The plant communities of Arches National Park
Transcript of The plant communities of Arches National Park
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Theses and Dissertations
1977-08-01
The plant communities of Arches National Park The plant communities of Arches National Park
John Stevens Allan Brigham Young University - Provo
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THE PLANT COMMUNITIES OF ARCHES NATIONAL PARK
A Dissertation
Presented to the
Department of Botany & Range Science
Brigham Young University
In Partial Fulfillment of the
Requirement for the Degree
Doctor of Philosophy
by
John Stevens Allan
August 1977
L J.
Looking north from Panorama Point: Blac::<brush in the foreground and the Fiery Furnace fins area in the background. Lower Salt Valley in the center of the scene supports a mosaic of blackbrush, saltbush, and grassland communities.
iii
ACKNOWLEDGEMENTS
There have been many people who have made this
study possible. First of all, thanks goes to my wife,
Elsie, whose patience, love, counsel and support as
well as typing of rough drafts are largely responsible
for this project reaching fruition. Dr. Kimball Harper
took over chairmanship of the Committee when Dr. Earl M.
Christensen passed away after a traffic accident in 1973
and has been a friend, a patient counselor and at the
same time a perceptive scientist whose encouragement and
critical reviews of the manuscript are deeply appreciated.
Dr. Christensen suggested. this study and enthusiastically
directed the research during most of the field work. His
association will always be.fondly remembered.
Dr. Jack Brotherson provided the computer program
and helped in setting up and running the cluster analysis.
Dr. Stanley Welsh made many corrections in the plant
collections and was very helpful in many identification
problems. Dr. Derby Laws, Dr. Glenn Moore and Dr. Samuel
Rushforth served on the committee and discerningly read
the manuscript, offering several needed suggestions and
corrections. Dr. Benjamin Wood also served on the commit-
tee until he left in 1976.
iv
Several people at the Environmental Studies Lab
of the University of Utah Research Institute assisted
as follows: Tawny Isakson, now with the Geoscience
Illustration Lab, assisted in several phases of produc-
tion of the vegetations map. Neil Olson worked on
several items of drafting. Marian Clem assisted in typing.
Dr. A. Clyde Hill, Director of the Lab, gave me time off
to finish, as well as patience and kindly encouragement.
Special thanks go to my sister, Mrs. Betty Jewel
Ulmer, for wading through several typings of the
manuscript. Thanks also go to my daughter, Analisa, and
to Dorothy Watkins for· typing some phases of the
dissertation and to my three sons for their patience and
understanding.
I extend grateful appreciation to the Rangers and
staff at Arches National Park Headquarters for allowing
the study to be done, proving collecting permits _and
allowing access to the historical files.
Brigham Young University Botany and Range Science
Department provided funding for the field research and
several other phases of the analysis. This _study would
not have been accomplished without this help.
There are many others not mentioned in this
acknowledgement that have assisted in one form or other.
Their help is also appreciated.
V
ACKNOWLEDGEMENTS.
LIST OF TABLES ••
TABLE OF CONTENTS
• • • • • • • • • • • • • •
. . . . . . . • • • . . • •
• • • •
• • • •
Page
iv
vii
LIST OF FIGURES •• • • • • • • • • • . . . . . . . • viii
INTRODUCTION. . . . . . . • • • • • • • • • • • • • •
SHORT HISTORY OF THE PARK. • • • • • • • • • • • • •
DESCRIPTION OF THE AREA. • • • • • • • • • • • • • •
METHODS. • • • • • • • • • • • • • • • • • • • • • •
Field • • • Laboratory. • • • • • • • • • • • • • •
• • • • • • • • • • • • • •
RESULTS AND DISCUSSION. • • • • • • • • •
. . . . . . . . . . . . • • • • • •
1
3
6
11
11 13
16
Macroclimate. • • • • • • • • • • • • • • • • • • • 16 Vegetative Cover. • • • • • • • • • • • • • • • • • 18 Flora of the Park. • • • • • • • • • • • • • • • • 20 General Biotic Characteristics of the Communities. 25 General Abiotic Characteristics of the Communities. 29 Species Composition of Plant Communities. • • • • • 33 Cluster Analysis. • • • • • • • • • • • • • • • • • 42 Lifeform Spectra. • • • • • • • • • • • • • • • • • 49 Discussion of the Plant Communities. • • • • • • • 54
SUMMARY AND CONCLUSIONS.
LITERATURE CITED. • • • •
APPENDIX. • • • • • • • •
• • • • • • • • • • • • • •
• • • • • • • • • • • • • •
• • • • • • • • • • • • • •
vi
86
89
95
LIST OF TABLES
Table Page
1. Major Community Types in Arches National Park. 19
2. Characteristics of the Flora •• • • • • • • • •
Areal Extent of Various Mapping Units. • • • •
21
24
4. Vegetational Characteristics of Communities. • 26
5. Environmental Characteristics of the Plant Communities •••• • • • • • • • • • • • • • • 31
6. Species Composition of Ten Major Plant Communities •••••••••••••• • • • • 35
7. Matrix Showing Compositional Similarity Among the Ten Plant Communities. • • • • • • • • • • 43
8. The Relative Importance of Various Plant Lifeform Categories •••••••••••
vii
• • • 50
LIST OF FIGURES
Fig~re
Frontice - Looking North from Panorama Point. • • •
1.
2.
Reference Map of Arches National Park •••
Streamside Vegetation in Courthouse Wash ••
3. (A & B) Climatograms of Two Weather Stations
. . • •
Page
iii
7
8
Near Arches National Park. • • • • • • • • • • 17
4. Vegetation Map (in pocket at back)
5. The Juniper-pinyon Community West of the Devil's Garden and Upper Fiery Furnace Areas. • 23
6. Cluster Dendrogram of Arches National Park Plant Communities. • • • • • • • • • • • • • • 47
7. Sand Dune Association on Willow Flats. • • • • 57
8. Grassland Vegetation South of Courthouse Wash. 67
9. Cache Valley with Gray Soils Derived from Mancos Shale ••••••••••••••• • • •
10. Hanging Garden in a Seep Area in Fresh Water
76
Canyon. • • • • • • • • • • • • • • • • • • • • 83
viii
INTRODUCTION
Arches National Park is located along the
northern bank of the winding Colorado River on the
northern edge of the "Red Rock Country" of southeastern
Utah. Park headquarters are located less than five miles
north of the town of Moab, Grand County. The Park
includes some of nature's most spectacular phenomena.
For decades explorers, trappers, pioneer agriculturalists,
tourists, students, and scientists from throughout the
world have marveled at the display of prodigious windows,
.graceful arches, massive towers and abutments, teetering
pinnacles, and narrow rock fins. Although geological
features have been the main attraction for visitors over
the years, Arches can also boast unique vegetative
characteristics. The flora has received little attention,
although an excellent annotated list of the plants
collected in the area has been published (Harrison il !l• 1964). The vegetation has been important to a few
ranchers in the area as a source of forage for sheep,
horses and cattle. However, under Park Service policies,
grazing will eventually be phased out in order to restore
the park to natural conditions.
1
2
On a visit to Arches National Monument in the
fall of 1971, the late Dr. Earl M. Christensen of Brigham
Young University suggested to me that the plant communities
of this area needed a definitive study, because the Park
exists in a phytogeographic transition zone. He noted
that information about the plant communities would also
enhance the enjoyment of many visitors to the Park.
Accordingly, this study was commenced in April of 1972
with these objectives in mind:
1, to map the major plant communities of the
park;
2, to quantitatively describe the composition
of the major communities; and
3, to correlate some of the measurable environ-
mental factors with selected vegetational characteristics
in an effort to better understand the distribution of the
communities in time and space.
SHORT HISTORY OF THE PARK
Arches National Park presently comprises about
73,234 acres of land. Before the area became a national
monument in 1929, it was visited by only a few early
explorers, prospectors, and possibly some trappers.
Stockmen probably trailed their herds through Arches
before and after Mormon ranchers settled in the Moab area
in 1875. Evidence from petroglyphs, artifacts, and
chipping grounds in the Park indicate that Indians were
regular visitors before and after white men came to
the area.
The first person to settle within the present
Park boundary was a man named John Wesley Wolfe, who
came west in 1888 on the advice of his doctor to seek a
drier climate (Newell, 1971). He and his son Fred found
the desert climate to indeed be dry, as they established
small fields along the banks of Salt Wash in a graben-
like area which is now called Cache Valley. He built a
cabin, started a cattle herd, and raised his own garden
in the peaceful valley. Cache Valley was at least a
day's ride from the nearest store in Moab. After 18 years
his daughter, her husband, and their two children joined
him at the ranch. The cabin and root cellar he built for 3
4
them still stands as a monument to this first agricul-
tural effort at Arches. His original cabin washed away
in 1906 in one of Salt Wash's occasional flash floods.
His ranch was later sold to Tommy Larson, who then sold
it to J.M. Turnbow in 1910. Turnbow continued ranching
there for several years. Eventually Turnbow sold grazing
rights to Emmet Elizando, who ran as many as 600 cattle
and 35 horses on the Cache Valley Unit. Bureau of Land
Management records for 1951 show that permits were
issued for 1,963 animal unit months (AUM's) on the area
used by Elizando.
Other grazing rights in the area were held by
such operators as Frank Paxton with about 110 AUM's in
Salt Valley. Also, James Sommerville held 2,200, W.D.
Hammond 500, J.M. Bailey 540, and Guss Morris held 1,320
AUM's on the Arches Unit. Many of these grazing rights
continue until today on these units, because the first
Monument proclamations and later bills leading to esta-
blishment of Arches as a National Park made special
provisions for life-long grazing rights for the original
permittees.
The movement to set Arches aside as a National
Monument was first begun by a visitor from the University
of Michigan, Prof. Lawrence M. Gould. He recognized that
the area was a special geological and scenic phenomenon.
Local leaders such as Dr. J. w. Williams (generally
considered the father of Arches) and L. L. Taylor of the
Moab Times Independent took up the campaign along with
other local leaders and organizations. Their efforts
were finally rewarded on April 12, 1929, when President
Herbert Hoover set aside an eight square mile area as
Arches National Monument. In 1938, President F. D.
Roosevelt enlarged the Monument to about 53.1 square
miles (34,010) acres). It was not until 1969 that the
Monument was enlarged to about 130 square miles (82,953
acres), by President Lyndon B. Johnson. This latter
area included Dry Mesa on the southeast. When the
Monument was upgraded to Park status by action on
November 16, 1971, Dry Mesa was eliminated, while other
areas on the northern end were added. After several
amendments, the Park area finally stands at about 114.4
square miles (73,234 acres). By the time the Monument
became a Park, most of the present improvements (e.g.,
roads, Visitors' Center, Devil's Garden Campground, and
historical restoration of Wolfe's Cabin) had been
completed under authorizations enacted during President
Dwight D. Eisenhower's administration.
5
DESCRIPTION OF THE AREA
Arches National Park is located in the Canyon
Lands section of the Colorado Plateau, where sandstone
plateaus have been dissected into deep canyons by a few
permanent and many intermittent streams. Such canyons
as Courthouse Wash on the southwest and Salt Wash on the
northeast have created relatively spectacular gorges as
they approach the main gorge of the Colorado River
(Fig. 1). The Courthouse Wash drainage slopes westerly
from the Windows Section. Massive abutments of Entrada
Sandstone and the Carmel Formations (which include the
Hambone Rock abutment near Balanced Rock) are scattered
throughout the Windows Section. Four minor drainages
southeast of the Courthouse Wash bridge branch off to the
northeast; all are bordered by steep canyon walls and
verdant growths of streamside vegetation. The streamside
vegetation is watered by springs which flow year around
during normal years (see Fig. 2). South and southeast of
the Courthouse Wash syncline are a group of bluffs and
erosional forms called the Courthouse Towers which end at
the Seven Mile Moab Valley anticline. The anticline
forms the southern border of the Park (Lohman, 1975).
North of the sandstone walls of the Courthouse
Wash complex is an area called Willow Flats. Willow 6
SCALE
D .. Salt LakeCity • Provo
UTAH
Arches Ntl. Pork
, Dark \. A'\l11e
'\. u'Q> Klondike\~
\ Bluffs , t,.
'~ \~ \
\ ' ,.. _,, ',.I
ARCHES NATIONAL
PARK Herdina Pork
Willow Flats
Plltrified Sand Dune
Windows Section \
J _.,...,-•-
"·-· ,.,..,i., ,, ,...,. Courthouse ~,. ·
Towers ! ,.-1-·
!
o 2 3 MILES
Fig. 1. Reference map of Arches National Park.
7
Fig. 2. Streamside vege�ation in Courthouse \'lash. Tamarix, willows, rushes, and Fremont cottonwoods dominate the view. Courthouse Towers and the LaSal �ountains are in the background.
8
Flats are named after a spring fed area where willows
and cottonwoods line the wash. This area was added to
the Park with the bill of 1971. As one travels north of
Willow Flats over sandy jeep roads, spectacular bluffs
and fins are encountered in Herdina Park. Near the
north boundary of the Park occurs a series of fins
which end in the Marching Men and Klondyke Bluffs. This
area comprises the northwest end of the ridge that
borders the Salt Valley and Cache Valley anticlines.
These anticlines have collapsed, because the salt dome
(part of the Paradox Basin salt dome) which supported the
anticline has dissolved away and left the overlying beds
unsupported (Dane, 1935). The northeast side of Salt
Valley has fin-like erosional forms which have developed
from cracked Entrada sandstone (see Frontice photograph).
The Entrada Formation has also given rise to
Fiery Furnace in the southeast, Devil's Garden in the
middle, and Eagle Park on the northwest end of the
Park. The northeast side of the Salt Valley anticline
slopes down to the Salt wash syncline, and the north-
eastern border of the Park. Along this northeast flank
are jointed white bands of the exposed Moab Member of the
Entrada with juniper and pinyon trees growing in the
joints. On the edge of the flank are patches of Sommer-
ville Formation which consists of dark reddish sandstone
covered with scattered bits of cherty rock.
9
10
The Cache Valley Graben at the easterly end of
the Park, is dotted by grayish, badland domes of Mancos
Shale which blend into the pinkish Morrison formation on
the north. These hills are dotted with greenish veins
of glauconite sands and shales which contrast with the
Morrison formation to give a virtual kaleidoscope of
colors. Drab sandstone caps on the hogback ridges nearby
are formed by the Dakota Sandstone. Northwest of the
Cache Valley Graben, the sandstone rises in tiers to
meet the abutments which border Winter Camp Flats. These
abutments contain one of the Park's most spectacular
formations, which is justly called Delicate Arch.
METHODS
Field
Field work was completed in the period between
April 1972 and June 1974. The major field work was done
during the spring, summer and fall of 1972 and 1973.
Some mapping work was done in 1974 and 1975.
Study areas that appeared homogeneous in respect
tp plant composition and environment characteristics
were selected in each plant community. The shrub and
grass stands were sampled by 10 transect lines that were
15.3m {50 ft.) long. The line-point method (Heady et. _tl.,
1959) was used to estimate plant cover along the transects.
Meter-square quadrats were placed every 3 m along the
transect to obtain frequency and density data. A total of
50 quadrats were read along the 10 line-point transects in
each stand. Subsamples of the surface soil were taken at
every other transect to a depth of 15 cm. All subsamples
were composited to yield a single sample per stand.
Forested stands in pinyon-juniper and streamside
vegetations were sampled by multiple methods. Trees were
sampled with the Bitterlich variable radius plot
technique (Grosenbaugh, 1952). Trees sampled with this
method were recorded by size class. The quarter-method
11
12
(Cottam and Curtis, 1956) was used to select individuals
for tree height and reproduction studies at 40 points
along a compass line. A m2 quadrat was placed at each of
the 40 points to sample herbaceous plants. Ten addi-
tional m2 quadrats were distributed randomly between
points so that a total of 50 quadrats were read per stand.
Shrubs in these stands were sampled by the quarter-method.
Elevation, slope, exposure, soil depth from pene-
trometer readings, soil texture, grazing pressure, and
all plant species in the vicinity of the transects were
recorded at each stand. Soil samples from each site were
analyzed in the laboratory for texture, pH, salinity, and
various elements.
Roadside vegetation was sampled by taking five m2
quadrats per mile at a distance of one meter from the
asphalt road edge along the right side of the road
running north into the Park. A total of 50 quadrats
were taken along a 10 mile stretch of road. This road-
side transect started on the highway switchbacks just
north and above the headquarters area. Roadside soil
samples were not taken, since the fill is often replaced
as the roadsides are repaired from time to time.
The clay hills derived from the Mancos Shale
Formation in the Cache Valley area were sampled. Samples
were drawn from the north and south slope of the hills
and pooled for a composite sample. All other factors
were sampled as reported for the shrub and grass stands.
Aerial photos were used to map the vegetative
communities (Kuchler, 1967). Mapped areas were checked
in the field to confirm species compositions. Notes
pertaining to the area mapped were compiled on numerous
exploration hikes and on drives where roads permitted
access.
Laboratory
The vegetation data were summarized to yield
absolute frequency data for all stands. The frequency
values became the basis for the analysis of similarity
among stands. A prevalent species list was compiled for
each vegetation type using average stand frequencies for
each species (Curtis, 1959). At least 90% of the occur-
rences observed for all species in the quadrats of each
vegetation type are accounted for by the species on the
prevalent species list of any community considered in
this study.
13
The vegetative similarity existing between speci-
fic pairs of plant communities was calculated using the
average frequency of each species in each community and
the equation: SI = Z Minimum Frequency Values
E Maximum Frequency Values X 100
This equation was first proposed by Ruzicka (1958). In
14
this equation the minimum frequency values for all
species in any pair of stands is summed. Likewise,
maximum frequency values are summed for all species in
the given pair of stands. Interstand similarity values
provided the basis for a computerized cluster analysis
of the community types. Procedures of Sneath and Sokal
(1973) were followed.
The percent sum of frequency (relative frequency)
was summed for all species of specific lifeforms. Such
data were used to make a lifeform spectrum for each
plant community-type.
Soils were air dried and screened before analysis.
Soil texture was determined using the hydrometer method
(Bouyoucos, 1936) with sodium silicate as a dispersing
agent. Soil reaction was determined with a glass elec-
trode pH meter on a 1:1 soil-to-water paste. The free
water was filtered from the 1:1 paste and tested for
total salinity with a Solubridge soil salinity meter.
This procedure gives an approximation of the total salt
content of the soils and is reported in mmhos of elec-
trical conductivity (EC).
Ten grams of each soil sample were extracted
with 200 ml of ammonium acetate. The extract was
analyzed for calcium, potassium, sodium and magnesium by
atomic absorption photospectrometry (David, 1960). Total
nitrogen was determined using the Kjeldahl method
15
described by Kirk (1950). Each soil was analyzed quali-
tatively for free carbonates with O.lN hydrochloriq acid.
The degree of effervescence was estimated using a four
point scale (1, none; 2, slow; 3, moderately fast; and
4, rapid to very rapid).
Correlation analyses were run between selected
vegetative characteristics and 17 environmental factors.
The simple linear correlations and significance tests
were carried out on a Tectronix 31 programmable desk
calculator.
The vegetation map was reduced to the desired
size photographically. The reduced map was duplicated
on an ozalid copier. Relative area of each mapping unit
was determined by weighing the total area mapped and the
area covered by each mapping unit. Mapping units were
cut from the map, dessicated in an oven and weighed to
obtain the percentage of the total area contributed by
each mapping unit. Area relationships were checked by
dessicating and weighing 32 pieces of the ozalid paper
cut to represent one square mile of area. These pieces
varied among themselves by. less than 0.01%, indicating
that the paper was of uniform weight.
Plant nomenclature follows Holmgren and Reveal
(1966) except for Ambrosia and Heterotheca for which
Welsh and Moore (1973) were followed and for Senecio
which is treated according to Harrington (1954).
RESULTS AND DISCUSSION
Macroclimate
Since there is no official weather station in
the Park, climatic data reported here are based on
weather stations in Moab and Thompson (U. s. Department
of Commerce, 1953-1973). Moab is approximately 7 Km
south, and Thompson is 17 Km north of the Park boundary.
The macroclimate of the Park should thus lie somewhere
between the values for .these two stations.
Data from the stations were summarized to obtain
20 year averages for temperature and precipitation.
(The averages are based on the period 1954-1973). Those
summaries are presented in Fig. 3A for Moab and Fig.
3B for Thompson. The methods of Walter (1963) were
followed. Average annual precipitation is 19.5 and 21.9
cm respectively at the two stations. Thempson is 341
meters higher than Moab and shows some slight variations
in climatogram patterns. Thompson has, on the average,
2.4 cm more precipitation than Moab and a longer winter
wet season. Moab experiences a longer dry season on the
average. Temperatures are somewhat warmer in Moab,
thus intensifying water deficits. Both areas have
October and December wet periods.
16
35
30
25
90
80
20 70
15
10
5
0
-5
-10
-15
60
50
0
Moab, Utah (1227 m)
(A)
0 13,8 .C 195 mm
Precipitation
Wet season mm Dry season
a~ ...... -----....------....,..------,---...--O
J F M A M J J A S O N D c° F 35 30
25
90
80
2 70
0
15 60
10 50
5 40
O 30 -5
-10
-15
20
10
Thompson, Utah (1568 m) 11.s 0 c 218.8 mm
(B)
Temperature--
M A
Wet season mm Dry season
s Fig. 3 A and B. Climatograms of two stations near
Arches National Park, Grand County, Utah.
17
36
32
28
24
20
16
12
8
4
0
mm
30
29
28
24
20
16
12
8
4
0
18
Vegetative Cover
The 10 major plant communities studied are
listed in Table 1. The number of stands sampled in each
type varied from 1 to 15. Several other communities such
as salt meadow, seepweed, shadscale, and sagebrush (near
Wolfe Cabin) occur in the area but cover less than one
hectare. Continued heavy grazing in the shadscale
(Atriplex confertifolia) community in Cache Valley area
by both sheep and cattle make the area a poor representa-
tion of this community type, so no efforts were made to
characterize it quantitatively. However, the community
has been delineated on the vegetation map (Fig. 4) in the
pocket in back. The vegetation pattern of the Park is
complicated by topographic variations occasioned by
canyons, flats, fins, and buttresses, and by variations
in geologic substrate.
Considerable variation exists within the plant
communities reported in Table 1. The juniper-pinyon
community, for example, could be separated into open
juniper and slick rock juniper-pinyon associations.
Some of the juniper-pinyon type could also be reported
as fin associations because of their occurrence between
the great fin like rock structures to be found in areas
such as Fiery Furnace, Devil's Garden, and Klondyke
Bluffs. In the interest of simplicity, such subdivision
of major community types were not made.
19 TABLE 1
MAJOR COMMUNITY TYPES OCCURING IN ARCHES NATIONAL PARK AND NUMBER OF STANDS OF EACH
CONSIDERED IN THIS STUDY
Community~
1. Blackbrush (Coleogyne)
2. Grass (Sporobolus cryPtandrus - Hilaria jamesii)
3. Juniper-pinyon (Juniperus osteosperma -Pinus edulis)
4. Streamside (Populus fremontii - Salix exigua)
5. Sand ~une (Oryzopsis hymenoides)
6. Roadside (Aristida longiseta - Ambrosia acanthicarpa)
7. Greasewood (Sarcobatus vermiculatus)
8. Tamarix (Tamarix pentandra)
9. Saltbush (Atriplex cuneata and A. corrugata)
10. Hanging garden (Adiantum capillus -veneris - Panicum tennesseensis)
Number of Stands
Studied
15
11
8
1
9
1
2
1
3
2
20
Flora of the Park
Lifeform characteristics of the flora are
reported in Table 2. The lifeform categories employed
are modified from Whittaker and Niering (1964). Three
hundred fifty-seven species are now known to exist in the
Park. Harrison il .§1_. (1964) listed 316 species. Forty-
four additional species have been added to the list as a
result of this study (Appendix A). Native species number
322 with 35 adventives. Forty-six of the species are
considered rare in this area (Table 2) and three occur
on the threatened and endangered list for Utah. These
three are Cymopteris newberryi, Machaeranthera grindeli-
oides var. depressa, and Primula specuicola. The nine
adventive trees are mainly ornamentals planted at park
headquarters, but several trees have become naturalized
in wash areas. Such trees as Russian olive, Siberian
elm, red mulberry, and green ash grow wild in Courthouse
Wash and its side canyons and in Salt Wash. Tamarix, an
introduced shrub which often reaches tree size, is
frequently found in dense patches along drainages with
permanent or semipermanent streams. Herbaceous species
contribute most of the species known from the Park, but
most of the dominant species are shrubs. Two trees (Utah
juniper and pinyon pine) are dominant in forested areas
(see Fig. 5). Relative importance of species of various growth
habits (lifeforms) is shown in Table 2. The herbaceous
21
TABLE 2
CHARACTERISTICS OF THE FLORA OF ARCHES NATIONAL PARK
Native Adventive Total No. of No. of No. of Rare Native
Growth Forms Species Percent Snecies Percent Species Percent Species
Trees Broadleaf deciduous 4 1.1 9 2.5 13 3.6 l 0.3 Needleleaf evergreen 2 o.6 2 0,6
Tree Subtotals ..§. l:l 2 1:.2. 15 id l 2.:1.
Broadleaf deciduous 30 8.4 30 8.4 4 1.1 Broadleaf evergreen 4 1.1 4 1.1 Narrow leaf
dicotyledon 8 2.2 8 2.2 2 o.6 Spinose deciduous 9 2.5 9 2.5 Monocotyledon
rosette l 0.3 l 0.3 Green stemmed 2 o.6 2 o.6 Woody vine 1 0.3 l 0.3 Suffrutescent 9 2.5 9 2.5 2 o.6 Stem succulent ..1. ..1. 0.3
Shrub Subtotals 22 0 _Q_ 65 18.2 8
Herbaceous Ferns 5 1.4 5 1.4 1 0.3 Perennial graminoids 55 15.4 8 2.2 63 17.6 11 3.l Annual graminoids Perennial deciduous
1 0,3 1 0.3 2 o.6 forbs 134 37.4 9 2.5 143 39.9 19 5.3
Winter annual forbs 6 1.7 l 0.3 7 2.0 2 o.6 Summer annual forbs 38 10.6 6 1.7 44 12.3 2 o.6 Stem succulents 6 1.7 6 1.7 Parasitic forbs l 0.3 l 0,7 2 o.6 2 o.6 Rushes _5 _5
Forb subtotals 251 70.3 26 1.:1 ll1. 'JLj_ 21 10.3 Totals 322 90,2 35 9.8 100.0 46 12.8 - - - - - - -
22
types account for almost 78% of the species; shrubs
contribute 18% and trees about 4% of the total. In areal
coverage, tree dominated vegetations are widespread with
juniper-pinyon covering 43.5% of the area. Blackbrush (a
shrub) covers 22.5% of the Park's area, while grassland
dominates 11.4% of the area, and the sanddune community
accounts for 5.2% (see Table 3). Two trees (Juniperus
osteosperma and Pinus edulis), one shrub (Coleogyne
ramossisima) and four grasses (Sporobolus cryptandrus,
Hilaria jamesii, Oryzopsis hYII).enoides, and Aristida
longiseta) make up the bulk of the vegetative cover.
Artemisia filifolia and other shrubs associated with it
are widespread in sand dune environments which occur
intermittently throughout the area, but only A. filifolia
among the shrubs is a regular member of this association.
Mat saltbush species such as Atriplex cuneata and A.
corrugata are characteristic of a limited area of Mancos
Shale exposed in Salt and Cache Valleys.
The map measurements in Table 3 indicate that
juniper-pinyon forest is the most widespread vegetation
type in the Park. In some areas designated as juniper-
pinyon, the trees are rather sparse with blackbrush as
an understory. Such areas could be classified as
juniper-pinyon-blackbrush or open juniper associations
depending on the presence or absence of pinyon in the
tree layer. Scattered individuals of juniper and pinyon
also overlap into sand dune associations. Such dunes
Fig. 5. The juniper-pinyon community west of the Devil's Garden and Upper Fiery Furnace areas.
23
TABLE 3
AREAL EXTENT OF VARIOUS MAPPING UNITS IN ARCHES NATIONAL PARK USING
DATA FROM FIGURE 2
Square Hectares Acres Miles
Juniper-pinyon 12,902 31,856 49.7
Blackbrush 6,674 16,477 25.8
Grassland 3,381 8,348 13.1
Sand Dune Association 1,542 3,808 6.0
Stream side 564 1,391 2.1
Saltbush 445 1,098 1.7
Shad scale 237 585 0.9
Greasewood 178 439 0.7
Fin Association 178 439 0.7
Tamarix 119 292 0.5
Miscellaneous 30 73 0.1
Rock and Rocky Slopes 32411 8 2421 13.2 Totals 29,661 73,227 114.5
24
Percent Area
43.5
22.5
11.4
5.2
1.9
1.5
0.8
o.6
o.6 0.4
0.1
11.5
100.0
25 have been classified with juniper-pinyon since they can
be considered as ecotonal associations. Most of the
juniper-pinyon community is located on slick rock areas in
this study. The Slickrock member of the Entrada Formation
is exposed in the Park and is extensively cracked or
jointed. Both juniper and pinyon become established and
survive well in such cracks and joints. The slickrock
areas east of the Fiery Furnace and the Devil's Garden and
southwest of Willow Flats support open juniper-pinyon
forests that are typical of those considered here.
Towards the east crest of the Salt Valley anticline,
extensive areas occur where erosion has produced vertical
walled, narrow channels between thin partitions of rock
which are called fins. Here the vegetation is also
dominated by juniper and pinyon except in the deepest
defiles. These have been delineated on the map as
separate entities from the rest of the juniper-pinyon
stands and occupy only o.6% of the total Park area.
General Biotic Characteristics of the Communities
Juniper-pinyon stands support a larger number of
species than any other of the vegetation types considered
in Table 4. A total of 90 species were encountered in
the juniper-pinyon community during the course of the
study. There was an average of 47 species per stand in
the community. Many species were also encountered in
roadside and streambank situations, but the sample
TABLE 4
VEGETATIONAL CHARACTERISTICS OF COMMUNITIES
--------------------------------community Type1
-------------------------------Characteristic BB G JP Str SD Rds Gr T SB HG
Number of Species Encountered 59 48 90 46 66 45 34 26 35 20
Number of Prevalent Species (Ave, No, Species/Stand) 22 ?O 47 46 ~4 45 20 26 21 15
Prevalents as% of Total Species Encountered 37 42 52 100 5? 100 59 100 60 75
Freq, of Prevalents as% of Freq, of all Species Encountered 91. 3 92.6 9?,3 100 9?,6 100 95.2 100 95.3 94,7
Average Number of Species per Quadrat 3,0 4,0 3.4 4.0 3.9 5,0 3.1 3,9 4.4 3,2
Number of Modal Species 2 4 11 ?6 25 19 17 9 8 13 17
Index of Community Distinctiveness 3 18,2 55 55.3 54,3 55.9 37,8 45 30,B 61,9 113,3
Average ~G Living Cover ?3.0 31,3 35.5a 65,0b 26,4 25,2 60.7 51.2 26.4 76,1
Average% Litter Cover 5.1 16,3 5.7 3,0b 8.7 5,0 9.1 16,3 1.9 16,0
Tree Basal Area (Sq dm/ha) 206.2 56,B
Cover Composition by Lifeform Class in the Understory b 3hrubs 82,4 5.6 60,0 32.lb 64,9 40,9 72.9 71.5 36,0 6.4
Perennial Grasses _and Rushes 6,5 76,4 3.4 64,2b 21.? 18,7 0.3 0,3 0,9 3?,6 Perennial Forbs 4.3 2.0 13,8 l.lb 4,7 11.0 0,3 4.1 5.3 59.5 Annuals 5,6 15,7 18.8 ?,lb 8.6 29,4 ?6.4 22.6 57.7 o.o Cryotogams 1,2 0,3 3,9 0,5 0,6 o.o 0.1 1.5 0,1 1.5
1BB= Blackbrush, G= Grassland, JP= Juniper-Pinyon, 3tr= Streamside, 3D= Sand Dune Association, Rds= Roadside, Gr= Greasewood, T= Tamarix, 3B= 3altbush, HG= Hanging Garden
?A modal species is one that reaches its maximum abundance in the area in the community of concern,
Ave,
46,9
29.6
67,7
95,3
3.8
14.9
48,7
41.3
8.7
1.7 .3 22,4 10.6 20,3
1.0
3The index of community distinctiveness is that suggested by Curtis (1959) and is calculated thus: Index= ~0 • ~odal 1SotctesxDO o. reva en vpec. aunderstory species only bEstimate df % Cover
I\)
°'
27 consisted of but a single stand for both communities.
At the other end of the floristic diversity gradient are
the hanging gardens with only 15 species per stand.
Hanging gardens are the most floristically unique
(distinctive) of the communities considered. Although
the blackbrush community is visually distinct in the
area because of the peculiar color and size of the domi-
nant shrub in the community, it is floristically non-
distinctive. No species is unique to the community and
only four species (including blackbrush) are modal there
(see Table 6 for information on individual species).
Saltbush appears to be a distinctive community with an
index of 61.9 (Table 4). Roadsides and Tamarix communi-
ties are relatively new ecological entities in the area
and appear to be derived from surrounding communities;
accordingly, they have low indices of distinctiveness.
Prevalent species have been defined by Curtis
(1959) as the commonest species in a community.
Prevalents are selected in a number equal to the average
number of species per stand. Operationally, one selects
prevalent species by arranging all species in a community
in decreasing order of average quadrat frequency in the
stands sampled. One then counts down that list until a
number of species equal to the average number of species
per stand is obtained. Those species are designated as
prevalents. The concept of prevalents permits the
phytosociologist to objectively arrive at a list of
28
important species and to ignore rare and uncommon species
for certain analyses. Table 4 shows that although
prevalent species contribute only 35 to 75% of the
species encountered in the several communities represen-
ted by more than a single stand, they contribute over
90% of the species occurrences in the frequency quadrats
of those communities. The prevalent species concept
thus greatly simplifies phytosociological discussions
without causing serious loss of data.
Average percent living cover and understory cover
by lifeform classes are also reported in Table 4. Cover
data for the streamside stand is based on ocular
estimates. Cover in the hanging gardens was determined
by sampling along the lip of the alcoves. Higher on the
wall, less plant cover occurs than on the lip of the
alcove. As would be expected, wetter situations (e.g.,
the gardens) produce greater cover than do the drier
sites such as are occupied by blackbrush or grassland.
Tree cover is listed as basal area per hectare.
Basal area was taken at a height of 30 cm above ground
in juniper-pinyon stands and at breast height (1.4m) in
the streamside community. Although cottonwood trees may
become very large, their low density results in a low
value for basal area in the streambank community. Much
more tree basal area occurs in the juniper-pinyon forests
than in streambank forests, even though the dominant
29
junipers and pines are small trees. The difference is,
of course, related to tree density in the two communi-
ties.
Relative shrub cover is greatest in blackbrush
and least in grasslands. Blackbrush, sand dune, and
juniper-pinyon communities are dominated in the under-
story by xeric shrubs that produce considerable cover.
The saltbush type occupies xeric sites with less shrub
cover. More mesic sites, such as those held by Tamarix
and greasewood, have over 70% of the living cover
contributed by shrubs.
Perennial grass cover is inversely related to
shrub cover as may be seen in grass and hanging garden
communities. Perennial forbs reach a peak in. the mesic
to hydrophytic hanging garden sites. Cover contributed
by annuals is greatest in saltbush communities and in
other sites with heavy textured soils such as greasewood
and Tamarix. Cryptogams did not contribute much cover
in any community, but they were most frequent in juniper-
pinyon stands. There they occurred on exposed rock
surfaces and on undisturbed shaded areas. Grass, Tamarix,
and hanging garden communities produced the greatest
average litter cover.
General Abiotic Characteristics of the Communities
Topography: Elevation of the stand sites sampled
ranges from 1,268 min Courthouse Wash to 1,648 mat
30 Eagle Park on the northern end of the Park (Table 5). The juniper-pinyon community grows at the highest average
elevation (1,533) of all the communities sampled. In all
probability, elevation per~ is not an important deter-
minant of vegetation pattern in the study area.
Percent slope ranges from almost level in the
streamside community to over 27% in the saltbush type.
Slope steepness undoubtedly influences moisture relations
on sites and exerts an important control on vegetation
patterns in the Park. Gentle slopes at the base of ridges
are made more mesic by runoff water from those ridges.
Vegetation on steep slopes generally has less water
available for use than actually falls as precipitation
because of gravitational redistribution.
Edaohic Factors: Thirteen soil factors are listed
in Table 5. For each factor, average values are reported
for each community. Most soils are sand to loamy sand in
texture, with only a few samples classified as clay loam,
sand clay and sandy clay loam. Three soils from saltbush
stands had so much gypsum that the silt and clay fractions
would not disperse and could not be measured by the hydro-
meter method. One of these stands had 28% sand and 72%
fines so may possibly fall into the clay loam textural class •.
All the soils are basic in soil reaction.
Grasslands had, on the average, higher pH values than
blackbrush and juniper-pinyon. Greasewood had the
TABLE 5
ENVIRONMENTAL CHARACTERISTICS OF THE PLANT COMMUNITIES CONSIDERED (See TABLE 4 for a key to the community abbreviations.)
---------------------------Community Type---------------------------------
Mean Environmental Factors BB G JP Str SD Rds Gr T SB HG
Elevation (m) 1,472 1,483 1,533 1,268 1,402 1,417 1,292 1,286 1,345 l,~63
Slope(%) 6.1 2.9 9.8 0.1 7.3 7.5 0.1 0.5 27.1 15.0
Soil Characteristics Rock >2mm diameter(% by Weight) 6.2 1.1 ?.7 o.5 1.5 * 1.7 o.o 17.0 13.2 Sand ~%I 82.8 77.7 83.0 82.5 89.1 * 58.5 67.5 52.7 71.2 Silt % 8.2 11.2 10.1 13.5 4.6 * 9.0 25.9 47.3+ 15. 7 Clay(% 9.0 11.1 6.9 4.0 6. 3 * 32.5 7.6 13.1 Soil Reaction 8.3 8.6 8.2 8.1 8.4 * 7.6 8.2 7.6 7.6 Calcium (mf/g seived soil) 3.86 3.04 4.86 5.06 2.04 * 2.95 6.46 2.87 3.15 Potassium mg/g seived soil) 0.07 0.12 0.06 0.06 o.42 * 0.31 o.15 o.42 0.09 Sodium (mg/g seived soil) 0.15 0.17 0.07 0.25 0.28 * 1.98 0.16 0.17 0.05 Magnesium (mg/g seived soil) 0.09 0.11 0.11 0.33 0.08 * o.n o.15 0.12 o.46 Nitrogen(%) 0.017 0.015 0.019 0.008 0.014 * 0.064 0.013 0.041 0.053 Relative Effervescence 3.0 2.6 3.4 3.5 3.1 * 3.8 4.0 3.3 3.8 Electrical Conductivity (mmhos/cm2 ) 0.2 0.2 0.3 1.7 0.2 * 12.5 0.5 2.9 0.5 Penetration of Soil Probe (dm) 2.9 2.5 1.7 7.4 4.6 * 2.6 5.2 3.8 o.5
*No soil data taken.
+Excessive amounts of gypsum caused flocculation, so silt and clay could not be determined.
Aver-age
1,388
12.6
4.9 73.9 12.3 11.3
8.1 3.81 0.19 0.36 0.30 0.027 3.4 2.1 3.5
\.>I I-'
32
lowest pH at 7.6, but average values for saltbush and
hanging gardens were also close to that value.
Calcium, potassium, sodium, and magnesium were
measured in mg/g soil. Nitrogen is reported as percent by
weight in the soil samples. Strong positive correlations + + ++ exist between K, Na, Mg and percent fines, and a very
high correlation is observed between Mg++ and K+ (Appendix
B) •
M ++ g •
Sodium is also strongly positively correlated with
Electrical conductivity (EC) correlates positively
with Na+, K+, and Mg++ and negatively with Ca++. EC also
correlates positively with fines, thus demonstrating a
relationship between heavier soils and high salinity at
Arches. Electric conductivity tests show greasewood
stands to have the highest readings (Table 5). These read-
ings are only approximate, since they were taken on a 1:1
soil: water paste and not on a saturated paste as is
normally reported. A reading of over 1.5 mmhos usually
signifies sufficient salinity to cause problems in agricul-
ture when readings are based on 1:1 paste (personal
communication with Dr. F. E. Lambourne of the Utah State
University Soils Lab). Saltbush stands all had conducti-
vity readings of over 2.5 mmhos, thus indicating high salt
content. Positive correlations between conductivity
readings and K+, Na+ and Mg++ suggest that salts of these
elements are responsible for much of the salinity.
Calcium, as would be expected, correlates
positively with effervescence, since caco3 is the
principal salt with which HCL reacts in effervescence
tests. Effervescence is greatest in soil underlying the
Tamarix stand; extractable calcium there was 6.5 mg/g
soil. Average effervescence values are also high for
greasewood and hanging garden soils (Table 5). Depth of penetration by a thin steel rod forced
into the soil by hand reveals something about depth
relationships of the soil and/or degree of soil compac-
tion at the time of sampling. Streamside soil in
Courthouse Wash was more easily penetrated than any
33
other in this study. Tamarix and sand dune associations
also grow on deeper and/or less compacted soils (Table
5). The sandy soils underlying blackbrush and juniper-
pinyon stands are shallow and skeletal. Soil penetration
in the heavy soils of saltbush associations is relatively
deep, even though many areas have surface exposures of
gravel-like rock that has apparently been exposed by
geologic erosion.
Species Composition of Plant Communities
The plant communities at Arches are relatively
well defined; as a consequence, mapping vegetative types
in the field was comparatively easy. Species composi-
tion was not complex in most stands studied. The number
of species encountered per stand ranged from 6 in a
blackbrush stand on a ridge south of the windows section
to 48 in a streamside stand sampled in Courthouse Wash
and a juniper-pinyon stand located east of the upper
Fiery Furnace area. Underlined values in Table 6
designate the community in which a species reaches
maximum frequency. Species are considered to be modal
in the community of maximum frequency (Curtis, 1959).
Certain analyses presented at a later point in this
paper are based on modal species only.
34
Table 6 is arranged with the columns in the
order in which the communities occur in the cluster
analysis (Figure 4). The table is arranged in such a
way that communities with many species in common occur
close together, while communities with few species in
common are widely separated. In general, the communi-
ties on the right in the table follow a definite
moisture gradient with the wettest community being
hanging gardens. The saltbush community is .the only
community in the sequence on the right that does not fit
the moisture gradient.
Table 6 provides a great deal of information
concerning ecological amplitude and habitat preferences
of individual species in addition to data concerning the
composition of the individual communities. The complex-
ity of the table makes it difficult, however, for one to
draw generalizations from the basic data without the
assistance of some kind of graphic technique that reduces
the hundreds of data points to a visual display. The
TABLE 6
SPECIES COMPOSITION OF TEN MAJOR PLANT COMMUNITIES OF ARCHES NATIONAL PARK (Values entered in table represent average frequency of each species
in the quadrats placed in each community type.)1
-------------------- COMMUNITY TYPE*--------------------SPECIES BB SD JP G Rds Gr T SB Str HG
Coleogyne ramossissima 70.4 2.4 55.0 0.2 4.0 Chaenactis stevioides N:n 1.3 4.0 2.0 27.3 Hilaria jamesii 20.5 7.3 1.3 54.1 4.0 -p Opuntia polyacantha 19.9 2.9 3.6 270" 1.0 1.0 Streptanthella longirostris u:r 8.7 34.9 0.9 4.0 4.o 1.0 Oryzopsis hymenoides 12.9 34.3 15.9 33.8 34.0 3.0 2.0 7.7 4.0 Moss sp. 12.5 (J.9 14.6 0.4 6.0 2.5 Festuca octoflora 12.4 13.1 I"r.9' 8.5 6.o 13.0 5.7 6.0 Ephedra viridis 12.1 8.2 w.-g 4.9 2.0 Gilia gunnisonii 11.9 18.4 '4-:7 8.7 2.0· 10.0 10.0 1.3 1.0 Stephanomeria exigua 8.5 24.7 2.8 4.4 3.0 4.o Gilia leptomeria 7.3 "T.'S 30.4 8.0 1.5 4.0 1.3 Ambrosia acanthicarpa 6.9 14.7 --r:; 4.0 42.0 15.0 40.0 22.0 Plantago purshii 6.3 2.4 2.5 30.9 - 2.0 2.3 Cryptantha crassisepala 5.9 7.6 15.3 T.3 4.0 8.0 2.0 Aristida longiseta 5.3 12.7 T.9 28.8 68.0 1.0 1.0 1.0 Eriogonum gordonii 4.3 17.2 0.4 T.o 12.0 33.0 Oenothera pallida 4.3 0.9 0 .Li 2.9 8.0
\JJ \J1
TABLE 6 (continued)
SPECIES BB SD JP G Rds Gr T SB Str HG
Cymopteris newberryi 4.o 3.3 Sphaeralcea parvifolia Y.9 7.3 20.0 2.0 Phacelia ivesiana 3.7 8.7 21.5 2.0 6.o 7.7 Lupinus pusillus 3.3 7.8 4-1" 1.0 Sporobolus cryptandrus 3.2 '-5 0.3 70.5 18.0 4.0 Artemisia filifolius 2.5 17.6 3.6 4.o 1.0 Rumex hymenosepala 2.1 0.9 0.3 0.7 Ephedra torreyana T:b 3.1 2.3 Bromus tectorum 1.5 2.0 375 1.5 76.o 4.0 2.0 11.3 2.0 Helianthus petiolaris 1.5 0.7 0.5 5.5 2.0 4.0 Cryptantha flava 1.3 7.8 9.5 3.0 Erigeron divergens 1.3 1.3 0.0 2.0 Heterotheca villosa 1.1 0.9 6.o 1.0 24.0 Astragalus mollissimus 1.2 0.9 4.0 Machaeranthera tanacetifolia 1.1 3.6 1.3 2.5 l'Zi:'TI 4.0 1.0 Salsola kali 1.1 0.2 29.9 nr.o 26.0 61.0 Abronia fragrans 0.9 2.3 0.3 0.9 1.0 Erigeron bellidiastrum 0.9 '9-:-S o.4 Atriplex canescens 0.1 (J.o 0.3 1.6 4.0 1.0 Muhlenbergia pungens 0.7 15.3 4.0 Eriogonum cernuum 0.7 1.0 0.2 14.0 Stipa comata 0.5 0.8 10.4 Astragalus amphioxys 0.5 0.2 2.4 Astragalus lentiginosus 0.5 1.8 0,5 o."5 4.0 1.0 Eriogonum leptocladon o.4 19.3 1.4 2.0 Quercus undulata o.4 14.7 Sporobolus flexuosus o.4 4.9 T.3 0.9 Lepidium montanum o.4 a."'- 11.1 0.9 15.0 2.0 \.>l Vanclevia stylosa 0.3 10.6 4.0 ---,.0- (1\
TABLE 6 (continued)
SPECIES BB SD JP G Rds Gr T SB str HG Euphorbia parryi 0.3 17.0 4.2 0.7 8.0 6.0 Chrysothammus nauseosus ssp
junceus 0.1 4.0 2.0 Sporobolus contractus 0.1 1.6 o.3 4.9 Asclepias macrosperma 0.1 1.1 Gutierrezia sarothrae 0.1 Q.4 26.0 1.1 24.0 Poliomintha incana 17.9 3.0 Dicoria canescens T4:c5' 1.0 4.0 2.0 2.0 Heliotropium convolvulaceum Petalostemon occidentale Q o.4 4.0 Lygodesmia grandiflora 7-"S Astragalus ceramicus n 2.0 5.3 Hymenopappus filifolius 1.6 0.5 20.0 Corispermum hyssopifolium 1.3 2.0 - 1.0 Dithyria wislizenii 1.3 -Chenopodium fremontii Q.4 0.1 10.4 3.3 Descurainia pinnata o.4 26.0 42.0 8.7 Yucca harrimaniae 0.2 13.6 4.0 8.0 Juniperus osteosperma 5.0 Pinus edulis w.-g Cowania mexicana ""Zo.7 Lichen sp. TS:t5 Fraxinus anomala Gutierrezia microcephala IT3 16.0 4.7 2.0 Cercocarpus intricata 8.8 Streptantha cordata 4.5 2.3 Amelanchier utahensis 4.4 Chrysothamnus viscidiflorus
vJ ssp. stenophyllus 2.4 2.3 --...J
TABLE 6 (continued)
SPECIES BB SD JP G Rds Gr T SB Str HG
Artemisia tridentata 2.3 13.0 2.0 Astragalus sabulonum 2.0 Cordylanthus wrightii 2.0 Senecio multilobatus 0.5 Eurotia lanata 5.5 Astragalus praelongus 2.9 Sporobolus giganteus o-:7 8.0 4.0 Chrysothamnus nauseosus ssp.
10~0 graveolens 1.0 26.0 Eriogonum corymbosum 2.0 Chrysothamnus nauseosus ssp.
gnaphalodes 4.0 29.0 Sarcobatus vermiculatus 2.0 66.o 10.3 Senecio multicapitatus 2.0 9.0 Draba cuneifolia 2.0 Erodium cicutarum "2-:TI Grindelia squarrosa 2.0 Lepidium densiflorum 37.0 14.0 1.0 Chenopodium incanum rr.n 20.0 2.0 Atriplex confertifolia I'o.o 1.3 Conyza canadensis Cleome lutea ?.O Tamarix pentandra 56.o 10.0 Chrysothamnus linifolius "54.TI" 1.0 Bassia hyssopifolium '38.o 3.0 Muhlenbergia asperifolia 12.1) 43.0 Allenrolfia occidentalis 8.0 Atriplex cuneata 4.0 59.0 \..)J
Medicago sativa 2.0 ():)
TABLE 6 (continued)
SPECIES BB SD JP G Rds Gr T SB Str HG
Phacelia corrugata 43.7 Eriogonum inflatum '38.7 Machaeranthera venusta B:3 Mentzelia dispersa w.TI Artemisia spinescens IT:'7 Malcolmia africana u:o Atriplex corrugata -,-;{j Tetradymia spinosa LL Populus fremontii 75.0 Melilotus alba '54:o Juncus torreyi Xanthium strumarium ;r.u Salix exigua Grindelia aphanactis IB:5 Haplopappus drummondii n:o Salix amygdaloides S:-0 Distichlis spicata E:'U Equisetum kansanum 4:15 Morus rubra ;:TI Elaeagnus angustifolia ;-:t5 Oxytenia acerosa Aster bractyactis Flavaria campestris 2.() Polypogon monspeliensis r.o Castilleja linariaefolia n 2.0 Solidago occidentalis 1.0 Glycyrrhiza lepidota 1.0 Adiantum capillus-veneris 68.5 '->I Panicum tennesseensis 46.o \.0
SPECIES
Andropogon scoparius Toxicodendron radicans Artemisia ludoviciana Aquilegia micrantha Primula speciucola Epipactis gigantea Apocynum cannabinum Solidago canadensis var.
scabra Commandra umbellata Brickellia longifolia Stephanomeria pauciflora Mimulus eastwoodiae
Number of species included
Total number species sampled
BB
52
59
TABLE 6 (continued)
SD
56
66
JP
63
90
G
42
48
Rds
45
45
Gr
33
34
T
26
26
SB
32
35
Str
46
46
1For each species, the modal community (community where the species performs best) is designated by underlining the frequency values.
HG
31.0 F.o '2'5:TI n;:n 143 rr.o 12.5 9.0 8.0 r.5 r.5 r.n 18
20
*BB= Blackbrush, SD= Sand dune, JP= Juniper-Pinyon, G = Grass, Rds = Roadside, Gr= Greasewood, T = Tamarix, SB= Saltbush, Str = Streamside, HG= Hanging Garden.
.p-o
following section demonstrates the use of such a tech-
nique for extracting general relationship from complex
data sets.
41
Many of the shrub species listed in Table 2 have
broad leaves and are deciduous (over 8% of the 18.2%
total for shrubs). The narrow leaved dicotyledonous
shrubs (both deciduous and evergreen) are apparently
better adapted to desert conditions, however, and contri-
bute more individuals (sum frequency) and more plant
cover in the Park than do the broadleaved shrubs.
Table 6 also lists one shrub species each of a
·woody vine (Clematis ligustisifolia) growing near more
permanent streams and springs in the area, a stem succu-
lent (Allenrolfea occidentalis) occuring in the Cache
Valley Tamarix community and a monocot rosette (Yucca
harrimaniae) occurring throughout the Park. None are
particularly abundant.
Among herbaceous species, perennial deciduous
forbs contribute most of the species, but the perennial
graminoids make a more significant contribution to the
plant cover of the area (Tables 2 and 4). Many of the
perennial deciduous forb species act much like annuals
in that they come up and flourish only in years of
exceptional rainfall. Many of the smaller annuals
germinate and set seeds even in moderately dry years,
but most of the annuals (both large and small) germinate
and flower profusely after wet fall and winter seasons.
42
Soil texture is also a definite factor in the occurrence
of annuals; they show moderately high correlation with
fines and a negative correlation with sand fractions of
the soil (see Appendix C).
Cluster Analysis
A community similarity matrix is presented in
Table 7. The similarity values shown for the several
community pairs are based on the frequency data for
prevalent species listed in Table 6. The data demon-
strate that the several communities are highly distinct.
Blackbrush and sand dune communities are the most similar
with a similarity value of 26%. When the matrix values
are totalled for each community type, blackbrush and
sand dune communities are shown to be more similar on
the average to the other communities than such communi-
ties as hanging gardens and,streamsides.
The similarity values reported in Table 7
provide another measure of distinctiveness of these
communities in addition to that provided by Curtis'
(1959) index of distinctiveness reported in Table 4. Both measures indicate that blackbrush is the least and
hanging gardens are the most distinctive communities in
the sample. Other communities differ widely in their
position along the distinctiveness gradient provided by
the two measures.
TABLE 7
MATRIX SHOWING COMPOSITIONAL SIMILtRITY AMONG THE 10 PLANT COMMUNITIES
Com- Sum Sum munity Simi- Simi-
Type BB G JP Str SD Rds Gr T SB HG larity larity
BB 100 112 15.7
B 18 100 87 12.2
JP 24 7 100 82 11.5
Str 4 3 3 100 37 5.2
SD 26 18 15 6 100 106 15.0
Rds 13 16 11 7 18 100 89 12.5
Gr 10 13 10 5 12 8 100 81 11.6
T 8 4 5 8 8 10 13 100 60 8.4
SB 0 8 7 2 5 6 11 5 100 53 7.5
HG .8 .1 .4 .1 .3 .8 .2 .4 .o 100 3.1 o.4 710.l 100.0
1similarity values are based on the frequency values reported in Table 6 and are obtained using the similarity index proposed by Ruzicka (1958). .p-
l..>l
44
Even though blackbrush and sand dune communities
have the greatest similarity of all the communities in the
study, there are numerous differences between them. Soil
conditions are generally alike except that depths are
often greater in sand dune associations. However, black-
brush may often occur on deeper soils which are contiguous
to sand dune associations. Coleogyne has 70.4% average
frequency in blackbrush communities, whereas its frequency
in the sand dune associations averages only 2.4% with a
range from Oto 16%. Oryzopsis hymenoides is a modal
species in the sand dune association with an average of
34.3% frequency (range Oto 72%), but its average fre-
quency is only about 13% in blackbrush. Similar
situations occur with many of the less important species.
About 68% of the prevalent species which occur in the·
sand dune association also occur in the blackbrush
community, but percent frequency values for those species
in the two communities is usually very different, thus
producing a low similarity.
The next highest similarity value between two
communities is that between blackbrush and juniper~
pinyon at 24%. Coleogyp.e occurs as the dominent
understory shrub in pinyon-juniper (55% average frequency
with a range from 4 to 88%). Sixty-eight percent of the
prevalent species of pinyon-juniper are common to
blackbrush communities too. As with the sand dune-
blackbrush situation cited above, species common to the
45
two communities perform very differently in the two
habitats. The same relationship also occurs between
blackbrush, grassland and roadside communities. They
have even lower similarities and fewer species in common
as may be seen in Table 6, but the modal species
especially behave differently in each community. Road-
side vegetation can be looked upon as a binding influence
as far as intercommunity similarities are concerned.
The roadway passes through several communities and has a
number of entities which occur consistently along its
length, even though the surrounding communities change
from blackbrush to sand dune to juniper-pinyon to grass-
land and back to blackbrush or sand dune associations.
The intercommunity similarity between Tamarix,
saltbush and streamside communities is very low. Very
little greasewood occurs in the Park, and the community
is not particularly similar to any other community (only
13% similarity to grassland and Tamarix). Moisture
levels in greasewood and Tamarix are usually high, since
they appear to prefer sites where runoff water accumu-
lates; salinity is generally somewhat higher than
average in these communities.
Based on the similarity matrix, the communities
were clustered using a procedure described by Sneath and
Sokal (1973), and utilized by West (1966), Singh and
West (1971), and Kleiner and Harper (1972). Three sets
of communities clustered above the 10% similarity level
46
(blackbrush and sand dune, grassland and roadside, and
greasewood and Tamarix) as shown in Fig. 6. Juniper-
pinyon has close affinities to blackbrush and sand dune
associations and clusters with them at about the 20% simi-
larity level. The grassland-roadside and greasewood-
Tamarix groups cluster with blackbrush at about the 14%
and 9% levels respectively. Saltbush, streamside, and
especially hanging garden communities show little simi-
larity to other vegetative types considered in this paper.
The use of cluster methods in gradient analysis
assumes that plant species act as meters of the environ-
mental conditions extant in the areas they occupy. West
(1966) put it this way, "Each plant indicates by its
presence, abundance, growth rate, etc., something about
the effective environment, and thus acts as a sort of
bioassay of the site." He further pointed out that
communities are much more effective in this "bioassay of
the site," because a combination of species brings in
competition which enhances ••• nindividual physiological
amplitudes ••• modified by the influences of other plants
and animals. This combination of indicators (the plant
community) integrates all factors of the biocoenotic
environment and reflects its biological effectiveness."
Factors which are very difficult to measure and interpret
can be assessed by quantitative relationships of the
plant species to each other. Environmental gradients
are confirmed both qualitatively and quantitatively by
Black brush
Sand dune
Juniper - Pinyon
Grassland
Roadside
Greasewood
Tamarix
Saltbush
Streamside
Hanging Garden
Percent Similarity 30 25 20 l? 10 ? 0 -, . •
- -
- ....
-
Fig. 6. Cluster dendrogram of Arches National Park plant communities.
47
48
degrees of similarity and by graphical distribution (Fig.
6). The figure provides an objective classification of
the communities. A degree of subjectivity cannot be
avoided in the choice of stands to sample, and a
preliminary classification has to be made based on the
physiognomic character of the dominants in the stand.
By use of cluster analysis, an integrated assessment of
the environment and dynamic interaction between species
is possible. The technique is economical in respect to
both time required and information retrieved.
Fig. 6 provides a graphical view of these plant
communities as determined by species frequency. The
communities are ordered to some extent along environ-
mental gradients. One obvious gradient is from xeric
conditions on the blackbrush-sand dune end of the figure
to the mesic conditions in hanging gardens and stream-
side communities. Modifications of the simple moisture
gradient are undoubtedly induced by salinity. Salinity
problems probably account for the placement of saltbush
between Tamarix and streamside in the cluster diagram.
It would seem best to conclude from Fig. 6 that
saltbush, streamside, and hanging gardens communities
are only slightly related compositionally and
environmentally and exist essentially as separate entities
with no closely similar vegetation units. Blackbrush,
sand dune, and juniper-pinyon make up the first cluster
group which is probably controlled by such factors as
xeric conditions, and texture of soils. Sand dune
associations occupy seral positions which in time may
develop towards some more stable association as the
dunes stabilize and soils mature.
Lifeform Spectra
49
The lifeform relations of the flora of the
Park have been quantitatively summarized by summing the
quadrat frequency of all species belonging to the
various lifeform categories of Raunkiaer (1937). Each
of Raunkiaer's major lifeform categories is divided into
component subclasses in Table 8. The relative importance
of the several lifeform categories in each of the 10
community types recognized in the Park is reported
(Table 8). The .average val~es for the Park show that
therophytes followed by caespitose hemicryptophytes and
nanophanerophytes are the most abundant contributors to
the lifeform spectrum.
The average contribution of each of the five
major lifeform categories for Arches National Park are
compared with selected lifeform spectra reported in
Gleason and Cronquist (1964) for the world, North
America, cold deserts of Utah, and the hot deserts of
Tucson and Death Valley. The Arches spectra seems to be
closest to those for Death Valley and Tucson.
The lifeform spectra reported by Gleason and
Cronquist (1964) are based on floristic values only
TABLE 8
THE RELATIVE IMPORTANCE OF VARIOUS PLANT LIFEFORM CATEGORIES IN THE PLANT COMMUNITIES OF ARCHES NATIONAL PARK1
(See TABLE 4 for a key to the community abbreviations.) -------Comparison of Life Form Spectra-------
Average Cold for all North Desert Tucson Death
BB G JP Str SD Rds Gr T SB HG Communities Arches World America Utah A.rlzona Valley
Phanerophytes 16.6 1.7 Megaphanerophytes
Mesophanerophytes 6.5 2,4 0.9 Microphanerophytes 18.2 6,0 0,4 21.3 15,3 2.5 6.4 Nanophanerophytes ..2!:.2 ...1..§ 26,9 lli1 6,3 6,7 0,9 ..1.:2. ll:.2
Sub Totals 31.5 1.8 51,6 40,7 15,4 6.7 28,0 37.3 3,4 7,9 22,5 20 46 17 2 18 26
Chamaephytes 0,6 1.8 9,7 0,4 5,4 9,3 2,9 1,1 "'· 7
13,8 6.9 13* 9 2 23 11 7
Hemicryptophytes 61.6 7,6 28,6 Caespitose 19,3 35,3 33,2 7,1 3,9 3,0 77.7 27,7
Rosette 0,4 1.7 o.4 0,7 5.1 0,6 0.9 Scapose -- -- -- -- -- -- -- -- --2!2 -- ...2.:.2
Sub Totals 19.7 63.3 8.0 35.3 29,3 30.3 7,7 3.9 12,3 77,7 29,5 29 26 49 56 24+ 18
Cryptophytes 1.7 0,3 0.9 0,9 3.0 o.4 0,3 1.8 0.9 7 6 19 5 7
Stem succulents 6,8 0,5 0,6 0.8 0.3 2,1 0.2 1.1
Therophytes 39J 32,3 29.2 22,7 46,l 45,3 60,8 55,6 58.6 0,6 39,1 _;a ..12 .1l ..![]_ .,!g Totals 100.0 100,0 100,0 100.0 100.0 100.0 100.0 100,0 100.0 100.0 100.0 =========== 100 100 100 100 100 ~-
1spectra are based on percent sum of frequency values (relative sum frequency of all species of a common lifeform), On the right hand portion of the table, results for this study are compared with biological spectra reported by Gleason and Cronquist (1964),
*Stem succulents included in Chamaephytes, +Hemicryptophytes and cryptophytes combined.
\J1 0
51 (percent of the species in the flora that belong to a
particular lifeform type), whereas the values for plant
communities of Arches are based on percent sum of
frequency. Thus, the values for Arches have been
weighted by the "success" of each lifeform category in
the vegetation. For the comparison of the lifeform
spectra for Arches with those reported for other regions
by Gleason and Cronquist (1964), the community spectra
have been averaged, and a new floristic spectrum has
been computed, so that a true comparison can be made
(Table 8). Both spectra are shown on the right side of
the table.
Two community types, juniper-pinyon and
streamside, had the highest total percentage of
phanerophytes based on percent sum of frequency (51.6%
and 40.7% respectively). Phanerophytes include trees
such as Populus (megaphanerophytes), Pinus and Juniperus
(microphanerophytes), taller bushes such as Cowania,
Fraxinus, Tamarix, and Amelanchier (microphanerophytes),
and low shrubs such as Atriplex and Coleogyne (nano-
phanerophytes). Nanophanerophytes as defined by
Dansereau's (1957) classification are the most frequent
phanerophytes in both forested and shrub communities in
Arches. The prevalence of meso, micro and nanophanero-
phytes in juniper-pinyon communities, and to a lesser
extent in streamside communities, imparts a stratifying
effect to community structure. The stratified
52 environment appears to result in greater numbers of
prevalent species in these two communities (see Table 6
also). Tamarix, blackbrush and greasewood communities
also support significant cover of phanerophytes. The
presence of the taller, more dense microphanerophyte
shrubs in greasewood stands (and Tamarix to a lesser
extent) is probably related to higher moisture condi-
tions in those communities than in others dominated by
the smaller nanophanerophytes.
Chamaephytes, cryptophytes, and stem
succulents appear to be of minor importance in the
Arches flora on the average, but chamaephytes reached a
fairly high average sum of frequency in saltbush and
hanging garden communities. Chamaephytes do well on the
one hand on sites made xeric by fine textured and salty
soils where mat-type shrubs, mostly chenopods, have
become adapted and, on the other hand, chamaephytes are
relatively common on very wet sites with coarse textured
and non-saline soils.
Hemicryptophytes reach fairly high frequencies
with most of the occurrences being contributed by grami-
noides in grassland and hanging garden stands. Locally
abundant grass hemicryptophytes reach 61.6% frequency on
the drier sites of the sandy soils of Salt Valley and
occasionally on ridgetop areas. Hanging gardens also
have a high percentage frequency of hemicryptophytes
(77.7%), but there the grasses are disjunct species
53 native to the Great Plains to the east. Twenty-eight
percent frequency of this lifeform is also attributed to
the fern Adiantum capillus - veneris and the orchid
Epipactis gigantea. These gardens represent miniature
islands in a sea of desert and are unique to the canyon
lands area (Welsh and Toft, 1975). Graminoides were also
moderately frequent in roadside, streamside and sand dune
communities, but the genera and species vary greatly from
those found at high frequencies in other communities.
Here again the availability of moisture provides a variety
of habitats to which hemicryptophytic plants have become
adapted.
Stem succulents are mainly restricted to the
cactus gro?p, with an exception being the halophytic
plant Allenrolfea occidentalis. The cacti are widespread
but do not reach great frequencies in the Park. Prickly
pear (Opuntia polyacantha) forms widely spaced clones in
sandy soils of blackbush, grassland and sand dune
associations, but the species is not as frequent in the
vegetation as an aspect view would seem to indicate.
Allenrolfea was sampled only in the Tamarix community
near Salt Wash Creek in Cache Valley. It accounts for
only 2.1% of the sum frequency there.
Annual plants (therophytes) are important
contributors to frequency in all communities except
hanging garden and streamside communities. The winter
of 1972-73 was a comparatively wet year and influenced
54
abundant therophytic growth in such communities as
greasewood, saltbush, Tamarix, and sand dune communities.
The roadside association has many annuals, apparently
because of regular disturbance in connection with
maintenance operations. The high percentages of
therophytes (both% presence and% sum of frequency)
makes the lifeform spectrum of Arches similar to that of
the hot deserts of the American Southwest.
Discussion of the Plant Communities
Black brush
About one million hectares of land is dominated
by blackbrush in Utah (Foster, 1968; West, 1974). Most
of this area is in the Colorado River Basin. Arches
National Park lies in the easte~n half of the distribu-
tion of blackbrush and is near the boundary of the
northernmost extention of the species along the Colorado
River (Bowns and West, 1976). Twenty-two percent of the
Park is mapped as blackbrush, and another 10-20% of the
area is scattered juniper with a blackbrush understory
(55% frequency of blackbrush). Shreve (1942) considered
blackbrush to do best on coarse textured soils which are
low in salts. Beatly (1975) correlated Coleogyne with
gravelly calcareous soils in southern Nevada. Thatcher
(1975) found that blackbrush in pure stands was limited
to shallow soils with vesicular crusts in northwestern
Arizona. He also observed that as soils became deeper,
55 diversity of plant species increased. Bowns and West
(1976) studied three blackbrush stands in western Utah and
found they occurred on soils containing 66, 67 and 76%
sand in the surface soil horizon and low salinity readings.
In Arches, the soils underlying blackbrush stands
average 83% sand and are relatively shallow, moderately
calcareous, low in salinity, and are often rather rocky.
In ridgetop stands, the composition is nearly pure
Coleogyne with few other species present, but where soils
are deeper, diversity increases considerably. On deeper
soils, blackbrush bushes are generally more robust,
especially in areas where moisture accumulates.
Blackbrush in Arches has rather wide tolerances
for local environmental conditions. That tolerance is
reflected in the distribution of the species in the Park
where it occupies a variety of sites differing in respect
to exposure, slope steepness, available soil moisture,
and soil chemistry. Since the species occupies such
variable habitats, the blackbrush community shows much
similarity to several other community types (Table 7). Theorophytes are comparatively abundant in the
blackbrush type and tend to bind that community to
several others. Such species as Chaenactis stevioides,
Streptanthella loneirostris, Festuca octoflora, Gilia
gunnisonii and Stephanomeria exigua are rather frequent
in blackbrush and other communities as well. Such
grasses as Hilaria jamesii, Oryzopsis hymenoides and
56
Sporobolus cryptandrus, and the widely distributed cactus,
Opuntia polyacantha, are also widespread in the Park, and
occur repeatedly in the blackbrush community.
Sand Dune Association
Since sandstone formations dominate the geology
along the Colorado River in the Park, the soils of Arches
range from very fine sand to coarse sand or sandy loam
textural classes. The sand dune plant association is very
widespread in the area. It is often contiguous to black-
brush, grassland and juniper-pinyon communities (Fig. 7). The dunes are rather unstable and support vegetation that
ranges from very low to moderate cover depending on the
seral stage of vegetative stabilization of the dunes.
The dunes generally form a rather rolling hummocky
terrain, but next to the buttresses of sandstone walls
where the Entrada and Carmel formations rise above the
peneplained Navajo sandstone formation, the dunes form
large hillocks 40 to 60 feet high. Along the edges of
Salt Valley and along other major drainages, extensive
areas of sand have accumulated as the wind and water have
transported sand particles from the ridges and flats above
to the lower edges of steep slopes and cliffs.
Dune soils average 89% sand with a range from 80%
in a stand next to Courthouse Wash to 95% at a stand east
of Landscape Arch in the Devil's Garden area. Soil pene-
trometer readings average 4.6 dm (range from 2.6 - 10+ dm),
Fig. 7. �he sand dune association on Willow Flats. Note hummocks of wavey leaf oak (Quercus undulata), scattered junipers and patches of grassland and blackbrush in the midbackground. Buttresses in the background are near Balanced Rock and the Windows Section.
57
58
which is a greater than average depth for soils in Arches.
Sand dune areas have numerous blowouts which often sur-
round rock outcrops and isolated, old juniper trees.
Soils in the blowouts are shallower and have a different
plant species composition than adjacent dune areas.
A total of 66 species were sampled in the dune
association with 56 of them appearing on the prevalent
species list. Excluding the juniper-pinyon communities,
these stands showed the greatest diversity of species
encountered in this study (Table 6). The large number of prevalent species in sand
dune, juniper-pinyon and streamside communities contri-
butes greatly to the positive significant correlation
observed between sandy soils and plant species diversity.
(See Appendix C.) Species composition is actually rather
different among blackbrush, grassland and juniper-pinyon
communities, in spite of close proximity of these
communities in space. In fact, there is a great deal of
diversity among the sand dune stands themselves. More
stable areas with the least sandy soils were often
dominated by Artemisia filifolius. There seemed to be no
consistency of occurrence among most subdominants
associated with Artemisia and other species, but Oryzopsis
hyrnenoides reached high frequencies in all but one of the
stands sampled. Other species which were found as
dominants in several stands were Poliomintha incana,
Vanclevia stylosa, and Eriogonum leptocladon. All of
59
these are seldom found outside the sand dune type.
Poliomintha is most often found on the larger, more
recently formed sand dunes which may indicate a pioneer
role for the species. Other grasses such as Aristida
longiseta, Sporobolus flexuosa, Muhlenbergia pungens and
the annual grass, Festuca octoflora, were often found as
subdominants. Large patches of Muhlenbergia pungens and
established clumps of Oryzopsis and Aristida often
indicate older sand dune communities. In wet years such
as 1972-73, annual species became very abundant with such
species as Gilea gunnisonii, Lupinus nusillus~ Dicoria
canescens, Stephanomeria exigua, and Ambrosia acanthicarpa
growing in profusion. These annuals reached a dominant
level when sampled in 1973. In other years, the annual
flora may not appear at all.
In summary, sand dune associations are apparently
seral in nature, with a great deal of variation from one
dune to another depending on location in Arches and the
degree of hummocking or dune size, with consequent differ-
ences in aspect, slope, and texture.
Juniper-Pinyan
The Utah juniper (Juniperus osteosperma) and the
pinyon pine (Pinus edulis) form an association which
extends along the foothills of the mountains, low plateaus,
mesas, and ridges throughout Utah and parts of Idaho,
Wyoming, Colorado, New Mexico, Arizona and Nevada. From
60 elevations of approximately 1300 to over 2300 meters,
depending on exposure and moisture conditions, these
forests are well developed. According to investigators
including Miller (1921), Pearson (1931), Cottam and
Stewart (1940), Jameson (1962), Johnsen (1962), Arnold et
&• (1964), and Blackburn and Tueller (1970), this forest
association is expanding by invasion into grasslands and
shrublands in low elevation habitats, due to the effects
of overgrazing, fire suppression and climatic changes.
Blackburn and Tueller (1970) indicate that juniper has
been present in various communities since about 1725 and
over the years has increased in density from about 15 trees per acre to closed forests of over 500 trees per
acre. Accelerated invasion apparently began about 1921
and continued in years when good seed crops were followed
by 5-6 years of average or better precipitation.
Blackburn and Tueller (1970) suggest that juniper seed-
lings become established first and are followed by pinyon.
At higher elevations pinyon becomes dominant, but juniper
retains dominance at lower elevations.
Juniper-pinyon types cover about 43.5% of Arches
National Park (Table 3). The types occupy a variety of
habitats ranging from ridgetops to dry rocky washes {see
also Fig. 5). Extensive areas of slick rock extend on
both sides of Courthouse Wash (especially in the western
part of the Park), Salt Wash, and west of Klondyke Bluffs
on the northwest. The entrada formation has cracked and
61
eroded into fins on convex terrain to ,form such areas as
Devil's Garden, Fiery Furnace, Herdina Park, Klondyke
Bluffs, and Eagle Park. Further down the slopes, the
cracks are filled with sediments and harbor linearly
arranged, north and south trending grovelets of juniper
and pinyon separated by massive outcrops of the Moab
member of the Entrada. The outcrops may have scattered,
stunted trees in minor cracks and pockets. The fins
themselves often support juniper and/or pinyon trees,
especially on the wider areas. Although such areas have
been mapped separately, some of the fin area could have
been mapped with the juniper-pinyon type.
Scattered juniper trees occur throughout the Park
and may represent an invasion of previously overgrazed
areas where juniper is responding to fire suppression.
Indications are that juniper-pinyon vegetation will
continue to expand into blackbrush, sand dune, and grass-
land areas (even those which are fairly stable), even
without grazing and fire suppression. If Park Service
policies eliminate grazing and permit natural fires that
do not endanger life or property, it is possible that the
postulated expansion of the type will stop. Climate, too,
will play an important role in the postulated expansion,
since good moisture supply must be available for seedling
establishment.
Many pinyon trees are dead or dying because of
damage inflicted by porcupine. Most pinyon trees have
62
wound areas from porcupine gnawing on the bark. In one
stand, almost 80% of the pinyon trees were damaged. This
is an apparent effect of predator control and of the
biological potential of this sedate but well adapted
denizen of our forests.
In all the juniper-pinion stands sampled at Arches,
juniper was dominant in both frequency and density. Many
stands had dwarfed junipers with numerous branches from
thick bases. Some of the sandier sites had junipers that
were half buried, but the branches were growing vigorously
as if each were an independent stem. Fifty percent of
the stands sampled had blackbrush as an understory
dominant. Other stands had such scrub species as Ephedra
viridis, Cercocarpus intricatus, or Cowania mexicana as
dominant understory species. Quercus undulata, Ephedra
torreyana, and Yucca harrimaniae often occur in the open
juniper areas as subdominants. Some of the subdominants
in denser forests are Chrysothamnus nauseosus var.
junceus, Fraxinus anomala, Gutierrezia sarothrae,
Poliomintha incana and Amelanchier utahensis. Herbaceous
species were generally very sparse and/or short lived
with some being found only under the tree canopy where
shade reduces moisture loss by transpiration. Perennial
forbs are rather few in kinds, but such species as
Lepidium montanum and Cryptantha flava may become fairly
abundant. Streptantha cordata and Cordylanthus wrightii
may be found rather widely distributed here and there in
63
the stands. Such annual species as Cryptantha crassisepa-
1!!, Phacelia ivesiana, Gilia leptomeria, Streptanthella
longirostris, and Eriogonum gordonii also reach short
periods of abundance, mainly under the protective shade
of the tree cano.py. The greatest number of species
encountered and the greatest number of prevalent
species occur in juniper-pinyon types (Table 6). The environmental factors which seem to have the
greatest influence in the juniper-pinyon types are not
greatly different from those influencing blackbrush, sand
dune and grassland associations. The soils are generally
shallow in juniper-pinyon stands, since most are situated
in rocky areas on the ridges and gentle slopes which have
a thin layer of aeolian or alluvial sands over the sand-
stone parent material. Moisture run-off from ~xposed
sandstone outcrops give extra moisture to such areas thus
enhancing tree growth. Deep cracks in the rocks permit
penetration of roots for acquisition of moisture during
dry spells. The cracks are probably crucial for the
survival of trees in these areas. Indications are that
the sandier soils which support these forest types do not
dry out as readily as the heavier soils derived from
Mancos Shale and Morrison Formation. The trees themselves
also modify their own microenvironment by shading and
litter cover. Litter immediately under the trees is
often heavy. The litter layer appears to retard soil
64
drying in the spring and to prevent light summer rains
from penetrating to the mineral soil. Several herbaceous
species, as noted above, thrive under the trees. Several
shrubs occur between the trees, but do not normally occur
outside of the juniper-pinyon areas except along washes
and roadsides where moisture is also more abundant.
Grasslands
Grasslands in southeastern Utah may be considered
an extentian of the southern desert grassland association
of Humphrey (1958), Shantz and Zan (1924) and Shreve
(1917). The same genera and some species cited as part of
that association by Humphrey also occur throughout the
Canyonlands area of which Arches is a part. Hilaria and
Aristida are genera considered to be typical of desert
grasslands by Humphrey and are well represented in the
Park. Bouteloua, another genus considered to be typical
of the desert grassland association, is less common in
the Park. Kleiner and Harper (1972) compared two grass-
land parks in the Needles Section of Canyonlands National
Park. They found Hilaria jamesii, Stipa comata,
Sporobolus crypandrus and Oryzopsis hymenoides to be
prevalent species there. Aristida was notably sparse,
and Hilaria was the most abundant grass species in that
study. By way of comparison, Sporobolus cryptandrus is
the most abundant grass in Arches (averaging 71%
frequency), followed by Hilaria (54%), Oryzopsis (34%)
and Aristida longiseta (29%). Stipa is limited to some
ridgetop stands south of the Windows Section and is
sparsely distributed elsewhere in the Park.
65
The abundance of sand dropseed (Sporobolus
cryptandrus) in some grasslands was considered by Archer
and Bunch (1953) and Quinn and Ward (1969) to be a
consequence of overgrazing. They considered the species
to be capable of occupying a wide variety of habitats,
if grazing had reduced the cover of more palatable
species. Grazing animals do not appear to utilize sand
dropseed as heavily as they do Oryzopsis and Hilaria in
the Park. Such differential palatability may explain why
great expanses of Salt Valley and other spots on the
ridges of the sunken anticline in the Park are dominated
by this species.
Humphrey (1953) concluded that several factors
such as suppression of fire, grazing by domestic live-
stock or rodents, plant competition and changes in
climate have permitted a number of species such as
Gutierrezia and Opuntia to become abundant in grassland
areas. Those factors may also account for the importance
of Ephedra, snakeweed and cacti in the grassland community
of Arches. Kleiner and Harper (1972) indicate that the
grasslands of Chesler Park in Canyonlands National Park,
which has been grazed by livestock, has more shrubby
species than Virginia Park which was not grazed. In
Arches, past and present grazing practices may combine
with fire suppression to weaken the grassland community
and permit the invasion of woody shrubs and trees.
Extensive areas of cheat grass (Bromus tectorum) and
Russian thistle (Salsola ~), both invader species,
occur around watering areas in upper Salt Valley and
Eagle Park ..
66
About 3400 hectares (11.4%) of the Park, were
mapped as grassland with most of the area occurring in
Salt Valley (Table 3). Smaller stands are found south of
the Windows Section in moist pockets of deeper soils,
north of Balanced Rock, next to Courthouse Wash in the
Towers Section (Fig. 7), in the Willow Flats area and
northwest of Willow Flats, and in small pockets in the
upper Fiery Furnace area. The abundance of increaser
plants such as Plantago purshii and Salsola kali also
gives credence to the adverse effects of grazing in the
Park. Sphaeralcea parviflora, a species considered to be
an increaser by Kleiner and Harper (1972), was frequent
in the ridgetop grassy areas.
Hilaria jamesii is prominant in the grassland
community and is a modal there. This species is ,
considered to be "distinctively a desert species" and
capable of surviving under such adverse conditions as
3.7 inches of average annual rainfall and temperatures
ranging from below zero in Wyoming to over 100°F on the
southern edge of its range (West et al. 1972). Growth of
galleta is closely related to precipitation. In areas of
Fig. 8. Grassland vegetation south of Courthouse Wash (foreground) and north of Courthouse Towers (background).
67
68 better rainfall, competition from other grasses may inhibit
the species. Vallentine (1961) lists galleta as an impor-
tant component of the blackbrush type along the Colorado
River. West and Ibrahim (1968) state that on the Colorado
Plateau galleta is primarily found on coarse textured, well
drained soils, but it is also observed to grow well on
finer textured soils in the area around Cisco, Utah.
Perennial grass cover at Arches showed positive
correlations with percent sand and pH, but the relation-
ships were not significant. Indications are that
grasslands at Arches do not develop on areas with heavier
textured soils that are high in soluble salts and
potassium. Soils are not usually as sandy as in areas
dominated by blackbrush, sand dune, juniper-pinyon, or
streamside communities. Grassland soils often have a
caliche layer which is relatively hard to penetrate.
Moisture that percolates below the caliche layer is not
rapidly depleted by plants since their roots do not
penetrate through the layer easily.
Roadside Vegetation
Roadside vegetation grows on the fill dirt on a
strip varying from 1 to 5 meters wide on each side of the
road. These strips receive the benefit of extra moisture
which drains off the asphalt surface and into the borrow
pits. Moisture varies according to the slope of the road
shoulder and the direction of slope of the road surface
(e.g., all water flows to the inside on curves).
69
The community consists of many of the native
species that occur in the surrounding communities and
several exotics which thrive under disturbance and mesic
conditions. The number of prevalent species is among the
highest observed at Arches. Roadsides are not closely
similar to any other community (average similarity value
of 12.5%); the community's closest affinities lie with
the sand dune association. That relationship is probably
related to the fact that the roadside supports a large
number of annual species which are also common in the
sand dune association. Species modal in this community
type include Bromus tectorum, Aristida longiseta, Ambrosia
acanthicarpa, Hymenopappus filifolius, Machaeranthera
tanacetifolia, Eriogonum cernuum. Of these six species,
five are annuals. Oryzopsis hymenoides, Gutierrezia
sarothrae, and Sporobolus cryptandrus are also abundant
along roadsides.
Rabbitbrush species and old man sagebrush are not
represented in the samples with high frequency, but
nevertheless, they are a prominent part of the vegetation.
These shrubs thrive close to the road, but just out of
reach of the grading machine's blade. There they benefit
from the extra moisture which runs off the road, but
escape destruction. Some sections of the highway receive
repairs infrequently; such sections support more shrubby
70
species. Shrubs grow well in the roadside environment
where they stabilize the soil and beautify the landscape.
In late summer and early fall, rabbitbrush and snakeweed
bloom profusely and border the highway with a pleasantly
variable ribbon of gold.
Greasewood
Although greasewood is not abundant in Arches
National Park, areas adjacent to the Park have large
expanses of this community type. The heavy textured
alluvial soils in Upper Salt Wash in Cache Valley and in
the area to the north of the Wolfe Cabin have dense
stands of greasewood. North of the Park boundary there
are extensive stream bottoms which also support large
stands. Several areas along Courthouse Wash have grease-
wood stands, but the edaphic conditions are quite
different since the soils have a sandy texture. Most of
the greasewood areas have received heavy grazing pressure
which has eliminated or weakened more palatable species
and favored greasewood. Protective shrub cover and
proximity to water have attracted concentrations of live-
stock to greasewood stands and led to a decrease in
edible grasses, shrubs, and forbs (Richard, 1967). Greasewood shows a wide tolerance to salinity
conditions. It shows vigorous growth in soils that are
not appreciably salt affected (Richards, 1954), but it
also occurs in soils paving considerable salts. Salt
71
tolerance of greasewood has been studied by McNulty (1952,
1969). He found that succulence varied according to the
concentration of salts. His studies indicate that sodium
chloride is involved in this response. Salts seem to be
diluted by the increase in cell sap and greater tolerance
is thus afforded.
The admixture of very large sagebrush plants with
greasewood in the area west of the Courthouse Wash bridge
suggest that there is less salinity there and that the
soil has good moisture and textural relations. In con-
trast, some of the saltiest soils in Cache Valley occur
along Salt Wash and support stands of almost pure grease-
wood. Heavy grazing in the past may have contributed to
the purity of this stand of greasewood.
Sarcobatus vermiculatus averages 60% frequency in
these stands, but the range is from 54% in Courthouse Wash
to 78% in Salt Wash. Electrical conductivity of the soils
average 12.5 mmhos/cm2 , but the Salt Wash stand has much
more salt (EC of 24.6 mmhos/cm2), whereas EC at Courthouse
Wash is only o.42. The average content of silt and clay
in the soil is quite high (41.5%), but silt plus clay
(fines) range from 18.1% in Courthouse Wash to 64.9% in
Salt Wash. The greasewood in Salt Wash is short, averag-
ing less than three feet in height. Only six species
were sampled in the Salt Wash stand, but 29 were sampled
in Courthouse Wash. The low plant diversity observed at
the Salt Wash area emphasizes the harshness of the site.
72
Other species which are prominent in this
community are Lepidium densiflorum, Chenopodium incanum,
Descurainia pinnata, Salsola ~. Ambrosia acanthicarpa,
and a tall variety of Lepidium montanum. The last of
these species are annuals.
Tamarix
The Tamarix stand considered in this study is
located in Cache Valley along Salt Wash just south of the
Cache Valley road. Tamarix species were introduced into
this country sometime before 1925 because they were well
adapted to desert climates (Christensen 1962). Since
their introduction, certain species, such as Tamarix
pentandra considered here, have become naturalized in
washes and river bottoms throughout the southwest. The
Tamarix species compete vigorously with such native species
as sandbar willow (Salix exigua) and the cottonwood
(Populus fremontii) in the Arches area. Gatewood!;,!~.
(1950) studied the use of water by species along the Gila
River in Arizona. They found great amounts of water to be
lost by transpiration from Tamarix and other phreatophyte
species. The Colorado River and its tributaries,
including washes such as Salt Wash and Courthouse Wash in
Arches, have been invaded by Tamarix which forms dense
groves along the margins of the streams and washes. Where
soils are fertile and stable, Tamarix often reaches small
tree size.
73
Tamarix species are able to withstand rather
extreme salt conditions. The mechanism for this toler-
ance has been studied by Decker (1961), Thompson and Liu
(1967), and Thompson, Berry and Liu (1969). Decker found
that Tamarix pentandra growing in saline seeps and washes
had salt 11whiskers" or a salt bloom on the foliage. The
source of the whiskers was found to be salt glands
imbedded in pits in the epidermis of the leaves. These
glands were concluded to be devices for eliminating salt
from the tissues of the species.
Thompson tl &• (1969) studied the salt glands of
Tamarix aphylla by electron microscopy. They found high
concentrations of the ion rubidium in small microvacuoles
in the secretory cells of the salt glands. They
concluded that salts are accumulated and then secreted by
ionic fusion with the plasmalemma. The secreted salt
forms minute granular whisker-like columns which emerge
from the glands. Gatewood~&• (1950) reports that
tamarisk shrubs along the Gila River exude fluids contain-
ing up to 41,000 ppm solids (mostly NaCl).
Accumulation of litter under tamarisk shrubs and
trees is probably rather high in salts and may be restric-
tive to plants growing in the understory. Salt tolerant
annuals such as Lepidum densiflorum, Chenouodium incanum
and Descurainia pinnata are quite prominent in the
understory. Bassia (Echinopsilon hyssopifolium) and
Ambrosia acanthicarpa were abundant in scattered
locations. Chrysothamnus linifolium reached high
frequency in the stand studied, but most of the indivi-
duals sampled were seedlings which were established in
the water year 1972-73, which had far better winter
moisture relations than normal. Adult plants were
scattered throughout the community, however. Iodine
bush, Allenrolfea occidentalis, occurred in only the
Tamarix community in this study. Iodine bush's presence
indicates high salt concentrations.
74
There is evidence that the area sampled for
Tamarix was the site of agronomic endeavors by John Wesley
Wolfe and later by J. w. Turnbow who lived in the
immediate area. Several patches of alfalfa, Medicago
sativa, persist in the area and were sampled along the
transects. Alfalfa was apparently planted there to
provide feed for the livestock which the settlers ran.
The Tamarix appears to have become established at this
site since the abandonment of the area as a farmstead in
approximately 1915. Wolfe is reported to have had a
garden close to the cabin which still stands to the north
of this stand, but no mention has been made of other crops
which he or Turnbow might have grown.
Saltbush
The shrubby members of the genus Atriplex of the
family Chenopodiaceae are often called saltbushes. The
family also has other genera that are common on saline
75 and/or alkali soils. Several species of saltbushes are
confined to heavy clay and clay loam soils in Utah. In
the Colorado Plateau section of Utah, such soils are
derived from marine deposits such as the Tropic Shale of
south central Utah and the Bluegate member of the Mancos
Shale in east central and southeastern Utah. There are
several exposures of Mancos Shale in lower Salt Valley
and throughout Cache Valley which is essentially a conti-
nuation of Salt Valley (see Fig. 9). The characteristic
undulating relief of the exposures of Mancos Shale has
its origin in the heavy runoff which originates on the
barren clays after even small storms. The runoff causes
extensive gullying and badland development.
Little contrast exists between the gray to blue-
gray soil and the gray colored matlike saltbush species
that grow on the Mancos beds. The obscure coloration of
the shrubs results in the area appearing more barren than
it actually is. The two saltbush species that dominate
the shale beds are Castle Valley clover (Atriplex
cuneata) and mat saltbush (Atriplex corrugata).
Branson (1967 and 1970) considered the classifi-
cation schemes for Great Basin Desert vegetation proposed
by Shantz (1925), Shreve (1942), Fautin (1946), and
Billings (1949) and recommended a new classification
based on maximum salt tolerances of major species or on
osmotic concentration of the soil solution at field
capacity. He recognized four major zones, Juniper-pinyon,
Fig. 9. Cache Valley with gray soils derived from Mancos Shale. Note the expanse of slickrock and Delicate Arch on the skyline at upper right. Red soils in the mid-background are derived from surrounding Entrada, Navajo and Dakota sandstone formations and support Atrinlex confertifolia while the gray hills of shale in the foreground are dominated by Atriplex corrugata and Atrinlex cuneata. Blackbrush and juniper in the immediate foreground grow on talus below the sandstone cliffs to the south of Cache Valley.
76
77 sagebrush, salt desert shrub, and salt marshes. His
scheme partly follows Shantz's (1925) classification of
the Salt Desert Shrub Formation, except that Shantz
placed mat saltbush with the Northern Desert Shrub Forma-
tion and ignored the Castle Valley Clover associe.
Branson's treatment of the Salt Desert Shrub Zone
subdivides it into seven communities, four of which occur
in Arches National Park (shadscale, greasewood,
Nuttall saltbush, and mat saltbush).
In studies conducted on soils derived from the
Bear Paw Shale in Montana, Branson (1970) considered
Nuttall's saltbush (_!. cuneata is the counterpart at
Arches) communities to occupy the most saline sites, but
other halophytic types dominated sites with less salinity.
Both Atriplex cuneata and!• corrugata occupy very saline
sites at Arches, but indications are that A. corrugata
may be the more salt tolerant of the two. In this study,
specific salts were not identified. Instead, salinity
was inferred from electrical conductivity of 1:1 soil:
water pastes. Electrical conductivity data indicate that
only the greasewood community occupies more saline sites
than the two saltbushes considered above.
Recent studies have attempted to clarify specific
limits within the Atriplex nuttallii complex. Hanson's
(1962) criteria indicate that two species are represented
in the complex at Arches - A. Cuneata with larger
burr-like fruit clusters and A. welshii (formerly
A. gardneri).
Approximately 18 or 20 Km to the east of Arches
National Park, a series of studies were conducted on
saltbush associations near Cisco, Utah. Those associa-
tions had previously been considered to belong to the
shadscale zone. Results of those studies have been
reported by Ibrahim (1963), West and Ibrahim (1968),
78
Singh (1971), and Ibrahim and West (1972). Their studies
included Nuttall and mat saltbush community types as well
as communities in which shadscale was codominant with
galleta grass and a taxon which they designated as~-
nuttallii var. gardneri. They studied soil-plant rela-
tionships extensively and showed mean EC differences of
.95 mmhos/cm2 between!:..• confertifolia - Hilaria Jamesii
and A. nuttallii var..nuttallii - Hilaria communities;
between A. nuttallii var.,nuttallii and Ji. nuttallii var.
gardneri an average difference of 0.11 mmhos/cm2 existed;
and between A• nuttallii var. gardneri and A. corrugata
they found a great difference of 21.25 mmhos/cm2 • This
makes a difference in EC of the soil solution of 22.31
mmhos/cm2 between A. confertifolia and~- corrugata
communities. They found the mat saltbush types to be
restricted to alluvial basins where salt and moisture
accumulated in the profile of the clayey soil. The
textural contribution of clay averaged 47% in A• corrugata
communities as compared to 27% in A. confertifolia and
37% in A. nuttallii var. nuttallii and~- nuttallii var.
gardneri communities. Richards (1954) did not list mat
saltbush as an indicator plant of salt affected soils,
79
but when compared to such species as shadscale and
greasewood, this species is even more indicative of
extreme salinity than Castle Valley clover. Generally,
greasewood is found on soils only slightly less saline
than those occupied by saltbush, but as indicated earlier,
that was not true in this study. Indications are that
Castle Valley clover and mat saltbush are obligatory
halophytes, whereas greasewood is a facultative halophyte,
since it is known to occur on soils low in salts (Gates
et al. 1956; Branson et al. 1967). __ ...... --Atriplex cuneata was modal in the saltbush
community with 59% average frequency (range 52 to 68%).
Of the 12 other modal species of the community, Salsola
~' Phacelia corrugata, Eriogonum inflatum, Eriogonum
gordoni, and Chaenactis stevioides had high frequency
values (see Table 7). These species are all annuals;
annuals contributed 58.6% of the lifeform spectrum of
this community (Table 8). Two shrubs, Artemisia
spinescens and Atriplex corrugata, occurred in the
community but with lower frequency values. One perennial
forb, Xylorhiza venusta, was scattered in one stand in
West Cache Valley and contributed considerable frequency
and cover.
80
Next to hanging gardens, the saltbush community
was the most distinctive in Arches. The distinctness is
undoubtedly related to habitat uniqueness associated with
salinity and soil texture with resulting effects on soil
moisture. Moisture runs off from these soils quickly, so
summer rains seldom have much influence on plant growth
here. When winter precipitation as snow is average or
above (as in 1972-73), the slow melting snow permits
water to percolate into the soil profile. Good soil mois-
ture levels trigger a vigorous growth of annual and
perennial forbs. Even in relatively dry years, there are
small annuals which germinate on these soils, but the most
spectacular displays occur in wet years. This prolifera-
tion of annuals is not so conspicuous in other habitats and
contributes appreciably to the distinctiveness of this
community.
Streamside Community
The streamside community sampled occurs along
Courthouse Wash, an intermittent stream. There are
perennial springs just west of and about one fourth mile
east of the bridge across the wash (Fig. 2). Flow from the
springs extends for only short distances before the live
water disappears. Evidence of flash floods in the form
of piles of trash and new water channels is present along
the length of the wash. The perennial woody species
which survive in the wash must thus be resistant to the
81
abrasive action of sediment and debris laden flood waters
which periodically inundate the streambed. In spite of
occasional floods, a large number of species occur in
this habitat. Soil moisture in the wash varies from
saturated to quite dry and thus provides habitat for
plant species which are obligated to live with their
roots in water as well as species that occur on the
nearby sand dunes.
Where there has not been recent scouring by
floods, the vegetation is often dense. Such shrubs as
tamarisk, sandbar willow, rubber rabbitbrush, and
Happlopappus drummondii occur frequently. Other species
of common occurrence include Muhlenbergia asperifolia,
Polypogon monspeliensis, Juncus torreyi, Eguisetum
kansanum, Grindelia aphanactis, Melilotus alba and
Castilleja linariaefolia. There is an ecological zona-
tion of species along an elevational gradient formed as
one moves from the stream bottom to older terraces at
right angles to the stream course. The younger escarp-
ments and the stream bottom have heavy growths of rush
and sedge species intermixed with muhly grass and white
sweet clover which dominate the next tier. The next
elevational zone is dominated by willows, rabbitbrush and
other shrubs; scattered trees and patches of tamarisk
occur here and there throughout the zone. Trees are
scattered rather diffusely along the streambed. Fremont
82
cottonwood (Populus fremontii) is by far the most
conspicuous tree. Numerous seedlings of Populus occur
in the stream bottom, but few survive the intermittent
floods that scour the channel. Occasional patches of
Russian olive (Elaeagnus angustifolia) and peach leaf
willow (Salix amygdaloides) occur as naturalized species,
but neither is abundant.
Similarity between this community and the other
communities considered is low, mainly because of the
unusually moist conditions along the streambanks. The
number of modal species in this community is exceeded only
by that for the juniper-pinyon community. The index of
community distinctiveness is high.
Hanging Gardens
Although Hanging Gardens are represented in the
Park by only a few small stands, their uniqueness
generates more than passing interest in those who come
upon a garden as they explore. The gardens occur
primarily in alcoves in the escarpments of the Entrada
sandstone and in the walls of canyons cut into the Navajo
Formation (Fig. 10). Water percolates along aquifers
sealed below by impervious surfaces until it emerges along
the exposed face of the sandstone wall. Eventually the
combined action of freezing and thawing and dissolution of
the carbonaceous materials that cement the sand grains
together produces an alcove in the wall at the site of
Fig. 10. Hanging garden in a seep area in Fresh 1.<later Canyon northwest of Wolfe Cabin.
83
the seep. Mesic plant species invade these seep areas
and take root in the slowly accumulating layer of
exfoliating rock along the lower lip of the alcove:•
Eventually plants may colonize the walls and even the
ceiling of the alcove.
84
Such species as scarlet-red monkey flower
(Mimulus eastwoodiae), an endemic primrose (Primula
snecuicola), and numerous algal and moss species cling
to the walls and ceilings and further enhance biological
and chemical erosion of the sandstone rocks. On the
lower edge of the alcove where a lip forms, such species
as maidenhair fern (Adiantum capillus-veneris),
helleborine orchid (Epipactis gigantea), panic grass
(Panicum tennesseensis), little bluestem grass
(Andropogon scoparius), columbine (Aauilegia micrantha)
and toadflax (Comandra umbellata) are found. Older
gardens may have a number of shrubs such as Gambel's oak
(Quercus gambelii), squawbush (~ trilobata), poison
ivy (Toxicodendron radicans) and virgin's bower (Clematis
ligusticifolia) which root in the deeper soils and talus
at the base of the lip.
These gardens allow for the migration of such
species as little bluestem and panic grasses which are
disjunct in this area from grasslands of the Great Plains
to the east. Moisture, shade and slope are the main fac-
tors controlling the composition in these communities.
85
These factors were discussed in the section on the inter-
relationships of abiotic factors with vegetation.
SUMMARY AND CONCLUSIONS
Average annual precipitation at Arches National
Park is about 20 cm. The moisture falls mainly during
late fall and early winter months. Annual temperature
averages about 12.5°c with a range from -6°c in January
to about 44°c in July. The spring and summer dry period
is pronounced and typical for southeastern Utah. Soils
are prevailingly sandy to sandy loams, but exposures of
marine shales in lower Salt Valley and in Cache Valley
provide virtual islands of uniquely contrasting soils and
vegetation.
The flora of the Park consists of 357 vascular
plant species. Approximately 78% (251) of the species
are herbaceous. In addition, there are 65 native shrubs
and six native tree species which together account for
22% of the flora. Although they are represented by few
species, the woody taxa account for most of the living
cover.
The lifeform spectrum for the flora and the vege-
tation of the Park is more like that for the hot deserts
of the American Southwest than the cold deserts of
western Utah. Annual plants contribute more species and
more individuals to the plant cover of the Park than any
86
87
other plant lifeform. The second most prominent lifeform
category is that of the hemicryptophytes. Lifeform
analyses were based upon species alone and upon species
weighted by quadrat frequency values. The latter
technique is considered to give a better evaluation of
the success of various lifeform strategies.
The major plant communities of Arches National
Park have been quantitatively described and mapped. The
juniper-pinyon community was found to cover more area
than any other (43 •. 5%) in the Park. The blackbrush
community covered about half as much of the area of the
Park (22.5%). Grasslands covered 11.4% and sand dune
association about 5.2% of the area. The remaining six
communities (streamside, roadside, greasewood, Tamarix,
saltbush, and hanging garden) each covered less than 3% of the Park. Extensive areas of barren slickrock occur
in the Park.
Blackbrush and sand dune communities are shown to
exhibit the greatest vegetational similarity of any of
the 10 communities considered. Curtis' (1959) index of
distinctiveness demonstrates, however, that all of the
community types considered have a high degree of unique-
ness and fully merit recognition as separate entities.
The blackbrush community has less distinctiveness than
any other and can be considered as a vegetational matrix
that ties the major vegetative patterns of the Park
88
together. The hanging gardens are the most distinctive
and least widespread of the Park's communities.
The blackbrush-sand dune-juniper-pinyon cluster
of communities occurs on the xeric end of a simple mois-
ture gradient which terminates with streamside and
hanging gardens on the mesic end. The saltbush community
does not fit into the moisture gradient just described
because of an unusual soil environment produced by shale
outcrops in a "sea" of sandstone. The saltbush community
is the second most distinctive in the study. Clayey
soils and salinity are concluded to be the major factors
controlling vegetational composition there.
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Beatley, J.C. 1975. Climate and vegetation pattern across the Mojave/Great Basin transition of southern Nevada. Am. Midl. Nat. 93: 53-70.
Billings, W. D. 1949. The shadscale vegetation zone of Nevada and eastern California in relation to climate and soils. Am. Midl. Nat. 42: 87-109.
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Cottam, w. P. and G. Stewart. 1940. Plant succession as a result of grazing and of meadow desiccation by erosion since settlement in 1862. J. Forest. 38:613-626.
Curtis, John. 1959. The Vegetation of Wisconsin: An Ordination of Plant Communities. Univ. of Wiscon. Press. Madison, Wisconsin.
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Dane, C.H. 1935. Geology of the Salt Valley Anticline and adjacent areas, Grand County Utah. U.S. Geol. Survey Bulletin 863. U.S. Gov. Print. Off., Washington D.C.
Dansereau, P. 1957. Biogeography: An Ecological Perspective. The Ronald Press Co. New York.
Decker, J.P. 1961. Salt secretion by Tamarix pentandra Pall. Forest Sci. 7:214-217.
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APPENDIX A
New Species Additions to the Arches National Monument List of Harrison et al. (1964)
Boraginaceae Cryptantha wetherillii (Eastw.) Payson Cryptantha tenuis (Eastw.) Payson
Chenopodiaceae Atriplex corrugata s. Wats. Chenopodium incanum (S. Wats.) Keller Chenopodium hratericola Nutt. ssp. fallax Corispermum yssopifolium L. cheno!odium !eptophXllum Nutt. Cyclo oma atriplicitolium (Spreng.) Coult. Kochia sco aria (L.) schrad. Suaeda ruiticosa (L.) Forsk.
Compositae Aster bractiactis Blake
Heise
Chrysothamnus nauseosus (Pall.) Britt. var junceus Circium nidulum (M. D. Jones) Petrak Circium rydbergii Petrak Dicoria brandegei Gray Haplopappus drummondii (Torr. and Gray) Blake Oxytenia acerosa Nutt. Machaeranthera ~indelioides (Nutt.) Shinners var
depressa (Maguire) Chronq. and Keck Machaeranthera canescens (Pursh.) Gray Senecio longilobus Benth.
Cruciferae Conringia orientalis (L.) Dumort Draba reptans (Lam.) Fern.
Cyperaceae Carex subfusca w. Boatt Scirpus poludosus A. Nels.
Equisetaceae Equisetum laevigatum A. Braun
Gentianaceae Centaurium exaltatum (Griseb.) Wight
Grarnineae Bouteloua gracilis (H.B.K.) Lag.
Hycrophyllaceae Nama demissum A. Gray
95
96 Juncaceae
Juncus nevadensis S. Wats
Leguminoseae Astragalus geSeri Gray Astragalus sa ulonum Gray Astragalus sabulosus M.E. Jones Lathyrus brachycalyoc Rydb. ssp. eucosmus (Butters & St.
John) Welsh Medicago sativa L.
Loasaceae Mentzelia dispersa Wats.
Oleaceae Fraxius velutina Torr.
Polemoniaceae Phlox austromontana Coville
Polygonaceae Eriogonum leptocladon T. & G. var Leptocladon Eriogonum ovalifolium Nutt. Eriogonum utahensis Gray
Ranunculaceae Delphinium nelsonii Greene
Salicaceae Salix exigua Nutt.
Scrophulariaceae Castilleja exilis A. Nels Penstemon cyananthus Hook.
APPENDIX ff
ENVIRONMENTAL FACTOR CORRELATION MATRIX*
Elev. SloEe As12ect Sand Fines EH EC Ca K Na
Elevation 1.000
Slope(%) -0,300 1.000
Aspect - + 1.000
Sand(%) + o.169 -0,207 1.000
Fines(%) - - -0.341 0,105 1,000
pH -0.116 0,313 -0.140 -0.215 -0.144 1.000
Electrical Conductivity - + -0.151 + o.gz -0.375 1.000
Calcium (Mg/g) - -0,164 - + 0.192 + -0.320 1.000
Potassium (Mg/g) - - -0.286 - 0._§2§ - 0,.2!!§ + 1,000
Sodium (Mg/g) - - - + 0,570 -0,186 0.876 -0,306 0.499 1.00
Magnesium (Mg/g) - - -0.203 -0.173 0.864 - 0.637 - 0.928 o.§19 Nitrogen(%) - - -0.110 0.283 + -0.411 0,329 -0.208 - 0,269
Effervescens + -0.153 - 0,284 + -0110 + o.470 -0.130 +
* Underlined values are significant at 5% level or better. values less than 0.09 are reported as+ and-.
Mg, ~· _N_Effe_r_,.
1.000
- 1.000
-0.173 + 1.000
Absolute
I..D -.J
APPENDIX C
SIMPLE CORRELATION MATRIX OF VEGETATION AND ENVIRONMENTAL CHARACTERISTICS (Positive and negative correlations less than • 099 are indicated b) +
or-. Correlations significant at the 80% level are underlined •
--------------------------------------------Environmental Factors---------------------------------------------
" As- " % % % % Soil Ve~etative Characteristics Elev. Sloee eect Rock Sand Silt Cla:z: Fines EH Ca K Na M~ % N EC Depth
Average% Living Cover -.553 .380 -.235 + -.178 .704 .331 .166 -.499 .279 -.398 .278 .442 .420 .366
Sp/quadrat -.124 -.286 .477 + -.162 .257 -.233 .291 .199 + .402 -.360 - -.386 -,300 -~ % Shrub Cover - -.534 .126 -.314 + -.137 .163 - + .229 .199 .347 - - ,332 .189
% Perrenial Grass Cover + - + -.246 .393 - -.286 -.399 ,422 -.ll8 -.356 -.257 -.?29 -.213 -,304 .175
% Perrenial Forb Cover + -~ -.~ .526 - .194 - - -.412 -.133 -.?74 -.283 .271 .425 -.236 --~ % Annual Cover -.189 - .528 .369 -.~ .176 .523 ·22! -.413 -.110 -~ .204 - .323 • 352
No. Prevalent Species .174 -.422 .337 -.~ -~ -.177 -.425 -.~ .348 -.251 -.~ -.216 -.385 --~ -.242 .491
No. Modal Species ·.22.? + - - .409 -.163 -.415 -.407 + + - -.271 - -.220 -.241 .167
Index of Community Distinct-ness -._101 -~ -.515 -~ -.121 + + .123 -.446 + + -.181 .375 .460 -.101 -.431
\.0 CX>
VEGETATIVE COMMUNITIES OF ARCHES NATIONAL PARK , UTAH
COMPILED BY JOHN S. ALLAN AS PART Fl.JLLFILLMENT Of A Ph.D. DISSERTATION, BRIGHAM YOUNG UNIVERSITY
C§§ JUNIPER-PINYON r;;:~7:txll.esrsFERMA -BI..ACt(BRUSH /~ RAMOSISSIMA)
~0tltl3IJ%t?!,, -GRASSLANDS HJL RIA _
SANO ClJNE ASSOCIATION
LEGEND
~SHAOSCALE&f11f!J.ll~
FINS
STREAMSIOE
SCALE
2 MILES --==---=
- • - • - PARK BOUNDARY
--- MAIN RO\D
- - - - UNPAVED ROAD
CJ SALTBUSH (ArRlpt£X '1l/i£MA - A._.~) BLACKBRUSH - GRASSLAND - BADLAND ASSOCIAT!Ct,1
[IT] GREASEWOOO /~ ~) ROQ( AND ROCKY SLDPES
TAMARIX~~/ - HANGING GARDENS
THE PLANT COMMUNITIES OF ARCHES NATIONAL PARK
John Stevens Allan
Department of Botany and Range Science
Ph.D. Degree, August 1977
ABSTRACT
Arches National Park, located in southeastern Utah, lies in a transition zone between the southwestern hot desert and the western cold desert, but it is floris-tically-- most similar to the hot desert. The major plant communities are as follows: Juniper-pinyon, blackbrush, grasslands and sand dune association. Other community types occur but occupy very limited areas. All of the communities studied have a high degree of uniqueness and merit recognition as separate entities. Blackbrush showed the greatest overall similarity to other communities and was most similar to the sand dune communities. The hang-ing gardens were the most distinctive and covered the smallest area of the communities present in the Park. Cluster analysis placed blackbrush, sand dunes and juniper-pinyon on the xeric end of a moisture gradient and streamsides and hanging gardens on the mesic en~