In cooperation with the National Park Service, Zion National Park 

Ecological Investigations of the Federally 

Endangered Shivwits Milk-Vetch (Astragalus 

ampullarioides) – 2006 Annual Report 

By Mark E. Miller1, Rebecca K. Mann1, Harland Goldstein2, and James D. Yount2

Open-File Report 2007-1050 

2007 

U.S. Department of the Interior 

U.S. Geological Survey 

1

 Southwest Biological Science Center, Grand Staircase-Escalante National Monument, 

190 E. Center St., Kanab, UT 84741 2

 Earth Surface Processes Team, Denver Federal Center, MS 980, Box 25046, Denver, CO 80225 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2007 

For product and ordering information: 

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS 

For more information on the USGS—the Federal source for science about the Earth, 

its natural and living resources, natural hazards, and the environment: 

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS 

Suggested citation: 

Miller, Mark, Mann, Rebecca K., Goldstein, Harland, and Yount, James D., 2007, Ecological 

investigations of the federally endangered Shivwits milk-vetch (Astragalus

ampullarioides) – 2006 annual report: U.S. Geological Survey Open-File Report 2007-

1050 [available on the World Wide Web at URL http://pubs.usgs.gov/of/2007/1050/ ]. 

Cover photograph: Shivwits milk-vetch (Astragalus ampullarioides) by Dr. Renee Van Buren 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

ii
Contents 

Acknowledgements........................................................................................................................ iv

Introduction..................................................................................................................................... 1

Methods........................................................................................................................................... 1

Population Surveys and Seedling Mortality ............................................................................... 2

Reproductive Output and Effects of Native Vertebrate Herbivory ............................................ 2

Descriptive Soil-Vegetation Sampling ....................................................................................... 2

Data Analyses ............................................................................................................................. 3

Results and Discussion ................................................................................................................... 4

Population Surveys and Seedling Mortality ............................................................................... 4

Reproductive Output and Effects of Native Vertebrate Herbivory ............................................ 5

Descriptive Soil-Vegetation Sampling ....................................................................................... 6

Range-Wide Patterns .............................................................................................................. 6

Site-Level Patterns................................................................................................................ 13

On-Going Work and Future Plans ................................................................................................ 18

Habitat Modelling ..................................................................................................................... 18

Experimental Studies of Red Brome Effects on Biological Soil Properties and Milk-Vetch 

Performance .............................................................................................................................. 19

Literature Cited ............................................................................................................................. 21

Appendix A – Map of Plot Locations .......................................................................................... 23

Appendix B – Graphs for Herbivory Experiment.........................................................................24

Appendix C – Plot-Level Quadrat data.........................................................................................26

Appendix D – All Soil-Vegetation Plots in Relation to Soil Texture Classes..............................33

iii
Acknowledgements 

We thank Becca Lieberg and Cheryl Decker of Zion National Park for their enthusiastic and 

skilled assistance with numerous aspects of this research. Denise Louie, Jeff Bradybaugh (both 

formerly of Zion National Park), and Heather Barnes (U.S. Fish and Wildlife Service) were 

instrumental in developing the vision for the project. Nancy Johnson, Bala Chaudhary, and 

Matthew Bowker of Northern Arizona University have provided key guidance and support for 

our on-going investigations of mycorrhizal relations of the Shivwits milk-vetch. Renee Van 

Buren (Utah Valley State College) and Bob Douglas (Bureau of Land Management) have been 

important sources of background information on milk-vetch ecology and habitat characteristics. 

We thank Glenn Rogers (Chairman, Shivwits Band of the Paiute Tribe) for granting us 

permission to work on Tribal lands. Walter Fertig (Moenave Botanical Consulting) assisted with 

plant identifications, and has been a key advisor in our on-going habitat-modeling work. Review 

comments from Richard Reynolds, Jayne Belnap, Charles Powell, and Mark Sogge improved the 

quality of the report. 

iv
1

Introduction

Astragalus ampullarioides (Welsh) Welsh, the Shivwits milk-vetch, is an herbaceous perennial

legume that was listed as federally endangered in September 2001 (U.S. Fish and Wildlife Service

2001). Known populations of this edaphic endemic species are restricted to Washington County,

Utah, with the majority of occurrences found on gently sloping outcrops of the Triassic Petrified 

Forest Member of the Chinle Formation at the edge of the Mojave Desert. At the time of listing in 

2001, surveys estimated a total of 1000 individuals for the species. In April-May 2006, surveys

estimated approximately 4205 individuals distributed among 6 populations (U.S. Fish and Wildlife

Service 2006). Of the total number of individuals estimated in spring 2006, over 75 percent were

distributed among three subpopulations in Zion National Park and approximately 60 percent

occurred at a single 0.3-ha site in the Park. In addition to small population sizes and limited 

geographic distributions, the species is threatened to varying degrees by urbanization, livestock 

grazing, off-road vehicle use, and invasive exotic plants (U.S. Fish and Wildlife Service 2001,

2006; Van Buren and Harper 2003).

In April 2006, the U.S. Geological Survey (USGS) initiated ecological investigations of the

Shivwits milk-vetch to support conservation management and recovery of the species by the

National Park Service (NPS; Zion National Park), the U.S. Fish and Wildlife Service (USFWS),

the Bureau of Land Management (BLM), the Shivwits Band of the Paiute Tribe, and other

cooperators such as The Nature Conservancy of Utah (TNC). To date, funding for this research 

has been provided by the Southwest Biological Science Center of the USGS Biological Resources

Discipline, the USGS-NPS Park-Oriented Biological Support Project, and the Earth Surface

Dynamics Program of the USGS Geologic Discipline. Additional logistical support has been 

provided by the Bureau of Land Management, Grand Staircase-Escalante National Monument.

General objectives of this research are (1) to develop a better understanding of species-environment

relations to support habitat modelling, future surveys for additional recovery populations, and 

potential efforts to establish new recovery populations; and (2) to evaluate effects of invasive exotic

plants on habitat conditions and measures of milk-vetch performance. Specific objectives are to:

1. Describe the distribution and abundance of milk-vetch populations and associated invasive

exotic plant species within and outside of Zion National Park (Zion NP) in relation to 

geologic / geomorphic setting, soil properties, and plant community composition.

2. In a field setting in Zion NP, conduct experiments to evaluate effects of invasive exotic

plants on reproductive output and seedling establishment of A. ampullarioides across a

gradient of exotic species biomass.

3. Conduct greenhouse studies and analyze soils to evaluate effects of invasive exotic plants

on soil biological properties (including mycorrhizal inocculation potential) that affect

cycling and plant uptake of essential mineral nutrients.

4. Based on environmental characteristics of known population locations, use Geographic

Information System (GIS) tools to prepare a predictive habitat model that can be used to 

guide future surveys and efforts to evaluate sites for reintroduction efforts.

This report describes 2006 progress and future plans for achieving these four objectives.

Methods

Work during 2006 focused on conducting population surveys and estimating seedling mortality,

experimentally evaluating effects of native vertebrate herbivory on milk-vetch reproductive output

at a site in Zion NP, sampling to describe soil-vegetation relations at five population locations, and 
2

initiating a field experiment to examine effects of the invasive exotic grass red brome (Bromus

rubens) on soil properties and milk-vetch performance. The work described in this report followed 

techniques approved by U.S. Fish and Wildlife Service Endangered Species Permit # TE130417-0 

and National Park Service Scientific Research and Collecting Permit # ZION-2006-SCI-0024.

Population Surveys and Seedling Mortality

During the April-May 2006 period, population surveys were conducted at seven study sites

associated with five of the six known milk-vetch populations. Surveys were conducted 

opportunistically while describing geologic settings of known populations and preparing for

descriptive soil-vegetation sampling. Surveys focused on areas with known milk-vetch 

occurrences and generally did not involve searches for new populations or subpopulations.

Individual milk-vetch plants were classified and enumerated as seedlings (cotyledons evident;

single, 1-mm diameter stems) or established plants (evidence of previous years’ growth; stems

greater than 1-mm in diameter; occasionally with multiple stems; no cotyledons). At one site (Zion 

Hilltop), 160 seedlings distributed among 12 plots were marked with plastic tags and tracked 

during a 1-month period (20 April – 23 May) to estimate seedling mortality. Plots measured 1-2 m

in diameter and had 10-30 marked seedlings apiece, depending on natural levels of abundance.

Fractional cover of litter, rocks, and plants were estimated in each plot to assess whether patterns of

seedling mortality were related to variations in these variables.

Reproductive Output and Effects of Native Vertebrate Herbivory

Shivwits milk-vetch is noted for its high degree of palatability, with its inflorescences commonly 

consumed by wildlife (Welsh et al. 2003). To reduce effects of herbivory on fruit production and 

thus increase our ability to collect seed required for subsequent field and greenhouse experiments

(Objectives 2 and 3, above), at the Zion Hilltop site we enclosed 62 established milk-vetch plants

within circular herbivore-exclusion cages on 20 April. Cages measured 40-cm in diameter and 

were 60-cm tall, with sides and lids constructed from wire hardware cloth with 0.5-in mesh. To 

quantitatively assess effects of herbivory on reproductive output, we paired each caged plant with a

nearby uncaged plant of similar size and vigor. After fruiting but before plant senescence in late

May, we measured canopy dimensions and counted reproductive shoots and fruits on caged and 

uncaged plants.

Descriptive Soil-Vegetation Sampling

A major objective of the spring 2006 field season was to describe range-wide and site-level

variations in the relative abundance of Shivwits milk-vetch and associated invasive exotic plants in 

relation to geologic substrate, geomorphic setting, and soil physical and chemical properties. In 

April 2006, we visited the six known populations of Shivwits milk-vetch (see Figure A1) and 

confirmed geologic substrates associated with milk-vetch occurrences on the basis of published 

geologic maps (Hintze and Hammond 1994, Willis et al. 2002, Biek 2003) and field observations

of lithology and stratigraphy.

Soil-vegetation sampling was conducted at sites characterized by relatively distinct spatial patterns

in the relative distribution and abundance of Shivwits milk-vetch and invasive exotic plants (Zion,

Pahcoon, Coral Canyon, and Harrisburg Bench populations), and at the Shivwits Paiute

Reservation where the milk-vetch population was found to occur on two separate geologic units.

At each site, soil, vegetation, and ground cover were sampled in plots subjectively located to 

characterize patterns in plant-environment relations. The size and configuration of soil-vegetation 

plots varied depending on spatial properties of the soil-vegetation patch being sampled, but each 

plot generally consisted of 12-20 square, 1-m2 quadrats placed at random intervals along 2-5 
3

transects. Transects varied in length from 8 to 30 m long, and sampled soil-vegetation patches

varied in size from 65 to 150 m2. Within each quadrat, we recorded occurrences of vascular plant

species within a series of square nested-frequency quadrats (0.01, 0.1, 0.5, and 1.0 m2) and 

estimated fractional cover of plants, standing dead brome grass, and ground cover (litter, woody 

debris, rocks by size class, and biological soil crusts) to the nearest 1 percent in the 1-m2 quadrat.

In this report (Table 3 and Appendix C), we only summarize frequency results for 1-m2 quadrats.

Within each plot, several types of soil samples were collected for laboratory analyses. Composite

soil samples were collected from 0-2 and 2-10 cm depth, with each composite consisting of 8-10 

subsamples collected with a hand trowel. Near the center of each plot, we used a soil auger (7.5 

cm diameter) to collect an additional set of samples from 0-10, 10-20, and 20-30 cm depth.

Finally, we used a hammer core sampler (4.7-cm diameter, 10-cm depth) to collect 2-3 intact

replicate samples for laboratory determination of bulk density and volumetric water content. In the

lab, composite and auger samples were air dried, weighed, and sieved to separate and determine the

relative proportion by mass of rock fragments (> 2 mm) and fine earth (< 2 mm). Splits from the

composite samples were sent to the Plant and Soil Analysis Laboratory at Brigham Young 

University for determination of pH, cation exchange capacity, organic matter content, and nutrient

availability (total Kjeldahl N; exchangeable Ca, Mg, K, and Na extracted with NH4-OAC at pH

8.5; NaHCO3-extractable K and P; and DTPA-extractable Mn, Cu, Zn, and Fe). Splits from

composite and auger samples were sent to USGS laboratories in Denver for particle size analysis

using a Malvern laser particle sizer, and for determination of gypsum and carbonate content.

Composite splits also will be analyzed in Denver for total elemental content following a two-acid 

digestion and determination by inductively coupled plasma atomic-emission spectroscopy (ICPAES). Most chemical analyses have not yet been completed, thus laboratory results presented 

below are restricted to data from the texture (particle size) analyses. Particle-size ranges for

reported sand (63-2000 m), silt (3.9-63 m), and clay (< 3.9 m) fractions follow the Modified 

Wentworth scale (Ingram 1982).

Slope, aspect, geographic coordinates, and elevation also were measured for each soil-vegetation 

plot. Slope and aspect were measured in the field with a hand-held magnetic compass. Geographic

coordinates were determined with a GPS (geographic positioning system) unit. Plot elevations

were determined in the office by extracting data from a 10-m digital elevation model (DEM) using 

plot coordinates in a Geographic Information System (GIS). Data for slope, aspect, and latitude

were used to calculate a topographic heat-load index for each plot following methods of McCune

and Keon (2002).

Data Analyses

Effects of herbivory on milk-vetch performance measures were evaluated with the nonparametric

Wilcoxon Matched Pairs test using Statistica v. 6.1 on a Windows platform (StatSoft, Inc. 2004).

P-values less than 0.05 were considered statistically significant. Two multivariate ordination 

techniques were used to examine variability in environmental measures and plant community 

composition among the 20 soil-vegetation plots. Principal components analysis (PCA; McCune

and Grace 2002) was used to evaluate among-plot variability in environmental measures using the

Factor Analysis module of Statistica v. 6.1 (StatSoft, Inc. 2004). Among-plot patterns in plant

community composition were examined with nonmetric multidimensional scaling (NMS; McCune

and Grace 2002). NMS analyses were performed using PC-ORD v. 4.34 for Windows (McCune

and Mefford 1999). In Statistica, correlation and multiple-regression analyses were used to relate

plot scores derived from the NMS ordination with raw environmental variables and with synthetic

environmental variables extracted with PCA. In addition to these ordinations, we present figures
4

illustrating among-plot variations in milk-vetch frequency and brome cover in relation to soiltexture classes.

Results and Discussion

Population Surveys and Seedling Mortality

Table 1 summarizes results of spring 2006 population surveys conducted by USGS and other

investigators. A notable result of these surveys was the USGS discovery that the milk-vetch 

population at the Shivwits Paiute Reservation occurs on two distinct geologic substrates – the

Triassic Petrified Forest Member of the Chinle Formation (TRcp) and the Jurassic Dinosaur

Canyon Member of the Moenave Formation (Jmd) (see Biek et al. 2000). Although over 99 

percent of all known individual plant occurrences are associated with the Petrified Forest Member

(Table 1), the occurrence of milk-vetch plants on the fine-grained Dinosaur Canyon Member and 

the relatively wide range of soil characteristics at Petrified Forest Member sites supporting milkvetch populations have important implications for our understanding of the species’ potential

habitat. On the Petrified Forest Member, Shivwits milk-vetch occurrences span the full thickness

of this highly variable sedimentary unit – from the very top of the unit where it contacts the

Dinosaur Canyon Member (Shivwits and Pahcoon sites), to the middle of the unit (Zion Hilltop 

and Trailside sites), to the very bottom of the unit just above its contact with the Shinarump 

Member of the Chinle Formation (Zion Petrified Forest site).

The other notable result of the spring 2006 surveys was the enumeration of larger numbers of

milk-vetch plants than had previously been documented at the Zion Hilltop and Trailside sites

(Table 1). Together, these two sites accounted for 85 percent of established plants and over 75 

percent of total plants (including seedlings) enumerated in spring 2006. Within an area less than 

0.3 ha, the Hilltop site alone accounted for 63.5 percent of established plants and 60.5 percent of all

known milk-vetch plants.

Over the 1-mo period from 20 April to 23 May, seedling mortality in 12 plots at the Zion Hilltop 

site ranged from 30.0 to 92.3 percent, with an average of 59.8 percent (CV = 26.1). Correlation 

analyses found no significant linear relations between percent seedling mortality and measures of

litter, rock, and plant cover.

Table 1. Results of Shivwits milk-vetch population surveys conducted during April-May 2006 (TRcp

= Petrified Forest Member of the Chinle Formation; Jmd = Dinosaur Canyon Member of the

Moenave Formation).
5

Population Site* (ownership) Individuals Pct of 

total Individuals Pct of total Comments

Coral Canyon Coral Canyon* 

(private) 72 37.5 120 62.5 192 4.6 TRcp

Pahcoon Spring 

Wash

Pahcoon Spring 

Wash (BLM)

- - - - 400** 9.5 TRcp

Chinle* (Tribal) 11 100.0 0 0.0 11 0.3 TRcp

Moenave* (Tribal) 12 46.2 14 53.8 26 0.6 Jmd

Harrisburg Bench* 

(BLM) 174 59.6 118 40.4 292 6.9 TRcp

Cottonwood (BLM) - - - - 50*** 1.2 TRcp

Silver Reef Silver Reef (BLM) - - - - 12*** 0.3 TRcp

Hilltop* (NPS) 1307 51.4 1238 48.6 2545 60.5 TRcp

Experimental site for 

investigations of herbivory and 

exotic-plant effects. Location of 

automated precipitation gage and 

soil-moisture sensors.

Trailside* (NPS) 450 69.8 195 30.2 645 15.3 TRcp

Petrified Forest* 

(NPS) 32 100.0 0 0.0 32 0.8 TRcp Nearly all reproductive shoots consumed by herbivores

GRAND TOTAL 2058 - 1685 - 4205

* Sites surveyed by USGS in April-May 2006

** Estimate provided by Dr. Renee Van Buren, Utah Valley State College

*** Data from USFWS (2006)

Zion

Geologic 

substrate

Pct of 

Grand 

Total

Harrisburg 

Junction

Shivwits

Established plants Seedlings

GRAND 

TOTAL

Reproductive Output and Effects of Native Vertebrate Herbivory

Herbivory by native vertebrates had statistically significant effects on numbers of reproductive

shoots and fruits produced by milk-vetch plants, but did not significantly affect canopy volume

(Table 2). Inside cages, 22 and 15 of 62 plants had reproductive shoots and produced fruit,

respectively. Outside cages, 18 and 2 of 62 plants had reproductive shoots and produced fruit,

respectively. (See histograms in Appendix B.)

These data suggest a 90 percent reduction in fruit production due to herbivory, and they illustrate

the capacity of native herbivores to severely limit reproductive output in small, geographically 

constrained milk-vetch populations – particularly in dry years when reproductive output is already 

limited by resource availability. All 32 plants in the Petrified Forest subpopulation at Zion showed 

signs of extensive herbivory by vertebrates, with nearly all reproductive shoots consumed. Based 

on field observations (infrequent ungulate tracks, abundance of lagomorph dung, sightings of

lagomorphs, and beveled cuts on stems), the most likely herbivores responsible for milk-vetch 

herbivory in this study were lagomorphs. The high degree of herbivory at this location may 

explain the observation that this was the only subpopulation where no seedlings were found during 

sampling in spring 2006. These results suggest that management actions which affect the

distribution and abundance of small herbivores (and/or their predators) in proximity to milk-vetch 

populations may indirectly affect dynamics of those populations through effects on reproduction 

and replenishment of the seed bank.

Compared with results of this study, Tepedino (2005) found much higher levels of fruit production 

in his recent work on Shivwits milk-vetch. In a set of 30 plants at Harrisburg Junction in spring 

2005, he found averages of 111.9 flowers per plant and 80 percent fruit set, resulting in an estimate

of 89.5 fruits per plant. Aside from the effects of herbivory, low levels of fruit production at the

Zion Hilltop site in 2006 likely were attributable to the relatively dry winter. During the October

2005 – March 2006 period, Zion NP received 198 mm of precipitation, which is approximately 85 

percent of the long-term average of 231 mm (only 50 percent of the long-term average was
6

received during the October-February period). In contrast, the October 2004 – March 2005 period 

preceding Tepedino’s work was the wettest in the 78-year record, with 630 mm of precipitation 

recorded for Zion NP.

Table 2. Mean estimates of canopy volume and numbers of reproductive shoots and fruits produced

by caged and uncaged Shivwits milk-vetch plants at the Zion Hilltop site in spring 2006.

Caged plants (n = 62) Uncaged plants (n = 62) Wilcoxon Matched Pairs Test

Variable Mean CV* Mean CV Z p

No. reproductive

shoots per plant 1.27 191.7 0.50 197.6 2.46 0.014

No. fruits per plant 3.37 249.7 0.34 651.9 2.93 0.003

Estimated canopy

volume (cm3)** 4,106.0 97.3 3,177.7 85.0 1.59 0.112

* Coefficient of variation (CV) = 100 x (standard deviation / mean)

* Canopy volume was estimated by multiplying plant height (in cm) by measures of maximum and minimum canopy

width (in cm).

Because of the low level of fruit production in spring 2006, we collected only 49 filled seeds from

a total of 15 plants at the Zion Hilltop site. During Jan-Apr 2007, these seeds will be used in pilot

studies of germination and growth requirements to support work planned for spring-summer 2007 

(Research Objective 3). Based on Tepedino’s (2005) estimate of 7 seeds per fruit and our estimate

of 632 fruits produced by the entire Hilltop subpopulation (209 fruits produced by 62 caged plants,

and an estimate of 423 fruits produced by 1245 uncaged plants), this level of seed collection 

represents approximately 1.1 percent of the 2006 seed crop for the Hilltop subpopulation. Because

our study design for Research Objective 2 called for 500 seeds, we will not be able to augment

experimental plots with milk-vetch seeds to assess effects of invasive exotic plants on seedling 

establishment in spring 2007.

Descriptive Soil-Vegetation Sampling

Range-Wide Patterns

Twenty soil-vegetation plots were sampled during April-May 2006 (Table 3; Appendices A and 

C), with Shivwits milk-vetch occurring in 17 of these. The remaining three plots at the Coral

Canyon, Pahcoon, and Harrisburg Bench sites were sampled to examine factors potentially 

responsible for abrupt boundaries between soil-vegetation patches with and without milk-vetch 

plants. Table 4 summarizes ranges, means, and variability of selected measures associated with the

17 plots supporting Shivwits milk-vetch plants. With respect to milk-vetch measures, the
7

Table 3. Summary of selected environmental and vegetation data for 20 soil-vegetation plots sampled during April-May 2006. Data for rock

fragments (> 2 mm) are percentages of the entire 0-10 cm sample by mass; data for sand, silt, and clay are percentages of the fine-earth fraction (<

2 mm) by volume. See Appendix C for detailed plot-level vegetation and ground-cover data. Population / site

Plot name

Plot code

(no. 1-m2 quadrats) Elevation

Slope

Aspect

Heat-load index

Shivwits milk-vetch

measures

Mean cover (CV*)

1-m2 frequency

Total density

Total live cover (CV)

Relative cover, exotics (CV)

Total rock cover (CV)

Geologic substrate

USDA texture class, 0-10 cm

Soil properties,

0-10 cm depth

Rock fragments

Sand

Silt

Clay

Zion National Park

Hilltop CORA 1

ZH_C1

(12)

1280 m

8 deg

220 deg

0.924

0.1 pct (346.4)

8.3 pct

0.1 plants m-2

13.2 pct (71.0)

25.0 pct (57.3)

5.2 pct (171.7)

Petrified Forest Member

Sandy clay loam

1.7 pct

46.1 pct

27.9 pct

26.0 pct

Hilltop CORA 2

ZH_C2

(12)

1279 m

9 deg

212 deg

0.937

0.1 pct (346.4)

8.3 pct

0.1 plants m-2

25.0 pct (65.9)

33.6 pct (46.6)

2.0 pct (85.3)

Petrified Forest Member

Loam

7.1 pct

39.8 pct

42.8 pct

17.4 pct

Hilltop ASAM Lo

ZH_Lo

(12)

1283 m

13 deg

312 deg

0.870

0.2 pct (346.4)

8.3 pct

0.2 plants m-2

15.8 pct (64.8)

92.3 pct (9.6)

2.1 pct (47.8)

Petrified Forest Member

Clay

6.2 pct

7.1 pct

36.9 pct

56.0 pct

Hilltop ASAM Hi 1

ZH_H1

(12)

1283 m

13 deg

312 deg

0.870

2.0 pct (64.0)

91.7 pct

2.8 plants m-2

18.8 pct (20.6)

49.4 pct (34.6)

3.7 pct (63.0)

Petrified Forest Member

Silty clay loam

13.3 pct

19.7 pct

42.4 pct

37.8 pct

Hilltop ASAM Hi 2

ZH_H2

(12)

1284 m

8 deg

300 deg

0.888

1.7 pct (82.2)

83.3 pct

3.4 plants m-2

19.8 pct (54.1)

65.0 pct (22.8)

3.0 pct (47.1)

Petrified Forest Member

Gravelly silty clay

17.6 pct

21.2 pct

37.0 pct

41.9 pct

Hilltop ASAM Hi 3

ZH_H3

(12)

1280 m

8 deg

200 deg

0.931

1.3 pct (77.2)

83.3 pct

3.3 plants m-2

20.8 pct (36.3)

80.0 pct (15.6)

1.6 pct (73.5)

Petrified Forest Member

Silty clay

2.9 pct

11.7 pct

42.7 pct

45.6 pct

Trail North

ZT_N

(17)

1255 m

10 deg

264 deg

0.943

1.1 pct (83.0)

70.6 pct

2.1 plants m-2

14.5 pct (35.8)

40.3 pct (40.5)

8.8 pct (82.0)

Petrified Forest Member

Gravelly loam

22.4 pct

40.3 pct

37.9 pct

21.9 pct

* Coefficient of variation (CV) = 100 x (standard deviation / mean)
8

Table 3, continued. Population / site

Plot name

Plot code

(no. 1-m2 quadrats) Elevation

Slope

Aspect

Heat-load index

Shivwits milk-vetch

measures

Mean cover (CV)

1-m2 frequency

Total density

Total live cover (CV)

Relative cover, exotics (CV)

Total rock cover (CV)

Geologic substrate

USDA texture class, 0-10 cm

Soil properties,

0-10 cm depth

Rock fragments

Sand

Silt

Clay

Zion National Park (continued)

Trail South

ZT_S

(16)

1256 m

1 deg

310 deg

0.855

0.4 pct (165.1)

31.3 pct

0.4 plants m-2

11.0 pct (96.7)

43.0 pct (41.2)

4.6 pct (118.4)

Petrified Forest Member

Sandy loam

0.8 pct

54.8 pct

33.0 pct

12.3 pct

Trail SAVE 

ZT_Sv

(12)

1257 m

7 deg

317 deg

0.860

0.8 pct (115.5)

50.0 pct

1.8 plants m-2

14.1 pct (129.0)

52.6 pct (50.9)

13.0 pct (96.5)

Petrified Forest Member

Gravelly clay loam

16.2 pct

21.7 pct

49.3 pct

29.1 pct

Petrified Forest

ZPF

(18)

1295 m

5 deg

200 deg

0.903

0.1 pct (291.0)

11.1 pct

0.2 plants m-2

19.3 pct (88.5)

30.7 pct (56.0)

2.3 pct (273.5)

Petrified Forest Member

Sandy loam

0.2 pct

64.4 pct

20.0 pct

15.7 pct

Coral Canyon

North

CC_N

(12)

928 m

22 deg

320 deg

0.818

0.9 pct (31.5)

91.7 pct

1.5 plants m-2

9.3 pct (23.0)

51.4 pct (44.2)

6.2 pct (56.1)

Petrified Forest Member

Silty clay loam

0.5 pct

8.0 pct

58.1 pct

34.0 pct

Middle

CC_M

(12)

928 m

20 deg

317 deg

0.839

0.0 pct

0.0 pct

0 plants m-2

24.3 pct (59.6)

76.7 pct (29.0)

23.8 pct (48.4)

Petrified Forest Member

Very gravelly clay loam

36.6 pct

25.9 pct

43.6 pct

30.5 pct

South

CC_S

(12)

928 m

22 deg

322 deg

0.809

0.2 pct (233.5)

16.7 pct

0.5 plants m-2

16.8 pct (22.9)

80.0 pct (23.2)

17.9 pct (34.1)

Petrified Forest Member

Gravelly clay loam

22.6 pct

23.9 pct

39.1 pct

37.0 pct

Pahcoon Spring Wash

East

P_E

(15)

1103 m

21 deg

337 deg

0.747

2.0 pct (90.6)

80.0 pct

15.9 plants m-2

13.9 pct (50.5)

49.4 pct (22.9)

11.2 pct (81.7)

Petrified Forest Member

Gravelly clay loam

18.3 pct

36.0 pct

32.9 pct

31.1 pct

West

P_W

(12)

1105 m

21 deg

342 deg

0.726

0.0 pct

0.0 pct

0 plants m-2

17.8 pct (87.5)

71.4 pct (16.0)

1.2 pct (49.5)

Petrified Forest Member

Clay

0.5 pct

6.4 pct

38.8 pct

54.9 pct
9

Table 3, continued. Population / site

Plot name

Plot code

(no. 1-m2 quadrats) Elevation

Slope

Aspect

Heat-load index

Shivwits milk-vetch

measures

Mean cover (CV)

1-m2 frequency

Total density

Total live cover (CV)

Relative cover, exotics (CV)

Total rock cover (CV)

Geologic substrate

USDA texture class, 0-10 cm

Soil properties,

0-10 cm depth

Rock fragments

Sand

Silt

Clay

Harrisburg Bench

Chinle Lower 

H_CL

(20)

961 m

8 deg

008 deg

0.771

0.8 pct (96.0)

65.0 pct

1.6 plants m-2

15.6 pct (35.3)

74.4 pct (22.2)

5.9 pct (173.3)

Petrified Forest Member

Clay

4.9 pct

14.9 pct

27.3 pct

57.8 pct

Chinle Upper 

H_CU

(16)

964 m

9 deg

000 deg

0.774

0.0 pct

0.0 pct

0 plants m-2

27.9 pct (34.1)

97.3 pct (2.5)

16.2 pct (67.3)

Petrified Forest Member

Clay loam

8.2 pct

40.0 pct

27.1 pct

32.9 pct

Gravel Surface

H_GS

(16)

961 m

8 deg

330 deg

0.837

0.1 pct (273.3)

12.5 pct

0.1 plants m-2

22.3 pct (36.4)

77.0 pct (13.3)

19.7 pct (82.4)

Petrified Forest Member

Clay

2.0 pct

29.9 pct

27.4 pct

42.7 pct

Shivwits Paiute Reservation

Chinle

S_C

(16)

1037 m

7 deg

010 deg

0.779

0.1 pct (273.3)

12.5 pct

0.6 plants m-2

11.4 pct (59.1)

83.4 pct (11.9)

14.1 pct (49.1)

Petrified Forest Member

Silty clay loam

8.4 pct

18.7 pct

42.0 pct

39.2 pct

Moenave

S_M

(12)

1027 m

Variable

Variable

0.838

0.3 pct (195.4)

25.0 pct

0.5 plants m-2

9.2 pct (69.1)

69.0 pct (43.0)

1.0 pct (0.0)

Dinosaur Canyon Member

Clay

3.9 pct

5.0 pct

38.0 pct

57.0 pct
10

Pahcoon East plot is particularly noteworthy relative to the others since average milk-vetch density 

(15.9 plants m-2) there was more than 7.5 times the average measure (2.1 plants m-2) for all milkvetch plots combined (Tables 3 and 4). This plot is coincident with Dr. Renee Van Buren’s longterm demographic monitoring plot. Approximately 44 percent of the milk-vetch plants in this plot

were seedlings (Table C6, Appendix C), a value that is generally similar to those found during 

surveys of other population locations in spring 2006 (Table 1).

Table 4. Ranges, means, and coefficients of variation (CV) of selected

environmental, milk-vetch, and vegetation cover variables for the 17 soilvegetation plots in which Shivwits milk-vetch was found to occur, April-May

2006.

Variables Minimum Maximum Mean CV*

Environmental

Elevation (m) 928 1295 1158.6 12.9

Heat-load index 0.75 0.94 0.86 7.0

Sand, 0-10 cm (pct) 5.0 64.4 27.2 63.5

Clay, 0-10 cm (pct) 12.3 57.8 35.4 39.9

Rock cover (pct) 1.0 19.7 7.2 82.3

Milk-vetch

1-m2 frequency (pct) 8.3 91.7 44.1 76.7

Density (plants m-1) 0.1 15.9 2.1 181.3

Vegetation cover

Total live cover (pct) 9.2 25.0 15.9 28.6

Relative exotic cover (pct) 25.0 92.3 58.6 35.1

Red brome cover (pct) 1.8 15.8 6.9 61.0

Cheatgrass cover (pct) 0.0 8.0 1.6 151.7

* Coefficient of variation (CV) = 100 x (standard deviation / mean)

Across the 17 milk-vetch plots, average relative cover of exotic plants (i.e., the exotic proportion of

total live cover) was 58.6 percent (Table 4), a substantially larger value than the 36.6 percent

average that Van Buren and Harper (2003) found in their studies. Red brome and cheatgrass (B.

tectorum) were the two most abundant exotics, as well as the two most abundant plants overall,

with average cover values of 6.9 and 1.6 percent, respectively. Though it was primarily restricted 

to Zion plots, galleta (Hilaria jamesii) was the most abundant native plant overall, with average

cover of 1.0 percent among the 17 milk-vetch plots and 1.7 percent among the 10 Zion plots. At

the range-wide scale, milk-vetch frequency in 1-m2 quadrats was not correlated with total live cover

(r = -0.29, p = 0.21) or relative cover of invasive exotic plants (r = -0.21, p = 0.37).

We found a large range in soil texture across the 17 plots supporting Shivwits milk-vetch plants

(Tables 3 and 4). Although over 99 percent of Shivwits milk-vetch individuals were found to 

occur on gently sloping Petrified Forest Member outcrops, the rocks are heterogeneous –

consisting of smectitic shale, siltstone, sandstone, and conglomerate with pebble- to cobble-sized 

clasts (Willis et al. 2002). As noted earlier, milk-vetch occurrences span much of this

heterogeneity across the full thickness of the geologic unit. In addition, milk-vetch settings receive
11

varying amounts of material inputs from surrounding geologic deposits, including Quaternary 

landslide and alluvial deposits bearing materials derived from sandstones, conglomerates, and 

intrusive igneous rocks (Willis et al. 2002, Biek 2003). As a consequence, texture classes of milkvetch plots were found to vary from sandy loam (Zion Trail South and Petrified Forest plots) to 

clay (Zion Hilltop Asam Lo, Shivwits Moenave, and Harrisburg Chinle Lower and Gravel Surface

plots; Table 3; Appendix D).

Principal components analysis of five environmental variables (elevation, topographic heat-load 

index, and three soil-texture fractions) extracted two principal components which together

explained 78 percent of the among-plot variability in the original five variables (Table 5). Elevation 

and topographic heat load were highly correlated with Axis 1, whereas sand and silt (the latter

negatively) were highly correlated with Axis 2.

Table 5. Loadings (Pearson correlation coefficients) of

five environmental variables on PCA Axes 1 and 2. The

PCA solution was rotated using the varimax

normalization procedure in Statistica.

Variable Axis 1 Axis 2

Elevation 0.843 0.068

Heat-load index 0.906 0.030

Pct sand, 0-10 cm 0.377 0.912

Pct silt, 0-10 cm 0.195 -0.812

Pct clay, 0-10 cm -0.584 -0.597

Proportion of total variation 0.411 0.371

Figure 1 illustrates the location of the 20 soil-vegetation plots in relation to the two environmental

axes extracted with PCA. Plot elevations and heat-load indices were significantly correlated (r =

0.70, p = 0.001), indicating that milk-vetch populations at higher elevation plots in Zion NP tended 

to occur in warmer topographic positions (higher topographic heat-load indices) relative to 

populations in lower elevation plots outside the Park (Figure 1; Table 3). This pattern might reflect

some degree of habitat selectivity by milk-vetch populations, or it could be an artifact attributable to 

environmental characteristics of available habitat patches. At the range-wide scale, among-plot

variability in milk-vetch frequency was not significantly correlated with variations in soil texture,

although some trends in milk-vetch – soil texture relations were evident at individual study sites

(see below). (See Appendix D for additional figures illustrating variations in milk-vetch frequency 

and brome cover in relation to soil-texture classes.)

As with milk-vetch frequency, total brome cover was not significantly correlated with variations in 

soil texture at the range-wide scale. However, patterns evident in Figure 1 suggest a possible

elevation-by-texture interaction with respect to brome cover. In the 10 relatively high-elevation 

plots at Zion NP, total brome cover was positively correlated with 0-10 cm clay content (r = 0.77, p

= 0.009) and negatively correlated with 0-10 cm sand content (r = -0.72, p = 0.018). In the 10 

lower elevation plots outside of Zion NP, there was a tendency for total brome cover to be

positively correlated with 0-10 cm sand content (r = 0.61, p = 0.059). Site-specific brome-texture

patterns are discussed in greater detail below.
12

Figure 1. Ordination of 20 soil-vegetation plots in relation to PCA axes 1 and 2. In

(a), point size is scaled by milk-vetch (Asam) frequency in 1-m2 quadrats. In (b),

point size is scaled by total cover of exotic annual brome grasses, with relative

proportions of red brome and cheatgrass indicated by red and blue segments of the

symbol, respectively. Dashed vectors indicate the relative loadings of elevation and

heat load, sand, silt, and clay on axes 1 and 2. (Coordinates for the head of each

environmental vector are twice the correlation coefficients associated with the two

PCA axes.) See Table 3 for key to plot codes.

Our investigation of range-wide environmental relations is hampered by the small number of milkvetch occurrences (thereby limiting our sample size). We also have a poor quantitative

understanding of how factors such as herbivory by native herbivores, competition from other

plants, livestock grazing and trampling, off-road vehicle travel, and urbanization may have affected 
13

relative levels of milk-vetch and exotic plant abundance, thereby complicating our search for plantenvironment relations. Additional insights into plant-environment relations may emerge once the

remainder of the soil data are received and analyzed.

Figure 2 illustrates the location of the 20 soil-vegetation plots in relation to two gradients in plant

community composition extracted with NMS analyses. Axis 2 and axis 1 accounted for 43.3 and 

29.9 percent of the among-plot variability in plant community composition, respectively. Because

red brome and cheatgrass were the two most abundant plants overall, most of the among-plot

variability in community composition was attributable to variations in the relative abundance of

these two exotic grasses. Plot scores for NMS axis 2 were significantly correlated with cheatgrass

cover (r = 0.69, p = 0.001), total brome cover (r = 0.44, p = 0.050) and relative cover of exotic

plants (r = 0.57, p = 0.008). Plot scores for NMS axis 2 were significantly correlated with red 

brome cover (r = -0.88, p < 0.001), total brome cover (r = -0.63, p = 0.003), and relative exotic

cover (r = -0.47, p = 0.035). Milk-vetch frequency was not significantly correlated with plot

scores for either NMS axis. (See Appendix C for detailed plot-level data on plant community 

composition.)

Regression analyses indicated that the gradients in community composition reflected by NMS axis

2 (cheatgrass abundance) and NMS axis 1 (red brome abundance) were significantly related to 

measured environmental variables. PCA axis 1 (positively related to elevation and heat load) was

the best single predictor for NMS axis 2 (beta = -0.799, R2 = 0.64, p < 0.00002), and PCA axis 2

(positively related to 0-10 cm sand content) was the best (albeit weak) predictor for NMS axis 1 

(beta = 0.469, R2 = 0.22, p = 0.037).

Site-Level Patterns

Although range-wide relations between milk-vetch frequency and measured environmental

variables were weak, spatial variations in milk-vetch frequency at study sites associated with 

several population locations appeared related to variations in soil texture and/or total rock cover.

The Zion Hilltop site where more than 60 percent of all known milk-vetch plants occur is perched 

on an isolated mound which is an erosional remnant of a once-larger landslide deposit (Willis et al.

2002). The center of the mound where the milk-vetch plants occur is an unmapped Petrified Forest

Member exposure analogous to a “donut hole” surrounded by sandstone-derived landslide debris

ranging in size from large boulders to fine gravels. At this site, we sampled six soil-vegetation 

plots to examine relations between soil variables and site-level variations in milk-vetch frequency.

We found that milk-vetch frequency in Zion Hilltop plots varied in a curvilinear fashion in relation 

to trends in 0-10 cm sand and clay content (Table 3, Figure 3a). Milk-vetch frequencies were low

at the sandy end of the texture gradient in plots CORA1 and CORA2, both of which were located 

at the interface between Petrified Forest Member exposures and surrounding landslide deposits and 

were co-dominated by blackbrush (Coleogyne ramosissima) and the exotic red brome (Table 3,

Figure 3a). Milk-vetch frequency also was low at the clayey end of the texture gradient (plot Asam

Lo), and was highest in three plots (Asam Hi1, Hi2, and Hi3) that were characterized with silty 

clay / silty clay loam textures (Table 3, Figure 3a). Relative to the plots with silty clay and silty 

clay loam textures, the clay plot with low milk-vetch frequency was in a geomorphic setting that

may have received less material inputs from surrounding landslide deposits. In contrast with milkvetch patterns, density of the escaped exotic cultivar Moluccella laevis (Bells of Ireland, Lamiaceae)

was highest in the clayey plot (21.6 plants m-2) relative to the silty clay / silty clay loam plots (3-

plot average of 0.8 plants m-2). Moluccella did not occur in the relatively sandy plots (see plot-level

data in Appendix C). Total brome cover tended to vary inversely with 0-10 cm sand content (n =
14

6; r = -0.80, p = 0.052; Figure 3c). In addition to direct effects of soil properties, low abundances

for milk-vetch, brome, and Moluccella in the sandiest plots may have been affected by the

competitive presence of blackbrush.

Figure 2. Ordination of 20 soil-vegetation plots in relation to NMS axes 1 and 2. In

(a), point size is scaled by milk-vetch (Asam) frequency in 1-m2 quadrats. In (b),

point size is scaled by total cover of exotic annual brome grasses, with relative

proportions of red brome and cheatgrass indicated by red and blue segments of the

symbol, respectively. See Table 3 for key to plot codes.
Figure 3. Graphs showing variations in milk-vetch (Asam) frequency and total brome cover in relation to 0-10 c

at the Zion Hilltop site (a, c), the Zion Trailside site (b, d) and the Pahcoon Springs Wash site (d). In (c) and (d), of red brome and cheatgrass are indicated by red and blue segments of symbols, respectively. See Table 3 for ke

15
16

Similar to the Hilltop site, plots at the Zion Trailside and Petrified Forest sites occurred on 

unmapped Petrified Forest Member patches in the midst of sandstone-dominated landslide

complexes (Willis et al. 2002). Among these plots, milk-vetch frequencies were lowest at plots

with sandy loam soils and highest at plots with loam and clay loam soils (Table 3; Figure 3b).

Moluccella density was highest in the Zion Trail South plot (sandy loam soil; 4.5 plants m-2),

although its abundance in this plot may have been reduced by past removals conducted by NPS

staff and volunteers. Moluccella occurred in the Zion Trail SAVE plot (clay loam soil; 0.5 plants

m-2), but not in the Petrified Forest and Trail North plots. No brome-soil relations were evident

among the three Trailside and Petrified Forest plots (Figure 3d).

At the Pahcoon Springs Wash site, we sampled two soil-vegetation plots to examine whether soil

properties could explain an abrupt change in milk-vetch density from 15.9 plants m-2 in the

Pahcoon East plot to a near-complete absence of milk-vetch plants in the Pahcoon West plot just a

few meters away. (A few milk-vetch plants did occur within the plot area, but they were not

present in the randomly located quadrats.) These plots were adjacent to one another on a

northwest-facing hillslope, just west of the northwest-southeast trending contact of the Petrified 

Forest Member and Dinosaur Canyon Member (Hintze and Hammond 1994). Differences in soil

coloration, texture, and abundance and lithology of rock fragments suggest that the two adjacent

plots occurred on different facies of the Petrified Forest Member exposure. The high-density 

Pahcoon East plot was characterized by a gravelly clay loam soil (Figure 3b), with abundant

limestone gravels weathering out of the Petrified Forest Member substrate. The adjacent Pahcoon 

West plot was characterized by a clay soil with much less sand (6.4 percent vs. 36.0 percent), much 

more clay (54.9 percent vs. 31.1 percent), and higher brome cover (13.9 percent vs. 6.8 percent)

relative to the Pahcoon East plot (Figure 3d, Table 3, Appendix C).

Plots at the Coral Canyon site were on a northwest-facing Petrified Forest Member hillslope

immediately below a bench formed by Quaternary fan gravels derived from the distant Pine Valley 

Mountains (Biek 2003). At this site, we sampled three soil-vegetation plots to describe distinct

patterns in the relative abundance of milk-vetch and invasive exotic brome grasses (Figure 4). The

Middle and South plots were armored with colluvial deposits consisting of sandstone and igneous

cobbles and gravels from the fan surface above. The North plot occurred on a relatively unarmored

slope that appeared to be protected from colluvial deposits by a boulder which occurred at the

shoulder of the slope (Figure 4). Among the three plots at this site, we found that milk-vetch 

frequency decreased (Figure 5a) and total brome cover increased (Figure 5b) with increasing rock 

cover and 0-10 cm sand content attributable to colluvial deposits.

We found similar patterns with respect to rock cover, 0-10 cm sand content, milk-vetch frequency,

and total brome cover at the Harrisburg site. At this site, all plots were located on Petrified Forest

Member exposures, but plots varied in degree of rock armoring and 0-10 cm sand content due to 

differences in geomorphic setting. We located the Gravel Surface plot at the foot of a slope that

was well-armored by rock cover derived from an upslope Quaternary talus deposit associated with 

the Shinarump (conglomerate) Member of the Chinle Formation (Trcs). The Chinle Lower plot

was located at a similar footslope position on an adjacent surface which did not receive material

inputs from the talus deposit. Upslope above the Chinle Lower plot, the gravel-armored Chinle

Upper plot was in a setting that received material inputs from rocky landslide and alluvial-fan 

deposits located above. As at the Coral Canyon site, we found that milk-vetch frequency decreased

(Figure 5a) and total brome cover increased (Figure 5b) with increasing rock cover and 0-10 cm

sand content attributable to these among-plot differences in geomorphic setting and geologic inputs.
17

Figure 4. Cross-sectional diagram illustrating spatial configuration of soil-vegetation plots at the

Coral Canyon site in relation to colluvium from the Quaternary alluvial fan (Qaf5 surface mapped by

Biek 2003) which caps the Petrified Forest Member (TRcp) hillslope. Scale is approximately 50 m

from left to right of figure.

Rock cover may influence milk-vetch and brome abundance at the Coral Canyon and Harrisburg 

sites through effects on seed retention and seedling establishment (i.e., availability of “safe sites”

sensu Harper 1977). Seed catchment may be enhanced directly due to effects of rock cover on 

soil-surface roughness (e.g., Harper et al. 1965) and indirectly due to retarding effects of surface

roughness on overland water flow and downslope seed movement. Increasing sand content in 

soils of these two low-elevation, fine-textured sites may enhance plant performance by reducing 

evaporative water losses (i.e., the “inverse texture effect” of Noy-Meir 1973). If one or both of

these effects are more beneficial for brome grasses than for the milk-vetch, and if the milk-vetch 

responds adversely to brome competition, then this would explain opposite trends in milk-vetch 

and brome performance in relation to these physical soil properties.

At the Shivwits site, the milk-vetch population was too small and sparsely distributed to indicate

spatial patterns suitable for investigation with comparative soil-vegetation plots. Instead, we

sampled to compare soil properties of the two geologic substrates (Petrified Forest Member and 

Dinosaur Canyon Member) where milk-vetch plants occurred. The 0-10 cm soil in Chinle plot

(Petrified Forest Member) was a silty clay loam with similar texture to the three high-frequency 

plots at the Zion Hilltop site (Table 3). The 0-10 cm soil in Moenave plot (Dinosaur Canyon 

Member) was clay with very similar texture to the Pahcoon West plot where no milk-vetch plants

occurred in sampled quadrats.
18

Figure 5. Graphs showing variations in (a) milk-vetch (Asam) frequency and (b) total brome cover

in relation to 0-10 cm sand content and total rock cover at the Coral Canyon (CC) and Harrisburg

(H) sites. In (b), relative proportions of red brome and cheatgrass are indicated by red and blue

segments of symbols, respectively. See Table 3 for key to plot codes.

On-Going Work and Future Plans

Habitat Modelling

We are currently proceeding with efforts to develop a GIS-based predictive habitat model that can 

be used to guide future surveys and efforts to evaluate sites for reintroduction efforts (Research 
19

Objective 4, above). Given the small number of known milk-vetch populations and thus the

limited availability of plant-environment data, we propose to use simple intersection methods in 

GIS rather than data-intensive statistical techniques to develop a potential habitat model (Fertig and 

Thurston 2003). Based on our current understanding of the species’ range-wide distributional

patterns (with 99 percent of the known occurrences are associated with patchily distributed 

Petrified Forest Member outcrops), geologic unit will be the most important predictive variable.

The complete suite of predictive variables that will be considered will include –

a. Geology—clay-rich substrates (categorical variable)

i. Petrified Forest Member of the Chinle Formation

ii. Dinosaur Canyon Member of the Moenave Formation (above Chinle

Formation)

iii. Upper red member (Biek 2003) of Moenkopi Formation (below Chinle

Formation)

iv. Quaternary landslide / mass movement deposits near cliff faces where

deposits may mantle, armor, or surround geologic units such as the Petrified 

Forest Member

b. Climate (continuous variables)

i. Elevation

ii. Mean seasonal / annual precipitation (exact variables dependent on 

availability of data)

iii. Mean seasonal / annual temperature (exact variables dependent on 

availability of data)

c. Topography (continuous variable)

i. Slope

ii. Topographic heat-load index

iii. Local relief

d. Land cover (categorical variable)

Range-intersection analyses in GIS will be supplemented with soil sampling and analysis. Soil

samples will be collected from additional clay-rich substrates (e.g., upper red member of the

Moenkopi Formation [Biek 2003]) that occur in close proximity to Petrified Forest Member

patches but are not currently known to support the milk-vetch. Characteristics of these soil

samples will be compared with those of samples previously collected from known population 

locations to evaluate whether these other substrates have the potential to support the milk-vetch.

Products will include a technical report and GIS / spatial data with metadata that comply with 

Federal Geographic Data Committee standards.

Experimental Studies of Red Brome Effects on Biological Soil Properties and MilkVetch Performance

In September 2006, we established 62 milk-vetch centered experimental plots at the Zion Hilltop 

site to investigate effects of red brome on soil properties and milk-vetch performance measures

using a neighborhood competition design (Goldberg and Werner 1983). Each circular plot

measures 80-cm in diameter and is centered on an individual milk-vetch plant that was used in 

herbivory studies in spring 2006. Each focal milk-vetch plant is protected from vertebrate

herbivores by a circular wire-mesh cage measuring 40-cm diameter by 60-cm tall. Standing-dead 

aboveground biomass of annual plants (primarily red brome), and aboveground biomass of

perennial plants were removed from each plot and weighed. Plots were randomly assigned to one

of four seeding treatments (Table 6) intended to establish an experimental gradient in red brome
20

biomass, and red brome seeds collected from local Zion populations were added to plots and mixed 

in the upper 1-2 cm of soil. An automated meteorological station also was installed at the Zion 

Hilltop site in September 2006 to monitor the size and frequency of precipitation events as well as

soil volumetric water content, temperature, and electrical conductivity at 5- and 15-cm depths in 

two experimental plots assigned to the “medium” and “none” red-brome seeding treatments.

In spring 2007, neighborhood plots will be revisited and milk-vetch performance will be evaluated 

on the basis of seedling emergence and survivorship, canopy volume of established focal plants,

and by numbers of flowering stems, pods, and seeds produced by focal plants. Seeds will be

collected from a subset of plants and seed weight and viability determined in the laboratory.

Aboveground biomass of exotics will be harvested from each neighborhood plot, dried, and 

weighed. To evaluate effects of red brome abundance on mycorrhizal associations of established 

milk-vetch plants, 12 focal milk-vetch plants (three from each of the four levels of brome

abundance) will be randomly selected and their roots collected and stored in a freezer until root

colonization by arbuscular-mycorrhizal (AM) fungi is quantified using root-staining procedures

(Johnson et al. 1999). (This procedure will result in the mortality of the 12 selected individuals.)

Finally, soils also will be collected from 30 of the 62 plots representing the exotic biomass gradient

and analyzed for soil enzyme activity and N mineralization rates.

Table 6. Levels and seeding rates used in

applications of red brome seeds to milkvetch centered experimental plots in

September 2006.

Seeding level Seeding rate (seeds m-2)

High 5000

Medium 2500

Low 1250

None 0

To further evaluate the potential effects of red brome on the mycorrhizal associations of Shivwits

milk-vetch, we also will perform a bait-plant bioassay (to assess densities of mycorrhizal

propagules) and AM fungi spore counts (to assess mycorrhizal species composition), following 

methods described by Johnson and others (1999). Intact soil cores measuring approximately 5 cm

in diameter by 15 cm deep will be collected from the Zion Hilltop study site at the end of the field 

experiment in spring 2007. Two cores will be collected from each of 62 experimental plots

representing a range of aboveground red brome biomass. One core will be extracted within 10 cm

of the focal milk-vetch plant; the other sample will be collected 40-60 cm away from the focal plant,

in an area representative of the plot’s overall red brome density / biomass. The cores will be

categorized into groups according to levels of red brome biomass observed at the end of the 2007 

growing season – high, medium, low, and no red brome – with approximately 15 core pairs per

group.

Each of the 124 cores will be split lengthwise so that half of each sample may be used for the baitplant bioassay and the other half for AM spore counts. Soil samples for bait-plant studies will be

transported in cone-pots to the native plant nursery at Zion NP. Two cores from each red-brome

abundance level will be planted with pre-germinated seed of Shivwits milk-vetch and the remaining 

cores will be planted with pre-germinated seed of Zea mays (corn). Both species will be used 

because Z. mays is known to be a reliable host plant, and nothing yet is known about mycorrhizal

relations of the milk-vetch. Plants will be harvested after 6 weeks of growth, and roots will be

collected and stored in a freezer until root colonization by AM fungi is quantified using root-
21

staining procedures (Johnson et al. 1999). Roots and shoots of milk-vetch plants also will be dried 

and weighed to evaluate variation in relation to different levels of red brome biomass and 

(potentially) different levels of AM fungi colonization.

Soil samples for AM spore counts will be homogenized and kept frozen until analyses are

preformed at Northern Arizona University (NAU) in fall of 2007. Spores will be extracted from

the soil samples through a process of centrifuging and vacuum filtration, then dyed and quantified 

using a compound microscope (Johnson et al. 1999).

Literature Cited

Biek, R.F. 2003. Geologic map of the Harrisburg Junction Quadrangle, Washington County,

Utah. Utah Geological Survey Map 191, 42 p., map scale 1:24,000.

Biek, R.F., G.C. Willis, M.D. Hylland, and H.H. Doelling. 2000. Geology of Zion National Park,

Utah. Pages 107-138 in D.A. Sprinkel, T.C. Chidsey, Jr., and P.B. Anderson, eds.

Geology of Utah’s Parks and Monuments, 2000 Utah Geological Association Publication 

28, Millenium Guidebook. Utah Geological Association, Salt Lake City.

Fertig, W., and R. Thurston. 2003. Modeling the potential distribution of BLM sensitive and 

USFWS threatened and endangered plant species in Wyoming. Report to the Bureau of

Land Management, Wyoming State Office, by the Wyoming Natural Diversity Database,

University of Wyoming, Laramie. 44 pp. + appendices.

Goldberg, D. E., and P. A. Werner. 1983. Equivalence of competitors in plant communities: A null

hypothesis and a field experimental approach. American Journal of Botany 70: 1098-1104.

Harper, J. L. 1977. Population biology of plants. Academic Press, San Diego.

Harper, J. L., J. T. Williams, and G. R. Sagar. 1965. The behaviour of seeds in soil. I. The

heterogeneity of soil surfaces and its role in determining the establishment of plants from

seed. Journal of Ecology 53: 273-286.

Hintze, L.F., and B.J. Hammond. 1994. Geologic map of the Shivwits Quadrangle, Washington 

County, Utah. Utah Geological Survey Map 153, 21 p., map scale 1:24,000.

Ingram, R.L. 1982. Modified Wentworth scale. In: Grain-size scales. AGI Data Sheet 29.1. In:

Dutro, J.T., R.V. Dietrich, and R.M. Foose. 1989. AGI data sheets for geology in the

field, laboratory, and office, 3rd edition. American Geological Institute, Washington, D.C.

Johnson, N. C., T. E. O'Dell, and C. S. Bledsoe. 1999. Methods for ecological studies of

mycorrhizae. Pages 378-412 in G. P. Robertson, D. C. Coleman, C. S. Bledsoe, and P.

Sollins, eds. Standard soil methods for long-term ecological research. Oxford University 

Press, New York.

McCune, B. P., and J. B. Grace. 2002. Analysis of ecological communities. MJM Software

Design, Gleneden Beach, Oregon.

McCune, B. P., and D. Keon. 2002. Equations for potential annual direct incident radiation and 

heat load. Journal of Vegetation Science 13: 603-606.

McCune, B. and M. J. Mefford. 1999. PC-ORD – multivariate analysis of ecological data, version 

4.3. MjM Software, Gleneden Beach, Oregon, U.S.A., http://www.pcord.com.

Noy-Meir, I. 1973. Desert ecosystems: Environment and producers. Annual Review of Ecology

and Systematics 4: 25-51.
22

StatSoft, Inc. 2004. STATISTICA (data analysis software system), version 6.1.

www.statsoft.com.

Tepedino, V. J. 2005. Reproduction and pollination of two rare species of Astragalus from

Washington County, southern Utah: A. holmgreniorum and A. ampullarioides. USDAARS Bee Biology and Systematics Laboratory, Department of Biology, Utah State

University, Logan, UT. 18 pp.

U.S. Fish and Wildlife Service. 2001. Endangered and threatened wildlife and plants;

Determination of endangered status for Astagalus holmgreniorum (Holmgren milk-vetch)

and Astragalus ampullarioides (Shivwits milk-vetch). Federal Register 66 (189): 49560-

49567.

U.S. Fish and Wildlife Service. 2006. Astragalus holmgreniorum (Holmgren Milk-Vetch) and 

Astragalus ampullarioides (Shivwits Milk-Vetch) recovery plan. U.S. Department of

Interior, Fish and Wildlife Service, Denver, CO. 114 pp. [Available online at

http://www.fws.gov/endangered/recovery/]

Van Buren, R., and K. T. Harper. 2003. Demographic and environmental relations of two rare

Astragalus species endemic to Washington County, Utah: Astragalus holmgreniorum and 

A. ampullarioides. Western North American Naturalist 63: 236-243.

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edition, revised. Brigham Young University, Provo, Utah. 912 p.

Willis, G.C., H.H. Doelling, B.J. Solomon, and E.G. Sable. 2002. Interim geologic map of the

Springdale West Quadrangle, Washington County, Utah. Utah Geologic Survey Open-File

Report 394, 20 p., map scale :24,000.
Appendix A – Map of Plot Locations 

Figure A1. General locations of six Shivwits milk-vetch populations in Washington County, Utah (from 

USFWS 2006). 

23
Appendix B – Graphs for Herbivory Experiment 

Figure B1. Histogram for estimated canopy volume of milk-vetch plants inside and outside of 

herbivore-exclusion cages at the Zion Hilltop site, spring 2006. 

Figure B2. Histogram for the number of reproductive shoots produced by milk-vetch plants 

inside and outside of herbivore-exclusion cages at the Zion Hilltop site, spring 2006. 

24
Figure B3. Histogram for the total number of fruit produced by milk-vetch plants inside and 

outside of herbivore-exclusion cages at the Zion Hilltop site, spring 2006. 

25
Appendix C – Plot-Level Quadrat data 

26
Table C1. Mean cover, frequency, and density data for Zion Hilltop soil-vegetation 

plots CORA1, CORA2, and Asam Lo1. 

4 transects 4 transects 4 transects

12 quadrats 12 quadrats 12 quadrats

Cover 1-m2 freq Cover 1-m2 freq Cover 1-m2 freq

Perennial forbs

Allium nevadense 0.3 25.0 0.3 25.0 0.1 8.3

Astragalus ampullarioides 0.1 8.3 0.1 8.3 0.2 8.3

Eriogonum inflatum 0.1 8.3 - - - -

Zigadenus paniculatus - -0.3 25.0 -

Annual forbs

Eriogonum subreniforme 0.1 8.3 0.2 16.7 0.1 8.3

Euphorbia spathulata - - - -0.1

Lactuca serriola* - - - -0.5 5

Moluccella laevis* - - - -0.9 9

Zion_AF2 0.3 25.0 0.5 50.0 - -

Zion_AF3 0.1 8.3 - - - -

Zion_AF6 - - 0.3 33.3 - -

Zion_AF7 - - 0.1 8.3 - -

Perennial grasses

Elymus elymoides - -0.1 8.3--

Hilaria jamesii 0.3 8.3 0.5 33.3 0.3 8.3

Annual grasses

Bromus rubens* 3.6 100.0 9.9 100.0 12.6 100.0

Bromus tectorum* 0.1 8.3 - - 0.3 33.3

Bromus, standing dead 2.5 100.0 9.5 100.0 23.2 100.0

Shrubs / subshrubs

Atriplex canescens - - 3.7 25.0 0.7 16.7

Chrysothamnus nauseosus 0.8 8.3 - - - -

Chrysothamnus viscidiflorus - - - -0.1

Coleogyne ramosissima 5.9 83.3 5.4 66.7 - -

Ephedra viridis 1.5 33.3 - - - -

Gutierrezia microcephala - -0.4 33.3 0.1

Psorothamnus fremontii 0.2 8.3 3.3 16.7 - -

Summary, vascular plants

Total live vascular cover 13.2 25.0 15.8

Total native cover 9.5 15.1 1.5

Total exotic cover 3.7 9.9 14.3

Relative native cover 75.0 66.4 7.7

Relative exotic cover 25.0 33.6 92.3

Total richness 13 14 12

Native richness 11 13 8

Exotic richness 2 1 4

Soil-surface features

Rabbit Dung (freq only) 83.3 83.3 83.3

Litter 5.8 100.0 33.0 100.0 34.2 100.0

Woody debris 0.6 50.0 0.1 8.3 0.2 16.7

Small Rock (< 20 mm) 4.2 100.0 1.8 91.7 2.0 100.0

Large Rock (> 20 mm) 1.0 33.3 0.2 16.7 0.1 8.3

Total Rock 5.2 100.0 2.0 91.7 2.1 100.0

Cyanobacterial crust 0.1 8.3 0.2 8.3 - -

Lichen crust - - - - - -

Moss crust 0.2 8.3 0.6 25.0 - -

Physical crust 66.6 100.0 51.3 91.7 53.3 91.7

Loose, unstable soil 5.9 83.3 3.6 50.0 0.1 8.3

Piping (freq only) - - 50.0

Density by height class Count Per m2 Count Per m2 Count Per m2

Astragalus ampullarioides

0.1-4 cm - - - - - -

5-12 cm 1 0.1 1 0.1 1 0.1

>12 cm ------

>12 cm, flowering - - - - 1 0.1

Total 1 0.1 10.1 2

Moluccella laevis*

0.1-4 cm - - - - 259 21.6

CORA 1 CORA 2 Asam Lo1

Zion Zion Zion

-

8.3

0.0

1.7

8.3

8.3

0.2

27
Table C2. Mean cover, frequency, and density data for Zion Hilltop soil-vegetation plots 

Asam Hi1, Asam Hi2, and Asam Hi3. 

4 transects 4 transects 4 transects

12 quadrats 12 quadrats 12 quadrats

Cover 1-m2 freq Cover 1-m2 freq Cover 1-m2

 freq

Perennial forbs

Allium nevadense 0.3 25.0 0.3 33.3 0.1 8.3

Astragalus ampullarioides 2.0 91.7 1.7 83.3 1.3 83.3

Delphinium sp. 0.6 58.3 0.2 16.7 - -

Sphaeralcea sp. - - - -0.1

Zion_PF1 0.1 8.3 - - - -

Annual forbs

Erodium cicutarium* 0.1 8.3 0.2 16.7 0.2 16.7

Euphorbia spathulata 0.2 16.7 0.4 41.7 0.1 8.3

Lactuca serriola* 0.2 16.7 0.1 8.3 0.2 16.7

Moluccella laevis* 0.5 50.0 0.3 25.0 0.3 33.3

Phacelia sp. - -0.3 25.0 -

Zion_AF3 0.1 8.3 - - - -

Perennial grasses

Elymus elymoides 0.2 16.7 0.3 25.0 0.4 33.3

Hilaria jamesii 4.6 100.0 1.3 58.3 0.3 25.0

Annual grasses

Bromus rubens* 8.2 100.0 12.3 100.0 15.8 100.0

Bromus tectorum* 0.3 16.7 - - 0.1 8.3

Bromus, standing dead 14.8 100.0 16.4 100.0 29.7 100.0

Shrubs / subshrubs

Atriplex canescens 1.5 25.0 2.5 25.0 2.0 41.7

Gutierrezia microcephala 0.1 8.3 0.3 25.0 0.1 8.3

Summary, vascular plants

Total live vascular cover 18.8 19.8 20.8

Total native cover 9.5 7.1 4.3

Total exotic cover 9.3 12.8 16.5

Relative native cover 50.6 35.0 20.0

Relative exotic cover 49.4 65.0 80.0

Total richness 15 13 13

Native richness 10 9 8

Exotic richness 5 4 5

Soil-surface features

Rabbit Dung (freq only) 91.7 100.0 75.0

Litter 30.2 100.0 28.8 100.0 44.8 100.0

Woody debris 0.1 8.3 0.3 25.0 0.1 8.3

Small Rock (< 20 mm) 3.3 100.0 2.8 100.0 1.5 100.0

Large Rock (> 20 mm) 0.3 25.0 0.2 16.7 0.1 8.3

Total Rock 3.7 100.0 3.0 100.0 1.6 100.0

Cyanobacterial crust - - - - - -

Lichen crust - - - - - -

Moss crust - - - - - -

Physical crust 52.1 100.0 59.2 100.0 44.6 100.0

Loose, unstable soil 0.3 16.7 0.3 16.7 - -

Piping (freq only) - - 16.7

Density by height class Count Per m2 Count Per m2 Count Per m2

Astragalus ampullarioides

0.1-4 cm 7 0.6 15 1.3 26 2.2

5-12 cm 21 1.8 21 1.8 10 0.8

>12 cm 6 0.5 3 0.3 -

>12 cm, flowering - - 2 0.2 3 0.3

Total 34 2.8 41 3.4 39 3.3

Moluccella laevis*

0.1-4 cm 15 1.3 7 0.6 4 0.3

5-12 cm - - 2 0.2 - -

>12 cm -----

>12 cm, flowering 1 0.1 - - - -

Total 16 1.3 9 0.8 4 0.3

Asam Hi1 Asam Hi2 Asam Hi3

Zion Zion Zion

8.3

-

-

-

28
Table C3. Mean cover, frequency, and density data for soil-vegetation plots at the Zion 

Petrified Forest and Trailside sites. 

3 transects 3 transects 3 transects 2 transects

18 quadrats 17 quadrats 12 quadrats 16 quadrats

Cover 1-m2 freq Cover 1-m2 freq Cover 1-m2 freq Cover 1-m2

 freq

Perennial forbs

Allium nevadense - - 0.4 35.3 0.1 8.3 0.2 18.8

Astragalus ampullarioides 0.1 11.1 1.1 70.6 0.8 50.0 0.4 31.3

Astragalus flavus 0.1 5.6 0.7 41.2 - - - -

Cymopterus purpureus 0.1 11.1 0.1 5.9 - - - -

Zigadenus paniculatus - -0.1 11.8-- -

Annual forbs

Chenopodium sp. - -0.1 11.8-- -

Eriogonum subreniforme - - - - - -0.1 12

Euphorbia spathulata - - - - - -0.1 6

Lactuca serriola* - - - - - -0.3 31

Lappula occidentalis - - - - - -0.1 6

Layia glandulosa 0.1 11.1 - - - - - -

Moluccella laevis* - - - -0.1 8.3 0.7 68

Plantago patagonica 1.0 77.8 - - - - - -

Salvia columbariae - - - - - -0.2 18

Viguiera longifolia - - 0.5 52.9 0.3 33.3 0.9 93.8

Zion_AF8 0.8 83.3 - - - - - -

Perennial grasses

Distichlis spicata - - - -0.1 8.3 --

Elymus elymoides 0.2 16.7 0.2 17.6 0.1 8.3 0.1 6.3

Hilaria jamesii 3.6 88.9 3.5 64.7 0.3 8.3 1.9 50.0

Stipa hymenoides 0.1 11.1 - - 0.1 8.3 - -

Sporobolus airoides 0.7 22.2 - - - - - -

Annual grasses

Bromus rubens* 4.1 100.0 5.6 100.0 4.0 100.0 1.8 100.0

Bromus tectorum* 1.6 44.4 - - - - 0.7 68.8

Bromus, standing dead 4.6 6.9 100.0 14.0 100.0 1.6 56.3

Shrubs / subshrubs

Artemisia tridentata var. wyom. 1.2 33.3 - - - - - -

Atriplex canescens - - - -0.2 8.3 --

Atriplex confertifolia - - - -0.2 8.3 --

Chrysothamnus nauseosus 0.3 16.7 0.5 23.5 1.7 66.7 0.3 25.0

Chrysothamnus viscidiflorus ------ --

Coleogyne ramosissima - - 0.6 23.5 - - 2.6 12.5

Ephedra nevadensis - -0.1 5.9-- --

Gutierrezia microcephala - -0.9 47.1-- -

Gutierrezia sarothrae 1.2 72.2 - - - - - -

Psorothamnus fremontii - -0.1 5.9-- --

Trees

Juniperus osteosperma 4.2 5.6 - - 6.3 25.0 0.8 6.3

Summary, vascular plants

Total live vascular cover 19.3 14.5 14.1 11.0

Total native cover 13.7 8.9 10.0 7.6

Total exotic cover 5.6 5.6 4.1 3.4

Relative native cover 69.3 59.7 47.4 57.0

Relative exotic cover 30.7 40.3 52.6 43.0

Total richness 16 15 13 16

Native richness 14 14 11 12

Exotic richness 2 1 2 4

Soil-surface features

Rabbit Dung (freq only) 88.9 82.4 41.7 81.3

Litter 25.1 100.0 16.2 100.0 27.1 91.7 6.2 93.8

Woody debris 0.4 27.8 - - - - 0.4 43.8

Small Rock (< 20 mm) 0.7 55.6 8.6 100.0 13.0 100.0 4.3 87.5

Large Rock (> 20 mm) 1.6 27.8 0.2 11.8 - - 0.4 12.5

Total Rock 2.3 61.1 8.8 100.0 13.0 100.0 4.6 87.5

Nostoc (vagrant cyanobacteria) - -0.1 5.9-- --

Cyanobacterial crust 0.8 22.2 - - - - - -

Lichen crust 0.1 5.6 - - - - - -

Moss crust 0.1 11.1 0.2 11.8 - - - -

Physical crust 56.9 94.4 65.3 100.0 47.1 100.0 78.8 100.0

Loose, unstable soil 0.6 27.8 1.9 70.6 2.4 41.7 6.0 100.0

Piping (freq only) - 35.3 33.3 25.0

Density by height class Count per m2 Count per m2 Count per m2 Count per m2

Astragalus ampullarioides

0.1-4 cm - - 2 0.1 3 0.3 1 0.1

5-12 cm 2 0.11 25 1.5 16 1.3 5 0.3

>12 cm 1 0.06 4 0.2 - - - -

>12 cm, flowering - - 4 0.2 2 0.2 - -

Total 3 0.17 35 2.1 21 1.8 6 0.4

Moluccella laevis*

0.1-4 cm - - - - 6 0.5 54 4.5

Zion Zion Zion Zion

Petrified Forest Trail North Trail SAVE Trail South

-

-

.5

.3

.3

.3

.8

.8

-

29
Table C4. Mean cover, frequency, and density data for Coral Canyon soil-vegetation plots. 

4 transects 4 transects 2 transects

12 quadrats 12 quadrats 12 quadrats

Cover 1-m2 freq Cover 1-m2 freq Cover 1-m2

 freq

Perennial forbs

Allium nevadense - - 0.1 8.3 0.1 8.3

Astragalus ampullarioides 0.9 91.7 - - 0.2 16.7

Eriogonum inflatum - - - -0.1

Sphaeralcea sp. - - 0.3 8.3 1.1 41.7

Annual forbs

Astragalus sp. - - - - 0.3 25.0

Chenopodium sp. - - 0.1 8.3 0.2 8.3

Erodium cicutarium* 0.8 75.0 0.2 16.7 0.7 66.7

Lappula occidentalis 0.1 8.3----

Lotus humistratus 0.2 16.7 - - - -

Plantago patagonica - - - - 0.5 50.0

Salsola sp.* 0.2 16.7 - - - -

Salvia sp. 0.3 33.3 - - - -

Coral_AF1 0.1 8.3 - - - -

Perennial grasses

Hilaria rigida 0.9 25.0 3.0 41.7 - -

Annual grasses

Bromus rubens* 2.7 100.0 19.0 100.0 11.7 100.0

Bromus tectorum* 0.9 83.3 0.6 50.0 1.0 100.0

Bromus, standing dead 2.1 91.7 10.1 100.0 5.6 100.0

Hordeum sp.* - - - - 0.4 41.7

Shrubs / subshrubs

Gutierrezia microcephala 2.3 83.3 0.6 41.7 0.8 16.7

Lepidium sp. - - 0.5 16.7 - -

Summary, vascular plants

Total live vascular cover 9.3 24.3 16.8

Total native cover 4.8 4.6 3.1

Total exotic cover 4.5 19.8 13.8

Relative native cover 48.6 23.3 20.0

Relative exotic cover 51.4 76.7 80.0

Total richness 11 9 12

Native richness 7 6 8

Exotic richness 4 3 4

Soil-surface features

Rabbit Dung (freq only) 91.7 50.0 75.0

Litter 4.0 100.0 35.8 100.0 17.8 100.0

Woody debris - - - - - -

Gravel (< 75 mm) 4.2 100.0 15.8 100.0 12.2 100.0

Cobbles (75 - 250 mm) 1.5 66.7 5.3 100.0 5.2 100.0

Stones (250 - 600 mm) 0.5 8.3 2.8 25.0 0.6 8.3

Total Rock 6.2 100.0 23.8 100.0 17.9 100.0

Cyanobacterial crust - - - - - -

Lichen crust - - - - 0.1 8.3

Moss crust - - 0.4 41.7 0.2 8.3

Physical crust 83.3 100.0 30.4 91.7 55.0 100.0

Loose, unstable soil 3.1 75.0 0.4 8.3 1.2 41.7

Piping (freq only) 33.3 8.3 41.7

Density by height class Count Per m2 Count Per m2 Count Per m2

Astragalus ampullarioides

0.1-4 cm 15 1.3 - - 6 0.2

5-12 cm 3 0.3 - - 7 0.2

>12 cm -- --1

>12 cm, flowering - - - - 2 0.1

Total 18 1.5 - - 16 0.5

North Middle South

Coral Canyon Coral Canyon Coral Canyon

8.3

0.0

30
Table C5. Mean cover, frequency, and density data for Harrisburg soil-vegetation plots. 

5 transects 4 transects 4 transects

20 quadrats 16 quadrats 16 quadrats

Cover 1-m2 freq Cover 1-m2 freq Cover 1-m2

 freq

Perennial forbs

Allium nevadense 0.7 65.0 - - 0.3 25.0

Astragalus ampullarioides 0.8 65.0 - - 0.1 12.5

Sphaeralcea sp. 0.2 20.0 - - 0.1 6.3

Zigadenus paniculatus - - - -0.1

Annual forbs

Astragalus sp. 0.1 5.0 0.1 6.3 - -

Chenopodium sp. - - 0.1 6.3 0.3 6.

Erodium cicutarium* 0.9 75.0 1.5 100.0 0.8 75.0

Eriogonum subreniforme 0.1 5.0 - - 0.1 6.

Lactuca serriola* - - - -0.1 1

Lotus humistratus 0.1 10.0 - - - -

Malcomia africana* 0.1 10.0 - - - -

Plantago patagonica 0.7 65.0 0.4 37.5 0.9 93.8

Salvia columbariae 0.2 20.0 - - - -

Salvia sp. 0.3 30.0 - - - -

Sisymbrium altissimum* - -0.1 6.3 -

Perennial grasses

Hilaria spp. 0.4 15.0 0.3 25.0 3.2 62.5

Hilaria rigida -----

Harris_PG2 0.1 5.0 - - 0.1 6.3

Annual grasses

Bromus rubens* 3.1 100.0 5.7 100.0 9.0 100.0

Bromus tectorum* 8.0 100.0 19.8 100.0 7.4 100.0

Hordeum sp.* 0.1 10.0 - - - -

Summary, vascular plants

Total live vascular cover 15.6 27.9 22.3

Total native cover 3.5 0.8 5.0

Total exotic cover 12.2 27.1 17.3

Relative native cover 25.6 2.7 23.0

Relative exotic cover 74.4 97.3 77.0

Total richness 16 8 13

Native richness 11 4 9

Exotic richness 5 4 4

Soil-surface features

Cow Dung (freq only) - - -

Rabbit Dung (freq only) 45.0 6.3 87.5

Litter 10.6 95.0 16.8 100.0 12.3 100.0

Woody debris 0.1 5.0 - - - -

Gravel (< 75 mm) 1.7 95.0 13.0 100.0 7.6 100.0

Cobbles (75 - 250 mm) 1.3 30.0 1.8 68.8 9.9 87.5

Stones (250 - 600 mm) 0.8 10.0 1.4 12.5 2.2 18.8

Boulders (> 600 mm) 2.3 5.0 - - - -

Total Rock 5.9 95.0 16.2 100.0 19.7 100.0

Cyanobacterial crust - - - - - -

Lichen crust - - - - - -

Moss crust 0.3 10.0 0.1 6.3 0.6 25.0

Physical crust 77.0 95.0 62.2 100.0 60.9 100.0

Loose, unstable soil 1.3 40.0 0.1 6.3 0.2 18.8

Piping (freq only) 10.0 - -

Density by height class Count Per m2 Count Per m2 Count Per m2

Astragalus ampullarioides

0.1-4 cm 23 1.2 - - 1 0.1

5-12 cm 8 0.4 - - 1 0.1

>12 cm -----

>12 cm, flowering - - - - - -

Total 31 1.6 - - 2 0.1

Harrisburg Harrisburg

Chinle Lower Chinle Upper Gravel Surface

Harrisburg

6.3

3

3

2.5

-

-

-

31
Table C6. Mean cover, frequency, and density data for Pahcoon and Shivwits soil-vegetation plots. 

3 transects 3 transects 2 transects 4 transects

15 quadrats 12 quadrats 16 quadrats 12 quadrats

Cover 1-m2 freq Cover 1-m2 freq Cover 1-m2 freq Cover 1-m2

 freq

Perennial forbs

Astragalus ampullarioides 2.0 80.0 - - 0.1 12.5 0.3 25.0

Chamaesyce albomarginata 0.4 40.0 - - 0.6 43.8 0.2 8.3

Cymopterus purpureus 0.3 26.7 0.4 41.7 - - - -

Sphaeralcea sp. - - 0.3 25.0 0.1 6.3 - -

Annual forbs

Chenopodium sp. - -0.1 8.3----

Erodium cicutarium* 0.1 6.7 - - 0.1 6.3 - -

Eriogonum subreniforme 0.1 13.3 0.1 8.3 0.3 25.0 0.6 58.3

Euphorbia spathulata --------

Helianthus sp. 0.5 46.7 0.9 91.7 - - - -

Lactuca serriola* 0.2 20.0 0.1 8.3 0.1 6.3 - -

Lotus humistratus 1.7 100.0 0.9 91.7 0.1 12.5 - -

Pahcoon_AF2 0.1 6.7 - - - - - -

Perennial grasses

Elymus elymoides - - 0.3 25.0 - - - -

Annual grasses

Bromus rubens* 3.7 100.0 11.7 100.0 6.3 100.0 3.8 100.0

Bromus tectorum* 3.1 100.0 2.2 100.0 3.3 100.0 1.2 100.0

Bromus, standing dead 1.5 86.7 6.3 4.2 93.8 2.8 100.0

Shrubs / subshrubs

Chrysothamnus viscidiflorus - - - -0.1 6.3--

Gutierrezia microcephala - - - - - - 0.6 25.0

Gutierrezia sarothrae 0.5 46.7 1.0 91.7 0.4 12.5 - -

Lepidium fremontii - - - - - - 0.8 16.7

Lycium andersonii 1.0 6.7------

Lycium pallidum 0.1 6.7------

Psorothamnus fremontii - - - - - - 0.2 16.7

Trees

Juniperus osteosperma 0.2 6.7 - - - - 1.7 8.3

Summary, vascular plants

Total live vascular cover 13.9 17.8 11.4 9.2

Total native cover 6.9 3.9 1.7 4.3

Total exotic cover 7.1 13.9 9.7 4.9

Relative native cover 50.6 28.6 16.6 31.0

Relative exotic cover 49.4 71.4 83.4 69.0

Total richness 15 11 11 9

Native richness 11 8 7 7

Exotic richness 4 3 4 2

Soil-surface features

Cow Dung (freq only) - 8.3 - -

Rabbit Dung (freq only) 20.0 41.7 62.5 66.7

Litter 6.6 100.0 19.5 100.0 10.9 100.0 7.0 100.0

Woody debris 0.4 40.0 0.5 33.3 0.4 18.8 0.1 8.3

Gravel (< 75 mm) 10.6 100.0 1.0 100.0 13.4 100.0 1.0 100.0

Cobbles (75 - 250 mm) 0.6 40.0 0.2 8.3 0.6 18.8 - -

Total Rock 11.2 100.0 1.2 100.0 14.1 100.0 1.0 100.0

Cyanobacterial crust - - - - - - - -

Lichen crust - - - - - - - -

Moss crust - - - - - - - -

Physical crust 71.7 100.0 68.8 100.0 47.5 100.0 84.6 100.0

Loose, unstable soil 1.9 33.3 2.2 75.0 21.3 87.5 2.5 83.3

Piping (freq only) 13.3 50.0 6.3 16.7

Density by height class Count Per m2 Count Per m2 Count Per m2 Count Per m2

Astragalus ampullarioides

0.1-4 cm 106 7.1 - - 2 0.1 3 0.3

5-12 cm 125 8.3 - - 7 0.4 - -

>12 cm -- -- - -3

>12 cm, flowering 8 0.5 - - - - - -

Total 239 15.9 - - 9 0.6 6 0.5

Pahcoon Pahcoon Shivwits Shivwits

East West Chinle Moenave

0.3

32
Appendix D – All Soil-Vegetation Plots in Relation to Soil Texture 

Classes 

33
Figure D1. Ordination of 20 soil-vegetation plots in relation to 0-10 cm soil texture classes. In (a), point 

size is scaled by milk-vetch (Asam) frequency. Green points indicate plots in Zion NP; black points 

indicate plots outside the Park. In (b), points sizes are scaled by total cover of exotic brome grasses, with 

the relative proportions of red brome and cheatgrass cover indicated by red and blue segments, 

respectively. 

34