The plant communities of Arches National Park

Brigham Young University Brigham Young University

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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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Arnold, J. F., D. A. Jameson, and E. H. Reid. 1964. The pinyon-juniper type of Arizona: Effect of grazing, fire and tree control. U.S. Dept. of Agr. Forest Serv. Prod. Res. Rep. 84. 28 p.

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.

Blackburn, W. H. and P. T. Tueller. 1970. Pinyon-juniper invasion in black sagebrush communities in east-central Nevada. Ecology 51:841-848.

Bouyoucos, G. J. 1936. Directions for making mechanical analysis of soils by the hydrometer method. Soil Sci. 42~ 225-228.

Bowns, J.E. and N. E. West. 1976. Blackbrush (Coleogyne ramosissima Torr.) on southwestern Utah rangelands. Utah Agr. Exp. Sta. Research Rep. 27.

Branson, F. A., R. F. Miller and I. s. McQueen. 1967. Geographic distribution and factors affecting the distribution of salt desert shrubs in the United States. J. Range Mngt. 20: 287-296.

Branson, F. A., R. F. Miller and I. s. McQueen. 1970. Plant communities and associated soil and water factors on shale-derived soils in northeastern Montana. Ecology 51: 391-407.

Christensen, E. M. 1962. The rate of naturalization of Tamarix in Utah. The Am. Midld. Nat. 68:51-57.

Cottam, G. W. and J. T. Curtis. 1956. The use of distance measures in phytosociological sampling. Ecology 37:451-460.

89

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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.

David, D. J. 1960. The determination of exchangeable sodium, potassium, calcium and magnesium in soils by atomic-absorption spectrophotometry. Analyst 85:495-503.

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.

Fautin, R. w. 1946. Desert Shrub.

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94

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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~