Mapping of Sonoran Desert Vegetation Communities and Spatial Distribution Differences of Larrea Tridentata Seed Density in Relat

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Mapping of Sonoran Desert Vegetation Communities and Spatial Distribution Differences of Larrea Tridentata Seed Density in Relation to Ambrosia Dumosa and Ambrosia Deltoidea, San Cristobal Valley, Arizona

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Authors Shepherd, Ashley Lauren

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/217053 MAPPING OF SONORAN DESERT VEGETATION COMMUNITIES AND SPATIAL DISTRIBUTION DIFFERENCES OF LARREA TRIDENTATA SEED DENSITY IN RELATION TO AMBROSIA DUMOSA AND AMBROSIA DELTOIDEA , SAN CRITSOBAL VALLEY, ARIZONA

Ashley Lauren Shepherd

______

A Thesis Submitted to the Faculty of the

SCHOOL OF NATURAL RESOURCES AND THE ENVIRONMENT

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE WITH A MAJOR NATURAL RESOURCES

In the Graduate College

THE UNIVERSITY OF ARIZONA 2011 2

STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED: Ashley Lauren Shepherd

APPROVAL BY THESIS COMMITTEE

This thesis has been approved on the date shown below:

______2 December 2011 Dr. Jeffrey S. Fehmi Date Assistant Professor of Rangeland Management

ACKNOWLEDGEMENTS

I would like to thank my advisor Dr. Jeff Fehmi for his guidance and support. In addition, thank you to my other committee members, Dr. Mitch McClaran and Dr. Phil Guertin, for their helpful advice, particularly Mitch who acted as my advisor while Jeff was deployed. I would like to thank Mickey Reed and Dr. Craig Wissler for their generous help with GIS questions. I would like to thank Jim Malusa for teaching me the ways of vegetation mapping. I would also like to thank my trusty field assistant, Cameron Warner, who helped with data collection and processing of seed density samples. I will never forget the kit foxes, “lord of the rings” mountains, “get outta there”, and all the random jokes we came up with. Thanks to Doug Whitbeck, Julia Sittig, and Meng Vue who volunteered to help me with data collection on several occasions.

Thank you to all of my family and friends, particularly Eva Levi and Kara Limke. I am forever grateful for you patiently listening to me as I expressed frustrations. Mom you taught me to enjoy and cherish the outdoors when I was younger. My parents who have supported me on every endeavor I have undertaken.

Last but not least, I would like to thank my fiancé John Hall who spent his days off helping me with data collection. Thank you for the continuous support and encouragement you offered me during the course of this project. You kept me grounded and sane during my most stressful moments.

TABLE OF CONTENTS LIST OF FIGURES……………………….…….…………………………...... …...5 LIST OF TABLES…………………………...………..….…………..……………....……7 ABSTRACT……………………………………………..…...………………………..…...8 CHAPTER I: MAPPING VEGETATION COMMUNITIES OF BARRY M. GOLDWATER RANGE, SAN CRISTOBAL VALLEY, ARIZONA…..……………..….9 Abstract…………………………………………………………...….…..……...…9 Introduction……………………………………...…………………...... …….....…9 Methods…………………………………………………………..……...... …..…10 Study Area ……...………………………………………….…….……..…13 Data Collection ……………………………...…………………....…...….12 Mapping ………………………………………………………...…...….…17 Vegetation Association Description……….. ...……. .….….17 Accuracy Assessment………….…………..…...... …...…..17 Results…………………………………………………………..……….….….....18 Vegetation Association Summary ……………………….…….……...... …18 Accuracy Assessment ……………………………………….....…..…...….20 Discussion and Conclusions……………………………..……………..…...... …21 CHAPTER II: SPATIAL DISTRIBUTION DIFFERENCES OF LARREA TRIDENTATA (CREOSOTE BUSH) SEED DENSITY IN RELATION TO AMBROSIA DUMOSA (WHITE BURSAGE), AND AMBROSIA DELTOIDEA (TRIANGLE-LEAF BURSAGE)….……………………………………………………………….……..…….27 Abstract……………………………...………………………………..….…..…...27 Introduction…………………………………………………………...…..…...….27 Methods…………………………………………………………………...…....…31 Study Area ………………………………………...………………….…...31 Data Collection ………………………………….……….………….……32 Data Analysis …………………………………...………….…….….……35 Results…………………………………………………..………….……..………36 Canopy, Site and Species Pair-wise Comparison ……….…….……....….36 Pair-wise Comparison Across All Treatments ………………..…….....…42 Discussion and Conclusions……………………………..………….……..…...…44 APPENDIX A: RELEVÉ COORDINATES……………………………….…….….....…54 APPENDIX B: ASSOCIATION DESCRIPTIONS……………………..…………..……57 APPENDIX C: CONTINGENCY TABLE ……………………………….….…………..86 REFERENCES……………………………………………………..….…...... …..………87

LIST OF FIGURES

Figure 1.1 Map of Barry M. Goldwater Range-East study area which encompasses the San Cristobal Valley and Mohawk Mountains. ………………..…………...... ….....12

Figure 1.2 Distribution of relevés across the Barry M. Goldwater Range-East, San Cristobal Valley. UTM coordinates of all relevés can be found in Appendix A. ……………………..….14

Figure 1.3 Datasheet Example…………………………….……………………………………..15

Figure 1.4 Percentage of vegetation associations of the San Cristobal Valley are in parentheses following association name. Values in front of the bar graph represent the total number of hectares occupied by each association. The total size of the study area is 60,642ha………....…19

Figure 2.1 Map of the three study sites and eight random sampling points. AMDE study site consist of Larrea tridentata -Ambrosia deltoidea . AMDU study sites consist of Larrea tridentata - Ambrosia dumosa . AMBR site consist of Larrea tridentata - both species of Ambrosia .....…….33

Figure 2.2 Larrea tridentata seed density by site type. Average seed density for live, dead and no canopy cover each site type. Different lower letter case letters indicate significant differences within plot combinations based on Wilcoxon rank-sum test ( p< 0.016). Site abbreviations are as follows: AMDU: Larrea tridentata -Ambrosia dumosa , AMDE: Larrea tridentata -Ambrosia deltoidea , and AMBR: Larrea tridentata - both Ambrosia species. Error bars are the standard error of the mean...... ……………………………..37

Figure 2.3 Linear regression to show correlation between Larrea tridentata cover and seed density by site type. Graph A represents seed density at the Larrea tridentata -Ambrosia deltoidea site (AMDE). Graph B represents seed density at the Larrea tridentata -both Ambrosia species site (AMBR). Graph C represents seed density at the Larrea tridentata -Ambrosia dumosa site (AMBR). All graphs include seed density of live, dead, and no canopy Ambrosia . …………………………………………….………………...... …………………38

Figure 2.4 Larrea tridentata seed density by canopy type. Seed numbers were averaged together for all sites to determine live Ambrosia , dead Ambrosia , and no canopy averages. Different lower case letters indicate significant differences within canopy type based on Wilcoxon rank-sum test (p< 0.016). Error bars are the standard error of the mean...... ……………….………….…39

Figure 2.5 Linear regression to show correlation between Larrea tridentata cover and seed density by canopy type. Graph A represents seed density under live Ambrosia plants, seed densities from Ambrosia deltoidea and Ambrosia dumosa . Graph B represents density under dead Ambrosia plants; seed densities from Ambrosia deltoidea and Ambrosia dumosa are included. Graph C represents seed density with no Ambrosia canopy...... ……………40

LIST OF FIGURES – Continued

Figure 2.6 Larrea tridentata seed density by Ambrosia species. Average seed density for both live Ambrosia species across all three sites. Different letters would have indicated significant differences between species based on Kruskal-Wallis test ( p < 0.05). Dead plants were not included because it was difficult to determine if the dead plant was A. deltoidea or A. dumosa at the Larrea tridentata -both Ambrosia species site (AMBR). Error bars are the standard error of the mean...... ………………..……..…….……41

Figure 2.7 Linear regression to show correlation between Larrea tridentata cover and seed density. Graph A includes seed density under live Ambrosia dumosa canopy from Larrea tridentata -both species of Ambrosia (AMBR) and Larrea tridentata -Ambrosia dumosa (AMDU) sites. Graph B includes seed density from Larrea tridentata -both species of Ambrosia (AMBR) and Larrea tridentata -Ambrosia deltoidea (AMDE) sites. Dead plants were not included in either graph because it was difficult to determine if the dead plant was A. deltoidea or A. dumosa at the Larrea tridentata - both Ambrosia species site (AMBR).…...... ……….……..……...…42

Figure 2.8 Larrea tridentata average seed density for all sites: Larrea tridentata -Ambrosia dumosa (AMDU), Larrea tridentata-Ambrosia deltoidea (AMDE), and Larrea tridentata -both Ambrosia species (AMBR) and all canopy cover types (live, dead and no canopy). Different letters indicate significant differences at p<0.0005 after Wilcoxon Rank-Sum. Error bars are the standard error of the mean...... 44

LIST OF TABLES

Table 1.1 Estimating Vegetation Cover Using the Ocular Method……………………....…….16

Table 1.2 Estimating Vegetation Cover Using the Diameter Method…………………….……..16

Table1.3 Producer and Observer accuracy for vegetation associations present in the San Cristobal Valley. The accuracy was not assessed for the Encelia farinosa/Parkinsonia microphylla on rocky slopes greater than 20% association because it was mapped using a Digital Elevation Model (DEM). The associated contingency table can be found in Appendix C...... 20

Table 2.2 Kruskal-Wallis and Wilcoxon rank-sum results for the 10-way comparison. Bolded p- values represent a statistically significant value. For Wilcoxon rank-sum test the relationship between plots was considered significant if p< 0.005; p-value adjusted for multiple comparisons by the Bonferoni correction factor. For the Kruskal-Wallis test, the relationship was considered significant if p< 0.05.……...... ……………...…...43

Table 2.3 Total amount of precipitation (mm) per month in Dateland, Arizona. Highlighted cells represent months with precipitation over 25 mm, the minimum amount of rainfall needed for Larrea tridentata germination. Dashes represent months with no available data (NOAA Satellite and Information Service, 2011). Fewer than half the years with data have sufficient rainfall for germination June – September..…...... …...…49

ABSTRACT

Vegetation in the San Cristobal Valley of Barry M. Goldwater Range-East was mapped using a combination of field surveys and aerial imagery interpretation to contribute to ongoing inventory of natural resources for the BMGR-East as well as assist in resource management decisions. Eighteen vegetation associations were identified and mapped through collection of

186 samples to characterize vegetation associations. The most common vegetation association was Larrea tridentata monotype, covering 29% of the area mapped. Larrea tridentata is a widely spread shrub throughout the Sonoran, Chihuahuan and Mojave deserts; therefore understanding germination and seedling survival patterns is crucial. Ambrosia dumosa and A. deltoidea exhibit nurse plant-protégé interactions with L. tridentata . Seed density of L. tridentata was studied under Ambrosia species to determine factors controlling germination and seedling density. As expected seed density was greater under Ambrosia canopy than areas with no canopy. Ambrosia species and canopy type did not affect seed density.

CHAPTER I: MAPPING VEGETATION COMMUNITIES OF BARRY M. GOLDWATER RANGE, SAN CRISTOBAL VALLEY, ARIZONA

Abstract

Vegetation in the San Cristobal Valley of Barry M. Goldwater Range-East (BMGR) was mapped using a combination of field surveys (relevés) and interpretation of aerial imagery in order to contribute to ongoing mapping efforts of Barry M. Goldwater Range -East. Throughout the San Cristobal Valley, 186 relevé samples were collected to characterize vegetation associations. Eighteen vegetation associations were identified and mapped, including a new

Atriplex polycarapa – Larrea tridentata (Cattle salt bush – Creosote bush) vegetation association.

Accuracy assessment of the map was conducted using a contingency table. The map was 79% accurate.

Introduction

Conservation of natural resources is a major concern for land managers, especially management of endangered species. The Goldwater Range lacks a detailed inventory of resources making resource management less focused on the specific areas that could most benefit from active management (Shupe and Marsh, 2004). This may have been in part due to the fact that little disturbance was a component of the intended use for the range given that its airspace is its main training resource. There is little public access (none is allowed on much of the range) and no livestock grazing is allowed. Disturbance levels have changed in recent years as the enforcement on the urban parts of the international border has pushed the illegal crossing traffic into remote areas such as the Goldwater Range which lies partially along the US-Mexico border.

A common disturbance now is the US Border Patrol patrolling or illegal entrants (Pielielek,

2009). The entrants themselves may also be a significant source of disturbance (Lathrop et al.,

2010) albeit a less immediately visible one.

Mapping resources in arid regions using remotely sensed images is a technique applicable for shrublands and savannas, although the herbaceous component of vegetation communities can be difficult to correctly map (Huttich et al., 2011; Mohamed et al., 2011). This makes developing an initial vegetation map complicated due to the need for ground-based surveys to verify the data from remotely sensed imagery (Smith et al., 1990). The ground-based surveys can use significant portions of the available project resources despite sampling a very small fraction of the mapped area; however, they are nonetheless critical to the mapping success

(Wentz et al., 2006).

Mapping of the Goldwater Range and adjacent areas began in 2003. To date 177,160 acres have been mapped (23% of BMGR). This project consists of adding to the community- level vegetation mapped area along the western most boundary of BMGR-East and ensuring that the vegetation associations and locations are comparable to maps of the surrounding areas of the

Cabeza Prieta Wildlife Refuge, Organ Pipe National Monument, North, South, and East Tactical

Range, Area B, and portions of BMGR-West. Unlike previous mapping efforts by Warren et al.

(1981), Malusa (2003), McLaughlinet al. (2007) and Osmer-Blodgett (2011) a more extensive effort to assess map accuracy was performed through creation of a contingency table based on

125 ground validation points.

Methods

Study Area

The Barry M. Goldwater range was established in 1941 for military training and is used by the United States Air Force and Marine Corps for air-to-air and air-to-ground aircraft

maneuvers, laser testing, and field training exercises (BMGR Fact Sheet, 2009). The range is

split into the East and West areas. The Eastern part is managed by the U. S. Air Force and the

Western part is managed by the U.S. Marine Corps. Covering 768,902 hectares, the Goldwater

Range consists of one of the largest remaining continuous areas of undeveloped Sonoran Des ert.

Annually the range receives three to nine inches of rain (BMGR Fact Sheet, 2009). Depending

on the region of the range summer temperatures can vary from 100°F to 109°Fand winter

temperatures varying from 40°F to 50°F, (Bagne and Finch, 2010; Western Regional Climate

Center,2011). The Barry M. Goldwater Range is in an aridic soil moisture regime and a

hyperthermic soil temperature regime, causing the soils to be primarily Aridisols (Soil Survey

Staff, Natural Resource Conservation Service, 2011). There are also areas classified with less

developed Entisols, as well as a small area classified as Andisols. A wide variety of geological

features occur throughout the range such as: lava cones and flows; alluvial fans and bajadas;

washes formed by ephemeral streams; playas, enclosed areas which receive surface waters from

ephemeral streams; dunes, river terraces and desert pavements (BMGR Fact Sheet, 2009). The

range consists of 23 mountain ranges which are of two physiographic types: sierras and mesas

(BMGR Fact Sheet, 2009). Sierras are more predominant and have jagged and sharply crested

profile. The Mohawk Mountains in the San Cristobal Valley are an example of a sierra-type

mountain. Mesas are blocky and uniform in shape, and relatively flat on top. The Aguila and

Growler Mountains which serve as the eastern boundary of the San Cristobal Valley represent

this type of mountain, but are not included in this study area. The range provides habitat for

diverse flora and fauna, including several endangered and threatened species such as;

Antilocapra americana sonoriensis (Sonoran pronghorn antelope), Glaucidium brasilianum

cactorum (cactus ferruginous pygmy owl), Phrynoso mamcallii (flat-tailed horned lizard), and

Leptonycteris curasoae (lesser long-nosed bat) ( Bagne and Finch, 2010; BMGR Fact Sheet,

2009).

The vegetation map created in this study covered 60,642 hectares of Barry M. Goldwater-

East (BMGR) encompassing San Cristobal Valley and Mohawk Mountains (Figure 1.1). The study area is located in the most western portion of BMGR-East bordering BMGR-West and

Cabeza Prieta National Wildlife Refuge to the south. The study area is bounded by the following

Universal Transverse Mercator (UTM) datum WGS 1984 coordinates: northwest corner

248472E 3625781N, northeast corner 256402E 3628421N, southwest corner 255754E

3589783N, southeast corner 275677E 3589563N.

Figure 1.1 Map of Barry M. Goldwater Range-East study area which encompasses the San Cristobal Valley and Mohawk Mountains.

Data Collection

In order to contribute to ongoing vegetation mapping efforts of BMGR-East and surrounding

areas, vegetation associations in the San Cristobal Valley were mapped using a two-stage method

including ground surveys and analysis of remote sensing data. The ground surveys, critical to

the map validity were designed around the relevé method outlined by the Manual of California

Vegetation (Sawyer and Keeler-Wolf, 1995; Wallace et al. 2000). The relevé method consists of walking through an area thought to be representative of a vegetation association and recording vegetation present. Perennial species, both woody and herbaceous, are recorded until no new species are encountered. Due to the low density of vegetation in the San Cristobal Valley this occurred within a search radius of 100-300 meters from the beginning of the relevé sample. This compares favorably to the estimate of a minimum of 39 meters needed for ground surveys in the

Mojave (Wallace et al. 2000). When sampling a wash the relevé was restricted to the width from bank-top to bank-top. A total of 186 relevés were sampled randomly across the study area

(Figure 1.2). This method was chosen to ensure similar map quality and provide comparable results to BMGR and adjacent areas, as they were mapped using this method (Malusa, 2003;

McLaughlin et.al, 2007; Osmer-Blodgett, 2011). Vegetation association information collected during the relevé sampling can be found in Appendix B.

Figure 1.2 Distribution of relevés across the Barry M. Goldwater Range -East, San Cristobal Valley . UTM coordinates of all relevés can be found in Append ix A.

Additional information was collected at each relevé to characterize vegetation associations (Figure 1.3). Vegetation characteristics of perennial plants (vegetation cover, species prominence, and average height of prominent species) and environmen tal characteristics

(soil surface texture, elevation, geomorphology, slope, and lithology), were recorded.

Vegetation characteristics (vegetation cover, species prominence, and average height of prominent species) collected with the relevés aided with cla ssification of associations. The relevé location and elevation were recorded using Universal Transverse Mercator coordinates with a

Garmin eTrex Legend HCx. Average shrub and herbaceous height were measured to the nearest

10 cm. Trees were measured to the nearest 0.5 m, given that taller trees are more difficult to measure. Slope was measured using a clinometer made out of a protractor, string, and small weight.

Figure 1.3.Datasheet example.

Vegetation cover was visually estimated as percent of ground covered by each species. Cover

was estimated independently from other species. Each species was given a cover code based on

percent cover the species occupied on the ground (Table 1.1). The “diameter method” from

Malusa (2003) was used to asses cover for a subset 40 of relevés. The diameter method

quantifies cover by using the length of the first randomly chosen plant to measure distance to the

nearest plant. This was repeated ten times, the average of the ten diameters was then used to

estimate vegetation cover (Table 1.2). This method was found to be an inadequate estimation of

vegetation cover and was not used in the creation of the vegetation map. (Unpublished studies

and personal communication with J.Fehmi).

Table 1.1.Estimating Vegetation Cover Table 1.2. Estimating Vegetation Cover Using Using the Ocular Method the Diameter Method

Cover Code Percent Cover 1 <1 Average Percent 2 1-4 Diameter Cover

3 5-9 0.75 25 4 10-14 1.2 15 5 15-25 2 9 6 26-40 7 41-60 3 5 8 61-80 8 1 9 81-100 In addition to estimating vegetation cover, species listed at every relevé were prominence ranked as another metric to characterize vegetation associations. Species were given a value from one to five. A dominant species was given a prominence of five. Two co-dominant species were designated with a four. If a dominant species was ranked, no co-dominant species could be present, and vice versa. The remaining species were ranked common (3), uncommon (2), and rare (1). Rare plants were species that were difficult to find, and were usually found only once in the relevé.

Mapping

Vegetation Association Description

Associations were described using the National Vegetation Classification Standard

(NVCS) (United States Geological Survey, 2010). Aerial color photographs with one meter resolution taken in 2003 and acquired through the Advanced Resource Technology Lab

(University of Arizona) were used to map vegetation associations. Geographic Information

Systems (ERSI Arc GIS version 9.2) were used to manually digitize associations using photo interpretation and field notes. Notes drawn on USGS 7.5’ quad sheets, taken while walking or driving and from vantage points were utilized when digitizing boundaries of associations. All associations, with the exception of watercourses less than five-meters wide, were mapped as polygons. The watercourses less than five-meters wide were mapped as polylines. Slopes over

20%were categorized using a Digital Elevation Model, relevés were not taken in these areas because they are defined by slope. The minimum mapping unit for all associations was 0.5 hectares.

Accuracy Assessment

After the vegetation map was completed, an accuracy assessment was conducted to determine the usability of the map. Because the San Cristobal Valley encompasses a large area only a subset of the association polygons were selected to test accuracy. Using the random point generator tool in ArcMap, 125points were created. The sampling points where restricted to within 150 m from roads in order to complete the assessment within the available time. If the vegetation association assigned to that location during mapping was not the correct association, the map was changed to reflect the correct association making the map more accurate than the

contingency table assessment. A contingency table was created using information gathered

during the accuracy assessment and can be found in Appendix C.

Results

Vegetation Association Summary

There were 18 vegetation associations mapped though out the study area (Figure 1.4).

The most prominent associations where Larrea tridentata monotype comprising of 29% of the area mapped and Larrea tridentata-Ambrosia deltoidea with 15%. The remaining portion of the

study area was classified at Larrea tridentata/Ambrosia deltoidea-Krameria with less than 10%

cover of Parkinsonia microphylla-Olneya tesota (12%), Larrea tridentata/Ambrosia deltoidea-

Krameria on pavements with less than 5% cover of Parkinsonia microphylla-Olneya tesota

(10%), Larrea tridentata-Ambrosia dumosa (9%), and Encelia farinosa /Parkinsonia microphylla on rocky slopes greater than20% (6%). The remainder of the study area (19%) is comprised of the last 12 associations, all contributed five percent or less to the total mapped area (Figure 1.4).

A new association was found in the San Cristobal Valley, consisting of dominant or co- dominant of Atriple polycarpa (cattle saltbush).A similar association has been described by

NVCS (United States Geological Survey, 2010), called Atriplex polycarpa Shrubland (Cattle

Saltbush Shrubland). The A. polycarpa association in the San Cristobal Valley did not have all of the species listed as part of the association by National Vegetation Classification Standard, which is characterized as sparse to moderately dense shrub layer dominated or co-dominated by A. polycarpa with shrubs including: L .tridentata , Ambrosia dumosa , Eriogonum fasciculatum

(buckwheat), Hymenoclea salsola (burrobush), Atriplex canescens (fourwing saltbush), Atriplex confertifolia (shadscale), Gutierrezia sarothrae (broom snakeweed), and Suaeda moquinii

(Mojave seablite). Perennial grasses are present to abundant including: Distichlis spicata (salt grass), Pleuraphis mutica (tobosa grass), and Sporobolus spp. Exotic annual grasses dominate

the understory in some stands. From this list the only species present at the study site were: A. polycarpa, L. tridentata , A. dumosa, A. confertifolia, and S. moquinii. Because not all species were present, this association was labeled at a sub-association of the NVCS Atriplex polycarpa

Shrubland. Detailed descriptions of all associations mapped in the San Cristobal Valley can be found in Appendix B.

Figure 1.4.Percentage of vegetation associations of the San Cristobal Valley are in parentheses following association name. Values in front of the bar graph represent the total number of hectares occupied by each association. The total size of the study area is 60,642ha.

Accuracy Assessment

A contingency table, included in Appendix C, was used to assess the map accuracy

because this is the method used by the National Park Service and others to assess vegetation

mapping (Foody, 2002; Lea and Curtis, 2010; Smart and Jones, 2010). User and producer

accuracy was calculated to determine whether errors were due to commission or omission (Table

1.3 and Appendix C) (Foody, 2002; Lea and Curtis, 2010; Smart and Jones, 2010). The

producer’s accuracy refers to the probability that a certain vegetation association on the ground is

classified correctly, while the observer’s accuracy refers to the probability that an area labeled as

a certain association in the map is really this class. For example, one can expect that roughly

74% of all the area classified Larrea tridentata monotype is indeed that on the ground; however,

only 68% was classified as such; therefore, this association was under classified. The Larrea

tridentata/Ambrosia dumosa association was over classified, meaning more area of the

association was originally mapped than there actually was on the ground and had to be corrected

before the map could be considered completed. Under classification of associations occurred

more often that over classification (Table 1.3). The overall accuracy of the map was 79%. This

was determined by dividing the number of correct points by the total number of sampling

locations (Smart and Jones, 2010). This is one percent below the National Park Service

vegetation mapping program standard (Jenkins, 2007).

Table 1.3. Producer and Observer accuracy for vegetation associations present in the San Cristobal Valley. The accuracy was not assessed for the Encelia farinosa/Parkinsonia microphylla on rocky slopes greater than 20% association because it was mapped using a Digital Elevation Model (DEM). The associated contingency table can be found in Appendix C.

Vegetation Producer Observer Code Vegetation Association Accuracy Accuracy 4 Human disturbance 100% 67% 10 Larrea tridentata monotype 74% 68% 11 Larrea tridentata/Ambrosia dumosa 67% 75% 12 Larrea tridentata/Ambrosia deltoidea 69% 73%

13 Larrea tridentata/Ambrosia deltoidea-A. dumosa 75% 82% 14 Larrea tridentata-Opuntia bigelovii/Ambrosia spp. 100% 100% 15 Larrea tridentata/Prosopis velutina-P. glandulosa floodplain 100% 100% 16 Larrea tridentata/Pleuraphis rigida 100% 50% 70 Atriplex polycarpa/Larrea tridentata 71% 100% 82 Prosopis glandulosa playa or barren floodplain 100% 100% Ambrosia dumosa/Pleuraphis rigida/Larrea tridentata on 26 dunes 100% 100% 80 Prosopis spp. woodland 100% 100% 214 Along watercourses with beds less than five-meters wide 100% 100% 81 Along watercourses with beds greater than five-meters wide 100% 100% Ambrosia deltoidea/Parkinsonia microphylla/Opuntia 24 bigelovii 100% 100% Larrea tridentata/Ambrosia deltoidea-Krameria grayi w ith less than 10% cover of Parkinsonia microphylla-Olneya 170 tesota 93% 76% Larrea tridentata/Ambrosia deltoidea-Krameria grayi on pavements with less than 5% cover of Parkinsonia 171 microphylla-Olneya tesota 83% 83%

Discussion and Conclusions

Assessing map accuracy can be a difficult task because it is difficult to isolate a single

source of error (Smart, 2010). Error can be caused by a wrong interpretation of the vegetation

association in the field, mistakes when collecting data, or misclassification during the remote

sensing process (Foody, 2002; Smart and Jones, 2010).A map with an accuracy of 85% of the

upper San Pedro Valley in Arizona was produced using Landsat 7 ETM+ data; however that map

was only classified to the community level and was not as detailed as the map created in this

current study (Sohn and Qi, 2005). Accuracy assessment of a map of Russell Cave National

Monument, Alabama found the map to be 62% accurate; in order to meet NPS standards two oak

forest associations with low user’s accuracy were combined increasing the accuracy to 89%

(Smart and Jones, 2010). Others have reduced vegetation classes in order to increase map

accuracy to the suggested standard, Jenkins (2007) followed this procedure in order to increase

accuracy from 71 to 80 percent. In this current study combining vegetation association with

lower accuracy would not be reasonable because they are all defined by different plant species.

It is important to note that in most cases, accuracy assessment is not done by the map

creator, for example the National Park Service uses a separate team of trained individuals not

involved in map making to assess accuracy in order to eliminate any possible bias. For this

project, it was not possible to have a separate team assess the map due to lack of funding

availability.

Vegetation associations with high accuracy were easy to distinguish on aerial imagery.

Larrea tridentata/Ambrosia deltoidea-Krameria grayi on pavements with less than 5% cover of

Parkinsonia microphylla-Olneya tesota (171) was particularly noticeable due to the desert

varnish (darkening) of rocks associated with desert pavement. Both watercourse associations

(214 and 81) were easy to distinguish due to the Parkinsonia microphylla and Olneya tesota

lining the banks of the washes. Ambrosia dumosa/Pleuraphis rigida/Larrea tridentata on dunes

(26) were often wavy and linear features in valley bottoms which made them apparent from other

associations typically found in valley bottoms, such as Larrea tridentata monotype (10), Larrea tridentata/Ambrosia dumosa (11), Larrea tridentata/Ambrosia deltoidea-A. dumosa (13), and others. Vegetation associations with lower accuracy were difficult to differentiate using aerial imagery. Larrea tridentata/Ambrosia deltoidea-A. dumosa (13), Larrea tridentata monotype

(10), Larrea tridentata/Ambrosia dumosa (11), and Larrea tridentata/Ambrosia deltoidea (12) had no distinguishing features when viewed from aerial imagery, therefore drawing boundaries when mapping was difficult. In order to draw boundaries of these associations, the coordinates of vegetation changes were recorded on USGS 7.5 minute quadrangle maps when driving through the valley bottom. This also accounts for the cluster of relevés in areas where vegetation changes

occurred frequently (Figure 1.2). It would be ideal to take even number of relevés near and far

away from the roads, however due to the size and lack of roads it was more efficient to locate

relevés near roads. In order to make sure areas near roads were not favored; relevés in remote

areas were also located. On days where hiking was required, a smaller area was covered and

fewer relevés were measured. Having a team of four or more people could greatly increase

efficiency of data collection because two teams of two can walk in different directions.

Using relevés for vegetation mapping and to collect information on associations can be a

time consuming process, especially in areas like the San Cristobal Valley, where roads are

almost non-existent. Other land classification, such as unsupervised classification of remotely

sensed imagery, are not applicable in areas with sparse vegetation cover (Huete, 1988; Franklin

et al., 1993; Goodchild, 1994). Large areas of bare ground in conjunction with the small size of

many desert plants cause the spectral reflectance of desert soils to be greater than vegetation

reflectance (Shupe and Marsh, 2004). This makes it not possible to rely only on analysis of

remotely sensed imagery to classify vegetation associations (Huete, 1988; Franklin et al., 1993).

Huete (1988) developed the Soil Adjusted Vegetation Index to correct for this problem; however,

it does not provide information of the composition of species, rather it only provides relative

abundance of vegetation cover. There can be difficulty detecting some desert species,

particularly those with small leaves, leaves with a waxy coating or branches that change position

throughout the day (Gates et al., 1965; Shupe and Marsh 2004). All three of these problems

apply to L. tridentata . The leaves of L. tridentata are small and covered in a resinous substance

(Runyon, 1934). The leaflets also have minor movements during the day, close towards each other at sunset and begin to open around midnight (Runyon, 1934).

There are also limitations to the use of remote sensing alone to create a vegetation map.

In arid environments, maps created through remote sensing typically only consist of broad categories, compared to using of field methods where a more detailed map can be created (Shupe and Marsh 2004). While completing relevés can be a lengthy process, they do provide more information on vegetation characteristics, such as cover, at a certain point on the ground, than maps from computer aided techniques. Smaller or succulent species can also be undetectable, such as Opuntia fulgida (chain-fruit cholla) which has a generally columnar growth form that minimizes its profile in aerial photos (Osmer-Blodgett, 2009).This Opuntia species is utilized by

Antilocapra americana sonoriensis (Sonoran pronghorn antelope)in times of drought, so not being able to map this species accurately will not satisfy the needs of wildlife biologists (de Vos and Miller, 2005). Opuntia bigelovii has a similar vegetative structure as O. fulgida and is a diagnostic species for two associations found in the San Cristobal Valley, Ambrosia dumosa/Parkinsonia microhpylla/Opuntia bigelovii (24) and Larrea tridentata – Opuntia bigelovii/Ambrosia species (14). Because O. fulgida is not detectable with unsupervised classification, it can be assumed that neither is O. bigelovii therefore these associations would be overlooked without the use of field-based methods. This limitation for many species may be resolved at some point in the future, possibly through the use of imaging spectrometers and/or

LiDAR imagers (Ustin and Gamon, 2010).

Recent increased activity of Border Patrol agents impacts vegetation and soils in the San

Cristobal Valley through creation of new roads and disturbing soil crusts. Creating additional roads destroys vegetation, which can be harmful in areas of high diversity, particularly in upper mountain bajadas and sand dunes. Desert pavement is prominent in the upper bajada of mountain gradient in the northern Mohawk Mountains and is easily disturbed by vehicles. While the

25 genesis of these pavements is unclear, pavements in other deserts of the Southwest were most likely formed at the end of the Pleistocene to the beginning of the Holocene (McFadden et al.,

1998; Wood et al., 2002; Adelsberger and Smith, 2009). If the Border Patrol continues its road proliferation, desert pavement will be disturbed and could cease to exist, because pavements are fragile and potentially take thousands of years to form. It seems important to minimize future disturbance in these areas. These pavements are readily detected with, and could be monitored through, aerial imagery (Metternicht et al., 2010).

In the lower San Cristobal Valley, cryptobiotic soil crusts are a commonly found across the landscape. These crusts play important part in ecosystem functions as they can increase rainfall capture, facilitate infiltration, improve soil fertility, and provide micro-sites for seed establishment (Belnap, 2006; Bainbridge, 2007). Like desert pavement, soil crusts are extremely fragile and are disturbed by vehicles and foot traffic. Similar to the desert pavements, these crusts can be detected and monitored through aerial imagery (Ustin et al., 2009).

The overall concern about road proliferation can also be readily tested using remote sensing data as shown by Gruen and Li (1995). Others (Cao et al., 2007; Lathrop et al., 2010), have used similar method to document foot traffic although it requires high resolution imagery.

The BMGR should strongly consider these investigations to document the apparent change in conditions. This remote sensing approach could be paired with on-the-ground observations to document the main uses of the new roads and trails. The future of vegetation diversity and soil erosion in the San Cristobal Valley is dependent on the reduction of road proliferation. Roads should be limited near upper bajadas and in the valley bottoms to protect these fragile areas.

The final product consists of a vegetation map of the San Cristobal Valley and Mohawk

Mountains, organized data sheets and photographs, and a Microsoft Access database. Each

relevé data sheet was scanned and organized with photo into folders based on which USGS 7.5

minute quadrangle where the relevé was located. This allows resource managers to maximize the

use of the photos and data sheets when needed. If resource managers are unfamiliar with

vegetation associations the photographs could be printed and taken into the field to aid in

determining which association is found in their area of interest. Organizing and making copies

onto a disk also minimizes the chance of products being lost. The Access database summarized

all the metrics measured in the field that were recorded on the datasheet; UTM coordinates,

photograph number, cover, prominence, and average height. The database created by this project

can be merged with databases previously created by mapping efforts on Barry M. Goldwater

Range to create one large database that can be easily accessed by resource managers. This

Microsoft Access allows multiple users to create tables and connect them together; later these

tables can be used to create queries and reports with the data. Having one database containing the

data collected throughout the range by multiple people allows resource managers to easily and

quickly access the data as needed instead of having to manually go through each scanned

datasheet.

In the future, research should be conducted to find a better way to distinguish

associations that have accuracy issues, such as Larrea tridentata monotype in order to reduce error and decrease time spent correcting errors made during mapping. The mapping effort of this project was an overall success and can be used to better focus resource management going forward.

CHAPTER II: SPATIAL DISTRIBUTION DIFFERENCES OF LARREA TRIDENTATA (CREOSOTE BUSH) SEED DENSITY IN RELATION TO AMBROSIA DUMOSA (WHITE BURSAGE), AND AMBROSIA DELTOIDEA (TRIANGLE-LEAF BURSAGE)

Abstract

Larrea tridentata (creosote bush) is a long-lived desert shrub that is widespread throughout the southwest and it used as habitat for many different types of wildlife; therefore understanding the germination and seedling survival patterns is crucial. Ambrosia dumosa and

A. deltoidea are known to exhibit nurse plant-protégé interactions with L. tridentata . Seed density of L. tridentata was studied under both Ambrosia species in order to determine the role of seed distribution in the nurse plant-protégé relationship. Analysis of seed density using

Kruskal-Wallis and Wilcoxon rank-sum was used to determine density was greater under both

Ambrosia species compared to areas with no canopy. Canopy type, live or dead, did not affect the seed density. An absence of L. tridentata seedlings and young plants in the San Cristobal

Valley was observed which could be due to specific germination requirements, soil crusting, and seed/seedling predation, but not the absence of seed.

Introduction

Larrea tridentata (creosote bush) is one of the most widely dispersed plants in desert regions in North America; its distribution encompasses the Sonoran, Mojave and Chihuahuan deserts (Chew and Chew, 1965; Barbour, 1969). It is a long-lived drought-tolerant shrub and is known for the ability to survive high temperatures and low atmospheric humidity (Runyon,

1934; McAuliffe et al., 2007). It is unique in that its leaves are persistent even through dry seasons; however the foliage density and color do change during drought. A resinous substance

prevents the leaves from going completely dormant and the plant can resume growing as soon as

favorable conditions return (Runyon, 1934). L. tridentata is an important plant for many species

of wildlife which use canopy cover to avoid high daytime temperatures in the summer, avoid

predators, or use it for a den. Two species of kangaroo rats, Dipdomys spectabilis (banner-tail kangaroo rat) and D. merriami (Merriam’s kangaroo rat), use L. tridentata for protective cover and a place to make dens (Monson and Kessler,1940). Baxter (1988) found 71% of Gopherus agassizii (desert tortoise) burrows were associated with L. tridentata in San Bernardino,

California.

Occurring with L. tridentata, Ambrosia dumosa (white bursage) and Ambrosia deltoidea

(triangle-leaf bursage) are common drought-deciduous species throughout southern Arizona. The distribution of A. dumosa is larger than that of A. deltoidea , with A. dumosa occurring in the

Mojave and Sonoran Deserts and A. deltoidea only in the Sonoran Desert (Fonteyn and Mahall,

1981; Stubbendieck et al., 2003; USDA, NRCS 2009). A. dumosa grows in arroyos, bajadas, valley bottoms and gentle slopes up to 3,000 feet. A. deltoidea is common on the area between upper and lower bajadas and also on steep gravelly slopes to the same elevation as A. dumosa

(Epple, 1995).Both species have a similar vegetation structure, with a hemispherical crown and a low lying canopy. A. dumosa is more palatable than A. deltoidea making it more important forage for herbivores (Stubbendieck et al., 2003). A. dumosa and A. deltoidea are of interest because of their ability to colonize open and disturbed areas before other species (Vasek, 1979;

Prose et al., 1987; McAullife, 1988). This colonizing capability allows Ambrosia to play a role as a nurse plant.

Several species of Ambrosia have been found to act as nurse plants in arid ecosystems. In

Sonora, Mexico, McAuliffe (1988) determined A. dumosa has positive relationships with

Bursera microphllya (elephant tree), Cercidium microphylla (little leaf palo verde), and two

Jatropha species. A similar relationship was seen in Baja California, Mexico between A. magdelenae and Fouquieria columaris (boojum tree) (McAuliffe, 1988; Callaway, 1995).

Canopy cover provided by A. deltoidea had a positive association with seedlings of shrubs, trees and succulents (McAuliffe, 1988).

Nurse plants can ameliorate harsh climatic conditions, such as low precipitation and high temperatures common to southwestern Arizona and other arid environments, and provide a more suitable microhabitat for germination and seedling recruitment as well as increasing available nutrients. In arid and semi-arid environments, high temperatures can be fatal for young seedlings

(Turner et al., 1966). Nurse plants offer a much needed shade source, leading to a positive association between seedlings and adult shrubs and trees. In addition to the shade it provides, the canopy cover also makes water more available to seedlings through water catchment and reduced evaporation (Turner et al., 1966). Water catchment occurs through channeling of water to the inner of the base of shrubs and trees (Pressland, 1976; Mauchamp and Janeau, 1993; Martinez-

Meza and Whitford, 1996). The shade also allows moisture to remain in the soil longer under canopy cover than open areas where water quickly evaporates due to higher temperatures, especially in warm, dry years (Shreve, 1931; Kitzberger et al., 2000). More nutrients are available beneath nurse plants due to accumulation of litter, increased animal droppings, and vertical and horizontal root uptake causing “fertile islands” within the soil profile (Garner and

Steinberger, 1989; Flores and Jurado, 2003). Additional nutrients may make germination and establishment greater under nurse plants as opposed to open areas which generally lack nutrients.

Episodic recruitment is a common phenomenon in arid and semi-arid regions because conditions for germination and survival are not favorable every year; therefore recruitment in

nature can be low (Shreve, 1917).In order for establishment to occur, a minimum amount of

rainfall is required for germination of seeds; L. tridentata seeds need at least 25 mm of rainfall

per storm in order for germination to occur (Ackerman, 1979). Mortality of desert perennial

seedlings often occurs in dry months following monsoon when there is no rainfall to support

growth (Shreve, 1931). Ackerman (1979) counted only five L. tridentata seedlings in 1971 with

no seedlings surviving the first year. Through the remainder of the four-year study, no seedlings

were found, compared to other species which had seedlings present every year or two out of four

years, but with limited survival similar to L. tridentata (Ackerman, 1979).Over a ten-year period,

only sixteen new L. tridentata established in the Mojave Desert (Beatley, 1974).

Despite the association of L. tridentata with nurse plants and the improved conditions

found there, a simpler explanation would be that these other species have a positive association

with Larrea seed distribution. There may just be more seeds associated with A. dumosa and A.

deltoidea and the distribution could be based on propagule pressure rather than environmental

differences. To answer questions about the role seed dispersal plays in the spatial distribution of

Larrea tridentata in the San Cristobal Valley, the density of L. tridentata seed under Ambrosia

canopy, and open areas were determined. The objectives of this project were to determine: 1) if

Ambrosia species are seed catchments for L. tridentata, 2) if there is a relationship between L.

tridentata seed abundance and cover of Ambrosia , and 3) if there is a difference between seed density underneath A. dumosa and A. deltoidea . If more seed is located under Ambrosia than the proportion of seedlings, then germination may be a limiting factor to the distribution of L

.tridentata . If more plants than seeds are found under Ambrosia, then the seed distribution may be a limiting factor to the distribution of L. tridentata . If the same proportion of seed and

seedlings are in the open and under Ambrosia, it can be assumed that dispersal and germination

contribute equally to the nurse-protégé relationship.

Methods

Study Area

Study sites were located in the San Cristobal Valley of Barry M. Goldwater Range,

approximately 22 kilometers southwest of Dateland, Arizona (latitude and longitude coordinates

: 32.79’529E, -113.539962W). The Barry M. Goldwater range was established in 1941 for

military training; because public access is limited, the San Cristobal Valley provides an almost

undisturbed area to study Sonoran Desert vegetation. Study sites were chosen based on the

specific composition of plants present. At each site Larrea tridentata was present, with Ambrosia

deltoidea , Ambrosia dumosa , Ferocactus wislizenii , Pleuraphis rigida at some of the sites. The

nearest rain gauge with available long-term data is in Dateland, which receives annual 10.31 mm

of rain in a year (NOAA Satellite and Information Service, 2011). Temperature can range from

an average high of 107°F in the summer to a low of 68.5°F in the winter(Table 2.1).The three

study sites chosen were all located on Mohall-Pahaka-Valencia complex 0-3% slope (Soil

Survey Staff, Natural Resource Conservation Service, 2011). This soil type is characterized as a

mixed alluvium fan fine sandy loam with 30% calcium carbonate and slightly to moderately

saline.

Table 2.1 Monthly average climate for the Dateland, Arizona (the nearest rain gauge with available long term data). Averages include data 1972 to 2010. (NOAA Satellite and Information Service, 2011). No De Jan Feb Mar Apr May Jun Jul Aug Sep Oct v c Average Max Temp.(F) 69 73 78 86 94 104 107 105 100 89 77 68 Average Min. Temp.(F) 39 42 44 49 56 64 72 73 66 55 44 38 Average Precipitation(mm) 16 15 13 4 1 0 11 18 13 9 11 16

Past land use of this area included military training. This training included gunnery practice on towed targets and air-to-air combat maneuvers but no ground-based training.

Targets, expended bullets, and unexploded ordinance are commonly found in this area, but do not presently pose a significant threat to vegetation or wildlife because these objects appear to cause little or no environmental degradation. Towed targets are no longer used, only gunnery practice with lasers and periodic field training exercises occur. While a small northern section of the San Cristobal Valley is degraded due to field training exercises with large military equipment, the area chosen for study sites is not degraded and has little history of anthropogenic disturbance. Activity from border patrol and illegal immigrants has increased during the past several years but has not directly impacted the sites selected for study.

Data Collection

In order to determine if seed density of L. tridentata differs under two species of

Ambrosia , sites containing one of the three combinations of plants: L .tridentata -A. dumosa

(AMDU), L. tridentata-A. deltoidea ( AMDE), and L. tridentata -both Ambrosia species (AMBR), were determined using a vegetation map. Within each of these combinations, eight hectare study areas were established. Eight locations within each site for sampling seed density were chosen by random point generator in ArcMap within the study areas (Figure 2.1).

Figure 2.1 Map of the three study sites and eight random sampling points. AMDE study site consist of Larrea tridentata -Ambrosia deltoidea . AMDU study sites consist of Larrea tridentata -Ambrosia dumosa . AMBR site consist of Larrea tridentata - both species of Ambrosia .

At the center of each sampling location, a 100-m2 circular plot was established using the

methods of McAuliffe (1988) to allow for comparison with data previously collected

approximately 21km from the study sties. In addition, a circular plot was used rather than over a

linear transect because the low amount of vegetation cover in San Cristobal Valley makes

searching for plants in a designated area more efficient than walking the length of transect

needed to capture sufficient plants.

Seed-bank distribution was determined generally following the methods used by Hutto et

al. (1986) to examine Carnegiea gigantea seed density under Parkinsonia floridum . They

collected samples in an equidistant circle from the bole of the tree at mid-canopy, at the edge of

the canopy, and in the open. The methods used here included one soil sample under the canopy

of every Ambrosia, on average there were seven plants within each circular plot (live and dead combined). It was also documented if the Ambrosia plant was live or dead to allow testing if canopy type affected the seed bank. No sample was taken at mid-canopy due to the small canopy size of Ambrosia . Ten samples were also taken in the open, at least two meters away from any plant, live or dead. Samples were collected usinga 10-cm diameter circular soil core to a depth of 2 cm. Samples were sorted using a 2-mm soil sieve. To ensure that only potentially viable L

.tridentata seeds were counted seeds that could easily be broken with finger pressure or with only seed fur left were discarded.

L. tridentata cover was measured for each plant in every 100 m 2 circular plot by taking the length and width of each plant located in the plot. These measurements were used with the equation of an ellipse (A= ((L/2 +W/2)* π) to determine the total area covered by L .tridentata in the 100-m2 plot. Every plot was located on valley bottom geomorphology with a fine sand soil

35 surface texture. All plots had 0% slope and had not been disturbed by vehicles. This was noted to make sure that geomorphology and surface texture were not variables affecting seed density.

Plots disturbed by vehicles were not included in the study because tire tracks could disturb canopy cover if plants had been damaged.

Data Analysis

The study was designed to use Analysis of Variance (ANOVA) as the statistical test to determine differences in seed density between the species of Ambrosia , site type (AMDU,

AMDE, AMBR), and canopy type (dead, live, no canopy). Before the ANOVA was run, the

Shapiro-Wilk test was conducted to verify the data set met the assumptions of the ANOVA. The

Shapiro-Wilk test revealed data was not normally distributed ( p < 0.05) and, despite increasingly sophisticated attempts to find an appropriate transformation, the data could not be made to meet the assumptions for ANOVA. The Kruskal-Wallis test was selected as the appropriate test because it is similar to one-way ANOVA but makes fewer assumptions about the underlying distribution of the data (Zar, 1974). The Kruskal-Wallis equality of population rank test was used to look for significant differences between the independent variable (seed density) and dependent variables (plot type, canopy cover, and species). If the Kruskal-Wallis test confirmed a significant difference between the independent and dependent variables, further testing with

Wilcoxon Rank-Sum test determined which sites and canopy type variables differed. Using

Wilcoxon rank-sum test, the relationship between sites was considered significant if p< 0.016, the p-value adjusted for multiple comparisons by the Bonferoni correction factor (Zar, 1974).

Linear regression was used to determine if L. tridentata cover could explain the variation of seed density between the species of Ambrosia , site type (AMDU, AMDE, AMBR), and

36 canopy type (dead, live, no canopy). The proportion of the total variability in seed density explained was estimated through the coefficient of determination (R 2) after regressing L. tridentata cover and seed density under every Ambrosia plant within the circular plot. A 10-way pair-wise comparison of L. tridentata seed density at all sites and canopy types was conducted using the Wilcoxon Rank-Sum test. The relationship between the variables considered significant if p< 0.005 with the p-value adjusted for multiple comparisons by the Bonferoni correction factor. All tests were conducted using the statistical program Stata (Version 11,StataCorp LP,

Texas).

Results

Canopy, site and species pair-wise comparison

The seed density was significantly different ( p = 0.0009) among the three sites AMDU

(L. tridentata -A. dumosa ), AMDE ( L. tridentata -A. deltoidea ), AMBR ( L. tridentata - both

Ambrosia species) (Figure 2.2). The AMBR site differed from AMDE site (p = 0.0002), with

AMBR having a higher seed average of 0.0233 seeds/cm 3 than AMDE with0.00468 seeds/cm 3 but did not differ from AMDU plots ( p = 0.0605). There was no significant difference between seed density at AMDE and AMDU plots ( p= 0.0218), with the seed density increasing only to

0.0095 seeds/cm 3. Moderate correlation (R 2 = 0.51) was found at the AMDU site as approximately half, 51%, of the variability among the observed values can be explained by the linear relationship between L. tridentata cover and average seed density (Figure 2.3C). There was little evidence of correlation (R 2 = 0.018 and R 2 = 0.039) between L. tridentata cover and seed density at AMDE and AMBR sites (Figures 2.3 A and B).

Seed Density by Site Type

0.035 b 0.03

0.025

0.02

0.015 ab 0.01 a 0.005 AverageSeed Density (Seeds/cm3) 0 AMDE AMBR AMDU

Figure 2.2. Larrea tridentata seed density by site type. Average seed density for live, dead and no canopy cover each site type. Different lower letter case letters indicate significant differences within plot combinations based on Wilcoxon rank-sum test ( p< 0.016). Site abbreviations are as follows: AMDU: Larrea tridentata -Ambrosia dumosa , AMDE: Larrea tridentata -Ambrosia deltoidea , and AMBR: Larrea tridentata - both Ambrosia species. Error bars are the standard error of the mean.

Figure 2.3.Linear regression to show correlation between Larrea tridentata cover and seed density by site type. Graph A represents seed density at the Larrea tridentata -Ambrosia deltoidea site (AMDE). Graph B represents seed density at the Larrea tridentata -both Ambrosia species site (AMBR). Graph C represents seed density at the Larrea tridentata -Ambrosia dumosa site (AMBR). All graphs include seed density of live, dead, and no canopy Ambrosia .

Canopy cover (dead, live, and no canopy) had a significant effect on seed density ( p =

0.0004) (Figure 2.4). There were no significant differences between canopy provided by dead or live plants ( p = 0.4207). The seed density for dead and live canopy only differed by 0.0016 seeds/cm 3.However, seed density was significantly different between both dead and live plants and samples taken without canopy cover ( p = 0.0037 and p = 0.0002, respectively). L. tridentata cover did not explain the distribution of seed under dead plants (R 2 =0.002), live plants (R 2 =0.052), or no canopy (R 2<0.0001) (Figure 2.5).

Seed Density by Canopy Type

0.035 0.03 0.025 a a 0.02 0.015 0.01 b 0.005 AverageSeed Density (Seeds/cm3) -6.94E-170 Live Dead No Canopy

Figure 2.4. Larrea tridentata seed density by canopy type. Seed numbers were averaged together for all sites to determine live Ambrosia , dead Ambrosia , and no canopy averages. Different lower case letters indicate significant differences within canopy type based on Wilcoxon rank-sum test ( p< 0.016). Error bars are the standard error of the mean.

Figure 2.5.Linear regression to show correlation between Larrea tridentata cover and seed density by canopy type. Graph A represents seed density under live Ambrosia plants, seed densities from Ambrosia deltoidea and Ambrosia dumosa . Graph B represents density under dead Ambrosia plants; seed densities from Ambrosia deltoidea and Ambrosia dumosa are included. Graph C represents seed density with no Ambrosia canopy.

There was no significant difference in seed density under A. deltoidea and A. dumosa (p

> 0.05) (Figure 2.6) as there was only a 0.003 seeds/cm 3difference in the seed density beneath the two species. There was similarly no significant correlation between seed density under either species of Ambrosi a (Figure 2.7). Dead plants were not included in the linear regression because it was difficult to determine if the dead plant was A. deltoidea or A. dumosa at the L. tridentata -both Ambrosia species site (AMBR).

Seed Density by Ambrosia Species

0.04 a 0.035 0.03 0.025 a 0.02 0.015 0.01 0.005 AverageSeed Density (Seeds/cm3) 0 A. dumosa A. deltoidea

Figure 2.6.Larrea tridentata seed density by Ambrosia species. Average seed density for both live Ambrosia species across all three sites. Different letters would have indicated significant differences between species based on Kruskal-Wallis test ( p < 0.05). Dead plants were not included because it was difficult to determine if the dead plant was A. deltoidea or A. dumosa at the Larrea tridentata -both Ambrosia species site (AMBR). Error bars are the standard error of the mean.

Figure 2.7.Linear regression to show correlation between Larrea tridentata cover and seed density. Graph A includes seed density under live Ambrosia dumosa canopy from Larrea tridentata -both species of Ambrosia (AMBR) and Larrea tridentata -Ambrosia dumosa (AMDU) sites. Graph B includes seed density from Larrea tridentata -both species of Ambrosia (AMBR) and Larrea tridentata -Ambrosia deltoidea (AMDE) sites. Dead plants were not included in either graph because it was difficult to determine if the dead plant was A. deltoidea or A. dumosa at the Larrea tridentata - both Ambrosia species site (AMBR).

Pair-wise comparison across all treatments

The seed density under live A. deltoidea at the AMBR site was significantly different from seed density in open areas at AMDE and AMDU sites ( p= 0.0006 and 0.0044, respectively;

Figure 2.8 and Table 2.2). The average seed density at AMDE and AMDE had a 0.02 seeds/cm 3 decrease compared to the live A. deltoidea at the AMBR site with density of 0.027 seeds/cm 3.

Live A. dumosa at the AMBR site was significantly different from AMDE live, AMDE open and

AMDU open ( p = 0.0046, 0.0006, and 0.0033, respectively) (Figure 2.13 and Table 2.2). The

average seed density of0.044 cm 3for live A. dumosa had an 0.04 seeds/cm 3 increase compared to

the three other significantly different sites. At the AMDU site, average seed density under live

plants increased by 0.02 seeds/cm 3 compared to AMDE no canopy with an average density of

0.0015 seeds/cm 3 (p= 0.0041; Figure 2.8 and Table 2.2). Seed density under no canopy cover at

the AMDE site was significantly different from no canopy areas at both AMBR and AMDU sites

(p= 0.0016 and 0.0013, respectively; Figure 2.8 and Table 2.2). The average seed density under

no canopy at the AMDE site was 0.0015 seeds/cm 3, which decreased to 0.008 seeds/cm 3 at the

AMBR site and increased to 0.0048 seeds/cm 3 at the AMDU site.

Table 2.2. Kruskal-Wallis and Wilcoxon rank-sum results for the 10-way comparison. Bolded p-values represent a statistically significant value. For Wilcoxon rank-sum test the relationship between plots was considered significant if p< 0.005; p-value adjusted for multiple comparisons by the Bonferoni correction factor. For the Kruskal-Wallis test, the relationship was considered significant if p< 0.05.

Figure 2.8.Larrea tridentata average seed density for all sites: Larrea tridentata -Ambrosia dumosa (AMDU), Larrea tridentata-Ambrosia deltoidea (AMDE), and Larrea tridentata -both Ambrosia species (AMBR) and all canopy cover types (live, dead and no canopy). Different letters indicate significant differences at p<0.0005 after Wilcoxon Rank- Sum. Error bars are the standard error of the mean.

Unusual differences were found in the amount of seed between sites. Seed density differed significantly between L. tridentata -A. deltoidea (AMDE) and L. tridentata -A. dumosa

(AMDU) sites, but both sites were similar to the L. tridentata -both Ambrosia species (AMBR) site.

Discussion and Conclusions

The 10-way pair wise comparison using Wilcoxon Rank-Sum yielded different results from the previously discussed comparisons. The differences found between L. tridentata-A.

dumosa (AMDU) and L. tridentata –A .deltoidea (AMDE) and other canopy and site types. L.

tridentata-A. dumosa (AMDU) was significantly different from five other canopy and site types

(live A. deltoidea and A. dumosa at AMBR, live AMDU, open AMDU, and open AMBR). L.

tridentata-A. dumosa (AMDU) site was significantly different from live A. deltoidea AMBR, live A. dumosa AMBR, and open AMDE. The other difference occurred between live A. deltoidea at AMBR site and live A. dumosa at the AMBR site. There were no differences found within any of the sites. These differences must be caused by these two site and canopy combinations having the lowest average seed density, with AMDE open having 0.0015 seeds/cm 3 and AMDU 0.0049 seeds/cm 3.

If one of the sites had more L. tridentata cover than another, this could explain the difference in seed density. Therefore, if there is more Larrea cover, there will be more seed.

Results from the Wilcoxon Rank-Sum testshow L. tridentata cover is not different among the sites. Linear regression only showed correlation between L. tridentata cover and seed density at the L. tridentata-A. dumosa (AMDU) site. At this site approximately half of the variability in seed density can be explained by the L. tridentata canopy cover. At the other sites there was no correlation between seed density and cover, even when L. tridentata cover was higher, seed density remained the same as when L. tridentata cover was low.This suggests seed under

Ambrosia canopy came from plants far outside of the plots, which contradicts a study by

Chambers and MacMahon (1994), which determined most desert species do not have characteristics promoting long range dispersal. An alternate explanation is that there is a storage capacity under shrubs, regardless of input only so much seed can be stored under shrubs.

Previous studies have found varying seed densities can occur under different shrubs and canopy types. Nelson and Chew (1977) reported different average seed densities under Lycium

and L. tridentata canopy cover between two different sites, with one site having a higher density

than another. Yet, these differences did not occur for every species in which seed was counted

and only occurred for four of the 11 seed categories. A cause for the dissimilarity in average seed

density was not discussed by Nelson and Chew (1977), though differences in the seed densities

could be due to a higher density of rodents in one of the plots compared to the other causing

higher seed predation lowering the density at one of the sites. Wind shadows can also cause

differences in seed density between sites. In Tucson, Arizona, Reichman (1984) determined

higher seed densities were associated with areas where wind shadows occurred, dropping seeds

into an area where they do not move again. If one site had a greater chance at catching

windblown seed, this would cause an increase in seed density; possibly explaining why the

average seed density at the L. tridentata - both Ambrosia species site was 0.023 seeds/cm 3, which

was higher than the L. tridentata - A. dumosa, 0.009 seeds/cm 3 and L. tridentata - A. deltoidea ,

0.004 seeds/cm 3 (Figure 2.13), however there was no visible difference between wind shadow among the sites. The same study by Reichman (1984) revealed seed spatial distribution was more heterogeneous when density was high, while in years with lower seed density, differences under canopy and open areas could be seen, but those differences disappeared once density increased.

This could also explain the lack of differences between density under canopy and open area one would expect to see in my study in the 10-way pair wise comparison; however multiple years of seed collection in the San Cristobal Valley would be needed to determine if this is in fact the driving force.

It has been often found that spatial variation in seed distribution exists and that seed density is typically the highest under plant canopies and lowest in open areas. In Patagonia,

Argentina, a greater density of L. tridentata seed was found under perennial grasses, Atriplex

lamapa (South American saltbush), and annual grasses compared to no canopy (Busso and

Bonvissuto, 2009). Caballero et al. (2008) reported similar results for the seed density of seven

different shrub species in Central Spain. This is consistent with the findings of Reichman

(1984)in Tucson, Arizona, with canopy cover and depressions in the ground collecting more

seeds than open areas. With these and many other examples of a patchy seed distribution, it was

not surprising that San Cristobal Valley would have comparable results.

Higher L. tridentata seed density occurs under Ambrosia presumably due to seed trapping by the canopy. While collecting soil samples, seed was only visually observed in open areas when it was caught in plant litter of dead annuals, specifically Plantago purshii (Pursh Plantain) which accounts for seeds still present in open areas, but at a lower density. Wind and low amounts of vegetation cover explain how seed in San Cristobal Valley are able to move longer distances in plant interspaces and become trapped beneath Ambrosia . Seed density under A. dumosa and A. deltoidea was not significantly different across all sites; this can be attributed to similar canopy structure provided by both species.

An original intent of this project was to study L. tridentata seedlings under Ambrosia species, following the methods of McAuliffe (1988). In Dateland, approximately 20 kilometers from the studies sites chosen for this project, A.dumosa only accounted for 5.9 percent of ground cover, yet 45% of young L. tridentata were found under the canopy. Similar results were also found in San Luis, Arizona 150 km from the San Cristobal Valley. The original plan was to add a seed bank analysis to determine if seed density could explain why the number of seedlings was greater under Ambrosia rather than nurse plant effects. However, in the San Cristobal Valley no

L. tridentata s eedlings were found under Ambrosia canopy or in open areas. This could be

considered unusual due to the considerable amount of literature on nurse- protégé interactions

commonly occurring in arid and semi-arid environments (Flores and Juardo, 2003). In Saguaro

National Monument outside of Tucson, Arizona, A. deltoidea was found to have positive associations with many desert species along a bajada gradient; including L. tridentata ,

Fouquieria splendens ( ocotillo) , Jathropha acadiophylla (limberbush) , Opuntia species as well as

other shrubs, trees and succulents (McAuliffe, 1988). Carnegiea gigantea (saguaro) are found

growing underneath the canopy of Olneya tesota (ironwood), A. deltoidea, L. tridentata , and

Lycium andersonii (wolfberry) than areas with no canopy cover (Hutto et al., 1986). Given seed

accumulation was greater under live and dead Ambrosia canopy; one would expect seedlings to

be present. There are many contributing factors that could be preventing seedling presence: lack

of precipitation, soil crusting, or seedling predation.

Germination of L. tridentata can be directly related to precipitation (Beatley, 1974;

Ackerman, 1979; Busso and Bonvissuto, 2009). In the Mojave desert, 80-150 mm of rainfall

results in 20-60% germination, with germination dropping below 20% if precipitation ranges

from 50-80 mm (Beatley,1974).A25mm minimum germination requirement for seedlings was

reported by Ackerman (1979). A 1971 rainfall event of approximately 25-29mm yielded five

seedlings (Ackerman, 1979). The following year 17mm and 21mm of precipitation was received

in the same area with no germination (Ackerman, 1979). The duration of rainfall events does not

seem to play a role in the germination of seedlings based on Barbour (1968). Current season

rainfall contributes to the success of reproduction each year, especially rain occurring in summer

months, specifically mid-June to September (Beatley, 1974; Ackerman, 1979). While no

literature was found on the effects of rainfall intensity on L. tridentata , amount of rainfall

received in 1983-1984could explain the differences seen in seedling emergence in between 1985-

1986 and 2010. The years 1983-1984 were the two years prior to McAuliffe’s study and were

some of the wettest in Arizona history, with rainfall exceeded 25 mm nine times; since then San

Cristobal Valley and Dateland have not received that amount of precipitation (Table 2.3).

Overall, precipitation minimum needed for L. tridentata germination rarely occurred in any

season which may explain the lack of seedlings (Table 2.3).

Table 2.3.Total amount of precipitation (mm) per month in Dateland, Arizona. Highlighted cells represent months with precipitation over 25 mm, the minimum amount of rainfall needed for Larrea tridentata germination. Dashes represent months with no available data(NOAA Satellite and Information Service, 2011). Fewer than half the years with data have sufficient rainfall for germination June – September. Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1980 18.54 17.53 14.99 10.16 0 0 10.16 0 0 0 0 0 1981 13.97 4.32 20.83 0 0 0 3.56 39.62 13.72 10.16 3.05 0 1982 9.14 6.60 51.05 0 0 0 11.68 17.78 24.13 0 18.03 52.32 1983 17.27 26.16 40.64 4.57 0 0 0 100.84 48.77 6.60 2.54 28.70 1984 11.18 0 0 13.21 0 0 78.49 29.21 25.65 0 13.72 74.68 1985 11.18 19.56 2.54 0.00 0 0 - 2.54 15.24 40.64 26.16 22.10 1986 0 7.37 12.95 0 0 2.79 12.70 10.41 4.32 24.38 7.62 7.37 1987 12.19 2.79 0 0 - 0 8.89 25.65 2.54 34.04 22.10 30.73 1988 9.40 6.10 4 28.45 0 0 11.43 20.57 0 6.86 0 0 1989 0 0 15.24 0 0 0 13.97 0 0 13.97 0 10.16 1990 8.89 5.59 0 0 0 0 14.99 0 13.21 2.79 0 0 1991 23.37 8.89 25.91 0 0 0 0 8.13 8.89 8.38 13.72 14.73 1992 25.65 43.43 53.85 12.70 10 0 8.13 12.19 0 3.05 0 36.32 1993 87.88 75.95 13.72 0 0 0 0 - 0 0 30.73 0 1994 0 - - - 0 0 11.68 5.59 24.13 0 0 33.02 1995 - 0 0 0 0 0 8.13 0 0 0 0 0 1996 0 0 0 0 0 0 0 - 0 0 0 0 1997 0 7.87 4.32 0 0 0 0 26.42 53.34 0 0 39.12 1998 0 34.04 18.80 0 0 0 16.00 9.65 26.42 0 7.11 0 1999 0 0 0 7.62 0 0 13.72 14.73 0 0 0 0 2000 0 0 - - 0 ------2001 - - 16.00 19.30 0 ------2002 - - - 0 ------0 2003 13.97 44.70 8.38 0 0 0 3.30 26.67 2.54 0 5.59 2.54 2004 15.24 3.81 17.78 - 0 0 0 - 0 64.77 45.21 35.56 2005 52.32 46.48 6.10 0 0 - 0 - - - - - 2006 0 - 0 ------2007 - - 6.10 3.81 0 0 28.96 5.08 27.94 0 25.40 19.05 2008 23.88 10.16 0 0 5.08 0 - 34.29 17.78 0 44.96 - 2009 0 7.62 0 12.70 2.54 0 5.08 0 - 0 0 3.81 2010 78.23 9.40 17.78 0 0 ------

It has also been observed air temperature is an important factor in germination and

growth of L. tridentata seeds (Went and Westergaard, 1949; Barbour, 1968; Beatley, 1974;

Ackerman, 1979). In a laboratory setting Barbour (1968) found L. tridentata germinated and

grew between 50-104°F, with an optimum temperature range between 73-84°F. Similar to

Barbour, Beatley (1974) found an optimum germination temperature of 75°F, also in a

laboratory. Air temperature following rain sufficient for germination is also an important factor

in germination and growth (Went and Westergaard, 1949; Ackerman, 1979). Following

September rain the minimal temperature for germination was approximately 60°F, with

temperatures not dropping below 46-50°F or exceeding 86°F (Went and Westergaard, 1949). A

rain event with 25mm precipitation which produced seedlings had the same air temperature as

the subsequent rain with less precipitation with no seedlings (Ackerman, 1979). Because there is

a correlation between the temperatures immediately following rainfall, perhaps conditions that

promote germination and development have not occurred recently in the San Cristobal Valley

which could account for the lack of seedlings and young plants.

A lack of L. tridentata seedlings in the San Cristobal Valley may also be attributed to crusting of the soil surface. Crusting prohibits seeds from becoming incorporated into the soil, lowering seedling emergence (Chamber and MacMahon, 1994). At each site soil crusting was greatest in open areas while under Ambrosia canopy, there was less crusting but often it was still

difficult to take samples. Large pieces of soil often stayed intact even after they were placed in

the sample bags. Shreve (1942) noted L. tridentata reproduction is low if soil is undisturbed which causes few seedlings to be found compared to the high abundance of mature plants. This fits the fact that the only two L. tridentata seedlings seen throughout the course of this project

51 were located in vehicle tracks where crusted soil had been loosened, suggesting soil crusting is preventing L. tridentata seedling establishment in the San Cristobal Valley.

Rather than crusting preventing seedling growth, it may instead present an unfavorable microsite for germination. Barbour (1968) found L. tridentata seed have a greater chance of germinating in darkness rather than left exposed to light in petri dishes, which translates to the need for seed to be buried in nature. Went and Westergaard (1949)found germination occurred mostly when seeds were covered with approximately one cm of loose sand. Seed collected in San

Cristobal Valley was located on the soil surface and was not able to be covered with the required amount of soil due to crusting.

Seedling predation commonly inhibits growth and survival of seedlings in arid environments (Chew and Chew, 1970; Soholt, 1973). The primary seed predator of L. tridentata is Dipodomys merriami (Merriam's Kangaroo Rat) (Chew and Chew, 1970;Boyd and Brum,

1983). Lepus californicus (Black-tailed Jackrabbit) has been shown to cause mortality of transplanted seedlings as indicated by the scat evidence of Boyd and Brum(1983). They determined that birds and ants did not take L. tridentata seeds from predation stations used in their study. In the course of the 2-year study, birds only took 2 seeds from these stations, while ants took none compared to the 31 seeds taken by rodents. Nelson and Chew (1977) similarly found that birds and ants were not a source of L. tridentata seed predation. Seed predation could explain earlier results, of high variability of seed density between sites if one site was centered around more rodent mounds than another. However in the San Cristobal Valley, there was no evidence of active rodent or ant mounds at any of the plots within the three study sites. At two of the replications at the AMBR site, abandoned rodent mounds were present and appeared to have been abandoned for at least two years. Rodent mounds were observed predominately near and

on sand dunes of San Cristobal Valley where the sand is loose. If rodents are the cause of

seedling death at the study sites, the rodents were traveling from 5-km away. The impacts of

rodents may not be all negative as Chew and Chew (1970) suggested that rodents burying seed

could aid germination. At the end of the study by Boyd and Brum (1983), survivorship of plants

excluded from predators and exposed transplanted seedlings was the same, with fewer than 20%

of seedlings remaining. This implied that plant establishment is not controlled by seed predation

or seedling herbivory.

The simplest explanation for a lack of seedlings is that the conditions were not suitable

for germination in 2009-2010. Literature suggests germination of L. tridentata is highly variable

from year to year and can be considered rare as conditions are often not favorable for

germination, establishment and seedling survival (Barbour, 1968).

Future research could occur over longer time span as opposed to one or two years, similar

to this study and others used as references. If a study was conducted over several years, scientists

could get a better understanding of changes in seed germination from year to year. Adding rain

gauges at each location where seed densities will be measured could better tease out the effects

precipitation has on L. tridentata germination and survival. Rain gauges at each of the micro sites could explain why seed densities where greater in one area over another, if by chance one site received more precipitation than another.

This study only visually observed effects soil crusting on the presence of seedlings. This could be better explored by studying areas with crusting and without it to determine the role crusting plays limiting establishment. Sites could also have the crusting reduced as part of a seed addition and watering study to test the interaction of the two likely controlling environmental factors.

Implications of low L. tridentata production could be detrimental for the continuation of the population. L. tridentata is one of the most widely distributed plants in desert regions in

North America and it is important to understand its life cycle and natural history (Barbour,

1969). An increase in exotic plant species could also alter the fire regime to a higher frequency, which L. tridentata is not adapted to. If a large fire or drought were to significantly reduce the population of L. tridentata, it would greatly affect the ecosystem given the lack of observed

seedlings; therefore, knowing how precipitation, predation, and soils affect L. tridentata

establishment is imperative to land managers. This may offer the opportunity to augment

recruitment after a fire or any other ecosystem disturbance. L. tridentata is a vital plant for many species of wildlife, which use canopy cover to avoid high daytime temperatures in the summer, avoid predators, or use it for a den. Understanding natural limits on L. tridentata will be even more important to understand the implications of climate change.

APPENDIX A: RELEVÉ COORDINATES

Relevé X Y Association Relevé X Y Association AMNW-01 266132 3612959 13 MMNE-26 264123 3612650 11 AMNW-02 265791 3613106 16 MMNE-27 255760 3622760 70 AMSW-03 266545 3608579 12 MMNE-28 256210 3623015 11 AMSW-04 265433 3611413 82 MMNE-29 255758 3621352 70 AMSW-05 265732 3612070 12 MMNE-30 259903 3617371 10 AMSW-06 266087 3611677 12 MMNE-31 259582 3617153 15 AMSW-07 266299 3603441 12 MMNE-32 259478 3616915 70 AMSW-08 267043 3599298 11 MMNE-33 255025 3622536 10 AMSW-08 265774 3611167 13 MMNE-34 259313 3622708 15 AMSW-09 266470 3605653 11 MMNE-35 255811 3619602 10 AMSW-10 268398 3598360 11 MMNE-36 262527 3615340 12 AMSW-11 264610 3605212 11 MMNE-37 255493 3627236 11 AMSW-12 267150 3602920 10 MMNE-38 255479 3625822 11 AMSW-13 269344 3603477 15 MMNW-01 248437 3625442 10 MMNE-01 260889 3615573 10 MMNW-02 250978 3621755 10 MMNE-02 260597 3615309 70 MMNW-03 251616 3621361 10 MMNE-03 263298 3613963 11 MMNW-04 250430 3619147 81 MMNE-04 263135 3613208 70 MMNW-05 250109 3617579 171 MMNE-05 262439 3613866 70 MMNW-06 253138 3622171 10 MMNE-06 262564 3612839 70 MMNW-07 253579 3622411 70 MMNE-07 262555 3612504 13 MMNW-08 251607 3622212 70 MMNE-08 263761 3613922 11 MMNW-09 251201 3622587 10 MMNE-09 264022 3614231 11 MMNW-53 255795 3601459 10 MMNE-10 262450 3615251 13 MMNW-63 250302 3615847 171 MMNE-11 261362 3615200 12 MMNW-64 251858 3627078 70 MMNE-12 260780 3616101 12 MMNW-65 251769 3617125 171 MMNE-13 260928 3614341 10 MMSE-01 256517 3602139 81 MMNE-14 260338 3615609 70 MMSE-02 256650 3602550 171 MMNE-15 259016 3616612 70 MMSE-03 255205 3600350 10 MMNE-16 260187 3616346 12 MMSE-04 259182 3602226 81 MMNE-17 257100 3619341 70 MMSE-05 260260 3601000 14 MMNE-18 257979 3615007 10 MMSE-06 259331 3601110 26 MMNE-19 258576 3616355 10 MMSE-07 264531 3608741 12 MMNE-20 259387 3616171 10 MMSE-08 265065 3607947 13 MMNE-21 261225 3613885 10 MMSE-09 265000 3607150 26 MMNE-22 258793 3616675 10 MMSE-10 263242 3609140 81 MMNE-23 259746 3616005 70 MMSE-11 263300 3608700 16 MMNE-24 259005 3616606 70 MMSE-12 263505 3608818 16 MMNE-25 258683 3615546 10 MMSE-13 262764 3608078 10

Relevé X Y Association Relevé X Y Association MMSE-14 260713 3605459 81 MMSE-53 261632 3607752 10 MMSE-15 262095 3607603 16 MMSE-53 255795 3601459 10 MMSE-16 261500 3604720 16 MMSE-54 262356 3604846 16 MMSE-17 259768 3602729 170 MMSE-54 254007 3603601 171 MMSE-18 260050 3602150 171 MMSE-55 253784 3608856 14 MMSE-19 260600 3602200 14 MMSE-55 256178 3603595 170 MMSE-20 260750 3602350 170 MMSE-56 254662 3607235 14 MMSE-21 260800 3602800 170 MMSE-57 256134 3599758 26 MMSE-22 261000 3603500 16 MW-01 271789 3589099 14 MMSE-23 260829 3604134 16 MW-02 267102 3594023 81 MMSE-24 262950 3605850 26 MW-03 275701 3589172 80 MMSE-25 260907 3611505 12 MW-03 267111 3591952 170 MMSE-26 259283 3611706 170 MW-04 274134 3589129 10 MMSE-27 259711 3611003 10 MW-05 267663 3591299 14 MMSE-28 259497 3610337 170 MW-06 266478 3591212 171 MMSE-29 262564 3612220 10 MW-07 265618 3597058 171 MMSE-30 264177 3610247 12 MW-08 266772 3596492 11 MMSE-31 265236 3607913 13 MW-09 266965 3595542 11 MMSE-32 264030 3609547 10 MW-10 274183 3589449 10 MMSE-33 255937 3612311 170 MW-11 267081 3594604 81 MMSE-34 254884 3610986 81 MW-12 274651 3589828 11 MMSE-35 254864 3610975 170 MW-13 274800 3593712 11 MMSE-36 260235 3601981 14 MW-14 272851 3595424 12 MMSE-37 260052 3602111 171 MW-15 268415 3590656 14 MMSE-38 260233 3602681 170 MW-16 268200 3593099 170 MMSE-39 260413 3602172 14 MW-17 269596 3595637 10 MMSE-40 260572 3602495 171 MW-18 268991 3590012 14 MMSE-41 262468 3606309 11 MW-19 269119 3597212 10 MMSE-42 264702 3612292 11 MW-20 268308 3593821 170 MMSE-43 259589 3603662 81 MW-21 271422 3595522 10 MMSE-44 257936 3601274 10 MW-22 269447 3592907 13 MMSE-45 258786 3601954 16 MW-23 272596 3594371 10 MMSE-46 259826 3603344 170 MW-24 270789 3590454 13 MMSE-47 262493 3608333 10 MW-25 269555 3589345 14 MMSE-48 262978 3608708 11 MW-26 269732 3595712 13 MMSE-49 262529 3609080 10 MW-27 267185 3593911 170 MMSE-50 261903 3609212 16 MW-28 265976 3593600 170 MMSE-51 261061 3608307 170 NOIP-01 264350 3593600 10 MMSE-52 261302 3607907 10 NOIP-02 260969 3596868 81

Relevé X Y Association NOIP-03 261591 3596491 81 NOIP-04 263850 3589330 81 NOIP-05 256524 3597997 12 NOIP-06 256087 3597301 10 NOIP-07 259147 3593339 12 NOIP-08 258590 3592541 10 NOIP-09 257448 3595257 10 NOIP-10 257866 3595666 12 NOIP-11 261150 3592780 12 NOIP-12 261391 3591744 10 NOIP-13 261735 3591968 81 NOIP-14 259125 3591781 12 NOIP-15 261275 3592598 10 NOIP-16 262591 3592309 10 NOIP-17 263686 3590153 170 NOIP-18 264678 3589765 24 NOIP-19 263548 3593646 10 NOIP-20 254197 3597786 11 NOIP-21 257196 3597350 12 NOIP-22 263902 3589808 24 NOIP-23 259446 3597668 13 NOIP-24 260031 3597968 170 NOIP-25 256957 3599233 11 NOIP-26 258269 3590782 10 NOIP-27 265453 3594821 11

APPENDIX B: ASSOCIATION DESCRIPTIONS

Vegetation code 10 - Association: Larrea tridentata monotype (Creosote monotype) Classification: 1154.110

Warren et al. (1981) classification: 1154.1114 - Larrea tridentata with annuals

Brown, Lowe and Pase (1979) classification: 1154.111 - Larrea divaricata association

NVCS association: There is a Larrea tridentata monotype shrubland currently in the database; the association in this study is a Larrea tridentata monotype sparse shrubland.

Description: Stands of pure or almost pure creosote bush. During wet winters, annuals such as Spaeralcea spp., Eriastrum diffusum, Cryptantha angustifolia , and Plantago purshii can be abundant, usually beneath the creosote. Scattered Pleuraphis rigida , Ambrosia dumosa, A. deltoidea , Prosopis glandulosa and P. velutina are rare but present in 22 or fewer sites, usually in small runnels where water collects. Also rare, and present in 6 or fewer sites, were, Atriplex polycarpa, Opuntia ramosissima, Ferocactus wislizenii, Parkinsonia microphylla and Carnegiea gigantea.

Location: On slopes of 0 to 3%, on near valley bottoms; however, this association can also be found close to the foot of steep mountains and bajadas. The association usually grades into Larrea tridentata/Ambrosia associations, or, where waters collect, into Larrea tridentata/Prosopis floodplain with poorly defined channels. Along large channels (arroyos with beds greater than 5 meters wide), Larrea tridentata flats are sometimes found on the inside of a broad bend, subject to inundation during rare floods.

Field Identification: An observer can stand amid the Larrea tridentata and not see Ambrosia or Krameria . There is often few Ambrosia in runnels, but locating them requires some searching. However, if runnels are common, and so are the Ambrosia within them – roughlyten to fifteen Ambrosia every twenty meters – the area was considered to be Larrea tridentata/Ambrosia association.

Photo Identification: Stands of pure be Larrea tridentata were recognized by their habit of each bush being regularly dispersed, with no other vegetation between. This makes a pattern of distinct dots on the photo.

Table 1: Summary statistics for 1154.110 - Larrea tridentata monotype (Creosote monotype) association (n = 41).

Median Prominence Median Cover Mean Height Species Sites (Range) (range) (m) Larrea tridentata 41 5 (5) 3 (2-4) 1.04 Pleuraphis rigida 30 1 (1-2) 1 (1-2) Ambrosia deltoidea 15 1 (1-2) 1 (1) Olneya tesota 14 1 (1-2) 1 (1) Ambrosia dumosa 13 1 (1-2) 1 (1) Prosopis veluntina 13 1 (1) 1 (1-2) Parkinsonia microphylla 6 1 (1-2) 1 (1) Ferocactus wislizenii 5 1 (1) 1 (1) Atriplex polycarpa 1 1 (1) 1 (1) Carnegiea gigantea 1 1 (1) 1 (1) Opuntia ramosissima 1 1 (1) 1 (1)

Vegetation code 11- Association: Larrea tridentata/ Ambrosia dumosa (Creosote/ White Bursage) Classification: 1154.111

Warren et al. (1981) classification: part of 1154.1111, which, in their scheme, includes either/both Ambrosia dumosa and A. deltoidea , sub-dominant to Larrea tridentata .

Brown, Lowe and Pase (1979) classification : 1154.12 – Larrea divaricata/Ambrosia dumosa association

NVCS association: There are two listed. The first is a Larrea tridentata – Ambrosia dumosa shrubland, however it is reported only in the Mohave Desert in Nevada and California, so this may be an extension of the same association except in Arizona it is a sparse shrubland. The second is the Larrea tridentata var. tridentata dwarf shrubland, listed in Arizona. However Ambrosia dumosa is listed first, which implies it is generally dominant or co-dominant over Larrea tridentata , which is not the case in the San Cristobal Valley.

Description: Larrea tridentata is dominant or co-dominant with Ambrosia dumosa prevailing on the interfluves. Krameria grayi is common, while A. deltoidea is rare, as are Pleuraphis rigida and Atriplex polycarpa, Parkinsonia microphylla, Prosopis veluntina, Ferocactus wislizenii, Hesperocallis undulate and others. Location: On slopes of 1 to 3%, this association is usually found just down slope of Larrea tridentata/Ambrosia deltoidea-Krameria grayi with less than 10% cover of Parkinsonia microphylla-Olneya tesota (1154.1170). This association can also be found in valley bottoms near Larrea tridentata monotype (1154.110) and Larrea tridentata/Ambrosia deltoidea association (1154.112). It can also be found in the swales of sand dunes on lower slopes.

Field Identification: Walking perpendicular to the runnels, you encounter Ambrosia dumosa .

Photo Identification : The characteristic pattern is thin dark lines of A. dumosa in runnels that also occupied by an occasional Prosopis . Between the runnels are the broader but more sparsely vegetated interfluves.

Table 2: Summary statistics for 1154.111 - Larrea tridentata/ Ambrosia dumosa (Creosote/ White Bursage) association (n = 21).

Median Prominence Median Cover Mean Height Species Sites (range) (range) (m)

Larrea tridentata 21 5 (4-5) 3 (2-4) .91 Ambrosia dumosa 21 3 (2-5) 2 (2-4) .46 Pleuraphis rigida 9 1 (1-2) 1 (1) Prosopis velutina 6 1 (1) 1 (1) Ferocactus wislizenii 5 1 (1) 1 (1) Olneya tesota 3 1 (1-2) 1 (1) Ambrosia deltoidea 2 1 (1) 1 (1) Atriplex polycarpa 1 1 (1) 1 (1) Echinocereus engelmannii 1 1 (1) 1 (1) Foqueria splendens 1 1 (1) 1 (1) Hesperocallis undulate 1 1 (1) 1 (1) Krameria grayi 1 3 (3) 1 (1) .5 Parkinsonia microphylla 1 2 (1-2) 1 (1)

Vegetation code 12 - Association: Larrea tridentata/Ambrosia deltoidea (Creosote/Triangle- leaf Bursage) Classification: 1154.112

Warren et al. (1981) classification : part of 1154.1111, which, in their scheme, includes either/both Ambrosia dumosa and A. deltoidea , sub-dominant to Larrea tridentata .

Brown, Lowe and Pase (1979) classification: An undescribed association of the Larrea tridentata/Ambrosia deltoidea series, 1154.11.

NVCS association: none currently listed. The association in this study is a Larrea tridentata/ Ambrosia deltoidea sparse shrubland.

Description: Larrea tridentata is dominant with Ambrosia deltoidea common in plant L. tridentata interspaces. Ferocactus wislizenii was rare but occurred in 10 out of 19 sites. Prosopis veluntina, Ambrosia dumosa, Pleuraphis rigida , and Olneya tesota are rare. During wet years annuals such as Plantgopurshii, Euphorbia albomarginata, Nama demissum, Argemone pleiancantha and Sphaeralcea spp. are common to uncommon.

Location: On slopes of 1 to 3%, this association is usually in areas boarding Larrea tridentata/Prosopis (1154.115) floodplain or within loosely braided Larrea tridentata/Prosopis floodplains in valley bottoms. This association is also found near Larrea tridentata monotype (1154.110) in valley bottoms or on lower slopes adjacent to Larrea tridentata/Ambrosia deltoidea-Krameria grayi less than 10% cover of Parkinsonia microphylla/Olneya tesota (1154.1170).

Field Identification: Walking perpendicular to the runnels, you encounter A. deltoidea as a common species. A. deltoidea, Prosopis spp. and Parkinsonia microphylla are uncommon, rare or absent. It can be difficult to draw the line between this association and Larrea tridentata/Prosopis floodplain when the floodplain has few Prosopis . One main difference between the two associations is higher A. deltoidea cover in floodplains, whereas in this association A. deltoidea cover does not exceed 15%.

Photo Identification: The association was identified based on a lack of trees, generally less than one tree per hectare or no trees. It does not have a distinct pattern of regularly dispersed plants like Larrea tridentata monotype.

Table 3: Summary statistics for 1154.112 - Larrea tridentata/ Ambrosia deltoidea (Creosote/ Triangle-leaf Bursage) association (n = 17). Median Prominence Median Cover Mean Height Species Sites (range) (range) (m) Larrea tridentata 17 5 (3-5) 3 (2-4) 1.16 Ambrosia deltoidea 17 3 (3-5) 2 (2-4) .48 Ferocactus wislizenii 10 1 (1) 1 (1) Prosopis velutina 9 1 (1) 1 (1) Ambrosia dumosa 7 1 (1) 1 (1) Pleuraphis rigida 3 1 (1-2) 1 (1) Opuntia bigelovii 2 1 (1) 1 (1) Olneya tesota 1 1 (1) 1 (1) Peniocereus greggii 1 1 (1) 1 (1) Castela emoryi 1 1 (1) 1 (1) Datura wrightii 1 1 (1) 1 (1) Schaeralcea ambigua 1 1 (1) 1 (1)

Vegetation code 13 – Association : Larrea tridentata/ Ambrosia dumosa-A. deltoidea (Creosote/ White Bursage - Triangle-leaf Bursage) Classification: 1154.1130

Warren et al. (1981) classification: part of 1154.1111, which, in their scheme, includes either/both Ambrosia dumosa and A. deltoidea , sub-dominant to Larrea tridentata .

Brown, Lowe and Pase (1979) classification: An undescribed association of the Larrea tridentata-Ambrosia series, 1154.11.

NVCS association: none currently listed. The association in this study is a Larrea tridentata/Ambrosia dumosa—A. deltoidea sparse shrubland.

Description: Larrea tridentata is dominant or co-dominant. Either species of Ambrosia could be present, and typically common, with A. dumosa and A. deltoidea present on interfluves and runnels. On occasion A. dumosa prevails on interfluves with A. deltoidea in the runnels between.

Location: On slopes of 1 to 5%, this association is usually found just downslope of the Larrea tridentata/Ambrosia- with less than 10% cover of Parkinsonia microphylla /Olneya tesota association (1154.1170). Here, below the “tree line”, there are small rises of relatively coarse alluvium, dissected by runnels and finer soils. Small patched can also be found in the valley bottom.

Field Identification: Walking perpendicular to the runnels, you encounter both species of Ambrosia .

Photo Identification: The characteristic pattern is thin dark lines of A. deltoidea in runnels with more sparsely vegetated interfluves. It is a matrix of both Ambrosia associations, and was often used as catch-all for those areas that did not cleanly fall into one or the other Larrea tridentata/Ambrosia association.

Table 4: Summary statistics for 1154.113 - Larrea tridentata /Ambrosia dumosa- A. deltoidea (Creosote/ White Bursage- Triangle-leaf Bursage) association (n = 19). Median Prominence Median Cover Mean Species Sites (range) (range) Height (m) Larrea tridentata 9 5 (3-5) 3 (2-4) .95 Ambrosia deltoidea 9 3 (2-4) 2 (1-4) .34 Ambrosia dumosa 9 3 (2-4) 2 (1-4) .40 Pleuraphis rigida 5 1(1-2) 1(1-2) Olneya tesota 3 1 (1) 1 (1) Carnegiea gigantea 2 1 (1) 1 (1) Ferocactus wislizenii 2 1(1) 1(1) Parkinsonia microphylla 2 1.5(1-2) 1.5(1-2) Prosopis velutina 2 1.5(1-2) 1.5(1-2) Atriplex polycarpa 1 1(1) 1(1) Encelia farinosa 1 2(2) 2(2) Hesperocallis undulata 1 1(1) 1(1) Krameria grayi 1 1(1) 1 (1) Opuntia ramosissima 1 1(1) 1(1) Schaeralcea ambigua 1 1(1) 1(1)

Vegetation code 14 - Association: Larrea tridentata-Opuntia bigelovii/Ambrosia spp. (Creosote-Teddy Bear Cholla/Bursage) Classification: 1154.114

Warren et al. (1981) classification: Not present at Organ Pipe Cactus NM.

Brown, Lowe and Pase (1979) classification: Listed as 1154.117, but only as an undescribed.

NVCS association: None currently listed.

Description: The diagnostic species for this association is Opuntia bigelovii . The association is similar to 1154.124 (Malusa, 2003), the uplands rocky pediment with Opuntia bigelovii , but here Larrea tridentata is the dominant or co-dominant species, Ambrosia dumosa or Parkinsonia are the most common in 1154.124.

Location: On slopes of < 3%, this association is downslope from the rocky pediment with Opuntia bigelovii (1154.124), or against mountain slopes >20% (1154.163). Opuntia bigelovii often occurs on coarse alluvial outwash that carries the plant far downslope into the valleys.

Field Identification: This association was mapped by hiking along the lower limit of Opuntia bigelovii along the bajada gradient. Binoculars were useful for spotting distant individuals, which were included in the range unless they were over 100 m (328 feet) from the rest of the population. The site was deemed 1154.114 if Larrea tridentata is the dominant or co-dominant species.

Photo Identification: The range of Opuntia bigelovii could not be discerned on photos, therefore drawings on USGS 7.5 minute quadrangles and notes taken during field surveys where primarily used to map the range of this association.

Table 5: Summary statistics for 1154.114 - Larrea tridentata-Opuntia bigelovii/Ambrosia spp. (Creosote-Teddy Bear Cholla/Bursage) association (n = 11). Median Median Cover Species Sites Mean Height (m) Prominence (range) (range) Larrea tridentata 11 5 (2-5) 2 (2-3) 0.97 Parkinsonia microphylla 11 2 (1-3) 1 (1-2) 4.46 Opuntia bigelovii 11 3 (2-5) 1.5 (1-2) 0.98 Krameria grayi 11 2 (1-3) 2 (1-3) Encelia farinosa 11 3 (2-3) 3 (2-3) 0.71 Olneya tesota 7 2 (1-2) 2 (1-2) Fouquieria splendens 6 2 (1-2) 1 (1) Ambrosia dumosa 6 2 (2-3) 2 (2-3) Carnegiea gigantea 4 2 (2) 1 (1) Echinocereus engelmannii 4 1 (1-2) 1 (1) Opuntia fulgida 3 2 (1-2) 1 (1) Mammillaria tetrancistra 2 1 (1) 1 (1) Jatropha cuneata 2 2 (2) 1 (1) Opuntia acanthocarpa 2 2.5 (2-3) 1 (1) Opunita versicolor 2 2 (2) 1 (1) Senna covesii 2 1.5 (1-2) 1 (1) Mammillaria grahamii 1 1 (1) 1 (1) Erioneuron pulchellum 1 1 (1) 1 (1) Hibiscus denudatus 1 2 (2) 1 (1) Hyptis emoryi 1 1 (1) 1 (1)

Vegetation code 15 - Association: Larrea tridentata/Prosopis spp. floodplain (Creosote/Mesquite Floodplain) Classification: 1154.115

Warren et al. (1981) classification: 1154.1115R

Brown, Lowe and Pase (1979) classification: Not classified.

NVCS association: There is no similar association. An equivalent could be the Larrea tridentata -Prosopis glandulosa shrubland listed from the Chihuahuan Desert in New Mexico and Texas, but not Arizona.

Description : Floodplains lack a well-defined channel, but can border large braided watercourses (although this does not occur in the scope of this study). Typically Larrea tridentata is dominant to co-dominant, with Prosopis species common. Ambrosia deltoidea and Atriplex polycarpa are also common to uncommon. During wet years annuals such as Sphaeralcea spp., Plantago purshii and Argemone Mexicana are common.

Location: This association is found in areas of low relief (1-3%) where occasional flooding occurs allowing growth of large Prosopis . Floodplains are more common in valley bottoms near Larrea tridentata monotype or Larrea tridentata/Ambrosia associations.

Field Identification: The dense patches of Larrea tridentata and Prosopis species in areas where soil was often cracked was used as an indicator. Also plant litter from pervious annuals was common.

Photo Identification: The floodplain in the valley bottom was recognized by Larrea tridentata monotype or Larrea tridentata/Ambrosia association fades into numerous dots ( Prosopis ) on aerial imagery, since the floodplain was not near mountains, it can be assumed these dots are Prosopis not Parkinsonia species or Olneya tesota as these species are not found in valley bottoms in the San Cristobal Valley.

Table 6: Summary statistics for 1154.115 - Larrea tridentata/Prosopis spp. floodplain (Creosote/Mesquite Floodplain) (n =3). Median Median Cover Mean Height Species Sites Prominence (range) (m) (range) Prosopis species 3 5 (5) 5 (4-5) 2.02 Larrea tridentata 3 2 (2-3) 2 (2-3) 1.38 Atriplex polycarpa 2 2 (2) 2 (2) Atriplex canescens 2 2 (2) 1.5 (1-2) Ambrosia deltoidea 2 3 (3) 2.5 (2-3) 0.39 Olnyea tesota 1 2 (2) 1 (1) Ambrosia dumosa 1 1 (1) 1 (1) Ferocactus wislizenii 1 1 (1) 1 (1)

Carnegiea gigantea 1 1 (1) 1 (1) Pleuraphis rigida 1 1 (1) 1 (1)

Vegetation code 16 - Association: Larrea tridentata/Pleuraphis rigida (Creosote/Big Galleta Grass) Classification: 1154.116

Warren et al. (1981) classification: Not classified, but they reported Hilaria rigida (= Pleuraphis rigida ) from 4 of 12 sites in their 1154.1115R ( Larrea tridentata/Prosopis floodplain), and in 4 of their 41 sites of their 1154.1112 ( Larrea tridentata/Ambrosia with occasional Parkinsonia and Olneya tesota ).

Brown, Lowe and Pase (1979) classification: Not classified. However, Turner and Brown (1982) suggest that Larrea tridentata/Pleuraphis rigida is a series (the level above association) of the Lower Colorado subdivision of the Sonoran Desert.

NVCS alliance: There is a Larrea tridentata shrubland alliance currently in the database; the alliance in this study is a Larrea tridentata sparse shrubland, with the “sparse” indicating less than 25% cover. There is also a Pleuraphis rigida Shrub Herbaceous Alliance in the database, but with no data for comparison.

NVCS association: There is no similar association. The closest parallel is the Ambrosia dumosa/Pleuraphis rigida Dwarf-shrubland association from sand dunes; however, this association lacks Larrea tridentata as the co-dominant/dominant species.

Description: On sandy swales, Larrea tridentata is co-dominant to dominant, while Pleuraphis rigida is common. Ambrosia dumosa is common at 9 out of 11 sites. Ferocactus wislizenii and Parkinsonia microphylla occurred at 5 out of 11 sites, but where rare.

Location: In areas that appear to be Larrea tridentata monotype near sand dunes and Larrea tridentata/Ambrosia dumosa (1154.111). This association was also found downslope from Larrea tridentata/Ambrosia deltoidea-Krameria grayi less than 10% cover of Parkinsonia microphylla-Olneya tesota (1154.1170), particularly in the most northern mountain pass of the Mohawk Mountains.

Field Identification: Larrea tridentata must be dominant or co-dominant, with Pleuraphis rigida having 1-4% cover. Occasionally, it is common in shallow watercourses.

Photo Identification: The soils favored by Pleuraphis rigida are visible as a “smear” on the photograph. Otherwise, the pattern of vegetation is similar to Larrea tridentata monotype (1154.110), with regular dispersion between the plants, particularly when the vegetation is almost entirely Larrea tridentata and Pleuraphis rigida .

Table 7: Summary statistics for 1154.116 - Larrea tridentata/Pleuraphis rigida (Creosote/Big Galleta Grass) association (n = 10). Median Median Cover Mean Height Species Sites Prominence (range) (m) (range) Larrea tridentata 10 5 (4-5) 3 (2-4) 1.08 Pleuraphis rigida 10 3 (3-4) 3 (1-3) 0.69 Ambrosia dumosa 8 3 (1-4) 1 (1-3) 0.51 Ferocactus wislizenii 5 1 (1) 1 (1) Parkinsonia microphylla 5 1 (1) 1 (1) Prosopis velutina 4 1 (1-2) 1 (1) Ambrosia deltoidea 3 1 (1-2) 1 (1) Fouquieria splendens 3 2 (2) 1 (1) Krameria erecta 2 2 (1-3) 1(1) Krameria grayi 2 1 (1) 1 (1) Opunita bigelovii 2 1 (1) 1 (1) Olneya tesota 1 1 (1) 1 (1) Opuntia echinocarpa 1 1 (1) 1 (1) Opuntia ramosissima 1 1 (1) 1 (1)

Vegetation code 170 - Association: Larrea tridentata/Ambrosia deltoidea-Krameria grayi with less than 10% cover of Parkinsonia microphylla-Olneya tesota (Creosote/Bursage/Ratany with <10% cover of Palo Verde/Ironwood) Classification: 1154.1170

Warren et al. (1981) classification: Most similar to 1154.1112, which is described as a “middle bajada” association, with Parkinsonia microphylla (= Cercidium microphylla ) present at 25 of 41 sites. In the present study’s scheme, however, Parkinsonia microphylla or Olneya tesota must be present to be included in this association, so this association would not include the treeless habitat in Warren et al.’s 1154.1112.

Brown, Lowe and Pase (1979) classification: The “mixed-scrub” series of the Lower Colorado Subdivision mentioned by Turner and Brown (1982) is clearly different, with a “poorer representation or absence of Little-leaf Palo Verde” ( Parkinsonia microphylla ) and Ambrosia deltoidea “conspicuously lacking.” Both of these species are characteristic of the association described below. Hence, in a BLP classification, this would be an undescribed association of the creosote-bursage series, 1154.11.

NVCS association: No similar association within the Larrea alliance.

Description: Larrea tridentata is the most abundant species, with the highest median prominence (5) and cover (10-14%). The association is recognized by the presence of Parkinsonia microphylla and Olneya tesota (both present at 10 out of 11 sample sites), with combined cover of less than 10%, and usually much. Common plants were Ambrosia dumosa (9 out of 11 sites) and Encelia farinosa (5 out of 11 sites).

Location: On slopes of 2 to 20%. Parkinsonia microphylla and Olneya tesota prefer slopes and coarser outwash materials from the mountains.

Field Identification: At its lower elevational limit, this association grades into Larrea tridentata/Ambros ia communities, so it is easy to draw the line where Parkinsonia microphylla and/or Olneya tesota become conspicuous. When mapping the limits of a population, the lower bounds were drawn to include the very lowest trees, unless there were over 100 m (330 feet) separating the tree from the rest of the population.

Photo Identification: Parkinsonia microphylla and Olneya tesota are generally easy to identify on the photos. At their lower limits they can be confused with mesquite ( Prosopis ).

Table 9: Summary statistics for 1154.1170 - Larrea tridentata/Ambrosia deltoidea-Krameria grayi with less than 10% cover of Parkinsonia microphylla-Olneya tesota (Creosote/Bursage/Ratany with <10% cover of Palo Verde/Ironwood) association (n = 18). Median Median Cover Species Sites Prominence Mean Height (m) (range) (range) Larrea tridentata 18 5 (4-5) 2 (2-3) 0.81 Olneya tesota 17 2 (2-3) 1 (1) Parkinsonia microphylla 17 2 (1-3) 1 (1) Ambrosia dumosa 10 3 (1-3) 1 (1-3) 0.49 Ambrosia deltoidea 10 2 (1-3) 2 (1-2) Krameria grayi 9 1 (1-2) 1 (1-3) Encelia farinosa 6 3 (2-4) 2 (1-2) 0.62 Carnegiea gigantea 5 1.5 (1-3) 1 (1-3) Pleuraphis rigida 5 1 (1-2) 1 (1) Ferocactus wislizenii 4 1 (1) 1 (1) Mammillaria tetrancistra 4 1 (1) 1 (1) Krameria erecta 3 1 (1) 1 (1) Mammillaria grahmii 2 1 (1) 1 (1) Fouquieria splendens 1 2 (2) 1 (1) Echinocereus engelmannii 1 1 (1) 1 (1) Senna covesii 1 1 (1) 1 (1) Erioneuron pulchellum 1 1 (1) 1 (1) Hibiscus denudatus 1 1 (1) 1 (1) Hyptis emporyi 1 1 (1) 1 (1) Opuntia ramosissima 1 1 (1) 1 (1) Lycium spp. 1 1 (1) 1 (1) Hymenoclea salsola 1 1 (1) 1 (1)

Vegetation code 171 Sub-Association: Larrea tridentata/Ambrosia deltoidea – Krameria grayi on pavements, with less than 5% cover of Parkinsonia microphylla – Olneya tesota (Creosote/bursage on pavements, with less than 5% cover of palo verde/ironwood) Classification: 1154.1171 (a sub-association as 1154.117)

Warren et al. (1981) classification: Not classified by Warren et al. This is a pediment and upper bajada association that can be seen as a more arid version of Warren et al.’s 1154.1212, without Parkinsonia and Ambrosia as dominant species.

Brown, Lowe and Pase (1979) classification: An undescribed association of the Larrea tridentata-Ambrosia series, 1154.11.

NVCS association: No similar association within the Larrea alliance.

Description: On alluvial fans, at the foot of mountains in areas that are dissected by runnels. The diagnostic feature of this association is a lack of vegetation on interfluves, with only desert pavement present. More than 50 percent of the surface is devoid of vegetation. The plants only grow in runnels or on the edge of runnels.

Location: On slopes of 2-10 percent, this association can be found on soils derived from any rock type. Two key ingredients are needed to form bare interfluves are (1) pebbles on a very old undisturbed surface; and (2) aridity on the order of less than seven inches annually.

Field Identification: The surface is at least 50% devoid of vegetation, with vegetation occurring on the only on the edge or in runnels.

Photo Identification: The vegetation of this association appears as dark areas, due to the desert pavement, on the interfluves with thin lines of vegetation following runnels coming off the mountain.

Table 10: Summary statistics for 1154.1171 - Larrea tridentata/Ambrosia deltoidea – Krameria grayi on pavements, with less than 5% cover of Parkinsonia microphylla – Olneya tesota (Creosote/bursage on pavements, with less than 5% cover of palo verde/ironwood) (n = 10) Median Prominence Median Cover Mean Height Species Sites (range) (range) (m) Larrea tridentata 10 5 (4-5) 2 (2-3) 1.1 Parkinsonia microphylla 10 3 (2-3) 1.5 (1-2) 4.4 Ambrosia dumosa 10 3 (2-5) 1.5 (1-2) 0.46 Olneya tesota 9 2 (2-3) 1 (1-2) Encelia farinosa 9 3 (2-3) 2 (1-2) 0.57 Carnegiea gigantea 9 1 (1-2) 1 (1) Krameria grayi 8 2 (203) 1 (1-2) Lycium spp. 4 1 (1) 1 (1) Fouquieria splendens 4 2 (1-2) 1 (1) Ambrosia deltoidea 3 2 (2) 1 (1) Opuntia versicolor 2 2 (1-3) 1 (1) Senna covesii 2 2 (2) 1 (1) Erioneuron pulchellum 2 1 (1) 1 (1) Hibiscus denudatus 2 1 (1) 1 (1) Opuntia acanthocarpa 2 2.5 (2-3) 1 (1) Ferocactus wislizenii 1 1 (1) 1 (1) Mammillaria graphamii 1 1 (1) 1 (1) Krameria erecta 1 1 (1) 1 (1) Pleuraphis rigida 1 1 (1) 1 (1) Opuntia bigelovii 1 1 (1) 1 (1) Echinocereus engelmannii 1 1 (1) 1 (1)

Vegetation code 214 – Sub-Association: Ambrosia deltoidea/Larrea tridentata-Lycium spp. /Parkinsonia spp. along water courses with beds less than 5-m wide (Bursage/Creosote- Wolfberry/Palo Verde) Classification: 1154.1214R (a sub association of 1154.121)

Warren et al. (1981) classification: 1154.1214R

Brown, Lowe and Pase (1979) classification: Not described

NVCS alliance: Currently not described, but would likely fall under “Intermittently flooded extremely deciduous subdesert shrubland (III.B.3.N.b)” as recommended by Malusa (2003).

NVCS association: Not described. Could possibly be described as “ Ambrosia deltoidea/Larrea tridentata intermittently flooded shrubland” as recommended by Malusa (2003).

Description: Along watercourses with beds less than five meters wide. Larrea tridentata and Ambrosia deltoidea are most likely always present and typically common. Lycium species were lumped together as it is not possible to identify plants when they lack flowers; they were usually common to rare, likewise were both species of Parkinsonia . Parkinsonia floridum preferred slopes around 1-2 percent, while P. microphylla was found in washes of 2-5 percent slope. Encelia farinosa was another species that preferred steeper rockier slopes.

Location: On slopes of 1-5 percent, from the mountains and foothills to valley bottoms; however smaller watercourses were more common in the mountains and foothills. In the valley bottom smaller watercourses were usually associated with Larrea tridentata/Prosopis spp. floodplain (1154.115).

Field Identification: The width of the open channel is five meters or less. If the channel was so narrow that the vegetation was a single strand, rather than two strands on either side of the channel then the watercourse was no mapped separately and was considered part of the surrounding vegetation. In the San Cristobal Valley washes with water beds less than five meters had the same species composition as washes with beds greater than five meters; therefore no data was taken in smaller washes.

Photo Identification: The smallest mapped watercourses had to have a visible open channel. Width of the watercourse was measured directly on the computer screen using ArcMap tools.

Vegetation code 24 – Association: Ambrosia deltoidea/Parkinsonia microphylla/Opuntia bigelovii (Bursage/Foothill Palo Verde/Teddy Bear Cholla) Classification: 1154.124

Warren et al. (1981) classification: This association is similar to the 1154.1212 of Warren et al. (1981). However, Stenocereus thurberi (organ pipe cactus) occurs in 80% of their samples, while it is entirely lacking in the association described here in the San Cristobal Valley.

Brown, Lowe and Pase (1979) classification: Probably part of the 1154.122 Ambrosia deltoidea-Carnegiea gigantea mixed scrub association of the Palo Verde-mixed cacti (“Arizona upland”) series (1154.12).

NVCS alliance: Most similar to the Ambrosia deltoidea shrubland; however, this alliance should be an Ambrosia deltoidea sparse shrubland.

NVCS association: No similar association yet to be described within the Ambrosia deltoidea shrubland alliance. Malusa (2003) suggests using Ambrosia deltoidea /Parkinsonia microphylla /Opuntia bigelovii sparse shrubland.

Description: The association is similar to Ambrosia deltoidea/Parkinsonia microphylla / Stenocereus thurberi (1154.122), the uplands rocky pediment with Stenocereus thurberi , but the association as described here lack Stenocereus thurberi . The diagnostic species for this association is Opuntia bigelovii , with L arrea tridentata and Ambrosia deltoidea common. Olneya tesota, Parkinsonia microphylla and Ambrosia dumosa were also present at every sample site, but were uncommon.

Location: On slopes 2 -20% (the extent of the study), occurring on coarse alluvial outwash. Field Identification: This association was mapped similar to Larrea tridentata-Opuntia bigelovii/Ambrosia spp. (1154.114). It was mapped by hiking along the lower limit of Opuntia bigelovii , the diagnostic species. Binoculars were useful for spotting distant individuals, which were included in the range unless they were over 100 m (328 feet) from the rest of the population. “Quick samples” were also useful in mapping this association; i.e. notes made on topographic maps as to where it occurred.

Photo Identification: Photos couldn’t discern the range of Opuntia bigelovii , therefore drawings on USGS 7.5 minute quadrangles taken during “quick samples” and other notes taken during field surveys where primarily used to map the range of this association.

Table 11: Summary statistics for 1154.124 - Ambrosia deltoidea/Parkinsonia microphylla/Opuntia bigelovii (Bursage/Foothill Palo Verde/Teddy Bear Cholla) association (n = 2). Median Median Cover Species Sites Mean Height (m) Prominence (range) (range) Larrea tridentata 2 4.5 (4-5) 2 (1-3) 0.99 Ambrosia deltoidea 2 3.5 (3-4) 2 (2) 0.40 Opuntia bigelovii 2 2.5 (2-3) 1 (1) 0.97 Olneya tesota 2 2 (2) 2 (2) Parkinsonia microphylla 2 2 (2) 2 (2) Ambrosia dumosa 2 2 (2) 1 (1) Krameria grayi 1 1 (1) 1 (1) Hyptis emoryi 1 1 (1) 1 (1) Trixis californica 1 1 (1) 1 (1) Opuntia ramosissima 1 2 (2) 1 (1) Lycium spp. 1 1 (1) 1 (1) Hymenoclea salsola 1 1 (1) 1 (1) Carnegiea gigantea 1 1 (1) 1 (1) Echinocereus engelmannii 1 1 (1) 1 (1)

Vegetation code 26 – Association: Ambrosia dumosa/Pleuraphis rigida/Larrea tridentata on dunes (White bursage/ Big Galleta grass/Creosote on dunes) Classification: 1154.126

Warren et al. (1981) classification: Not classified

Brown, Lowe and Pase (1979) classification: Not classified

NVCS alliance: Ambrosia dumosa dwarf-shrubland alliance. The alliance in this study is better described as sparse dwarf-shrubland, with sparse indicating less than 25% cover.

NVCS association: Ambrosia dumosa/Pleuraphi srigida spare dwarf-shrubland association from sand dunes. However this association lacks Larrea tridentata as a common species, and it is present on dunes in this study.

Description: Ambrosia dumosa and Pleuraphis rigida are co-dominant on sandy rises while Larrea tridentata is common on sandy rises as well as swales between dunes. Following a wet year Hesperocallis undulata is common on sandy rises as well as swales between dunes and sandy areas leading up to the dunes. During wet years common annuals include; Abronia villosa, Cryptantha angustifolia, Calycoseris wrightii, and Mentzelia multiflora (which is biennial).

Location: On both western and eastern side of the Mohawk Mountains, low sandy swales on slopes of 1-15%. Field Identification: Swales of sand that can be seen in the distance, upon hiking closer to them Ambrosia dumosa and Pleuraphis rigida are dominant.

Photo Identification: The wind-blown sand forms a distinctive crest/swale pattern on aerial imagery.

Table 12: Summary statistics for 1154.126- Ambrosia dumosa/Pleuraphis rigida/Larrea tridentata on dunes (White bursage/ Big Galleta grass/Creosote on dunes) association (n = 3). Median Median Cover Species Sites Mean Height (m) Prominence (range) (range) Ambrosia dumosa 3 4 (3-5) 3 (2-3) 0.76 Larrea tridentata 3 3 (3) 2 (2-3) 1.38 Pleuraphis rigida 3 4 (3-5) 2.5 (2-4) 0.46 Hesperocallis undulata 2 2 (1-3) 1(1) Krameria erecta 2 2 (1-3) 1.5 (1-2) Foqueria splendens 2 2 (2) 1 (1) Ferocactus wislizenii 2 1 (1) 1 (1) Psorothamnus emoryi 2 1 (1) 1 (1) Parkinsonia microphylla 1 1 (1) 1 (1) Krameria grayi 1 3 (3) 1 (1) 0.34

Vegetation code 70 – Association: Atriplex polycarapa/Larrea tridentata (Cattle Saltbush/Creosote) Classification: 1154.170

Warren et al. classification: 154.1762 – which includes Atriplex linearis as common to co- dominant at half of the sites. A. linearis was present at 3 out of 15 sites and was uncommon.

Brown, Lowe and Pase classification: Most similar to Atriplex spp. –Prosopis juliflora torreyana association (154.173), however this association was only observed and no data is provided.

NVCS alliance: Atriplex polycarpa shrubland. However the alliance in this study of the San Cristobal Valley is an Atriplex polycarpa sparse shrubland, with the “sparse” indicating less than 25% cover.

NVCS association: None currently listed.

Description: Atriplex polycarpa is dominant while Larrea tridentata is uncommon at 14 out of 15. Suaeda moquinii was common at 3 sites. Prospois velutina and Ferocactus wislizenii were rare but present at 12 sites. Uncommon species included; Ambrosia deltoidea , A. dumosa, Atriplex linearis and Pleuraphisrigida .

Location: This association is located in the northern valley bottom of the San Cristobal Valley. It is surrounded mainly by Larrea tridentata monotype (1154.110) and also small patches of Larrea tridentata/Ambrosia deltoidea (1154.112) and Larrea tridentata/A. dumosa (1154.111). The northern most extent of this association is also bordered by areas of human disturbance.

Field Identification: This association is identified by walking through the valley bottom and encounter Atriplex polycarpa as the dominant species with Larrea tridentata as rare to common.

Photo Identification: They appear as conspicuously light-colored areas surrounded by slightly darker Larrea tridentata monotype.

Table 8: Summary statistics for 1154.170 – Atriplex polycarpa/Larrea tridentata (Saltbush/Creosote) association (n = 15). Median Median Cover Mean Height Species Sites Prominence (range) (m) (range) Atriplex polycarpa 15 5 (5) 2 (2-3) 0.49 Larrea tridentata 14 2 (1-3) 1 (1-3) 1.09 Prosopis veluntina 12 1 (1-3) 1 (1-3) 1.48 Ferocactus wislizenii 12 1 (1) 1 (1) Pleuraphis rigida 8 2 (1-3) 1 (1-2) Ambrosia dumosa 7 2 (1-3) 1 (1-3) 0.358 Ambrosia deltoidea 4 2 (1-3) 1 (1) Suaeda moquinii 3 3 (1-3) 3 (1-3) 0.495 Atriplex canescens 3 1 (1-2) 1.5 (1-2)

Vegetation code 80 – Association: Prosopis spp. Bosque (Mesquite woodland) Classification: 1154.180

Warren et al. (1981) classification: 124.711R, which is “open stands of trees 15 to 20 feet tall, forming in continuous corridors along large intermittent drainages.”

Brown, Lowe and Pase (1979) classification: Bosques are categorized as Mesquite series (224.52) of the Sonoran Riparian and Oasis Forests (224.5). See figure 182 in Turner and Brown (1982) for an illustration of a bosque.

NVCS alliance: Prosopisglandulosavar. torreyana, velutina woodland

NVCS association: Prosopisglandulosa var. torreyana, velutina woodland Description: Thickets of Prosopis spp. with open patches Ambrosia deltoidea, A. dumosa, Atriplex polycarpa and Larrea tridentata are present.

Location: There are several bosques in the San Cristobal Valley, however many of them were smaller than the five hectare mapping unit, and were not surveyed; only two bosques were large enough to be included. The first occurs at the end of San Cristobal wash located on the boundary of the CPNWR and Barry M. Gold Water Range (BMGR) was previously described by Malusa (2003). This bosque totals approximately 40 hectares, with the majority being in CPNWR; only 12 hectares are on BMGR. The other is located at the most northern extent of the study site, and is caused by a slight decrease in slope. There is also an area near the Stoval Airfield with similar characteristics to a bosque; however it was mapped as an area of human disturbance as it was assumed the bosque was caused by watering draining off the air strip.

Field Identification: There is nearly continuous cover of Prosopis spp. with no clear channel in the bosque, or around it. If there is a channel it is classified as a wash. This association can grade into a wash or Larrea tridentata/ Prosopis spp. floodplain.

Photo Identification: The crowns of larger trees are visible on aerial imagery and mapped were it appears to form a continuous canopy.

Vegetation code 81 - Association: Olneya tesota/Parkinsonia floridum/Acacia greggii/Lycium spp. along watercourses with beds greater than five meters wide (Ironwood/Blue Palo Verde/Catclaw Acacia/Wolfberry) Classification: 1154.181

Warren et al. (1981) classification: 1154.1215R

Brown, Lowe and Pase (1979) classification: Somewhat similar to 1154.115, which is called the “ Cercidium (= Parkinsonia ) floridum -Olneya tesota -Dalea spinosa (= Psorothamnus spinosa ) association”. However, as described in Turner and Brown (1982), this association is characterized by the “poor representation or absence” of Prosopis

NVCS alliance: Currently not described.

NVCS association: Not described.

Description: Along watercourses (also known as washes or arroyos) with beds greater than five meters (16 feet) wide. Parkinsonia floridum is always present, and typically co-dominant. Typically common or co-dominant are Larrea tridentata , Lycium spp., Olneya tesota , Ambrosia deltoidea , and Acacia greggii . Lycium are lumped into a single category because it wasn’t possible to identify species without flowers. In this study there was not as much species diversity compared to watercourses in previous studies by Malusa (2003) and Osmer-Blodgett (2010), therefore a small number of relevés were collected for this association.

Location: Slopes of 1-4%, predominantly in mountain foothills, forming in large canyons.

Field Identification: The width of the open channel is at least five meters over at least 50% of the watercourse surveyed. If the channel was braided so that the islands between were continuous blue Parkinsonia floridum / Olneya tesota , then the widths of the two strands of the braid were summed. If the islands between were a different association, then the strands were mapped separately, which sometimes resulted in a large arroyo turning into two or more small washes, then rejoining as a large wash.

Photo Identification: The width of the open channel was measured directly from the photos using tools in ArcMap to determine if the association should be categorized as 1154.181 or 1154.1214R (Ambros ia deltoidea/Larrea tridentata -Lycium spp. / Parkinsonia spp. along water courses with beds less than 5-m wide). The open channel was easily viewed from aerial imagery; therefore a small number of relevés were taken for this association.

Table 14: Summary statistics for 1154.181 Prosopis spp. / Parkinsonia floridum / Acacia greggii /Lycium spp. along watercourses with beds greater than five meters wide (Mesquite/Blue Palo Verde/Catclaw Acacia/Wolfberry)) association (n = 12). Median Median Cover Mean Height Species Sites Prominence (range) (m) (range) Larrea tridentata 12 2 (1-3) 1 (1) 1.37 Parkinsonia microphylla 12 3 (2-4) 2 (1-3) 5.28 Lycium spp. 12 4 (2-4) 2 (1-3) 1.21 Olneya tesota 11 3 (1-4) 2 (1-3) 5.02 Hymenoclea salsola 11 3.5 (1-5) 2 (1-4) 0.95 Hyptis emoryi 10 2 (1-4) 2 (1-3) 2.00 Acacia greggii 9 2.5 (1-4) 2 (1-2) 3.13 Ambrosia dumosa 9 2 (1-3) 1 (1-2) Encelia farinosa 9 3 (2-5) 2 (1-3) 0.90 Ambrosia deltoidea 8 1 (1-3) 1 (1) Bebbia juncea 7 2.5 (1-3) 1.5 (1-3) 0.71 Funastrum cynanchoides 6 1 (1-2) 1 (1) Parkinsonia floridum 6 2 (1-3) 1 (1-2) Trixis californica 4 2 (1-2) 1 (1) Krameria grayi 3 1 (1) 1 (1) Carnegiea gigantea 3 1 (1) 1 (1) Pleuraphis rigida 3 3 (1-3) 2 (1-2) 0.89 Lupinus arizonicus 1 1 (1) 1 (1)

Vegetation code 82 – Association: Prosopis spp. playa or barren floodplain. Classification: 1154.182. In this scheme 1154.18 is a Sonoran Desert Prosopis spp. shrubland series; 1154.182 is an association with no obvious watercourse channel and at all time with little or no vegetation.

Warren et al. (1981) classification: Not classified.

Brown, Lowe and Pase (1979) classification: Not classified.

NVCS alliance: There is no equivalent at the alliance level, but at the higher formation level there is the North American Warm Desert Plata System, which is composed of one or more Atriplex species with other halophytic plants are present to co-dominant.

NVCS association: Not classified. Description: Closed basin drainage with little to no vegetation.

Location: A closed basin in the San Cristobal Valley. Field Identification: A barren depression with in the valley that has at least a hectare with no vegetation. Similar to Atriplex polycarapa /Larrea tridentata (1154.170) association, but with much less vegetation cover. Photo Identification: Appears devoid of vegetation in aerial imagery, looks similar to Atriplex polycarapa /Larrea tridentata (1154.170) association in that playa is a lighter color than the surrounding association.

Table 15: Summary statistics for 1154.182 Prosopis spp. playa or barren floodplain (n = 1). Median Median Cover Mean Height Species Sites Prominence (range) (m) (range) Atriplex polycarpa 1 4 (4) 2 (2) 0.48 Ambrosia dumosa 1 4 (4) 1 (1) 0.35 Larrea tridentata 1 2 (2) 1 (1)

APPENDIX C: CONTINGENCY TABLE

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