Early-Successional Breeding Bird Communities in Y anaged ......Early-Successional Breeding Bird...

Southeastern Naturalist

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F.L. Owens, P.C. Stouffer, M.J. Chamberlain, and D.A. Miller2014 Vol. 13, No. 3SOUTHEASTERN NATURALIST2014 13(3):423–443

Early-Successional Breeding Bird Communities in ntensi ely anaged ine lantations n uence o Vegetation Succession but Not Site Preparations

Falyn L. Owens1, Philip C Stouffer1,*, Michael J. Chamberlain1, 2, and Darren A. Miller3

Abstract - Birds that require early-successional habitat are declining in North America due to habitat loss. Their increasing reliance on anthropogenic landscapes, such as the extensive Pinus spp. (pine) plantations of the southeastern US, makes it important to assess how man-

preparation variables, tree row spacing (4.3 m vs. 6.1 m) and arrangement of post-harvest

managed Pinus taeda (Loblolly Pine -

munities. All measures of bird communities responded positively as vegetation structure and cover increased over time. However, neither row spacing nor debris placement affected

-lishment; bird communities responded to successional changes and variation among plots, but not to site preparation. Land managers seeking to provide early-successional habitat in recently established plantations for disturbance-dependent birds can do so by increasing structural complexity and groundcover through selective herbicide applications, mechanical treatments, or other means.

Introduction

Birds that live exclusively in early-successional landscapes are among the most threatened avian habitat specialists in North America. Fifty-six percent of grassland species, 39% of shrub-scrub species, and 33% of savannah species have experi-

Bird Conservation Initiative 2009). As of 2011, breeding bird survey data from the US and Canada show declining population trends for 44% of successional or scrub-breeding species, with increases for only 9% of these 160 species (Sauer et al. 2013). Historically, these species preferred habitat conditions perpetuated with regular burning via natural and anthropogenic origins, which prevented encroach-ment of woody vegetation and maintained habitat structure in a sub-climactic successional state. Today, those habitat types have been drastically reduced by

1School of Renewable Natural Resources, Louisiana State University Agricultural Center, Ba-ton Rouge, LA, 70803. 2University of Georgia, Athens, GA 30602. 3Company, Columbus, MS, 39704.*Corresponding author - [email protected].

Manuscript Editor: Paul Leberg

Southeastern NaturalistF.L. Owens, P.C Stouffer, M.J. Chamberlain, and D.A. Miller

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harvest (Beissinger et al. 2000, North American Bird Conservation Initiative 2009, Trani et al. 2001; see Twedt et al. 1999 for a summary of trends in the Mississippi Alluvial Valley). Young, intensively managed Pinus spp. (pine) plantations provide habitat conditions that can support more birds than historically disturbed landscapes

can provide a significant amount of disturbed habitat. In the southeastern US, pine plantations account for 20% of forest cover, with Pinus taeda L. (Loblolly Pine) plantations covering 13.4 million ha (Schultz 1997, US Forest Service 2008). The economic value of plantations helps prevent land conversion to more intensive anthropogenic uses, making them important refugia for disturbance-dependent birds (Brawn et al. 2001, North American Bird Conservation Initiative 2009). Timber managers’ decisions about how they manage their forests, includ-

production, production costs, and value for wildlife. To understand and improve bird resources in intensively managed timberlands,

practices, how they interact to affect birds, and how these patterns change by geo-

stands where debris is shredded or removed (Horn 2000; Jones et al. 2009a, b; Lohr et al. 2002). If woody debris remains on-site, timber managers have the choice of spreading it between newly planted rows or creating debris piles; this decision may

-erhaeuser Company, one of the largest industrial landowners in the southeastern US, recently switched row spacing from 4.3 m to 6.1 m. In Georgia, Lane et al. (2011) found that wider spacing between rows (6.1 m vs. 3.0 m) improved species richness and abundance, but the study confounded row spacing with debris management; data are limited relative to tree spacing and avian habitat quality. Therefore, we examined how breeding bird communities responded to both row spacing (4.3 m vs. 6.1 m) and woody debris placement (piled vs. scattered) treatments in regenerating Loblolly Pine plantations in Louisiana. Vegetation structure and diversity have been examined on the same plots where we studied birds; neither plant diversity nor species richness

spacing effects on breeding bird species richness, abundance, and breeding activity

changing vegetation composition and structure on breeding bird communities dur-


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F.L. Owens, P.C. Stouffer, M.J. Chamberlain, and D.A. Miller2014 Vol. 13, No. 3

on breeding bird communities; and (4) recommend which combination of row spac-

bird communities.

Methods

Site characteristics and experimental design-

Jackson (site B) parishes, and 2 were in southeastern Louisiana, in Tangipahoa (site -

aged these sites for production of Loblolly Pine plots following standard industry practices (D.A. Miller, pers. observ.). Typical sil-viculture on this area included clearcut harvest at approximately 27–32 years of age, followed by site preparation and planting (~1100 trees/ha), vegetation management, a commercial thinning (target reduction to ~309 trees/ha), pruning, and fertilization. The study plots at each site were established within a single large clearcut, which in turn was embedded within a much larger area of managed Loblolly Pine forest. Small portions of most sites were designated streamside management zones (SMZs), where undisturbed forested vegetation, primarily mature hardwood stands, bordered watercourses. Sites shared similar annual precipitation, temperature, elevation, and soil characteristics; soil drainage ranged from poorly (site C) to well-drained (site D) (Natural Resources Conservation Service 2009, Owens 2011). Following harvest, sites were prepared for planting with a combination of me-chanical and chemical treatments tailored to achieve successful regeneration at

-tive industry choices for row spacing and debris treatments, managers established experimental stands in a randomized block design to compare all combinations of woody debris placement (piled or scattered) and row spacing (4.3 m vs. 6.1 m) in four 10-ha plots at each of the 4 sites (Fig. 1). In piled plots, plantation managers

the corners of the plots. Scattered sections had woody debris distributed between rows throughout the plot; the rows of trees were elevated onto soil beds to reduce inundation of seedlings and prepare a good planting substrate. To temporarily reduce competing vegetation, all sites received a combination banded application (i.e., herbicide only applied to beds of planted tress) of the herbicides Arsenal® AC (4 oz/ac, BASF Corp. Research Triangle Park, NC) and Oust Extra®

Vegetation sampling


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circular vegetation plots, equally spaced so that they extended diagonally across

avoid debris piles. Stem-count data consisted of total live softwood and hardwood

2

categorized vegetation as either fern, Ilex vomitoria Aiton (Yaupon), forb, vine, woody, grass, debris, or bare ground. Due to layering of vegetation, total percent cover exceeded 100%. Yaupon received its own category because of its prevalence

-

13 different measures of composition and structure on 80 vegetation plots each year. To simplify analyses, we averaged measurements to the vegetation-plot level, yielding 40 observations per individual treatment per year (or 20 observations per treatment combination per year).

Avian community sampling-

veyed the northernmost sites (A and B) during 2006 directly following plantation

activity, with gaps of at least 10 days between surveys to increase temporal inde-

(following Hamel et al. 1996).

Figure 1. Factorial arrangement of row spacing (4.3 m or 6.1 m) and debris placement

Circles represent locations of debris piles on piled plots and avian survey-points on all plots. Orientation of plots in relation to one another is not necessarily accurate because plot posi-


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-

4 corners (Fig. 1). For piled treatment plots, we shifted survey locations the mini-mum distance necessary to provide acceptable visibility around debris piles. To increase sample independence and reduce edge effects, we placed survey locations

et al. (1996), as adapted by the Lower Mississippi Valley Joint Venture (2004). At each location, during 10-min observation periods, observers noted species, age, sex, distance and direction from sampling points, and any behaviors indicative of

-pling by reversing survey order for each visit. After completing point counts each morning, observers conducted extended searches, revisiting each plot for 1 hour to look for additional evidence of breeding activity. Extended searches typically

-

-cies were forest interior and edge specialists that were not present in plots without

the program SPECRICH2, which estimates number of species present even if not all are detected, assuming that individual species vary in detectability (Hines 1996,

For abundance, we determined mean number of individuals per species per

and sometimes we detected more individuals than actually used the plots all season (during territory establishment). Therefore, we reported mean abundance to ac-

yielding total abundance per plot per year. It is important to note that abundance values were valid only relative to each other and should not be used as absolute

-tial problem of birds using plots without breeding (Brawn et al. 2001, Van Horne

to breeding territories based on strength of evidence that young have successfully

for as few as 2 weeks to account for territories that may have been active, but un-detected, for a longer period. This method is limited to non-cryptic species whose young are altricial, and whose breeding behaviors are relatively detectable (Rangen et al. 2000, Rivers et al. 2003). For this reason, we excluded Colinus virginianus (L.) (Northern Bobwhite ) and Archilochus colubris (L.) (Ruby-throated Hummingbird)


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Molothrus ater

was the sum of territory scores for all species with territories in the plot that year.

Statistical analysis

to identify and retain components that explained the most variance and were most

VARIMAX rotation to increase interpretability of retained components and pri-

al. (2011) conducted a similar analysis of the vegetation data, but our analysis also included pine stem counts to account for variation in pine seedling survival in the

null hypothesis that avian community metrics, vegetation components, and

conservation concern (2009 and 2010 only) did not differ among row spacing and debris-distribution treatments. Predictor variables were row spacing, debris place-

Pnormality by examining skewness, kurtosis, normal probability plots, and Shapiro-

model selection for 14 candidate models that included debris-placement treatment, vegetation components, and their interactions in combinations that could be bio-

sing, monitor a distinct area, or act aggressively toward other males.

Score Breeding behavior

0.33 Territorial male present 2 weeks 0.66 Territorial male present 3 weeks 1 Territorial male present 4+ weeks 2 Territorial male and female present 4+ weeks 3 Adults with nesting material, laying or incubating eggs, or diverting attention from nest 4 Adults carrying food or fecal sacs


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row spacing was represented by proxy in the vegetation data (pine stem counts); this variable was also uninformative in a prior analysis of vegetation diversity on

analyses of covariance (ANCOVA) with repeated measures (PROC MIXED; SAS

Using these ANCOVA models, we considered bird-community responses to debris C) and com-

C < 4) (Burnham and Anderson 2002).

Results

Vegetation summary

plots. Although Loblolly Pine was the only softwood species, sites hosted an array of hardwoods, including natives L. (Sweetgum), Sassafras albidum (Nuttall) (Sassafras), Acer rubrum L. (Red Maple), Yaupon, Rhus copal-lina Quercus spp. (oaks), and the non-natives Ligustrum sinense Lour. (Chinese Privet) and Triadica sebifera (L.) Small (Chinese Tallow). A patchy shrub layer was dominated by Callicarpa americana L. (American Beau-tyberry), Baccharis halimifolia L. (Eastern Baccharis), and Cyrilla L. (Swamp Titi), interwoven with abundant canes of Rubus spp. (blackberries) and some Smilax spp. (greenbriers). Dominant grasses belonged to genera Andropogon and Schizachyrium spp. (bluestem grasses); Solidago spp. (goldenrods), Eupato-rium spp. (Joe-pye weeds), Ambrosia spp. (ragweeds), and Aster spp. (asters) were

Table 2. Set of candidate models used in AIC-based model selection to determine the response of breeding avian communities to debris placement and vegetation characteristics in four young Loblolly Pine stands in 2006, 2007, 2009, and 2010 in Louisiana. Variables include debris placement and 3 principal components describing vegetation structure (Table 3).

Variables

Vegetation Evergreen GroundcoverModel Debris (D) structure (S) cover (E) (G) Interactions

GLOBAL D S E G D*S D*E S*E D S E G D S E D S D*S D S D E D*E D E S E G S*E S E G S E S*E S E S ENULL


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in species composition—the wettest site (C) was dominated by lowland hardwood and freshwater marsh species (Nyssa spp. and Saururus cernuus and the driest site (D) was characterized by species associated with upland areas (Yaupon and bluestem grasses). Principal component analysis of the 13 vegetation measures (pine and hard-wood stem counts, percent groundcover categories, and height measures) yielded

overall vegetation structure, evergreen cover, and groundcover (Table 3). Vegeta-

tall, dense vegetation, mostly encompassing the variation in hardwoods. Evergreen cover (Eigenvalue = 1.74) represented a gradient in cover between the 2 evergreen species, Loblolly Pine and Yaupon. Groundcover (Eigenvalue = 1.17) represented a gradient between bare or debris-covered ground and dense grass cover. Although this component accounted for relatively little variance, we retained it for analysis because it was the only metric that notably changed directionality through time, representing the shift from bare ground in 2006 to grassy cover in 2007, and then

-tion structure (F = 12.88, P < 0.001), evergreen cover (F = 76.04, P < 0.001), and groundcover (F = 14.01, Ppreparation on vegetation, we found that none of the vegetation metrics varied with debris placement (F1, 12.3–12.6 P > 0.46), row spacing (F1, 12.3–12.6 < 1.74, P > 0.21), or their interaction (F1, 12.3–12.6 < 0.33, P

Avian community response-

bance-dependent species based upon their classification as dependent upon

Table 3. Correlations between retained principal components and original vegetation measurements. A indicates vegetation characteristics that are highly correlated (P

Vegetation metric PC1-Vegetation structure PC2-Evergreen cover PC3-Groundcover

Pine stem count 0.20 0.81A 0.00Hardwood stem count 0.64A A *

% cover fern 0.19 -0.10 -0.17% cover Yaupon 0.30 0.78A -0.20% cover forb 0.18 0.34 0.24% cover vine 0.49A 0.32 -0.12% cover woody 0.76A -0.20 -0.90A

% cover grass -0.60A -0.11 0.86A

% cover debris -0.60* -0.26 -0.63*

* 0.18 -0.61*

Minimum height 0.74* 0.48* 0.16Maximum height 0.70* 0.43* 0.33Average height 0.82* 0.17 0.30


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grassland, savanna, shrubland, shrubland, or generalized shrub habitats by Askins (1993) (see Appendix A). The remaining species were habitat generalists, passage migrants, or late-departing winter residents, or primarily occupied SMZs. Of the disturbance-dependent breeders, 71% (n = 10) displayed reproductive activity.

well as Sitta pusilla Latham (Brown-headed Nuthatch) and Icterus spurius (L.) (Orchard Oriole). The 4 most common species, accounting for 42% of all detections, were dis-turbance-dependent: Icteria virens (L.) (Yellow-breasted Chat ), Passerina cyanea (L.) (Indigo Bunting), Setophaga discolor Pas-serina caerulea (L.) (Blue Grosbeak). In addition to the disturbance-dependent species, we irregularly detected some species associated with more developed forest, such as Poecile carolinensis (Audubon) (Carolina Chickadee), Cyanositta cristata (L.) (Blue Jay), and Baeolophus bicolor (L.) (Tufted Titmouse). As expected, species composition changed as stands matured, with ground-for-aging specialists such as Spizella passerina (Bechstein) (Chipping Sparrow) using plots only in the initial 2 years, and shrub-nesting species like Yellow-breasted Chat

Figure 2. Changes in vegetation structure through time. Lower and upper box edges repre-th th percentiles; whiskers represent 10th and 90th percentiles. Lines bisecting

boxes represent medians and points signify outliers.


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Figure 3. Changes in evergreen cover and groundcover through time. Lower and upper box th th percentiles; whiskers represent 10th and 90th percentiles. Lines

bisecting boxes represent medians and points signify outliers.


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Cardinalis cardinalis (L.) (Northern Cardinal), remained present in comparable numbers, but declined in proportional presence as species richness and overall abundance increased through time. Indigo Bunting was unique in maintaining high relative abundance through all 4 years; it was the most frequently detected species in 2006 and 2007, and second only to Yellow-breasted Chat in 2009 and 2010. For all years and plots combined, the three avian community metrics were strongly correlated (Spearman r2 > 0.41, P < 0.001). For individual years, however,

r2 < 0.27, P > 0.09). By the third year, breed-r2 = 0.23,

P and breeding score were at least weakly correlated (Spearman r2 = 0.19, P <

F = 10.9, P < 0.001), abundance (F = 71.6, P < 0.001), and breeding activity (F = 81.1, P < 0.001). Avian communities did not differ based on debris placement (F P > 0.30), row spacing (F < 0.01, P > 0.93), or their interaction (F < 1.7, P to individually test two species of conservation concern, neither of which showed

F1, 12 P > 0.48) and Yellow-breasted Chat (F1, 16 < 3.61, P > 0.08).

Figure 4. Estimated number of species per plot in young Loblolly Pine plantations in Loui-

seasons (late April–early June) post-planting. Error bars represent standard error.


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Top models for all bird-community metrics included vegetative structure and evergreen cover (Table 4). Upon examination of model estimates, we found that species richness, abundance, and breeding score were positively correlated with

breeding seasons (late April–early June) post-planting. Error bars represent standard error.


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and more heterogeneous, there was an overall increase in all of our measures of -

rics except species richness. Although number of species per plot was not positively correlated with grass cover, more grass cover supported more individuals and more breeding activity, a logical trend because all of the targeted species use herbaceous stems for nest building.

Discussion

6.1-m row spacing, or between piled and scattered debris. Likewise, vegetation struc-ture and composition, the primary cues for birds searching for breeding territories,

Although the evergreen structure component was important for birds and included

between row-spacing treatment and this component (Owens 2011). Stand age was important to birds through its effect on vegetation structure, a pattern consistent with

Successional change appeared to be particularly important for facilitating breed-ing because breeding scores, a measure of overall breeding activity on the plots, Table 4. Model-selection results comparing analyses of covariance (ANCOVA), which test response of avian species richness, abundance, and breeding activity to debris placement and 3 vegetation characteristics. L represents likelihood. S, E, and G represent composite variables vegetation struc-ture, evergreen cover, and groundcover, respectively (see Table 3). D refers to debris placement, and

C < 4), global, and null

E G D*S D*E S*E.

Response variable/model AICC C

Species richness

Abundance

Breeding score


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-creased more modestly, approximately doubling in the same interval.

characterized more by addition of species than by replacements. This trend has been observed previously in young, regenerating forest stands, where loss of early-successional bird species did not occur until canopy closure, sometime between the

th and 10th

our study, we saw increased abundance of some closed-canopy forest species, such as Carolina Chickadee and Tufted Titmouse, and a decline in some early-succes-sional species, such as Eastern Bluebird (Sialia sialis(Tyrannus tyrannus closed-canopy forest species as canopy and understory developed. By 7–10 years after planting, we would expect stands with narrow row-spacing to support closed-canopy species such as Limnothlypis swainsonii Bassett-Touchell and Stouffer 2006). Our study focused on community-level trends, but it is important to note that the

-agement recommendations, has its limitations. Individual species belonging to these communities differ in preferred foraging substrate, preferred nesting substrate, and level of specialization—variation that can go undetected when community-level metrics are employed. Land managers require information that enables them to provide habitat conditions for multiple species, but when particular species are of interest, species-level studies help tailor management strategies to their par-

species may effectively provide habitat for some species of conservation concern.

measures to debris placement and vegetation characteristics, as determined via model selection. Tests on species richness and abundance used square root transformed data.

Response variable/predictor variable Estimate SE df t P

Species richness

Abundance Intercept 32.89 0.124 3.9 16.31 <0.001

Breeding Score Intercept 29.96 2.008 4.1 14.92 <0.001 Vegetation structure 13.01 1.960 47.7 6.64 <0.001


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However, this does not necessarily reduce importance of attending to variation on the species or guild level. Because the row spacing and debris treatments we studied did not affect birds, we recommend that managers of intensively managed pine forests in the south-eastern US implement the combination of row spacing and debris placement

-ing examined in this study may be favorable for disturbance-dependent birds in other settings. For example, Lane et al. (2011) found that birds benefited from 6.1-m row spacing (one of the widths in our study) versus 3.0-m rows (a spacing common in industrial plantations, but narrower than those tested in our study) in North Carolina Loblolly Pine plantations, although these results were confounded

canopy closure occurs, potentially extending the longevity of beneficial habitat conditions for early-successional bird species. Because disturbance-dependent birds responded to general structure, evergreen cover, and groundcover, site preparation and stand establishment methods that positively influence these veg-etation characteristics may prove more beneficial to birds than row spacing per se. Timberland managers already work toward maximizing growth of target tree species, concurrently speeding development of structure and cover for birds. Sim-ilarly, past research has indicated that increased herbaceous groundcover is often a consequence of vegetation control during stand establishment (e.g., Chamber-lain and Miller 2006, Jones et al. 2009a, Miller et al. 2009). Once plantations develop woody structure between planted pine rows, selective herbicides used to control hardwoods (e.g., imazapyr) can extend the window of time that herba-

on our experimental plots. As species turnover in the bird community occurs over time and forest specialists begin to replace early-successional species, community responses to row spacing and debris arrangements may appear. For example as men-tioned above, wider row spacing may affect timing of canopy closure, extending the early-successional phase of stands. Clearly, there are research needs and opportuni-ties regarding early-successional bird use of intensively managed pine plantations.

Acknowledgments

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was approved for publication by the Director of the Louisiana Agricultural Experimental


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ore

for

2006

20

07

2009

20

10

si

tes

Pile

s Sc

atte

red

Pile

s Sc

atte

red

Pile

s Sc

atte

red

Pile

s Sc

atte

red

Spec

ies

A+B

C+D

4.3

6.

1 4.

3 6.

1 %

4.

3 6.

1 4.

3 6.

1 %

4.

3 6.

1 4.

3 6.

1 %

4.

3 6.

1 4.

3 6.

1 %

To

tal

Yrs

TUTI

13

14

3

2

0

3 1

4 1

1

2

0 14

3

‡ -

-

0

2 2

2 3

2

0

4 1

1 14

2

*†‡

GC

FL

12

13

1

1

2

2

1

1 2

1 1

1 1

1

1 0

12

4RT

HU

12

13

1

1 2

1 1

1

1

2

2 1

1 1

1

0 12

4

CO

GR

11

11

0

2 2

3 2

2

0

1

0 10

2

GR

CA

11

9

0

1

0

2 2

2

1 1

1

0

9 3

CG

DO

*‡

16

11

0

1

1 1

2

0 2

0

6 3

REV

I 11

11

3

1 2

4

0

0

0 6

1A

MC

R

11

10

1

1

0

1 1

1

0

0

4 2

BH

NU

‡ 20

19

2 2

0

1 0

1

0 4

3C

HSP

9

11

1 1

2

2 1

0

0

4 2

RTH

A

9 9

0 2

1

1

0

0

3 1

SOSP

8

-

2 2

1

0

0

0 3

2


443


Con

serv

atio

n M

ean

abun

danc

e

scor

e fo

r 20

06

2007

20

09

2010

si

tes

Pile

s Sc

atte

red

Pile

s Sc

atte

red

Pile

s Sc

atte

red

Pile

s Sc

atte

red

Spec

ies

A+B

C+D

4.3

6.

1 4.

3 6.

1 %

4.

3 6.

1 4.

3 6.

1 %

4.

3 6.

1 4.

3 6.

1 %

4.

3 6.

1 4.

3 6.

1 %

To

tal

Yrs

AM

RO

6

9 1

1

0

0

0 1

1B

AC

S*‡

21

20

0

1 0

0

0

1 1

TUV

U

9 10

1

1

0

0

0 1

1

YB

CU

†

Early-Successional Breeding Bird Communities in Y anaged ......Early-Successional Breeding Bird...

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