammen 1998).Survival and reproductive success are greatlyaffected by predation and competition for lim-ited resources (e.g., food and breeding sites).Introductions of new species, particularlyhighly successful or predatory ones, can dra-matically decrease the ability of some nativespecies to survive and reproduce in what oth-erwise would be suitable habitat (table 3.12).

In a statewide survey of non-indigenousspecies, Dudley and Collins (1995) concludedthat the South Coast Bioregion was particu-larly hard hit, with more non-native speciesthan any other California bioregion. To better

The historic flow pattern in southern Cali-fornia streams reflects the region’s climate oflong, dry summers and short, wet winters.Thus, flows would peak in the winter and earlyspring and decline dramatically in the sum-mer months, where in many cases they woulddry up in the uppermost and lowermostreaches (Faber et al. 1989). The high variabil-ity of runoff and precipitation in southernCalifornia also produced large flood events,which periodically scoured channels and re-distributed sediment.

There is little ability to recreate large floodevents, and the sediment transport that comeswith them, below existing dams (fig. 3.4). Yetin some drainages, rather minor changes inthe management of water releases could greatlyimprove habitat capability for species of con-cern. On Piru Creek, spring and summerdischarges from Pyramid Lake used to fluctu-ate on a daily or weekly basis from zero to 150cubic feet per second (cfs) and arroyo toadclutches and larvae were often stranded orswept away. In 1992, a shift to constant re-leases during the spring/summer periodresulted in a large increase in larval arroyo toadsurvivorship (Sweet 1993).

Similar changes would be beneficial inother drainages within the assessment area.The resource management agencies shouldpursue opportunities to work with water andflood control agencies to address flow releaseissues (timing, duration, and volume of water

Figure 3.4. Sutherland Dam on Santa Ysabel Creekin the Cleveland National Forest is typical ofimpoundments in the assessment area. Water fromSutherland is released downstream only in highrainfall years when the lake level rises to the spillwayheight. GENA CALCARONE

The timing and duration of water releasesfrom reservoirs can greatly influence down-stream habitats. Large, sudden releases ofwater, particularly in the summer months, canquickly scour away a whole year’s reproduc-tive effort for native species such as arroyotoad, red-legged frog, pond turtle, and Cali-fornia newt. Conversely, low-level year-roundflow regimes facilitate the spread of exoticpredators (e.g., bullfrogs, sunfish, bass, blue-gill, catfish, and Asian clams) into downstreamareas that historically would have gone dry inlate summer (Sweet 1992). Neither of thesewater release schedules is similar to historicflow conditions.

releases) on a site-specific basis. In particular,efforts should be made to limit the practice ofrapid, large changes in the volume of springand summer water releases.

77

Chapter 3Table 3.12. Key ecological issues that are affected by the spread of invasive, non-native species.

document the extent of this problem in theassessment area, we developed a database thatcompiles occurrences of the most problematic,non-native species by stream or watershed.Many of these species are associated with ri-parian habitats and thus their presence orabsence on individual streams is important toconsider when assessing overall habitat capa-bility. The database (displayed in appendix C)provides a good snapshot of what is currently

known about the distribution of exotic pestspecies. However, it does not allow us to con-clusively say where they do not occur; areasmay lack observations of these species simplybecause thorough surveys have not been con-ducted. Also, in most areas where we know anexotic species is present, we lack accurate in-formation on the extent of the infestation.These are important information needs.


Most Affected

Effects Associatedwith the Spread of Non-

Native SpeciesCurrent Trends andAreas Most Affected

Shifts in compositionand structure of plantcommunities.

Declines in survivalrates of nativeanimals that breedin aquatic habitats.

Declines inreproductive successof native animals

Shifts in compositionof invertebrate fauna.

• Riparian habitats• Grasslands• Coastal scrub

• Arundo, tamarisk, and othersuccessful non-natives candramatically alter thecomposition and structure ofriparian habitats.

• Non-native grasses and forbshave come to dominate manygrassland and coastal scrubhabitats, displacing nativespecies.

Arundo is spreading rapidlyin many low-elevationstreams. Efforts to control oreradicate it are ongoing inseveral areas and havebeen successful, but whereuncontrolled it is increasing.Tamarisk is present in manyfoothill streams, but does notseem to be spreadingrapidly in most of them,particularly if stream channelis rocky.

• Red-legged frog• Yellow-legged

frogs (mtn & fthill)• Arroyo toad• Santa Ana sucker• SA speckled dace

Predation and competition byaquatic non-natives (bullfrogs,African clawed frogs, bass,sunfish, bluegill, brown trout,bullhead, and crayfish) cancause steep declines in survivalrates.

• Least Bell’s vireo• Willow flycatcher• Riparian birds• CA gnatcatcher• Native fish and

amphibians• Purple martins

• Cowbirds parasitize the nestsof many bird species

• Non-native frogs and fishconsume egg masses andyoung of native amphibiansand fish

• European starlings displacenative cavity nesters

• Aggressive cowbird controlacross so. CA has helpedincrease Bell’s vireonumbers

• Most native fish andamphibians are declining

• Aquatic non-native speciesare well established inmany streams; those belowreservoirs are particularlyprone to infestation.

• Some targeted controlefforts have recently beeninitiated

• Coast horned lizard• Habitats along theurban interface

Argentine ants and redimported fire ants displacenative ants and otherinvertebrates in areas near theurban or agricultural interface.Native ants are the primaryfood of coast horned lizardsand arroyo toad.

Argentine ants appear to bespreading, particularly inhabitat fragments and inriparian areas. Redimported fire ants have justappeared in southern CA,so it is too early to say howfar and fast they will spread.

78

Non-Native Forest PathogensThe pitch canker fungus, Fusarium

subglutinans ssp. pini (also called Fusariumcircinatum), is established in native and plantedMonterey, knobcone, and bishop pines fromMendocino County south. This fungal patho-gen is native to the southeast United States.Although there appears to be some natural re-sistance in the Monterey pine population (genepool), it is predicted that 25 percent of theMonterey pines in infested stands will be killedby the fungus. Because the disease is new tothe West Coast it is not known how manyother pine species will be similarly affected.Several pine species and Douglas-fir are capableof being infected by the fungus (Dallara et al.1995), but it may be rare for some of thesespecies to develop the disease. Pines native tosouthern California which may be at risk in-clude bishop pine (Pinus muricata), Coulterpine (P. coulteri), gray or foothill pine (P.sabiniana), knobcone pine (P. attenuata),Monterey-knobcone cross, ponderosa pine (P.ponderosa), lodgepole pine (P. contorta), andTorrey pine (P. torreyana) (Dallara et al. 1995).Even with resistant genes, re-establishing a for-est is an expensive and slow process, andsurvival of other plant, wildlife, and micro-bial species dependent on the affected coniferscould be threatened by the disease.

Unfortunately, pitch canker is probablyonly the first of many exotic pests of nativetrees which will profoundly affect southernCalifornia forests. Despite restrictions on im-portation of raw wood products, increasingtrade and movement of people have increasedthe probability of the inadvertent or deliber-ate introduction of pest species. One pathogenexpected to appear soon in southern Califor-nia forests is white pine blister rust(Cronartium ribicola), which affects sugar pine.

Invasive, Non-Native PlantsOver one thousand non-native plants have

become naturalized in California wildlandssince the late 1700s when European settlementbegan (Randall et al. 1998). Some of theseplants have caused little impact, while others

are both invasive and damaging to natural eco-systems. The California Exotic Pest PlantCouncil (CalEPPC 1996) has developed a listof seventy-six exotic plants known to be in-vading native ecosystems and plantcommunities. These species can cause ecologicand economic damage by changing the natu-ral processes associated with succession,nutrient cycling, hydrology, substrate stabil-ity, soil chemistry, or the frequency andintensity of wildfires (Randall et al. 1998;D’Antonio and Haubensak 1998). Many ofthese species outcompete native plants,thereby changing the composition and struc-ture of ecological communities and sometimesreducing the quality of forage and cover forwildlife. Non-native plants can also hybridizewith related native species [e.g., the non-native dandelion (Taraxacum officinale) is hy-bridizing with California dandelion (T.californicum) in montane meadows].

Probably because many non-native plantsfirst became established in coastal areas ofCalifornia (i.e., in and around ports, missions,and early settlements), their numbers tend todecline with increasing elevation and increas-ing distance from the coast. A relatively lownumber of exotic plants (approximatelytwenty-five) have invaded the desert areas ofsoutheastern California (Kemp and Brooks1998). High levels of disturbance and habitatmodification tend to favor a non-native flora.For example, powerline right-of-ways that runthrough intact vegetation in southern Cali-fornia have been shown to be points-of-entryfor several exotic species, including black mus-tard (Brassica nigra) and ripgut brome (Bromusdiandrus) (D’Antonio and Haubensak 1998).In addition, hydrologic changes to streamsbrought on by dams and diversions appear toreduce the ability of native riparian plants tosurvive, creating conditions that promote theestablishment of exotic species.

CalEPPC’s Exotic Pest Plants of GreatestEcological Concern list (1996) is divided intoseveral categories based on level of invasivenessand distribution. The non-native plants consid-ered to be of particular concern in our assessmentarea are addressed individually below.

79

Chapter 3Arundo or Giant Reed (Arundo donax)

Arundo is a large, perennial grass that hasbecome widespread in many states (Dudley1998). It was intentionally introduced to Cali-fornia in the 1820s in the Los Angeles area asan erosion-control agent in drainage canals(Robbins et al. 1951; Bell 1999). It formsdense thickets primarily in riparian areas butalso in places that receive runoff (e.g., road-sides) or where there is a shallow water table(fig. 3.5).

Within the assessment area arundo occursin foothill areas, primarily along large streamsbut also in other areas where there is pooledwater. It reaches peak abundance downstreamof the assessment area along major rivers inthe coastal basins. The Ventura, Santa Clara,Santa Ana, Santa Margarita, San Luis Rey, andSan Diego river systems are particularly in-fested. Arundo has generally not spread intothe mountains or up the steep, narrow can-yons that characterize lower montane areas. Itapparently is restricted to low elevations (pri-marily below 2,000 feet according to Hickman1993) and requires well developed soils tobecome established. We have documented thepresence of arundo in fifty drainages withinthe assessment area.

We briefly describe the effects of arundohere, but see Bell (1999) for a thorough re-view of arundo’s impacts in southernCalifornia streams. Arundo tends to have acompetitive advantage in riparian areas wherethere is a modified hydrologic regime. It hasrapid growth rates; in a comparison betweenarundo and two willow species (Salix goodingiiand S. laevigata), arundo grew 2.1 to 4.9 timesfaster (Rieger and Kreager 1989). Arundo canreportedly reach heights of 8 to 13 feet in lessthan one growing season. This rapid growthis sustained by the consumption of prodigiousamounts of water—as much as 2,000 liters permeter of standing arundo (Iverson 1994)—and causes a decline in the availability ofsurface water.

Once established, the reed often formsmonocultural stands that physically inhibit thegrowth of other plant species. These stands

provide neither food nor cover for most na-tive species of wildlife (Bell 1999; Reiger andKreager 1989). Only a small number of birdspecies have been observed using arundo fornest sites and dramatic reductions (50 percentor more) in the abundance and diversity ofinvertebrates were documented in arundothickets compared with those found in nativewillow/cottonwood vegetation (Dudley1998). Arundo also provides less shade in ri-parian areas when compared to nativevegetation, causing increased water tempera-tures and lower oxygen concentrations, whichin turn negatively affect fish and other aquaticanimals (Kan 1998).

Arundo thickets are highly flammable andknown to carry wildfire up and down ripar-ian corridors (Scott 1994; D’Antonio andHaubensak 1998). In recent years there havebeen a significant number of fires fueled byarundo in the Prado Dam area and along theSanta Ana River (J. Wright, Riverside CountyFire Dept., pers. comm.). The most recentoccurred in 1998 when an intense wildfirethreatened to burn homes in the Santa AnaRiver drainage. Firefighting in arundo thick-ets is proving to be a significant drain on firemanagement resources (J. Wright, RiversideCounty Fire Dept., pers. comm.; R. Hawkins,Cleveland NF, pers. comm.).

A number of private and public organiza-tions (including the U.S. Forest Service) haveformed alliances (Team Arundo) to coordinate

Figure 3.5. Arundo donax forms dense thickets likethis one along Santa Ysabel Creek in San PasqualValley, San Diego County. GENA CALCARONE

80

Tamarisk or Salt Cedar (Tamarix spp.)

Tamarisk is widely distributed in south-ern California, in both coastal and desert-sidedrainages. There are at least four different spe-cies of tamarisk invading native riparianhabitat in the assessment area: Tamarixchinensis, T. gallica, T. parviflora, and T.ramosissima.

Tamarisk has the ability to uptake largequantities of water from the soil, effectivelylowering the water table and reducing theamount of available surface water. One ma-ture tree can reportedly absorb upwards of 200gallons of water per day (Johnson 1987). Insome areas, tamarisk has reduced or eliminatedwater supplies for bighorn sheep, pupfish, sala-manders, and desert palm groves (Johnson1987).

Tamarisk also provides poor forage andnesting sites for wildlife. The scale-like leavesare unpalatable to grazers and, in one studydone by Bertin Anderson and Robert Ohmartof Arizona State University, birds were shownto favor native riparian vegetation over tama-risk at a ratio of approximately 38:1 (Johnson1987). Tamarisk is often called salt cedar be-cause it exudes salts from its leaves. These saltsaccumulate in the soil, making the area lesshospitable to native plants.

Tamarisk appears to be most successful indrainages with unnatural or reduced flow re-gimes, such as those containing dams ordiversions (D’Antonio and Haubensak 1998).Robert Ohmart of the Center for Environ-mental Studies at Arizona State Universitybelieves that tamarisk is not displacing cot-tonwoods but actually replacing them in areasnow incapable of supporting a native riparianvegetation.

Because the species is sometimes plantedas an ornamental on private lands, invasionsinto riparian habitat are likely to continue. The

tree produces enormous quantities of seedwhich are dispersed by wind and water(Schierenbeck et al. 1998; Johnson 1987).

Tamarisk is documented in at least sixtydrainages in the assessment area. It appears tospread most aggressively in foothill and desertstreams with deep alluvial channels (e.g., ar-royos). It occurs in a number of lower montanedrainages as well, but seems to spread slowlyin narrow bedrock channels.

Brooms

Three weedy species of European broomhave become naturalized in California. Theseplants are members of the legume family thatwere introduced into the state as ornamentalsand have since escaped into native habitats.Now well established in our study area, theseshrubs have proven to be very difficult andexpensive to eradicate.

Of the three brooms, French broom(Genista monspessulana) is the most wide-spread. It ranges from northern Californiasouth to San Diego County and east to SanBernardino County (McClintock 1985). Inthe assessment area, it is reported below 1,700feet in the Santa Lucia Ranges, southern LosPadres region, and San Diego region. It hasbeen found in coastal scrub, grasslands, oakwoodlands, and the understory of Santa Luciafir forests. The Jepson Manual reports the spe-cies to be toxic to both humans and livestock(Hickman 1993).

Scotch broom (Cytisus scoparius) occursprimarily in northern and central California(including Monterey County) where it growsup to 3,300 feet (McClintock 1985). Occur-rences are also reported further south, in theinterior valleys of Los Angeles, San Bernar-dino, Riverside, and Orange counties. Thespecies is not as aggressive as French broom;however, it is beginning to invade chaparraland lower montane habitats in the San Ber-nardino Mountains (E. Allen, UC Riverside,in litt. 1998).

Spanish broom (Spartium junceum) is dis-tributed from northern California to SanDiego County but is less widespread than the

efforts in controlling the spread of thisspecies. Considerable progress has been madein the refinement of techniques for effectivearundo eradication (Lawson 1998; Nickerman1999).

81

Chapter 3other brooms. In the assessment area it is mostprevalent below 2,000 feet in the Santa LuciaRanges, southern Los Padres region, Castaicregion, and the interior valleys of Los Ange-les, San Bernardino, Riverside, and Orangecounties. This species primarily occupies dis-turbed areas and is not as invasive in nativehabitats (McClintock 1985).

Knapweeds and Star Thistle(Centaurea spp.)

The genus Centaurea contains many in-vasive weeds including yellow star-thistle (C.solstitialis) and spotted knapweed (C.maculosa). Yellow star-thistle is one of the mostpervasive weeds in California, occupying pas-tures, roadsides, and disturbed grasslands orwoodlands below approximately 4,300 feet.The Jepson Manual reports yellow star-thistleas cumulatively toxic to horses (Hickman1993).

Spotted knapweed is widespread in Cali-fornia, occurring in disturbed areas up to6,600 feet (Hickman 1993). The biennial spe-cies is reported in the assessment area in thesouthern Peninsular Ranges. Its early springgrowth makes spotted knapweed very com-petitive for soil moisture and nutrients. Thespecies tends to thrive under agricultural con-ditions and is listed as a “noxious weed” byboth state and federal governments.

Mediterranean Grasses

Grasses account for the greatest number(181) of non-native plants in California. Over40 percent of grasses in the state are exoticand now dominate vast areas of California’sgrasslands and savannas (Randall et al. 1998).Some of these grasses have become especiallyproblematic, outcompeting native perennialbunchgrasses and hardwood seedlings. Themost widespread grasses are the Mediterraneanannuals, which include the oats, bromes, andbarleys. They are well established in the as-sessment area and it is unlikely they could everbe eradicated on a broad scale.

All oat species are non-native. Three oc-cur in the assessment area: slender wild oat

(Avena barbata), wild oat (A. fatua), and cul-tivated oat (A. sativa). All three are highlysuccessful in disturbed areas.

Red brome (Bromus madritensis ssp.rubens) is known to carry fire in areas belowapproximately 3,200 feet in the San Bernar-dino and San Jacinto mountains (R. Minnich,UC Riverside, pers. comm.). Red brome, oats,barley (Hordeum spp.), and foxtail fescue(Vulpia myuros) have invaded coastal sagescrub and chamise chaparral in many areas.These invasions have led to increased fire fre-quencies and type conversion ofshrub-dominated habitats to grassland(Minnich and Dezzani 1998).

The primary distribution of red bromeoccurs east of the assessment area in theMojave and Sonoran deserts, where it has theability to invade intact native habitats. Redbrome is also prevalent in the Cuyama Valley(J. O’Hare, Angeles NF, pers, comm.). Thegrass spreads rapidly in wet years, and studieshave indicated that repeated fires fueled bythis grass have occurred in places where firewas previously rare (D’Antonio andHaubensak 1998; Kemp and Brooks 1998).While fires fueled by red brome are periodic(depending on rainfall patterns), their cumu-lative effect over time is expected to alter nativevegetation.

Cheatgrass (Bromus tectorum) is distrib-uted primarily in the Great Basin, MojaveDesert, and Sonoran Desert. However, it isalso found within the assessment area, prima-rily on desert-facing slopes around MountPinos and in the San Gabriel, San Bernardino,San Jacinto, and Laguna mountains. It has in-vaded a variety of mainly arid habitats,including pinyon-juniper woodlands, yellowpine and mixed conifer forests, montane chap-arral, and pebble plains (M. Lardner, SanBernardino NF, pers. comm.).

Like red brome, cheatgrass has the ability toinvade pristine habitats. However, occurrencesof cheatgrass in the assessment area are sparserand distributed at higher elevations than redbrome. Where abundant, cheatgrass is knownto cause increased fire frequencies (D’Antonio

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Invasive, Non-Native AnimalsThe introduction and spread of invasive

non-native animals have been particularlyprevalent in riparian and aquatic habitats.These infestations often coincide with habi-tat disturbance, making it difficult to separatethe influence of one from the other. For ex-ample, introduced fish and amphibians tendto thrive in highly modified habitats, con-

and Haubensak 1998), but there is little evidenceto suggest that this is currently a problem in theassessment area (R. Minnich, UC Riverside,pers. comm.).

Ripgut brome is distributed widely in theassessment area. It forms a dense understoryin open ponderosa pine forest near Lake Gre-gory, west of Lake Arrowhead in the SanBernardino Mountains. At this location thegrass poses a fire threat and appears to be in-hibiting conifer recruitment (R. Minnich, UCRiverside, pers. comm.).

Pampas Grasses

Two species of pampas grass have beenintroduced in California. Cortaderia selloana,native to Argentina and southern Brazil, sel-dom spreads from where it is planted. It oftenis cultivated as a lawn ornamental in warmerareas. In the past, it was planted by the SoilConservation Service for supplemental dry-land pasture in Ventura and Los Angelescounties (Hitchcock and Chase 1971).

Andean pampas grass (Cortaderia jubata),native to Bolivia, Peru, and Ecuador, is veryinvasive. It was originally introduced for land-scaping and by the 1960s was spreading intointact native ecosystems (e.g., redwood for-est) in coastal areas of California (Kerbavaz1985). Now considered a major weed, the spe-cies is very difficult to eradicate. In theassessment area, Andean pampas grass is es-pecially problematic along the coast ofMonterey County, where it frequently occu-pies road cuts, cliff habitat, and hillsides. Thespecies is susceptible to frost, however, andmay remain naturally restricted to milder cli-mates near the coast.

founding habitat degradation with the exoticpredators as the primary source of native am-phibian declines. However, observations ofsuccessful breeding activity by native amphib-ians in extremely modified breeding sites thatwere free of exotics supports the interpreta-tion that the exotic species themselves are animportant problem (Fisher and Shaffer 1996;Kiesecker and Blaustein 1997).

Table 3.13 lists the principal non-nativeanimals that are considered to be a problemin southern California. The ones consideredto be most problematic within the assessmentarea are described below.

Bullfrog (Rana catesbeiana)

Bullfrogs are strongly implicated in thedecline of many native amphibians and aquaticreptiles (Schwalbe and Rosen 1988; Jenningsand Hayes 1994). First introduced into Cali-fornia in 1896 (Jennings and Hayes 1985),they have progressively spread over much ofthe state and today occur in most suitablestreams and water bodies west of the SierraNevada Mountains and southern deserts(Stebbins 1972). They are an effective preda-tor of amphibians and aquatic reptiles,including California red-legged frogs (Buryand Luckenbach 1976; Hayes and Jennings1986), arroyo toads (Sweet 1992), westernpond turtles (Holland 1994) (fig 3.6), andtwo-striped garter snakes (Sweet 1992). Re-cently in San Mateo Creek, a single bullfrog wasfound to have three adult arroyo toads in its stom-ach (P. Griffith, UC San Diego, pers. comm.).

Bullfrogs have a competitive advantage overnative frogs and toads because of their large size,generalized food habits, extended breeding sea-son which allows for production of two largeclutches each year, and larvae that are less palat-able to predatory fish (Kruse and Francis 1977;Bury and Whelan 1984). They also tolerate el-evated water temperatures better than nativefrogs, which is often advantageous in human-modified habitats (Jennings 1988). Bullfrogs areable to occupy a wide variety of aquatic habitats,from coastal estuaries to mountain waters at el-evations over 5,000 feet (e.g., Doane Pond onPalomar Mountain).

Table 3.13. Some of the non-native animals occurring in southern California wildlands with anassessment of the level of threat they pose (modified slightly from Dudley and Collins 1995).Threat level category definitions: 1 = Serious, documented threat to sensitive species or ecosystems;2 = Moderate threat to native species or ecosystems; 3 = Benign, low risk; 4 = Potential threat,but impacts not well documented. Species with multiple threat levels are considered a threat insome areas, but not a problem in other areas.

Invertebrates Threat Level Mollusca

Potamocorbula amurensis Asian clam 1 Arthropoda

Apis mellifera scutellata Africanized honey-bee 4Apis mellifera ssp. European honey-bee 3Forficula auricularia European earwig 3Linepithema humile Argentine ant 2Solenopsis invicta red imported fire ant 4Procambarus clarkii Louisiana crayfish 2

Reptiles and AmphibiansChelydra serpentina snapping turtle 4Chrysemys picta, C. scripta red-eared slider, painted turtle 4Rana catesbeiana bullfrog 1Xenopus laevis African clawed frog 1

Fish Centrarchidae

Lepomis spp. green sunfish, bluegill, pumpkinseed 1Micropterus spp largemouth and smallmouth bass 1

Cyprinidae (minnows and carps)Carrasius auratus goldfish 2Cyprinella lutrensis red shiner 1Cyprinus carpio carp 2Pimephales promelas fathead minnow 2

Ictaluridae (catfish)Ameiurus (Ictalurus) melas black bullhead 1Ictalurus punctatus channel catfish 3

PercichthyidaeMorone saxitilis striped bass 1,3

PoeciliidaeGambusia affinis mosquitofish 1

SalmonidaeOncorhynchus mykiss rainbow trout (stocked pops.) 1,3Salmo trutta German brown trout 1

MammalsCastor canadensis beaver 1,3Didelphus virginiana opossum 3,4Equus cabullus feral horse 2Equus asinus feral burro 2Rattus rattus, R. norvehicus black rat, Norway rat 1Sus scrofa European boar, feral pig 1Vulpes fulva red fox 1Felis domesticus feral cats 2

BirdsBubulcus ibis cattle egret 3Meleagris gallopavo wild turkey 4Molothrus ater brown-headed cowbird 1Sternus vulgaris European starling 1

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African Clawed Frog (Xenopus laevis)

African clawed frogs are currently not aswidespread as bullfrogs (eleven known occur-rences in the assessment area), but they are apotent predator of native fish and amphibians.Concerns about their consumption of the en-dangered unarmored threespine sticklebackfish have led to eradication efforts on the SantaClara River in Soledad Canyon (Dick 1988).Although trapable, African clawed frogs aredifficult to eradicate because they are highlyaquatic and resistent to chemical toxins suchas rotenone (Dick 1988).

African clawed frogs tend to become es-tablished in ponds and spread from there. Theplanting of mosquitofish by vector-controlagencies may be contributing to their spreaddue to the presence of clawed frog larvae inseveral mosquitofish source ponds in San Di-ego County (R. Fisher, USGS BiologicalResources Division, pers. comm.).

Predatory Warm-Water Fish(Centrarchids, Ictalurids, Cyprinids)

Green sunfish (Lepomis cyanellus), bluegill(Lepomis macrochirus), largemouth bass(Micropterus salmoides), black bullheads(Ameiurus melas), fathead minnows(Pimephales promelas), carp (Cyprinus carpio),and red shiners (Cyprinella lutrensis) have beenwidely planted into south coast reservoirs andstreams as sport fish or as bait for sport fish(Dudley and Collins 1995). These are hardyfish that thrive in warm waters of lakes, ponds,and low-elevation streams. They all prey onone or more life stages (i.e., eggs, larvae,metamorphs or adults) of native amphibiansand fish.

Native frogs are often absent from aquatichabitats where benthos-disturbing ictalurid(bullheads) and centrarchid (sunfish, bass) fishare introduced (Hayes and Jennings 1986).

ing present in fifty-three drainages within theassessment area. Of those fifty-three occupieddrainages, forty-three (81 percent) are alsoknown to be occupied by predatory fish (pri-marily sunfish, bass, and bullheads).

Figure 3.6. Non-native bullfrogs prey on many nativeamphibians and reptiles, including western pondturtles. ROBERT H. GOODMAN JR.

The effect of bullfrogs on red-legged frogshas been particularly well documented. Hayesand Jennings (1988) found that California red-legged frogs were still present at 81 percent(n=70) of sites lacking introduced bullfrogsand no longer present at all sites (n=10) wherebullfrogs were established. Using field enclo-sure experiments, Kiesecker and Blaustein(1998) found an 84 percent survival rate ofred-legged frog metamorphs when bullfrogswere absent; the survival rate was only 27 per-cent when adult bullfrogs were present.

The work of Kiesecker and Blaustein(1998) suggests an increased negative effectwhen bullfrogs occur in combination withpredatory fish. Survival rates of red-legged frogtadpoles averaged 89 percent when occurringalone or in the presence of only bullfrog tad-poles or only smallmouth bass. However, thesurvival rate decreased to 47 percent whenbullfrog tadpoles and smallmouth bass wereboth present. Apparently, red-legged frog tad-poles respond to the presence of bullfrogtadpoles by retreating to deeper waters and re-ducing their activity levels. This can beeffective at reducing competition. But whensmallmouth bass (or other predatory fish) arepresent in the deeper water, they prey exten-sively on the tadpoles (Kiesecker and Blaustein1998). This phenomenon probably affects thesurvival of other amphibians as well.

Our database of species occurrences bywatershed and drainage shows bullfrogs be-

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Chapter 3This is caused by high levels of predation onfrog eggs and tadpoles, particularly when tad-poles and predatory fish are crowded into smallpools during periods of interrupted surfaceflow during the driest parts of the year(Jennings 1988). This pattern of interruptedsurface flow is common in many streamswithin the assessment area.

Red shiners and fathead minnows are ef-fective predators on the eggs of native fish. Redshiner predation is believed to be a primaryfactor in the disappearence of Santa Ana speck-led dace from Big Tujunga Creek (Moyle etal. 1995).

One or more of these warm-water fish areknown to be present in eighty-one streamswithin the assessment area. As described in thesection on bullfrogs, the impact of these preda-tory fish appears to be exacerbated whenbullfrogs are also present (Kiesecker andBlaustein 1998). They are known to co-occur inforty-three steams within the assessment area.

German Brown Trout (Salmo trutta)

As with many of the warm-water fish,brown trout have been introduced into moun-tain streams in southern California as a sportfish. They tend to be more predatory on na-tive fish and amphibians than rainbow trout,and thus are considered more of a problem.The extirpation of Santa Ana suckers from theupper Santa Ana River has been attributed tobrown trout predation (Moyle et al. 1995).

Although brown trout have historicallybeen stocked into many streams, they have notpersisted in most locations. Currently, they aredocumented as present in only three assess-ment area streams: upper Little Rock Creek,Bear Creek, and the upper Santa Ana River.

Crayfish (Procambarus clarkii)

Non-native crayfish are commonly sold aslive bait and have been widely introduced intostreams, lakes, and ponds. Crayfish are om-nivorous and thus consume aquatic plants,algae, invertebrates, amphibian eggs, and fisheggs (Hobbs et al. 1989). In laboratory andfield experiments, Gamradt and Kats (1996)

found that crayfish were effective predators ofCalifornia newt (Taricha torosa) egg masses andlarvae, inflicting mortality rates of greater than80 percent.

In natural habitat within the Santa MonicaMountains of southern California, newts wereabsent from all streams where crayfish werepresent (Gamradt and Kats 1996). In one in-stance where crayfish were washed out of astream by winter floods, newts were backbreeding in the stream the next summer.

Crayfish have been documented in forty-three streams within the assessment area.

Mosquitofish (Gambusia affinis)

Mosquitofish are distributed freely bycounty vector-control personnel (Gamradtand Kats 1996) and thus have been introducedinto a large number of aquatic habitats. Oncebelieved to be an environmentally benign bio-logical agent for mosquito control, studies havesince determined that they can cause consid-erable ecological impact (Dudley and Collins1995). Mosquitofish prey on amphibian eggsand hatchlings (Grubb 1972; Gamradt andKats 1996) and are capable of dramaticallyaltering aquatic community structure(Hurlbert et al. 1972).

In the Santa Monica Mountains, Gamradtand Kats (1996) found that California newtswere present in all eight streams wheremosquitofish and crayfish were absent, butnewts were absent from all four streams thatcontained either of these two exotics.

Our database shows that mosquitofish arepresent in forty-seven drainages within the as-sessment area. This is likely to be a substantialundercount, however, since mosquitofish areoften taken for granted and not recorded infish surveys.

Brown-Headed Cowbird(Molothrus ater)

Brown-headed cowbirds are brood para-sites that lay their eggs in the nests of other“host” birds, particularly those that buildopen-cup nests (fig 3.7). Because many hostsraise cowbird young instead of their own,

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Figure 3.7. Speckled brown-headed cowbird eggsin a least Bell’s vireo nest. The cowbird hatchlingswill be fed and raised by the adult vireos as if theywere their own offspring. USFWS

birds forage on insects attracted by the live-stock concentrations and on the hay and grainthat are supplied to such areas (Rothstein etal. 1980). They are capable of traveling con-siderable distances between foraging sites andbreeding areas. In the San Luis Rey River Val-ley in San Diego County, Nickel (1992) foundradio-tagged male cowbirds travelling as muchas 5.4 miles (9 kilometers) from foraging tobreeding sites. Females traveled a maximumof 2.1 miles (3.5 kilometers) (Nickel 1992).

Cowbirds occur throughout the assess-ment area but are especially numerous in thefoothills where riparian woodlands are in closeproximity to grass or agricultural lands. Ri-parian woodlands support a rich diversity ofnesting birds from which the cowbirds selecthosts (Unitt 1984). Densities of cowbirds aremuch lower in montane coniferous forests(Verner and Ritter 1983) and desert-montanehabitats where high-quality foraging habitatis scarce.

Many birds are parasitized by cowbirds insouthern California, including threatened andendangered species such as the least Bell’s vireo,southwestern willow flycatcher, and Califor-nia gnatcatcher. One of the primary recoveryactions for the least Bell’s vireo has been thewidespread trapping of cowbirds near knownvireo populations (Beezley and Rieger 1987).These trapping efforts have been highly suc-cessful in some areas.

On the Santa Margarita River within theCamp Pendleton Marine Corps Base, the rateof cowbird parasitism on least Bell’s vireo nestswas at 47 percent in 1983 when the base be-gan an intensive cowbird trapping program.With annual trapping, by 1990 the broodparasitism rate had dropped to less than 1 per-cent (Griffith and Griffith, in press). Thepopulation of Bell’s vireos on the SantaMargarita River rose from 60 pairs in 1983 to319 pairs in 1993 (Griffith and Griffith 1995).Since the initiation of annual cowbird removalprograms, similarly dramatic population in-creases have occurred on the Tijuana and SanLuis Rey rivers and in the Prado Basin (Kus1995; Kus 1996; Pike and Hays 1997).

Brown-headed cowbirds are native toNorth America but prior to European settle-ment were largely confined to short-grassprairies in the middle of the continent(Mayfield 1965). Cowbirds feed by walkingon the ground in areas of short grass and bareground. They originally followed the herds ofbison present in the prairies and are likely tohave used scattered trees and riparian wood-lands within prairie areas for nest searching(Robinson et al. 1995).

European settlement was beneficial tocowbirds and enabled them to expand theirrange both westward and eastward. Irrigatedagriculture, livestock grazing, and urbaniza-tion all facilitated the spread of cowbirds andthey were well established in coastal southernCalifornia by the 1920s (Rothstein 1994).

In southern California, cowbirds reachtheir highest densities near dairies, stables, andother areas where livestock are concentratedand provided with supplemental food. Cow-

brood parasitism can substantially reduce hostbreeding productivity. High levels of brood para-sitism can threaten some host populations; thus,cowbirds have been implicated in the decline ofmany North American birds (reviewed inRobinson et al. 1995).

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Chapter 3European Starling (Sturnus vulgaris)

European starlings cause ecological prob-lems because of their sheer abundance andtheir ability to outcompete native birds for nestsites in tree cavities. Starlings have benefitedfrom human habitat modifications, irrigatedagriculture in particular (Ehrlich et al. 1988).

First introduced in New York City in1890, starlings were first documented in Cali-fornia in the 1940s (Jewett 1942). Populationsin southern California apparently exploded inthe 1960s. San Diego Christmas Bird Countsduring the 1960s show the following patternin starling numbers: 153 in 1963, 974 in 1964,1500 in 1965, 4,448 in 1968, and 7,928 in1969 (Unitt 1984).

The purple martin is a native bird whosedecline in southern California has been largelyattributed to competition for nest sites fromstarlings (Garrett and Dunn 1981). Westernbluebirds have also been significantly affected.

Argentine Ants (Linepithema humile)

Argentine ants are abundant in many ar-eas of human habitation, particularly wherethere is irrigated landscaping. They have spreadinto wildland habitats from developed areasand thus are primarily a problem near the ur-ban interface and in areas fragmented bydevelopment.

Suarez et al. (1998) studied Argentine antinvasions in habitat fragments of various sizesin urbanized coastal San Diego County. Ar-gentine ants were found in each fragment, butactivity was correlated with proximity to theurban edge and the amount of exotic vegeta-tion. Activity was always high within 320 feet(100 meters) of an urban edge.

Areas invaded by Argentine ants had fewernative ant species than uninvaded areas. Spe-cies most frequently absent in areas occupiedby Argentine ants were army ants(Neivamyrmex spp.) and harvester ants (gen-era Messor and Pogonomyrmex) (Suarez et al.1998). Studies elsewhere have documented simi-lar declines in the abundance of native antspecies in areas where the Argentine ant hasbecome established (Ward 1987; Holway 1995).

Ants and other invertebrates are funda-mental components of many ecologicalcommunities and large shifts in abundanceand species composition are likely to have sig-nificant effects on other species. Harvester antsare an important food source for the coasthorned lizard. These lizards appear to be de-clining in natural habitat fragments insouthern California. This decline may be re-lated to the influence of Argentine ants onharvester ants.

Red Imported Fire Ants(Solenopsis invicta)

Red imported fire ants have only recentlyinvaded southern California. They were firstdiscovered in November 1998 at a nursery andgolf course in Orange County (CDFA 1998;Schoch 1999). Since that time, colonies havebeen discovered in San Diego, Los Angeles,Riverside, and Kern counties (CDFA 1999).The ant is now thought to have been presentin the region for five to seven years (anony-mous 1999).

The red imported fire ant is native to thePantanal region of Brazil, Paraguay, and Ar-gentina, and is thought to have beenaccidentally introduced multiple times toMobile, Alabama, between 1933 and 1945(Buren et al. 1974; Greenberg et al. 1999).Concerns about its arrival in southern Cali-fornia stem from the well-documented damagecaused by infestations of red imported fire antsin twelve southeastern states. In that region,the ant has invaded residential areas and somenatural habitats. It aggressively stings when dis-turbed and thus is considered to be a majornuisance pest in developed areas.

From an ecological standpoint, the threatposed by imported fire ants is similar to thatof the Argentine ant, although perhaps greaterin magnitude. Like the Argentine ant, the redimported fire ant readily invades disturbedareas around human habitation. It requiresmoisture and cannot survive cold temperatures(Vinson and Greenberg 1986). Thus, occu-pation of wildlands is expected to be limitedto lower elevation riparian zones or irrigated

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areas adjacent to urban areas. However, redimported fire ants have recently invaded areasof west Texas formerly thought to be too dryfor the species, and there is evidence that thisrepresents a heritable adaptation (Mackay andFagerlund 1997; Li and Heinz 1998; Phillipset al. 1996). Thus, there is potential for theants to eventually occupy portions of Califor-nia previously thought to be too dry. At aminimum, they pose a threat to the integrityof any habitats that lie along the urban-wild-land interface, particularly small wildlandpatches that are largely surrounded by devel-opment or irrigated land.

Similar to the Argentine ant, red importedfire ants have greatly reduced the abundanceof native ants and other invertebrates in por-tions of the southeastern United States (Porterand Savignano 1990; Morris and Steigman1993). Yet, they have the additional impactof being an aggressive predator of vertebratenests and young, commonly swarming thenests of ground-nesting birds, mammals, andreptiles (Hill 1969; Mount et al. 1981;Ridlehuber 1982; Drees 1994; Allen et al.1995).

Management Considerations forExotic Species Control

Exotic species are widespread and most aredifficult to eradicate even from small areas.The potential is high for control efforts to beineffective if they are not carefully planned andsustained. Consequently, management activi-ties to control exotics should (1) have clearlydefined and achievable objectives, (2) be sus-tained over time, and (3) be monitored in anadaptive management framework to ensureobjectives are being met and the most effec-tive techniques are being used.

To succeed, exotic species control effortsprobably need to be narrowly targeted to spe-cific key areas where both the circumstancesfor control are favorable and the potential forrecovery of rare habitats or species is high.Examples of successful, targeted control effortscurrently ongoing within the assessment areainclude:

• Arundo removal to restore high-quality,low-elevation riparian habitat along SanFrancisquito Creek and Elizabeth LakeCanyon in the Angeles National Forestand along the Santa Margarita River inSan Diego County;

• Brown-headed cowbird trapping tocontrol nest parasitism on thesouthwestern willow flycatcher and leastBell’s vireo along the San Luis Rey Riverin the Cleveland National Forest;

• Bullfrog control to improve arroyo toadand red-legged frog survivorship alongportions of Sespe Creek in the LosPadres National Forest; and

• Mediterranean grass control through thecareful timing of prescribed fire toincrease the abundance of native grassesand forbs and improve Engelmann oakregeneration on the Santa Rosa PlateauReserve in Riverside County.

Another important management consid-eration is how best to minimize or preventadditional introductions of undesirable, non-native species. This is a difficult task, sinceintroductions can occur in a multitude of waysthat are usually difficult to anticipate and pre-vent. However, some feasible preventativemeasures include (1) close coordination withCDFG representatives on planned introduc-tions and stockings; and (2) careful screeningof seed mixes or plantings used for erosioncontrol, landscaping of recreation facilities,and habitat restoration projects.

The Influence of NativeInsect and Disease Outbreaks

Vegetation is continually preyed upon byindigenous insects and pathogens. Most of thetime these organisms remain at levels wherethey do not cause rapid, large-scale changesin the structure or composition of plant com-munities. Yet certain conditions can triggermajor insect or disease outbreaks that resultin substantial plant mortality. The specificinsects and diseases prone to damaging out-breaks are often described as pest species.

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Chapter 3Historically, pests of forest trees have re-

ceived more attention than those of othernative plants, perhaps because of the economicvalue of the commodity affected and the highlyvisible nature of concentrated tree mortality.Native insect herbivores and pathogens of for-est trees perform important functions innatural ecosystems, killing decadent trees, cre-ating dead and down woody habitat for otherspecies, recycling nutrients, and creating gapsfor regeneration (Pronos et al. 1999). How-ever, these pests also increase fuel loading,contributing to fire hazards in forests. The fol-lowing discussion concerns the major forestpests (in terms of numbers of trees damagedor killed) in southern California.

The pests discussed below are not inclu-sive; there are many other insects andpathogens of importance in southern Califor-nia forests. Of particular interest here are thosepest species whose populations have greatlyincreased as a result of twentieth-century man-agement activities, particularly tree removaland changes in natural fire regimes.

Root DiseasesForemost among the root diseases in

southern California is annosus root disease ofpine, caused by a strain of Heterobasidionannosum. This fungus colonizes freshly cut,untreated conifer stumps and grows downthrough the woody tissue and into the roots,where it may survive saprophytically for up tofifty years. Live pines and other susceptiblewoody plants become infected when theirroots contact infected roots in the soil. Thefungus may kill the pines directly or debili-tate them to the point where they are readilycolonized and killed by bark beetles or otherwoodboring insects (Smith 1993). Annosusroot disease has significantly reduced vegeta-tive cover in some recreation sites, particularlysince the openings created by the disease can-not be replanted with pines. Infection by thispathogen can be prevented by treating freshlycut stumps with borate (Sporax®)(Graham1970; Smith 1970). Tree removal in southernCalifornia forests, particularly in the yearsprior to the mid-1970s, when borate treatment

became common, is thought to be responsiblefor the widespread occurence of annosus rootdisease centers. This disease is particularlycommon in the Jeffrey pine forests of LagunaMountain and to the northeast of Big BearLake in the San Bernardino Mountains wherewestern juniper is also affected, and in themixed conifer forests of the San Bernardinoand San Gabriel mountains, as well as in otherforested lands in the Transverse and Peninsu-lar ranges.

Another strain of H. annosum causes aroot, butt, and heart rot of true fir. The fun-gus enters the wood through logging and otherinjuries, fire scars, broken tops, and freshly cutstumps (Scharpf and Goheen 1993). In firsthis disease causes a general decline rather thanrapid mortality, and is found in mixed coniferforests throughout the Transverse and Penin-sular ranges.

Black stain root disease, caused byLeptographium wageneri, causes extensive mor-tality in one species of single leaf pinyon pine(P. monophylla) in portions of the San Bernar-dino Mountains, but not elsewhere insouthern California. In the San BernardinoMountains, 8,000 acres are reported to be af-fected. The disease has not been reported fromtwo southern California endemics, P.californiarum ssp. californiarum, a lower eleva-tion single leaf pinyon, and P. quadrifolia, Parrypinyon. Spread is through root contact andmost likely, though not adquately investigated,through the activities of root-feeding insects.Trees infected with black stain are often at-tacked and killed by the pinyon pine engraver,Ips confusus (see below), although the diseasealone often kills trees. This disease is secondonly to stand-replacing fires as a mortalityagent in pinyon. It is not known if manage-ment activities have affected the incidence ofthe disease (Merrill et al. 1992).

Armillaria root disease, caused byArmillaria mellea, can build up on dead ordying native oaks and attack and kill youngconifers nearby. In southern California thisfungus does not cause extensive mortality butcan be a problem when large oaks are removed

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from a site and conifers are planted. The newlykilled oak stumps provide a large food base,allowing the fungus to grow rapidly andovercome nearby conifers.

Dwarf and True (Leafy) MistletoesThe dwarf mistletoes (Arceuthobium spp.)

are serious parasites of pines in southern Cali-fornia. These mistletoes are both water andnutrient parasites, and heavily infected treesare readily killed by bark beetles and otherinsects or drought. The most widespread spe-cies are the western dwarf mistletoe, A.campylopodum—which infects ponderosa, Jef-frey, knobcone, and Coulter pine—and sugarpine dwarf mistletoe, A. californicum, whichinfects sugar pine. A. occidentale, which infectsgray (foothill) pine, as well as A. divaricatum,in pinyon pines, and A. cyanocarpum, in lim-ber pine, also occur in southern California(Scharpf and Hawksworth 1993). Althoughbirds can carry dwarf mistletoe seeds on theirfeet and feathers, infection most often occurs asa result of the forceful ejection of seeds from thefemale plant. Thus, susceptible understory treescan be infected by mistletoe in the overstory.

Management of dwarf mistletoes can beaccomplished by removing diseased overstory,isolation of susceptible understory from dis-eased overstory trees by distance or the use ofbuffers (nonhost trees planted between the in-fected and uninfected trees), and pruning orremoval of infected trees (Scharpf et al. 1988).The latter method is used in southern Cali-fornia campgrounds and other high-userecreation sites where the value of individualtrees can justify treatment costs. Dwarf mistle-toe is a good example of an organism whichshould not be considered a pest where infec-tion, dieback, and some tree mortality do notinterfere with management objectives. Themistletoe plants support their own herbivores,and the witches’ brooms, dead limbs, and deadtrees that result from mistletoe infections cre-ate habitat for other species.

It is not known if fire suppression andother management activities in the twentiethcentury have changed the relative abundance

of dwarf mistletoes. Stand-replacing fires caneliminate local populations as the host treesare able to return to sites more rapidly thantheir mistletoe parasites. Spotty fires can leaveinfested overstory trees which both regener-ate the stand and reinfect it. Heavily infestedstands may contain more fuels because of theaccumulation of dead witches’ brooms andtrees, and fires in them may turn into confla-grations. Smoke may inhibit dwarf mistletoeseed germination, depending on length of expo-sure (all reviewed by Hawksworth and Wiens1996). It is likely that prior to the arrival of Eu-ropeans in southern California, dwarf mistletoeswere abundant, at least in patches.

True mistletoes, Phoradendron spp., infecthardwoods, white fir, incense-cedar, and ju-nipers in southern California. Unlike dwarfmistletoes, these species photosynthesize andare primarily water parasites and thus are farless damaging to their hosts. The berries areeaten by birds, which then disperse the seeds.True mistletoes can be serious pests where in-dividual trees are of high value, such as incampgrounds. Heavily infected trees have re-duced growth rates, are weakened, and aresometimes killed outright. Weakened treesmay be attacked and killed by insects or maysuccumb in times of drought. There is no evi-dence that general management activities haveincreased the frequency of infection by thesespecies, except perhaps in the case of whitefir, where fire suppression is thought to haveincreased the occurrence of the host and thus,too, of the parasite. Mistletoe infections inwhite fir contribute, with annosus root andbutt rot, to general decline of trees, leading totopkill or whole tree mortality when insects(particularly bark beetles and roundheadedborers) attack.

Bark BeetlesBeetles in the family Scolytidae are best

known for delivering the “coup de grâce” toconifers stressed by disease, drought, or otherfactors. When populations of some speciesbuild up during droughts, even vigorouslygrowing trees may be successfully attacked andkilled. Two genera are primarily responsible

91

Chapter 3tack. Thus proper sanitation is believed to beessential to the management of these beetles(Furniss and Carolin 1977).

Scolytus ventralis, the fir engraver, is themost commonly found bark beetle in whitefir. This nonaggressive scolytid may kill patchesof the phloem, which may heal over; tops oftrees; and whole trees; depending upon thesize of the trees and the relative level of stressto the trees from pathogens and other agents(Furniss and Carolin 1977).

Preventing losses to bark beetles requireskeeping stressors—such as root disease anddwarf mistletoe—at low levels. Thinning toreduce stocking density should be used to re-duce the risk of drought stress, but shortagesof personnel and Timber Stand Improvement(TSI) dollars have reduced the number of acresthinned in recent years. Forest Pest Manage-ment pest prevention and suppression dollarscan be used, when available, to thin stands atrisk of bark beetle-caused mortality, and tosuppress dwarf mistletoe and other pests.

Round and Flatheaded BorersRound and flatheaded beetles are sometimes

important mortality agents. Two species are ofparticular importance in southern California, theCalifornia flatheaded borer, Melanophilacalifornica (Buprestidae), and the roundheadedfir borer, Tetropium abietis (Cerambycidae). M.californica infests and kills mature to decadenttrees and is usually found in dying trees in thelargest diameter classes, e.g., the large old Jeffreypines which were once common on LagunaMountain in San Diego County. T. abietis is acommon mortality agent of white fir stressed byother pests, drought, or poor growing condi-tions (Pronos et al. 1999). Other cerambycidsand buprestids feed in dead and dying trees,returning nutrients to the soil and servingthemselves as food for birds. These insects aresometimes considered pests because their feed-ing decreases the value of lumber (Furniss andCarolin 1977). Fire suppression is thought tohave increased the proportion of white fir instands that were formerly primarily pine, in-creasing the abundance of T. abietis and otherpests on the off-site firs.

for pine mortality in southern California,Dendroctonus and Ips. The former includesspecies such as the western pine beetle, D.brevicomis, which has several generations peryear and can build up rapidly in stressed trees.This species has been associated with wide-spread Coulter pine mortality on the westernslopes of the San Jacinto Mountains and por-tions of Palomar Mountain in the early 1990s(Merrill, pers. obs.; Merrill 1991), as well ashistorically in Lost Valley and the northernslope of Hot Springs Mountain in San DiegoCounty (Hall 1958). Other species in the ge-nus—including the Jeffrey and mountain pinebeetles, D. jeffreyi and D. ponderosae, respec-tively—have one generation per year. Like D.brevicomis, these species can attack and killotherwise vigorous trees when beetle popula-tions are high. In southern California thesebeetles are most often found in Jeffrey pine(D. jeffreyi), and ponderosa and sugar pines(D. ponderosae). For unknown reasons bothspecies have patchy distributions among themountains of the Transverse and Peninsularranges in southern and Baja California. D.valens, the red turpentine beetle, infests freshlycut stumps and roots and lower bole of livingtrees, particularly those damaged by fire orroot disease. This species rarely causes treemortality but does contribute to the declineof trees which are then attacked by more ag-gressive species (Furniss and Carolin 1977).

Ips species are commonly called engraverbeetles for their habit of feeding on (engrav-ing) the cambial surface of the xylem as wellas the phloem of pines. These beetles are usu-ally not considered as aggressive asDendroctonus spp., although they are responsiblefor much tree mortality, particularly of pinyonpines with black stain root disease (the pinyonips, I. confusus) and smaller diameter trees orportions of trees. For example, I. paraconfususand I. pini commonly kill tops of large pines. I.emarginatus can kill Jeffrey, ponderosa, sugar, andlodgepole pine in southern California. All ofthese species of Ips have several generations peryear. Ips beetle populations may build up in slashto levels where small diameter trees and tops ofmature trees in the vicinity are at risk for at-

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Figure 3.8. An aerial view of ski area developmentsnear Big Bear Lake on the San Bernardino NationalForest. JOHN STEPHENSON

The Influence of RecreationActivities

Public lands in the southern Californiamountains and foothills are popular outdoorrecreation areas. Recreation is the principalland use activity in the region’s state andcounty parks and it is also the most commonactivity in the national forests. With a rapidlygrowing urban population nearby, the num-ber of recreationists visiting the assessment areais steadily increasing. Some go in search ofcalm and serenity, while others pursue adven-ture, excitement, or simply escape from theurban environment. Activities that fall into thecategory of outdoor recreation include, al-though are by no means limited to, camping,picnicking, driving, hiking, site-seeing, wild-life viewing, hunting, fishing, target shooting,off-highway vehicle (OHV) driving, horsebackriding, mountain bike riding, skiing, andmountain climbing.

The land management agencies do a vari-ety of things to accommodate and enhancethese outdoor recreation experiences. A vastnetwork of roads and trails is maintained. Pic-nic areas and campgrounds (both developedand remote) are established and maintained.Information centers and interpretive programsare provided. Through special use permits, sitesare leased to private entities for downhill skiarea developments (fig. 3.8), organizationalyouth camps, recreation residences, and shoot-ing ranges. Habitat improvement projects areundertaken to enhance game and sport fishpopulations, and the California Departmentof Fish and Game stocks many lakes andstreams with catchable fish. These develop-ments and services are popular and there is asteady demand for improvements and addi-tions.

While some level of recreation activityoccurs almost everywhere, the vast majority isconcentrated in a relatively small number ofpopular areas (fig 3.9). These areas are oftenassociated with developed facilities and easilyaccessible by road. Developed sites provide ameasure of environmental protection by keep-

ing impacts localized and by providing facili-ties such as toilets and trash cans. However,concentration of activity also tends to causeecological impacts (Boyle and Samson 1985).Frequent traffic in an area causes reductionsin vegetative cover, with the rate of reductionbeing highly influenced by the type of activ-ity (e.g., motorized vehicle or horse trafficreduces ground cover more rapidly than foottraffic)(Liddle 1997). Concentrated humanactivity is also more likely to cause incidentalanimal mortality (e.g., trampling of nests or eggmasses) and can cause disturbance-sensitivespecies to avoid areas that would otherwise bysuitable habitat (e.g., bighorn sheep).

Localized impacts from recreation activi-ties can be relatively benign. Problems arisewhen high-use recreation areas overlap withsensitive habitats or rare species populations(table 3.14). In southern California, the po-tential for overlap is heightened by the factthat areas rich in rare habitats and species—riparian areas, montane meadows, and coni-fer forests—also tend to be popular locationsfor recreationists. In some of these areas, nor-mally harmless activities become seriousthreats because of the extreme rarity or vul-nerability of a species occurring in the vicinity.

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Figure 3.9. Developed recreation sites and other areas that receive concentrated recreation use in theassessment area.

et al. 1988; Gutzwiller 1991; Knight andGutzwiller 1995; Liddle 1997). Making mat-ters worse is the lack of scientific studies onthe ecological effects of recreation activities inthe southern California mountains and foot-hills. All of the local information we couldfind on this subject was based on anecdotalobservations. There is a real need for formalscientific studies to assess the effects of recre-ation activities on rare species and habitats andto evaluate the efficacy of management actionscurrently being taken to avoid or mitigatethose effects.

For example, people walking in a creek is anormally harmless activity, but at certain timesof the year in the few remaining areas wherearroyo toads or mountain yellow-legged frogsstill occur, it can greatly affect the survival ofthese imperiled species (Jennings 1998; Sweet1992).

Our scientific understanding of the effectsof recreation activities on wildlife is rudimen-tary at best (Knight and Cole 1995).Numerous studies on the ecological effects ofrecreation have been conducted, but theknowledge gained is disparate and seldomdefinitive (see reviews in Boyle and Sampson1985; Hammitt and Cole 1987; Pomerantz

94

Human activities in and around these sites(e.g., driving, biking, walking through thestream, and picking up animals) are report-edly causing significant adult mortality anddeclines in reproductive success (Sweet 1992;USFWS 1998a). Similar adverse effects result-ing from recreational activity have beenreported for pond turtles (Holland 1991), red-legged frogs (Jennings and Hayes 1994), andmountain yellow-legged frogs (Jennings1995a, 1998).

Management efforts to avoid or mitigatethese impacts include seasonal closures of someroads and recreation areas and restrictions onvehicle access in some areas (e.g., walk-incampgrounds). Most of these measures have

Table 3.14. Key ecological issues that are influenced by recreation activities.

Many of the anecdotal reports of negativerecreation impacts pertain to riparian andaquatic habitats. Foothill river corridors arecool, pleasant places that are often only a shortdrive from urban areas. They attractrecreationists in large numbers (fig. 3.10), andover the years that demand has been accom-modated through the establishment ofcampgrounds and picnic areas in popular ar-eas. Only recently has it been recognized thatmany of these same areas are also importanthabitats for imperiled species.

Developed recreation sites are particularlyprevalent near low-gradient stream and ter-race habitats occupied by the endangeredarroyo toad (Sweet 1992; USFWS 1998a).



with Recreational ActivitiesCurrent Trends andAreas Most Affected

Declines in conditionof sensitive habitatsor direct mortalityof rare species.

Indirect impacts todisturbance-sensitivespecies.

• Riparian habitat• Arroyo toad• Meadows• Pebble plains• Alpine plants

• Reductions in vegetative coverare common in areas thatreceive frequent recreation use

• Direct mortality occursprimarily from vehicular traffic,but also is caused by trampling,pollution, or harassment (e.g.,capturing or plinking slowmoving animals)

• Impacts are localized but canbe significant; the level ofimpact is strongly related to theamount of use an area receives

• Facilities operated by privateentities under special usepermit (e.g., ski areas,organizational camps,recreation residences) aresometimes located in sensitivehabitats or near rare species.

• Recreation use is believedto be increasing in mostareas; there is a highdemand for additionalrecreation facilities

• Popular recreation areasthat also contain many rarespecies include LagunaMtn., Big Bear Valley,Holcomb Valley, SanGabriel River, Little RockCk, Big Tujunga Ck, SespeCk, and Santa Ynez River

• Popular trails to thesummits of Mt. SanGorgonio, Mt. San Jacinto,Mt. San Antonio (Baldy) andMt. Baden-Powell causesome impacts to alpinehabitats

• Bighorn sheep• Mule deerfawning habitat(meadows)

• Bat roosts(abandonedmines andbuildings

• Bighorn sheep are extremelysensitive to human activity andmove to avoid it; this hascaused them to retreat fromsome of their most suitablehabitat areas.

• Mule deer will avoid suitablefawning habitat if there is a lotof human activity

• Bats will abandon roost sites ifthere is a a high level of humanactivity

• Bighorn sheep are beingaffected in the eastern SanJacinto Mts near PalmSprings and in the SanGabriel Mts in Lytle Creekand around Mt. Baldy

• Some of the best fawninghabitat in the upper SantaAna River watershed isavoided by deer due to highlevels of recreation use(Nicholson 1995)

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Chapter 3only recently been instituted. Much could belearned by careful monitoring of their effec-tiveness, both in terms of controllingrecreationists and reducing impacts to the tar-get species.

Organizational camps, recreation areas,and public campgrounds are numerous in co-nifer forests and montane meadows (e.g.,Laguna Mountain, Cuyamaca, Idyllwild,Barton Flats, Big Bear/Holcomb Valley,Lake Arrowhead, Big Pines, Crystal Lake,Mount Pinos/Cuddy Valley, and PineMountain). The facilities and interpretiveprograms provided in these areas offer impor-tant opportunities for young people fromsouthern California’s cities to learn about thenatural environment. The organizationalcamps in particular tend to have strong envi-ronmental education programs and areconscientious about minimizing human im-pacts. However, in some areas these facilitiesoverlap with highly sensitive ecological areasand can cause declines in habitat capability.

Figure 3.10. Recreation use in and along the San Gabriel River, Angeles National Forest. ROBERTGOODMAN JR

Sensitive plants are particularly common inmontane meadows and, in dense conifer for-ests, some recreation facilities are in closeproximity to spotted owl nest sites. Nicholson(1995) reported that mule deer largely avoidedareas regularly occupied by humans (e.g.,campgrounds and summer cabins), to the ex-tent that they did not utilize meadow habitatsthat would otherwise be high quality foragingand fawning areas.

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Table 3.15. Key ecological issues that are influenced by the presence or density of roads.



with RoadsCurrent Trends andAreas Most Affected

Declines in survivaland recruitment ratesof some species.

Illegal collecting orpoaching of animals.

Barriers to animaldispersal.

Declines in conditionof sensitive habitats.

• Riparian habitats• Arroyo toad• Spadefoot toad

Animal mortality caused byvehicle traffic on roads can besubstantial. Stream crossingsand roads adjacent to riparianhabitats pose particularconcerns for slow-movingspecies (e.g. toads, frogs).

Roads on stream terracesand crossings in low-gradient foothill and desertstreams are affecting theendangered arroyo toad.Seasonal closures andmodifications to crossingsare being done to reduceimpacts.

• Mtn. kingsnakes• Rosy boas• Pond turtles• CA newts• Mule deer

Can cause substantial declinesin species abundance inheavily collected areas. Roadsfacilitate this activity becausecollecting is almost invariablydone along or near them.

Mountain lions Busy highways (particularlyinterstate highways) can bevery difficult for some animalsto cross, and may be resultingin population fragmentation.

Interstates 8 and 15 crossthe Cleveland NF; I-10 and I-15 separate portions of theSan Bernardino NF; I-5 runsbetween the Angeles andLos Padres NFs.

It is difficult to determinetrends in this activity.

• Pebble plains• Riparian habitats

• Illegal or unauthorizedactivities are more likely tooccur in roaded areas andare difficult to prevent; thisincludes pollution, vandalism,driving in unauthorized areas.

• Increased flow of sedimentinto streams

There is little new roadconstruction on public landsand some problem roadsare being obliterated.

The Influence of Roads

Roads are the primary means by whichpeople access the outdoors. Thus, the amountof human use in a area is highly correlatedwith an area’s road accessibility. There are manybenefits to having areas accessible by road: itimproves firefighting effectiveness, increasesopportunities for habitat management work,and provides basic access to the public lands.However, the presence of roads also leads toimpacts associated with vehicular traffic andincreased human use (table 3.15).

Roads in and adjacent to riparian areas cancause substantial impacts. Roads located on

stream terraces, or that frequently crossstreams, can be a major source of mortality toslow-moving animals such as the arroyo toad.These nocturnal toads actually move onto dirtroads at night to feed and many individuals canbe killed by a few vehicles (USFWS 1998a). Thisis a particular problem in and around camp-grounds that are located on stream terraces neararroyo toad breeding habitat (Sweet 1992). Simi-lar problems of high mortality rates where a roadruns close to breeding habitat have been observedfor the spadefoot toad (E. Ervin, San Diego StateUniversity, pers. comm.).

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Chapter 3

The increased flow of sediment intostreams is one of the most commonly citedenvironmental effects of unpaved roads. Roadsreportedly contribute more sediment tostreams than any other land management ac-tivity (Gibbons and Salo 1973; Lee et al.1997). Old roads that were not designed us-ing current “Best Management Practices”(BMP) standards often have the greatest en-vironmental impact, particularly if located insteep terrain (fig 3.11). Sediment productionfrom logging roads in steep terrain in Idahowas 770 times higher than in undisturbed ar-eas; approximately 71 percent of the increasedsediment production was due to mass erosionand 29 percent was due to surface erosion(Megahan and Kidd 1972). Increases in masserosion due to plugged culverts and fill slopefailures are especially common on abandonedor unmaintained roads (Weaver et al. 1987).

Figure 3.11. Gully erosion caused by runoff from aculvert on Gator Road, Laguna Mountain, ClevelandNational Forest. Restoration efforts have since beenimplemented and the area is recovering. DEVEREEVOLGARINO

Roads tend to cross streams in low-gradi-ent reaches where the current slows.Unfortunately, those areas are also where sandypools form, the primarily breeding habitat forarroyo toads. Vehicle traffic on roads that crossthrough, or adjacent to, breeding pools causemortality of eggs and juvenile toads. Effortsare underway in several areas, particularly onthe Los Padres and Cleveland national forestswhere this problem is most common, tomodify stream crossings to reduce impacts toarroyo toads.

Unlawful activities tend to be a chronicproblem in some road-accessible areas. Illegalcollecting of reptiles, unauthorized woodcut-ting, illegal OHV activity, poaching,vandalism, and dumping of hazardous mate-rials: all of these are difficult law enforcementissues that occur almost exclusively along ornear roads. Non-native species introductions(both purposeful and inadvertent ones) alsooccur predominately in areas that are acces-sible by road. All of these things causesignificant declines in habitat capability in lo-calized areas. The inherent difficulty inpreventing these impacts from occurring inroaded areas is a compelling reason for main-taining some areas in a roadless condition.

As part of our watershed-scale analysis welooked at “roadedness” in several differentways. First, we identified all existing roadlessareas that are larger than 1,000 acres (fig 3.12).Second, we looked separately at each water-shed, calculating the percentage of thewatershed that falls within 250 meters of anactive road (table 3.16). Not surprisingly,many of these “least-roaded” watersheds alsoshow up in table 2.15 (chapter 2) in the listof drainages that have high potential formaintaining aquatic ecological integrity dueto low land use intensity and low numbersof exotic species.

Figure 3.12. Roadless areas of 1,000 acres or more are shaded. The black lines outline the boundaries offormally designated roadless areas (i.e., designated wilderness areas or areas specified as unroaded in theForest Plan).

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Table 3.16. The fifteen least-roaded watersheds in the assessment area based on the percent ofthe watershed that lies within 250 meters of an existing road.

Sisquoc River (above Cuyama confl.) So. Los Padres 10% 87%Big Sur River No. Santa Lucia 11% 84%Upper Sespe Ck (above Timber Ck) So. Los Padres 14% 96%Upper San Gabriel R. (East Fork) San Gabriel Mts 12% 98%West Fk, San Gabriel R. San Gabriel Mts 16%

Little Rock Creek San Gabriel Mts 15% 97%Santa Cruz Creek So. Los Padres 14% 72%Upper Ventura River So. Los Padres 14% 94%Little Sur River No. Santa Lucia 17% 56%Up. Arroyo Grande (above Lopez Res.) So. Santa Lucia 18%

Up. Santa Ynez (above Gibraltar Res.) So. Los Padres 18% 98%Lower Sespe Ck (below Timber Ck) So. Los Padres 19% 84%Castaic Creek Castaic Ranges 20% 93%Palm Canyon San Jacinto Mts 20% 30%Deep Canyon San Jacinto Mts 21% 37%

Percent ofwatershed thatlies within 250

meters of a road

Percentpublicland in

watershedMountain Range

SubareaWatershed

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

The Influence of Timber andFuelwood Harvest

Most of the land base suitable for com-mercial timber harvest in southern Californiais within the San Bernardino National Forest.An active timber program was sustained onthat forest from the late 1940s (post WorldWar II) through the mid-1980s (fig 3.13).Harvest levels peaked in the 1960s, with 27.4million board feet (MMBF) harvested on theSan Bernardino National Forest in 1963 alone(McKelvey and Johnston 1992). Volume datafrom the California Department of Forestryand Fire Protection (1947 to 1978) and theCalifornia State Board of Equalization (1979to 1990) for San Bernardino and Los Angelescounties show that 362.3 MMBF of timberwere removed from those counties between1947 and 1990 (McKelvey and Johnston1992). Some of that would have come fromthe San Gabriel Mountains within the Ange-les National Forest, but most was from themore densely forested San Bernardino Moun-tains.

Figure 3.13. Logging intensity in San Bernardinoand Los Angeles counties, 1947 to 1990. Most ofthis timber came off the San Bernardino NationalForest (from McKelvey and Johnston 1992).

Some commercial timber harvesting wasdone in the Cleveland and Los Padres nationalforests during peak years in the 1960s and1970s, but it was short lived. The smallvolumes produced in these areas were not suf-ficient to support viable sawmill operations;

Mill

ions

of B

oard

Fee

t (sc

aled

)

0

5

10

15

20

25

30

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990

Year

100

The Influence of LivestockGrazing

Livestock grazing has been a traditionalactivity on both public and private land in thesouthern California mountains and foothillssince at least the early 1800s (Lockmann1981). When assessing the effect of this activ-ity on ecosystems and species, it is importantto distinguish the impact of historic grazingfrom that which can be attributed to grazinglevels occurring today. Abusive grazing prac-tices in the late 1800s and early 1900s causedenvironmental changes that are orders of mag-nitude greater than anything seen in recenttimes.

Livestock numbers reached their peak inthis region from approximately 1860 to 1900,when sheep grazing was in its heyday. Use wasparticularly high in the montane meadows ofthe San Bernardino and San Jacinto moun-tains; it is reported that 30,000 sheep wereherded into Big Bear Valley in the late 1860s(Lockmann 1981). There are numerous ac-counts of extensive devegetation and erosiondamage occurring during this period(Lockmann 1981; Minnich 1988) and, al-though sheep grazing was discontinued in themountains in the early 1900s, the damagedone was evident long afterwards (Pillsbury1933).

Table 3.17. Key ecological issues that are influenced by fuelwood harvesting.


Most Affected

Effects Associatedwith Fuelwood Harvest

ActivitiesCurrent Trends and

Areas Most Affected

Retention andrecruitment of largediameter trees, snags(standing dead trees),and downed logs.

Increases in small-diameter trees inthe forest understory.

Cavity nesters, snag-dependent species.

Large snags that arereachable by roads can bedifficult to retain because ofunauthorized cutting.The same is true of largedowned logs.

Snag retentionrequirements in existingForest Plans are adequate,but enforcement is difficultin popular woodcuttingareas.

Mesic mixed coniferforests.

If fuelwood demand can be metthrough harvesting small trees,this activity could help controlthe problem.

Problem is most acute in thewestern San BernardinoMtns. but is occurring inmany montane coniferareas.

thus, timber had to be trucked long distancesto the nearest mill. This same problem ulti-mately affected the San Bernardino NationalForest timber program when dropping har-vest levels in the late 1970s led to closure ofthe last mill in the area.

For the past decade (much longer in someareas), small timber programs on the south-ern forests have focused on (1) forest healthissues (e.g., treatment of insect and diseasecenters, understory thinning, and fuels reduc-tion); (2) administering individual permits toaccommodate local demand for fuelwood; and(3) identifying and removing hazard trees.Small-scale salvage operations to remove treeskilled by wildfire or bark beetles are also occa-sionally done.

When evaluating the influence of timberharvesting on southern California ecosystems,we must separately consider historic effectsfrom current effects. Past timber harvesting,particularly in the San Bernardino and SanJacinto mountains, has probably resulted in asubstantial reduction in the number of largetrees, with ponderosa and Jeffrey pines incur-ring the greatest reductions. It may also havecontributed to the increased dominance ofwhite fir.

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Chapter 3

Figure 3.14. Livestock grazing at Hudson Ranch adjacent to the Los Padres National Forest. BrushMountain can be seen in the background. DAVE CLENDENON

Since 1900, cattle have been the principallivestock animal on southern California range-lands. Grazing can occur year-round in foothillsavannas and grasslands and during the sum-mer months in montane meadows and forests(fig. 3.14). Over the years there has been agradual decline in the intensity and extent ofcattle grazing in this region. Once the domi-nant use of meadows in the San Bernardinoand San Jacinto mountains, grazing has beengreatly reduced in these ranges as ranching inthe surrounding valleys has declined and otherland use activities, particularly recreation, havereceived greater emphasis.

Today, grazing within the assessment areais concentrated in and adjacent to the Los Pa-dres National Forest and, to a lesser extent, inthe San Diego County foothills within andadjacent to the Cleveland National Forest(table 3.18) (fig. 3.15). Rangelands in theseareas are predominantly oak savannas, grass-lands, montane meadows, and openings inchaparral and scrub.

Ecological changes most commonly attrib-uted to overgrazing by cattle involve declinesin the condition of riparian, oak woodland,grassland, and meadow habitats. More specifi-cally, livestock grazing has been implicated inreduced tree regeneration, substantial reduc-tions in vegetative cover, streambankdestablization, water quality degradation, andthe spread of non-native weeds (table 3.19).

A comprehensive review of studies assess-ing the impact of livestock on Californiaecosystems, with particular emphasis on theSierra Nevada, was recently conducted by agroup of scientists with expertise in Califor-nia rangeland issues (see Allen-Diaz et al.1999). Their findings suggest that despite themany studies of grazing and its impact on eco-systems, there are still far more questions thananswers regarding this issue. There appears tobe a scarcity of studies which quantify the ef-fects of different grazing intensities,frequencies, and seasons of use. Instead moststudies simply compare the impacts of heavy

Figure 3.15. Locations of current grazing allotments on national forest system lands within the assessmentarea.

Table 3.18. Shows acres of national forest system land that are within grazing allotments, by mountain rangeand over the entire assessment area. Also, the percentage of all national forest system lands that are withinthese allotments. Some of the allotments are not currently being used.


SanDiego

Ranges

SantaAnaMts

SanJacinto

Mts

SanBernar-dino Mts

SanGabriel

Mts

CastaicRanges

S. LosPadresRanges

S. SantaLuciaRng

N. SantaLuciaRng

Acres 129,147 5,017 76,917 94,968 0 22,344 560,619 184,202 51,898 1,133,456

Percent of National 45% 4% 39% 24% 11% 44% 99% 59% 32%

Forest System Land

Area within ForestService GrazingAllotments

EntireAssess-mentArea

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Chapter 3Table 3.19. Key ecological issues that are influenced by livestock grazing activities.


Most AffectedEffects Associated with

Livestock Grazing ActivitiesCurrent Trends andAreas Most Affected

Declines in conditionof sensitive habitatsor direct mortalityof rare species.

Lack of oakregeneration.

Spread of invasivenon-native speciese.g., brown-headedcowbirds, star thistle,Mediterraneangrasses) .

Fuels reduction.

• Riparian habitat• Meadows

Grazing in riparian areas cancause increased sediment yield,stream-bank degradation,reductions in vegetative cover,and direct mortality of rarespecies.

• Impacts have been reducedsubstantially in recent yearsdue to excluding livestockfrom some riparian areasand improved managementof stocking rates andseason of use in otherareas

• Entrenched downcutscaused by past overgrazingstill remain in somemeadows

• Blue oak woodlands• Engelmann oakwoodlands

Grazing can negatively affectoak regeneration throughseedling removal and soilcompaction.

Recent studies have shownthat livestock grazingcontributes to this problembut is not the sole or even theprimary cause in most areas.

• Riparian habitat• Grasslands• Oak woodlands• Least Bell’s vireo• Willow flycatcher• CA gnatcatcher

• Studies suggest that grazingattracts cowbirds, but itsinfluence varies based on othersurrounding land uses

• Overgrazing can facilitatespread of star thistle and otherweeds

Grazing historically was amajor factor in the spread ofundesirable plants, but thecontinued spread of thoseplants today is oftentriggered by other factors.

Nonspecific. Grazing can be used as a tool forfuels reduction in grasslands andon fire breaks.

Some fuel breaks arecurrently maintained bylivestock grazing.

grazing with no grazing (Blackburn 1984;Allen-Diaz et al. 1999). There are few solidscientific assessments of the ecological effectsof management practices that fall in “the greatmiddle ground” between abusive grazing andno grazing (Allen-Diaz et al. 1999).

Despite these limitations, some studies arepertinent to the ecological issues within ourassessment area. The effect of grazing onriparian habitats and species is of interest be-cause there are many sensitive resources inriparian areas and they are also a preferredhabitat for cattle (Kie and Boroski 1996).Overgrazing by cattle was identified as a prob-able cause of limited cottonwood saplingestablishment along much of the NacimientoRiver in the northern Santa Lucia Range(Shanfield 1984). Studies on the Blitzen Riverin Oregon found dramatic increases in wil-low flycatcher and yellow warbler populations

when the intensity of year-round cattle graz-ing was reduced and willow cutting andspraying were eliminated (Taylor 1986; Tay-lor and Littlefield 1986). The researchershypothesized that the mechanism involved wasthat cattle grazing reduced willow nestingcover for these species.

Several studies have assessed the effect oflivestock grazing on the survival of blue oakseedlings. The results have been mixed; someresults suggest that grazing reduces blue oakrecruitment while others show no effect (Daviset al. 1991; Allen-Diaz and Bartolome 1992).There is general consensus, however, that graz-ing is just one of many factors that may beaffecting oak seedling survival.

Recent changes in the management of live-stock grazing allotments on national forestsystem lands have included (1) fencing to

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exclude cattle from some sensitive riparian andmeadow habitats (figs. 3.16), (2) reductionsin stocking rates, and (3) changes in the sea-son of use, reducing the amount of summer/fall grazing in favor of a winter/early springuse regime.

Figure 3.17. A limestone quarry in the SanBernardino Mountains. DEVEREE VOLGARINO

Ecological impacts from these operationsare localized and present a significant prob-lem mainly in areas where they overlap with

The Influence of Mining

Much of the assessment area is under min-ing claim, with the notable exception of largeportions of the San Gabriel Mountains, butcommercial mining in the region is not ex-tensive. Most claims are small, individualoperations. The primary hub of mining activ-ity is in the northeastern San BernardinoMountains, where high-grade limestone de-posits are extracted by several large companiesin open-pit mines and quarries (fig. 3.17).Smaller limestone mines are also in operationat the north end of the San Rafael Mountains

Figure 3.16. (Left) Overgrazing of cattle contributed significantly to reduced vegetative cover in the LasBancas area of Pine Valley Creek, Cleveland National Forest in 1991. (Right) The same area along Pine ValleyCreek supported dense riparian vegetation two years after cattle were excluded and native willows wereplanted. DEVEREE VOLGARINO

and in the Santa Lucia Ranges near Little Sur.There is also active exploration for oil and gasreserves occurring in southeastern portions ofthe Los Padres National Forest.

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Chapter 3Table 3.20. Key ecological issues that are influenced by mining activities.



with Mining ActivitiesCurrent Trends andAreas Most Affected

Habitat degradationor impacts to TESspecies from in-streammining operations.

Habitat degradationor impacts to TESspecies from hardrockmining.

Potential impacts tohabitats or speciesfrom futuredevelopment ofexisting mining claims.

Aquatic and riparianhabitats/species.

Suction dredging, sand andgravel mining, and someprospecting activities can causelocalized habitat degradationand/or direct mortality to TESspecies. Of primary concern iswhere such activities overlapwith occurrences of sensitivehabitats or species.

Coordination between FSand CDFG is occurring toclarify permit process forsuction dredging and identifyareas for closure. Low-elevation, large-orderstreams are most affected.Suction dredging occursfrequently on the SanGabriel River.

Limestone outcrops andassociated endemicplants.

• High-grade limestone depositsin the northeastern SanBernardino Mountains has ledto the development of open-pitmines in an area where thereare a large number of rareplants.

• Active mining of tourmalineand other gemstones primarilyon private lands in the PalomarMountain area.

Nonspecific, butgreatest potential is indesert-montanehabitats.

Much of the assessment areais under mining claims. Thereis potential for commerciallyviable deposits of low-gradegold, gemstones, or oil andgas.

Currently there are fewactive commercial minesoutside of the SanBernardino Mountains,limestone region.

• A site-specific conservationstrategy is currently beingdeveloped to address theSan Bernardino Mtslimestone issue.

• Some localized habitatdegradation is resulting fromother hardrock mines, but ingeneral the assessmentarea is not an active miningregion.

sensitive habitats or species (table 3.20). Themost prominent example of such overlap isthe occurrence of an entire assemblage of en-demic, rare plants on high-grade limestonedeposits in the San Bernardino Mountains.

A commonplace form of mining in theregion’s larger streams is suction dredging.Suction dredges utilize high-pressure waterpumps driven by gasoline-powered motorswhich create suction in a flexible intake pipe.A mixture of streambed sediment and wateris vacuumed into the intake pipe and passedover a sluice box mounted on a floating barge.Dense particles (including gold) are trappedin the sluice box. The remainder of the en-trained material is discharged into the streamas “tailings” or “spoils,” which can form largepiles where dredges have remained in one lo-cation for a long period (Fredley 1995).

Suction dredging can have a number ofimpacts on aquatic habitats: (1) increased wa-

ter turbidity, (2) disturbance of channel mor-phology and bottom substrates that serve asspawning areas for fish, and (3) direct mortal-ity of fish and amphibian eggs and larvae inthe sediment vacuuming process. The signifi-cance of these impacts varies by site anddepends largely on the site’s ecological integ-rity (e.g., naturalness of the hydrologic regime,other prevailing land uses, presence of rare orat risk species, and presence of exotic species).

The State of California regulates suctiondredging activities. The Department of Fishand Game (CDFG) is required to issue per-mits to suction dredge if it determines thatthe operation will not be deleterious to fish.They can also institute seasonal closures toreduce impacts. The CDFG is currently con-ducting a statewide environmental review ofits policy on suction dredging (USFWS 1998a).

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Figure 3.18. Housing construction in an isolatedarea adjacent to the Cleveland National Forest. JOHN

STEPHENSON

The Influence of Air Pollution

Long-term studies to determine the effectsthat air pollution is having on forest vegeta-tion have occurred in the San BernardinoMountains and, to a lesser extent, in the SanGabriel Mountains (Miller et al. 1996; Millerand McBride 1999). Prevailing climatic con-ditions transport most of the air pollution fromthe Los Angeles Basin into these mountains(Miller et al. 1989). The two depositionalcomponents of air pollution that have thegreatest effect on ecosystems are ozone (re-viewed in Miller et al. 1996) and nitrogen(reviewed in Bytnerowicz and Fenn 1996).

Ozone DepositionStudies have determined that ponderosa

and Jeffrey pine trees, and to a lesser extentbigcone Douglas-fir, are experiencing foliageinjury from ozone deposition (Miller et al.1989; Peterson et al. 1995). Other tree spe-cies in the area appear to be considerably moretolerant of ozone. Chronic ozone injury toponderosa pines was first identified in the SanBernardino Mountains in the 1950s (Milleret al. 1963). Mortality and damage was high-est in the 1970s when ozone concentrationsreached their peak. Ozone concentrationssteadily declined between 1976 and 1991 anda concurrent reduction in injury to the crownsof ponderosa and Jeffrey pines was observed(Miller et al. 1996).

The Influence of Private LandDevelopment

Development on private lands is steadilyconsuming wildland habitats (fig. 3.18) andreducing connectivity between the natural ar-eas that remain. This trend poses somesignificant challenges for conservation of habi-tats and species on public lands (table 3.21).In the southern end of the assessment area,rapid development has the potential to elimi-nate habitat corridors between the mountainranges. These corridors are believed to be im-portant for the movement of somewide-ranging animals. Mountain lions in par-ticular are vulnerable to declines if individualsin one mountain range become cut off fromthe larger population (Beier 1993).

Development tends to simplify ecologicalcommunities, eliminating some species andincreasing the abundance of others. Specieswith wide tolerances and generalized habitatrequirements (common traits of exotic species)are the ones that typically thrive in developedareas. In addition, a number of plants com-monly used in landscaping are on CalEPPC’slist of Exotic Pest Plants of Greatest Ecologi-cal Concern, including arundo, tamarisk, iceplant, pampas grass, Russian olive, fountaingrass, and Brazilian pepper tree.

Sand and gravel mining operations occur ina number of foothill drainages where there arewell-developed alluvial deposits. Most of theseoperations are on private lands. Sand and gravelmines completely alter the drainage channel andusually result in the creation of deep pools.

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Chapter 3Table 3.21. Key ecological issues that are influenced by development on private lands.


Most Affected

Effects Associatedwith Private Land

DevelopmentCurrent Trends andAreas Most Affected

The distribution,extent, and integrityof habitats andspecies which occurpredominantly onprivate lands.

Fragmentation ofanimal populationscaused by the lossof wildland habitatcorridors betweenmountain ranges.

Effects associatedwith expansion of theurban–wildlandinterface.

Effects associatedwith increased urbaninfrastructure needson public lands.

• Coastal sage scrub• Engelmann oak

woodland• Valley oak woodland• Grassland• Montane meadow

Development on private land isreducing the extent of nativehabitats and fragmenting thosehabitats into disjunct patches.This increases the significanceof these habitats on publiclands.

Development is occurringmost rapidly in Orange, SanDiego, Riverside, SanBernardino, Ventura, andSanta Barbara counties.Several counties aredeveloping habitat orspecies conservation planswhich attempt to conservekey areas and providecorridors to the surroundingpublic lands.

Species with largearea requirementsthat disperse alongor near the ground(e.g., mountainlions).

Buildout on private lands caneliminate habitat connectionsbetween mountain rangesunless natural habitat corridorsare designated and protected.

• Peninsular bighornsheep

• Many habitats/species affected byaltered fire regime andspread of non-natives

• Drives disturbance-intolerantspecies away from preferredhabitats

• Increases the risk anddifficulty of using fire as amanagement tool

• Contributes to rise ininvasive, non-native species

Urban interface is expandingrapidly on both the desertand coastal sides of the SanGabriel, San Bernardino,and San Jacinto mountainsand on the coastal side ofSan Diego and southern LosPadres ranges.

Imperiled habitatconnections include: SantaAna Mts — Palomar Mtn;Palomar Mtn —San JacintoMts; San Jacinto Mts — SanBernardino Mts.

Nonspecific. Power lines, pipelines, waterstorage, communicationfacilities, highways, landfills,sewage treatment areas, etc.can cause localized habitatdegradation and habitatfragmentation and provideavenues for the spread ofinvasive, non-native species.

Requests for infrastructuresto cross through or belocated in the mountains areincreasing as urban areasexpand.

Pine mortality was highest during ex-tended periods of low precipitation (droughts),when these trees are most vulnerable to barkbeetles. Trees with chronic ozone injury entera period of drought without the reserves re-quired to mount an active defense against barkbeetle attack (Miller et al. 1991).

In the San Bernardino Mountains, thereis a clear west-to-east gradient in both ozone

levels and tree damage. Forests on the westernside of the range are exposed to much higherlevels of ozone and are experiencing the mostdamage (Miller et al. 1989). Monitoring ofstudy sites in the west-side forests over afourteen-year period (1974 to 1988) foundthat ponderosa and Jeffrey pine are losing basalarea in relation to competing species that aremore tolerant to ozone, namely, white fir,

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incense-cedar, and black oak (Miller et al.1996). The accumulation of more stems ofozone-tolerant species in the understory presentsa fuel ladder situation that jeopardizes the re-maining overstory trees in the event of acatastrophic fire.

Quantitative information on ozone dam-age is scarce for other mountain ranges withinthe assessment area. However, given the loca-tion of major pollution sources and prevailingwind patterns, it appears that areas of highpotential for damage are probably confinedto the eastern San Gabriel and western SanBernardino mountains (P. Miller, RiversideFire Lab, pers. comm. 1997).

Nitrogen DepositionThe effects of nitrogen deposition on lo-

cal forests and shrublands have not beenstudied for as long as ozone and are only be-ginning to become apparent. High rates ofnitrogen deposition have increased soil fertil-ity and surface litter decomposition rates insome mixed conifer forests in the San Bernar-dino Mountains (Fenn 1991b). However,excessive nitrogen inputs can lead to variousnegative effects, including nutrient deficien-

Table 3.22. Key ecological issues that are influenced by air pollution.


Most AffectedEffects Associatedwith Air Pollution

Current Trends andAreas Most Affected

Vigor and longevityof forest trees,particularly of thosespecies mostsensitive to ozonedamage;ramifications tostructure andcomposition of mixedconifer forests.

Shifts in the structureand composition ofplant communitiesand reduced waterquality related toexcessive nitrogeninputs.

• Ponderosa andJeffrey pine

• Bigcone Douglas-fir

High levels of ozonedeposition is a chroniccondition in some areas and isknown to reduce the vigor oftrees sensitive to it. This leadsto increased mortality andappears to be contributing to ashift in tree speciescomposition.

• Rates of ozone depositionhave declined from 1970speaks, but are still some ofthe highest in the U.S.

• Western San BernardinoMountains and eastern SanGabriel Mountains are mostaffected.

• Coastal sagescrub

• Mixed coniferforests

High levels of nitrogendeposition is a chronic conditionin some areas. Elevatednitrogen levels in the soil has afertilizing effect for somespecies, altering communitydynamics. Runoff into streamsand groundwater is elevatingwater nitrate concentrations.

Western San BernardinoMountains and eastern SanGabriel Mountains are highlyaffected, as are lowlandareas on the coastal side ofthe mountains (e.g., westernRiverside and SanBernardino counties).

cies, soil acidification, altered species compo-sition, decreases in mycorrhizal root symbiosis,and elevated concentrations of nitrate in soil,groundwater, and streams (Bytnerowicz andFenn 1996; Padgett et al. in press). Recentstudies in Riverside County indicate that highlevels of nitrogen deposition may be contrib-uting to the decline of coastal sage scrub andits conversion to Mediterranean annual grass-land (Allen et al. 1997).

Spatial patterns in levels of nitrogen depo-sition mirror that described for ozone. EasternLos Angeles County and western San Bernar-dino and Riverside counties receive the highestconcentrations. In the mountains, the coastalside of the eastern San Gabriel and westernSan Bernardino mountains are the most pol-luted (Bytnerowicz and Fenn 1996). Inmontane conifer forests, the fertilizing effectof nitrogen may be accelerating understorydevelopment of white fir and incense-cedar,thereby elevating fuel loads and potentially in-creasing the risk of stand-replacing fires.

Riggan et al. (1985) reported elevated con-centrations of particulate nitrate in streamwater emanating from watersheds exposed tohigh nitrogen deposition in the San Gabriel

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Chapter 3

Climate ChangeConsiderations

The subject of long-term climate changeis really beyond the scope of this report. Re-search on this topic is generally conducted atcontinental or global scales, making it diffi-cult to determine how local landscapes mightbe influenced. However, several researchershave attempted to interpret predictions fromglobal climate change models in terms of howsouthern California ecosystems, and in par-ticularly local fire regimes, might be affected.Although highly speculative, some of the lo-cal climate change predictions described inthose studies are worth describing.

Davis and Michaelsen (1995) andWestman and Malanson (1992) simulated thepotential effects of climate change on fire re-gimes in southern California chaparralecosystems. To figure out what those climatechanges would be, they used predictions fromthree widely accepted general circulation mod-els (GCMs) that assume a doubling ofatmospheric carbon dioxide (CO

2). Under this

scenario, several changes are predicted withvarying levels of confidence.

The most probable climatic change occur-ring in the assessment area would be anincrease in average daily maximum and mini-mum temperatures of 1 degree to 4 degreesCentigrade. There is more uncertainty associ-ated with precipitation predictions, but thevarious GCM results are in general agreementthat winter and spring precipitation should in-

Mountains. Stream water particulate nitrateconcentrations in watersheds heavily influ-enced by urban air pollution were one to threeorders of magnitude greater than in watershedswhich were not exposed to high concentra-tions of air pollution. Sharp peaks inparticulate nitrate levels occur during the firstwinter storms when the ecosystem is loadedwith nitrogen accumulated during the drysummer months. Additional information isneeded on the extent of this problem and howit is affecting aquatic ecosystems.

crease. The three GCMs predicted increasesin precipitation for the months of Novemberthrough March of 36, 21, and 21 percent. Pre-dicted increases for March and April were 59,17, and 27 percent (Davis and Michaelsen1995).

The fire regime simulations were very sen-sitive to predicted increases in fire seasontemperatures and equally sensitive to largechanges in stand productivity. Total areaburned was predicted to increase and the fire-recurrence interval was predicted to significantlydecrease (Davis and Michaelsen 1995).Westman and Malanson (1992) suggest thatthese changes could lead to potentially largechanges in chaparral composition.

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