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Las Vegas Wash Coordination Committee Land Cover Types of the Las Vegas Wash, Nevada March 2008 Land Cover Types of the Las Vegas Wash, Nevada SOUTHERN NEVADA WATER AUTHORITY Las Vegas Wash Project Coordination
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Las Vegas Wash Coordination Committee Land Cover Types of the Las Vegas Wash, Nevada March 2008 Land Cover Types of the Las Vegas Wash, Nevada SOUTHERN NEVADA WATER AUTHORITY Las Vegas Wash Project Coordination Team Prepared for: Las Vegas Wash Coordination Committee Prepared by: Seth A. Shanahan 1, Dave Silverman 2, and Art Ehrenberg 3 1 Southern Nevada Water Authority Las Vegas Wash Project Coordination Team 100 City Parkway, Suite 700 Las Vegas, Nevada Xeric Specialties Consulting 437 Calle De Collie Ridgecrest, California Southern Nevada Water Authority Data Resources Division 100 City Parkway, Suite 700 Las Vegas, Nevada March 2008 ACKNOWLEDGEMENTS The U.S. Bureau of Reclamation (BOR) provided funding for this project under assistance agreement number 04FG Clark County Parks and Recreation and the BOR provided access to study sites. We wish to acknowledge the contributions of Lee Watson with SpecTIR. Nick Rice provided valuable logistical support by coordinating ground based spectrometer data acquisition and Cindy Hopkins conducted field surveys. We would like to thank the members of the Research and Environmental Monitoring Study Team for reviewing this document and the Las Vegas Wash Coordination Committee for their continued support for this project and the implementation of the Las Vegas Wash Comprehensive Adaptive Management Plan. ii Land Cover Types of the Las Vegas Wash, Nevada Table of Contents Page No. Acknowledgements... ii Table of Contents... iii List of Figures... vi List of Appendices... vii 1.0 INTRODUCTION Biotic Communities Historical Vegetation Classifications Las Vegas Wash Vegetation Study ( ) Clark County Wetlands Park Environmental Impact Statement (1994) Southwest Regional Gap Analysis Program (2003) Clark County Wetlands Park Improvements Environmental Assessment (2005) MATERIALS AND METHODS National Vegetation Classification System System Formation Class Formation Subclass Formation Group Formation Subgroup Formation Alliance Association Field Surveys Survey Plots Spectral Radiometer Geographic Information Systems and Remote Sensing Tools Spatial Data Photointerpretation Accuracy Assessment Waters of the U.S. Determination...10 iii Page No. 3.0 RESULTS AND DISCUSSION Unvegetated and Sparsely Vegetated Cover Types Open Water Disturbed Area Human Disturbed Area Natural Vegetated Cover Types Forest Formation Class Populus fremontii-salix gooddingii Temporarily Flooded Forest Alliance (Cottonwood-Willow Riparian Forest) Woodland Formation Class Prosopis spp. Woodland Association (Mesquite Woodland) Acacia greggii Woodland Association (Catclaw Wash Scrub) Shrubland Formation Class Salix exigua Temporarily Flooded Shrubland Alliance (Sandbar Willow Riparian Scrub) Atriplex spp. Shrubland Alliance (Saltbush Scrub) Atriplex lentiformis Shrubland Association (Quailbush Thicket) Atriplex canescens Shrubland Association (Fourwing Saltbush Scrub) Atriplex polycarpa Shrubland Association (Desert Saltbush Scrub) Larrea tridentata Shrubland Alliance (Creosote Bush Scrub) Larrea tridentata Shrubland Association (Creosote Bush Pure Stand) Larrea tridentata/ambrosia dumosa Shrubland Association (Creosote Bush-Bursage Scrub) Larrea tridentata Wash Shrubland Association (Creosote Bush Wash Scrub) Larrea tridentata-atriplex spp. Shrubland Association (Creosote Bush Chenopod Scrub) Tamarix ramosissima Shrubland Alliance (Salt Cedar Thicket) Tamarix ramosissima-atriplex lentiformis Shrubland Association (Salt Cedar-Quailbush Thicket) Tamarix ramosissima/phragmites australis Shrubland Association (Salt Cedar-Common Reed Thicket and Marsh) Dwarf Shrubland Formation Class Atriplex hymenelytra Dwarf Shrubland Association iv Page No. (Desert Holly Scrub) Ambrosia dumosa/larrea tridentata Dwarf Shrubland Association (Bursage-Creosote Bush Scrub) Allenrolfea occidentalis Intermittently Flooded Dwarf Shrubland Association (Iodinebush Alkaline Meadow) Atriplex confertifolia Dwarf Shrubland Association (Shadscale Scrub) Herbaceous Formation Class Graminoid Formations Pleuraphis rigida Herbaceous Association (Galleta Grass Wash) Schoenoplectus spp. Permanently to Semipermanently Flooded Herbaceous Alliance (Tule Marsh) Typha domingensis Permanently Flooded Herbaceous Alliance (Cattail Marsh) Phragmites australis Semipermanently Flooded Herbaceous Alliance (Common Reed Marsh) Distichlis spicata Intermittently Flooded Herbaceous Alliance (Saltgrass Alkaline Meadow) Forb Formations Scree Herbaceous Association (Talus/Scree Slope) Rocky Slopes Herbaceous Association (Outcrop Rocky Slope) Desert Pavement Herbaceous Association (Desert Pavement) Plantago ovata Herbaceous Association (Wooly Plantain Field) Schismus spp. Herbaceous Association (Splitgrass Field) Sisymbrium irio Herbaceous Association (Ruderal Field) Bassia hyssopifolia Herbaceous Association (Bassia Field) Non-Native Intermittently Flooded Herbaceous Association (Weedy Sandbars and Mudflats) Soil Classification Wetlands and Other Waters of the U.S RECOMMENDATIONS LITERATURE CITED...38 v List of Figures Page No. Figure 1. Level IV ecoregions of the Las Vegas Wash from Bryce et al. (2003)...3 Figure 2. Off-highway vehicle disturbance in Las Vegas bearpoppy habitat...12 Figure 3. Recent germination by cocklebur, Goodding s willow, and salt cedar on a recently created sandbar as a result of flooding...13 Figure 4. Populus fremontii-salix gooddingii Temporarily Flooded Forest Alliance...14 Figure 5. Acacia greggii Woodland Association...15 Figure 6. Salix exigua Temporarily Flooded Shrubland Alliance...16 Figure 7. Atriplex spp. Shrubland Alliance...17 Figure 8. Atriplex lentiformis Shrubland Association in the foreground and the Tamarix ramosissima Shrubland Alliance in the background. The Disturbed-Natural land cover type is also represented in between the two communities...18 Figure 9. Atriplex polycarpa Shrubland Association...19 Figure 10. Larrea tridentata Shrubland Alliance. An Ambrosia dumosa/larrea tridentata Dwarf Shrubland Association grading into a Pleuraphis rigida Herbaceous Association is visible in the foreground Figure 11. Larrea tridentata/ambrosia dumosa Shrubland Association...21 Figure 12. Larrea tridentata Wash Shrubland Association...22 Figure 13. Larrea tridentata-atriplex spp. Shrubland Association...23 Figure 14. Tamarix ramosissima Shrubland Alliance...24 Figure 15. Atriplex hymenelytra Dwarf Shrubland Association...25 Figure 16. Ambrosia dumosa/larrea tridentata Dwarf Shrubland Association...25 Figure 17. Schoenoplectus spp. Permanently to Semipermanently Flooded Herbaceous Alliance...27 Figure 18. Typha domingensis Permanently Flooded Herbaceous Alliance...28 Figure 19. Phragmites australis Semipermanently Flooded Herbaceous Alliance...29 vi Page No. Figure 20. Distichlis spicata Intermittently Flooded Herbaceous Alliance...29 Figure 21. Sisymbrium irio Herbaceous Association...31 Figure 22. Soil survey for the Clark County Wetlands Park prepared by the Natural Resources Conservation Service in Figure 23. Wetlands (1,043 acres) within the study area that were mapped by the U.S. Fish and Wildlife Service for their National Wetland Inventory program...35 Figure 24. Wetland areas (317 acres) within the study area that may meet the U.S. Army Corps of Engineers definition of a wetland or water of the U.S List of Appendices Appendix A Appendix B Appendix C List of Plant Species Documented by Shanahan and Silverman (2006) that Occur in the Various Land Cover Types found along the Las Vegas Wash Dichotomous Key to the Land Cover Types found along the Las Vegas Wash Land Cover Types of the Las Vegas Wash vii 1.0 INTRODUCTION Vegetation type, extent, continuity, and structure are some of the most important factors that determine wildlife diversity and distribution. Other contributing factors that shape wildlife communities include disturbance, competition, climate, and water availability. Because vegetation communities in the southwestern U.S. gradate sharply along zones of soil moisture, wildlife are often restricted to specific vegetation types. Along the Las Vegas Wash (Wash), Nevada, more than 250 wildlife species have been documented to occur in distinct wetland, riparian, and upland vegetation types. Recent studies have investigated the diversity and distribution of amphibians, birds, fishes, mammals, and reptiles (Shanahan 2005, 2005a, Van Dooremolen 2005, O Farrell and Shanahan 2006, Larkin 2006). Moreover, focused surveys for the endangered southwestern willow flycatcher (Empidonax traillii extimus) and Yuma clapper rail (Rallus longirostris yumanensis) have been conducted since as early as 1998 (SWCA 1998, 1999, 2000, 2001, 2002, 2003, 2005, 2006; McKernan and Braden 2001, 2002). Field surveys have concluded that wildlife habitats are improving. Habitat analyses are integral components of the biological surveys that are conducted in the Wash. Because survey locations are finite, however, vegetation descriptions are often spatially limited. Vegetative communities described from a landscape perspective are helpful to understand the landscape structure and its effects on the distribution and abundance of organisms. The Las Vegas Wash Coordination Committee, a multi-stakeholder collaborative planning group, has been facilitating biological resource inventories and ecological improvements along the Wash for the past several years. Besides the wildlife studies previously described, on the ground activities have included constructing multiple erosion control structures and stream bank protection facilities. Moreover, extensive revegetation projects have been completed to further protect the channel bed and banks from eroding as well as to improve wildlife habitat values. These activities are directed by a planning document that was completed in 2000, the Las Vegas Wash Comprehensive Adaptive Management Plan (CAMP). Among the action items that were listed in the CAMP was a recommendation to prepare a long-term wildlife management plan for the Wash, which is currently underway (Shanahan et al. 2007). In order for wildlife management planning to be successful, however, the availability and extent of wildlife habitats must be considered. Often, wildlife management is effectively accomplished by focusing management recommendations towards habitats. The goal for this study is to identify and delineate land cover types along the Wash with specific attention given to vegetated cover types (i.e., vegetation communities). Vegetation communities are described by using standardized vegetation classifications (Association for Biodiversity Information 2001), Geographic Information System (GIS) technologies, and appropriate ecological methodologies (e.g., Barbour et al. 1999, Mueller-Dombois and Ellenberg 1974). This study provides a critical catalog of vegetative communities along the Wash using a repeatable standardized nomenclature. This study was conducted to facilitate wildlife management planning along the Wash (Shanahan et al. 2007), however, ecosystem restoration initiatives (Kloeppel et al. 2006, Bickmore 2003) were intended to benefit from these data as well. Specifically important land cover classifications, such as wetlands, are also presented to help plan for and meet long-term management goals along the Wash. Land Cover Types of the Las Vegas Wash, Nevada 1 1.1 Biotic Communities Plants and animals are distributed in different parts of the world for a variety of reasons. For example, continental scale distributions are typically artifacts of past geologic activity whereas watershed scale distributions are often artifacts of local climate, topography, substrate type, and catchment size. Regardless of the mechanisms that drive where species occur, there are often observable units of similarity across the landscape. Natural units of similarity include areas that are characterized by like physical, climatological, or biological components whereas artificial units of similarity are often described politically or socially. For the purposes of this study, we are interested in units of similarity that are characterized by biological components, specifically vegetation. Merriam and Steineger (1890) were the first to popularize the biotic community concept in the U.S. with their description of the life zones of San Francisco Peak, Arizona. Merriam and Steineger (1890) described six life zones, which were based almost exclusively on elevation. Each life zone had a characteristic flora and fauna that was readily observed and distinguishable from one another. From lowest to highest, the life zones include the lower sonoran, upper sonoran, transition, canadian, hudsonian, and arctic-alpine. The lower sonoran life zone, which encompasses biological communities between 100 and 3,000 feet above mean sea level, describe the Wash. This life zone is further characterized by the dominance of creosote bush (Larrea tridentata) and white bursage (Ambrosia dumosa) vegetation. Since the development of the life zone concept, biotic community classifications have grown in complexity and geographic extent. For example, Bailey (1983) prepared a map of functionally similar ecosystems (i.e., ecoregions) in the U.S. for the purposes of facilitating environmental conservation and estimating ecosystem productivity. From coarse to fine resolution, Bailey (1983) described four classification levels; the domain, division, province, and section. The Wash, for example, is within the dry domain, desert division, American desert (Mojave- Colorado-Sonoran) province, creosote bush section. Brown et al. (1998) prepared a classification similar to Bailey s (1983) but for both the U.S. and the remaining parts of North America. Their classification uses a biogeographic approach that incorporates both zoogeographic and phytogeographic information. Brown et al. (1998) describe seven levels of hierarchal classification in North America which they split between the neartic and neotropical biogeographic realms. Their levels include the hydrologic regime, formation type, climatic zone, biotic community, series, association, and stand. Brown et al. (1998) have classified the Wash as a part of the neartic realm, natural upland vegetation regime, desertlands formation, warm temperate desertlands zone, Mojave desertscrub community with the Mojave desertscrub community being nearly 48 miles 2. Classifications past the community level were not prepared. The most recent ecoregion mapping efforts have been facilitated by the U.S. Environmental Protection Agency s Western Ecology Division. The most detailed ecoregion classification (Level IV) for Nevada was completed by Bryce et al. (2003) and the Wash is listed as being within the creosote bush-dominated basins, arid footslopes, and arid valleys and canyonlands (Figure 1) Land Cover Types of the Las Vegas Wash, Nevada 2 LJ StudyArea \ Las Vegas Wash IIIII Arid Footslopes For Planning Purposes Only Prepared by the Southern Nevada Water Authority Arid Valleys and Canyonlands Creosote Bush-Dominated Basins 0 _\ N I I I 0.25 Figure 1: Level IV ecoregions of the Las Vegas Wash from Byrce et al. (2003). Land Cover Types of the Las Vegas Wash, Nevada 3 Although biotic community classifications at a regional scale are helpful towards understanding the patterning of broad geographic areas, local landscape characteristics are important for achieving finer scale resolution. Bradley and Deacon (1965) prepared the earliest and most comprehensive description of the biotic communities of Southern Nevada from a fine scale by compiling information from field observations, peer-reviewed literature, and local ecological knowledge. Classifications were based mostly on physiognomic and species information, hydrologic regime, and position in the landscape. Based on their biotic community descriptions, the Wash is defined as part of the stream riparian and stream communities. 1.2 Historical Vegetation Classifications Plants are a component of the biotic community and they are often the most easily observed and measured unit of the community. Recent advances in the collection and analysis of remotely sensed data make plants even more easily measured. With these new techniques, several vegetation classifications have historically been prepared for the Wash to meet various goals. Unfortunately, these vegetation classifications were not typically prepared using a hierarchal standard and are therefore not easily replicated. Moreover, because the Wash is a spatiotemporally dynamic system, historical classifications are not indicative of present conditions Las Vegas Wash Vegetation Study ( ) The earliest vegetation classification that was prepared for the Wash incorporated color infrared aerial imagery from 1975, 1982, and (BOR 1987). The objective of this study was to inventory the aerial extent and document temporal changes in the extent of the vegetation communities found along the Wash. This classification listed several vegetation/land cover types described as salt cedar, mixed shrub, desert, barren/disturbed, eroded/scoured, dead, thistle/smotherweed, reed marsh, cattail marsh, mixed marsh, wetland annuals, open water, and facilities Clark County Wetlands Park Environmental Impact Statement (1994) In 1994, a delineation and classification of vegetation communities was prepared to support the preparation of environmental documents for the Clark County Wetlands Park (Wetlands Park; Southwest Wetlands Consortium 1998). This vegetation survey established nine vegetative communities within the Wetlands Park boundary. The communities include emergent wetland/hydroriparian, strand, common reed, tamarisk, alkali, disturbed, upland, xeroriparian, and Atriplex Southwest Regional Gap Analysis Program (2003) The Southwest Regional Gap Analysis Program (SWReGAP) began in 1999 as a five state collaborative mapping project for assessing biodiversity (Lowry et al. 2005). SWReGAP provides the most comprehensive description of land cover types near the Wash, however, mapping resolution is poor and classifications are misapplied and not indicative of current conditions. Eight cover types were described for the Wash area, which include: (1) developed open space-low intensity, (2) Sonora-Mojave creosote bush-white bursage desert scrub, (3) Sonora-Mojave mixed salt desert scrub, (4) North American warm desert bedrock cliff and outcrop, (5) North American warm desert wash, (6) North American warm desert pavement, (7) North American warm desert badland, and (8) invasive southwest riparian woodland and shrubland. Land Cover Types of the Las Vegas Wash, Nevada 4 1.2.4 Clark County Wetlands Park Improvements Environmental Assessment (2005) In 2004, SWCA (2005a) prepared an Environmental Assessment for various trails, interpretive, and habitat enhancement projects in the Wetlands Park. A new vegetation classification was not created, rather, the classification schema previously developed by the Southwest Wetlands Consortium (1998) was used. SWCA (2005a) found that the plant communities in the park changed only slightly with most communities decreasing in extent. The most substantial change appears to be an increase of nearly 200 acres of upland vegetation from 1994 to MATERIALS AND METHODS Land cover types within the study area have been delineated by using digital spatial information products, a standardized classification nomenclature, and field surveys. Although this report primarily identifies and delineates the vegetation types found near the Wash, relevant land cover classifications conducted by others have also been included. Moreover, a specific classification for wetlands and other waters of the U.S. was prepared. 2.1 National Vegetation Classification System The National Vegetation Classification System (NVCS) was a collaborative product of the Nature Conservancy and natural heritage programs across the country (Grossman et al. 1998). Although originally developed to help meet the goals of the
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