PRELIMINARY ASSESSMENT OF BIODIVERSITY VALUES AND MANAGEMENT FRAMEWORK ADAPTATION FOR THE EXPANDED KOFA COMPLEX AND YUMA RESOURCE MANAGEMENT AREA IN SOUTHWESTERN ARIZONA August 2003 (Revised Version, February 2004) The Nature Conservancy in Arizona, Tucson PRELIMINARY ASSESSMENT OF BIODIVERSITY VALUES AND MANAGEMENT FRAMEWORK ADAPTATION FOR THE EXPANDED KOFA COMPLEX AND YUMA RESOURCE MANAGEMENT AREA IN SOUTHWESTERN ARIZONA Stephanie Weinstein Conservation Planner Anne Gondor Geographic Information Systems Specialist John A. Hall Director of Public Land Conservation Strategies and Sonoran Desert Program Manager August 2003 (Revised Version, February 2004) The Nature Conservancy in Arizona, Tucson Cover photograph: Tyson Wash in the La Posa Plain, Yuma Proving Ground, Arizona. Facing south- southwest (Photo: S. Weinstein). ACKNOWLEDGMENTS This project was supported by funding from the Department of Defense Legacy Resource Management Program and the Bureau of Land Management. We would like to thank the many individuals and agencies that supported this project. Many datasets, including Geographic Information Systems data, were critical components of this assessment and were provided to us by Barbara Bowles and Jack Johnson (Bureau of Land Management), David Lashlee and Valerie Morrill (Yuma Proving Ground), Bob Henry (Arizona Game and Fish Department), and Susanna Henry (Kofa National Wildlife Refuge). Numerous staff from the Arizona Game and Fish Department (Region IV-Yuma), Bureau of Land Management Yuma Field Office, Kofa National Wildlife Refuge, and Yuma Proving Ground generously offered us their time and valuable advice in several meetings and subsequent correspondence. In particular, we would like to thank Karen Reichhardt and Roger Oyler (Bureau of Land Management), Russ Engel, Bob Henry, and Bill Knowles (Arizona Game and Fish Department), Ron Kearns (Kofa National Wildlife Refuge), and Valerie Morrill and Randy English (Yuma Proving Ground) for all the input they provided us with in meetings, phone calls, and emails. Bob Henry (Arizona Game and Fish Department) generously shared his knowledge of the current status and dispersal areas of desert bighorn sheep in southwestern Arizona. We would also like to thank Randy English and Tim Green for accompanying Nature Conservancy staff in the field on Yuma Proving Ground to look for the Mojave fringe-toed lizard. Finally, we thank the U.S. Army at Yuma Proving Ground for a helicopter flight over the region that gave us a glimpse of this truly inspirational landscape. Any omissions or errors in interpretation presented in this report are our own. EXECUTIVE SUMMARY This report documents a preliminary assessment of biodiversity values for portions of the Bureau of Land Management (BLM) Yuma Resource Management Area, including a large Sonoran Desert landscape, the “Expanded Kofa Complex.” The Expanded Kofa Complex is an area of approximately 2.7 million acres (1.1 million hectares) within the BLM Yuma Resource Management Area that includes large blocks of land managed by the BLM, the U. S. Army at Yuma Proving Ground (YPG), and the U.S. Fish and Wildlife Service (USFWS) at Kofa National Wildlife Refuge. The assessment results contribute to the development of a biodiversity management framework for the Expanded Kofa Complex. The initial steps of framework development reported here—conservation element selection, status, and potential threat identification—provide the preceding federal agencies and the Arizona Game and Fish Department (AGFD) with information that can facilitate their ability to work individually and cooperatively, but still within the bounds of their individual missions, to manage and conserve the biological diversity (biodiversity) of the region. Within this report we describe the challenge of developing a biodiversity management framework for an area, such as the BLM Yuma Resource Management Area, that includes land managed by numerous agencies and landowners. In some cases these lands also are fragmented by significant movement and dispersal barriers for the area’s biota, such as by roads or incompatible land use. A first step in confronting this challenge was to delineate a functional conservation area that could serve as the focus of our analysis. A functional conservation area is a geographic domain that maintains focal ecosystems, species, and supporting ecological processes within their natural ranges of their variability. We chose to focus on a relatively contiguous block of federal land, centered around the Kofa National Wildlife Refuge and identified in this report as the Expanded Kofa Complex, to establish a starting point for delineating a functional conservation area. Information on the biodiversity of the Sonoran Desert Ecoregion provided a regional context for this area and an initial basis for determining in part what ecosystems and species should be a focus for management. We next employed a “coarse filter-fine filter” analysis to select appropriate species, specialized habitats, and plant communities (collectively termed “conservation elements”) to represent the native biodiversity of the Expanded Kofa Complex. The coarse filter-fine filter approach applies contemporary principles from conservation biology and incorporates information from the scientific literature, geospatial datasets, and expert knowledge to select conservation elements that become the focus of management. We took into account the ecoregional information mentioned above and agency management concerns for individual species, specialized habitats, and plant communities in deriving the appropriate conservation elements. The coarse filter-fine filter approach is recognized by conservation biologists as one of the most rigorous approaches to conservation planning because it takes into account the many ways in which biodiversity exists on the landscape—including its different levels of biological organization, the different spatial scales at which it occurs, and different levels of rarity. We hypothesize that with appropriate selection and management of conservation elements, most of the biodiversity of the Expanded Kofa Complex is likely to be protected over the long-term. i A total of seventeen natural communities (plant communities and physical habitats that with one exception, desert tinajas and springs, constitute the coarse filter), species, and guilds are proposed as preliminary conservation elements for the Expanded Kofa Complex (Table ES.1). The preliminary conservation elements include nine natural communities, five individual species, and three guilds (a total of 13 species contribute to the guilds). These species, guilds, and natural communities were selected from over 160 potential conservation elements. The selected conservation elements (1) are representative of biodiversity within the Sonoran Desert Ecoregion; (2) account for the occurrence of biodiversity at different spatial scales, across taxonomic categories, and different levels of rarity; (3) are relevant to natural resource management; and (4) in some cases, are most effectively managed by the cooperative efforts of multiple agencies. By accounting for scale and other patterns that shape the overall biodiversity of an area, the conservation element selection process also attempts to capture the relevant supporting ecological processes that are important in maintaining biodiversity. We also present a preliminary map of the distribution of natural community conservation elements of the Expanded Kofa Complex (Figure ES.1). The natural community distributions are based in part on available geospatial datasets and on biophysical models that had been previously developed to map conservation element distributions on the Barry M. Goldwater Range and the Sonoran Desert National Monument. Although preliminary, the natural community map is a significant outcome of this assessment because there are no other vegetation maps for the Expanded Kofa Complex region that are mapped at a scale appropriate for natural resource management in the Yuma Resource Management Area. As a result, the preliminary natural community map provides land managers with a starting point for considering biodiversity management in a landscape context. In addition to selecting conservation elements and mapping natural communities for the Expanded Kofa Complex, we present information on the status and regional threats of the species and natural communities and the relative importance of the Expanded Kofa Complex in their conservation. We also provide information on areas within the Yuma Resource Management Area (outside the Expanded Kofa Complex) that have significant biodiversity value, including portions of the Colorado and Gila Rivers. Some of the notable findings discussed in more detail in the report include: • A population of Mojave fringe-toed lizards (Uma scoparia) is confirmed to occur on isolated sand dunes on YPG. • The Expanded Kofa Complex and its surroundings include the largest unfragmented habitat for desert bighorn sheep in Arizona. • Twenty-two of Arizona’s twenty-eight bat species are expected or known to occur within the Yuma Resource Management Area. • Large patches of the Mountain Upland natural community occur at the higher elevations of the Kofa Mountains in the Kofa National Wildlife Refuge and include chaparral and woodland relic species, including the globally rare Kofa barberry (Berberis harrisoniana). ii • One of only two naturally occurring populations in Arizona of the state’s only native palm, the California fan palm