The Nature Conservancy in Arizona - An Ecological Analysis of Conservation Priorities in the Sonoran Desert Ecoregion

An Ecological Analysis of Conservation Priorities in the Sonoran Desert Ecoregion

April 2000

EXECUTIVE SUMMARY

Sand Tanks-Sauceda Mountains Complex
Conservation Site 32 in Arizona © R. Marshall/TNC

A bi-national team was convened in 1998 to compile and analyze biological and ecological data for the 55-million acre (22 million ha) Sonoran Desert Ecoregion, which comprises parts of Arizona, California, Sonora, and Baja, California. The objective of this project was to use a science-based approach to identify a network of Conservation Sites throughout the Ecoregion that, with proper management, would ensure the long-term persistence of the Ecoregion's biodiversity, including rare and common species, native vegetation communities, and the ecological processes needed to maintain these elements of biodiversity. The technical team convened to compile and analyze data included staff from The Nature Conservancy, Sonoran Institute, Instituto del Medio Ambiente y el Desarrollo Sustentable del estado de Sonora, and Arizona Game and Fish Department with assistance from more than 100 experts from public agencies, academic institutions, conservation organizations, Tribes, and private resource professionals. To generate awareness of the project and attract participation by natural resource entities throughout the Ecoregion we initiated an outreach program that included development of a project website and presentations at more than 20 local, regional, and national meetings, symposia, conferences, etc.

Saguaro Cactus Blossoms
© Tad Nichols

We selected a representative sample of the Ecoregion's species and natural vegetation communities to serve as Conservation Targets, the basic unit of analysis for this exercise. We selected a total of 353 species from six taxonomic groups (amphibians/reptiles, birds, fish invertebrates, mammals, plants). Emphasis was placed on selecting species endemic to the Ecoregion. We also used 78 natural vegetation communities to represent a broader level of biological organization across the Ecoregion. The approach of using both fine-scale data on species and coarse-scale data on vegetation communities was presumed to be a robust way to represent the broadest array of biodiversity.

We used a variety of data sets, including species' population data housed in Natural Heritage Programs, spatially-referenced data on vegetation, land use, hydrography, topography, land management, etc. To fill data gaps and obtain contemporary data we convened a two-day experts workshop at the University of Arizona where 106 experts participated from 51 agencies, universities, Tribes, private resource professionals, and conservation groups. All data were subjected to a set of Conservation Criteria that established numeric goals for each Conservation Target. Contemporary data provided by experts were used as the nuclei for identifying the network of Conservation Sites. Sites throughout the Ecoregion were evaluated for the number and types of Conservation Targets considered viable within their boundaries. We also constructed a biophysical model using spatial data for climate, vegetation, elevation, slope, and aspect to derive an independent index of the diversity of the Sonoran Desert Ecoregion.

Sonoran Desert Ecoregion © Anne Gondor/TNC

In total, 100 large landscapes and 79 small, localized areas were identified across the Ecoregion as a network of Conservation Sites where conservation opportunities should be pursued. The network includes 23,108,106 acres (9,355,508 ha) of lands in Mexico and the U.S. Landscape-scale Conservation Sites capture entire ecosystems, such as a complex of mountain ranges and valleys, where ecological processes remain largely intact. The 79 localized Sites capture some of the Ecoregion's rarest plants and animals and were, generally, isolated from areas identified for the larger landscape Sites. When compared to the biophysical model, the identified network of landscape-scale Conservation Sites captured 89% of the Ecoregion's biophysical variation. Areas that were not adequately represented¾mostly in the Plains of Sonora and Arizona Uplands portions of the State of Sonora 3/4 include some of the least well-known areas in the Ecoregion.

A "GAP" management analysis of the Ecoregion revealed that, at present, less than the 20% of the network of Conservation Sites is managed to promote the long-term persistence of Conservation Targets. Of the 18 Conservation Sites identified to conserve the Ecoregion's riverine, riparian, and aquatic systems, only 9% are managed to promote the long-term persistence of biodiversity. Several recommendations were identified for improving the conservation status of the network of Conservation Sites. The results of this project can serve regional and local conservation efforts by: (1) identifying the most important areas Ecoregion-wide for conservation of biological diversity; (2) providing a baseline characterization from which to evaluate the status of Conservation Targets and trends in major stressors across the Ecoregion, and; (3) providing an ecoregional context for designing and evaluating projects, drafting conservation proposals, and anticipating and framing budget needs.

Given that Conservation Sites overlap lands managed by public, private, and communal entities, a variety of approaches may be needed to accomplish the overall goal of biodiversity conservation. For lands already designated for conservation purposes, implementing conservation programs that abate or minimize major stressors to Conservation Targets will enable true adaptive management. Several agencies and organizations throughout the Ecoregion are already having success with this approach. For lands in which conservation is one of multiple management goals, integrating Ecoregional data and a goals-based approach into comprehensive land management planning will help insure that the Ecoregion's biodiversity is adequately characterized, evaluated, accounted for, and conserved through development of appropriate management programs. For lands in which the goal does not include conservation, opportunities should be identified to increase attention to conservation of biodiversity by developing collaborative programs among public and private entities (e.g., U.S. Fish and Wildlife Service's Partners for Wildlife Program, environmental management area designations in Sonora, conservation easements, etc.).

The map below identifies the general location and areal extent of the 100 landscape-scale conservation sites mentioned in the Executive Summary above. Colors distinguish individual sites, but they do not denote any priority for conservation action. The organizational logos accompanying the map identify those entities that played a key role in bringing the Sonoran Desert ecological analysis to fruition. Additionally, this cooperative project could not have been accomplished without the support of the Department of Defense's Legacy Resource Program, as well as the support of other numerous agency and institutional partners. Following the map is a brief description of what landscape-scale conservation sites represent. The complete ecological analysis document (text plus 15 figures, .pdf, 1MB) can be accessed in pdf format.

What is a landscape-scale conservation site?
At a minimum the aggregate of all landscape-scale conservation sites represents a hypothesis: that implementing appropriate management at each of the identified sites would ensure the long-term persistence of most of the Sonoran Desert Ecoregion's biodiversity. "Appropriate management" does not imply any single type of management regime, nor does it imply the elimination of all human activities. Appropriate management means that major stressors-agents that are the source of degradation and impairment afflicting conservation targets at a particular site-are identified and abated/minimized through management actions, including restoration.

If conservation actions taken today are to be relevant tomorrow, they must represent a wide range of ecological conditions. We incorporated the concept of "ecological gradients" as an explicit criterion in identifying and evaluating the robustness of individual landscape-scale conservation sites for maintaining included biodiversity elements over time. Ecological gradients encompass variability in elevation, slope, aspect, soil types, and insolation (e.g., the gradients expressed within a mountain-valley-mountain complex). By maintaining a high level of variability in ecological conditions within a site, we provide opportunities for species distributions to track changes in environmental conditions, such as in response to local fluctuations in wet and dry cycles or more regional long-term changes in climate. Additionally, the integration of landscape-scale factors such as ecological gradients into conservation planning also helps to ensure that ecological processes (e.g., hydrologic regimes), which often operate at such scales, remain intact.

Preferred citation for the full ecological analysis:
Marshall, R.M., S. Anderson, M. Batcher, P. Comer, S. Cornelius, R. Cox, A. Gondor, D. Gori, J. Humke, R. Paredes Aguilar, I.E. Parra, S. Schwartz. 2000. An Ecological Analysis of Conservation Priorities in the Sonoran Desert Ecoregion. Prepared by The Nature Conservancy Arizona Chapter, Sonoran Institute, and Instituto del Medio Ambiente y el Desarrollo Sustentable del Estado de Sonora with support from Department of Defense Legacy Program and agency and institutional partners. 146 pp