Ecoregion-Based conservation in the Chihuahuan Desert

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Ecoregion-Based conservation in the Chihuahuan Desert

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Title: Ecoregion-Based conservation in the Chihuahuan Desert
Author: Dinerstein, E.; Olson, D.; Atchley, J.; Loucks, C.; Contreras-Balderas, S.; Abell, R.; Iñigo, E.; Enkerlin, E.; Williams, C. & Castilleja, G.; Atchley, J.
Abstract: Deserts, by their very name, are seldom regarded as important reservoirs of biological diversity. But some deserts are extraordinarily rich in species, rare plants and animals, specialized habitats, and unique biological communities. One example is the Chihuahuan Desert, identified by a WWFsponsored global assessment of biodiversity as one of the most important arid ecoregions on Earth (Olson and Dinerstein 1998). Spanning an area of almost 629,000 km2 from the southwestern U.S. to the Mexican Central Plateau, the Chihuahuan Desert is world renowned as a center of diversity for cacti (family Cactaceae). Besides cacti, many desert plants, fish, and reptile species show rather localized patterns of endemism and exhibit high turnover of species with distance - the hallmark of a biologically rich ecoregion. The complexity of the freshwater fish assemblages elevates the Chihuahuan as the only desert ecoregion recognized for both its freshwater and terrestrial biodiversity in the Global 200 analysis (Olson and Dinerstein 1998). The conservation of Chihuahuan biodiversity requires a comprehensive ecoregion-scale strategy rather than ad-hoc activities at isolated sites. This document contains the first layer of information needed to create such a strategy- a biological assessment and a biodiversity vision. We address the following key questions: 1) How can we accurately delineate the biological features that elevate the Chihuahuan Desert as one of the highest priority ecoregions in the world? 2) What constitutes a vision of success for conservation of these outstanding features over the next fifty years? To preserve Chihuahuan biodiversity over the long term, we applied an ecoregion-based conservation (ERBC) approach. The goal of ERBC is to conserve the full range of species, natural communities, habitats, and ecological processes characteristic of an ecoregion. The ERBC process began with a series of meetings to enhance collaboration among many U.S. and Mexican scientists, conservationists, and representatives from government agencies and non-governmental organizations. We then conducted an extensive literature review and preliminary mapping study of the Chihuahuan Desert. Together with our collaborators - Comisión Nacional para el Conocimiento y Uso de la Biodiversidad (CONABIO), PRONATURA Noreste, The Nature Conservancy, and the Instituto Tecnilogico y de Estudios de Superiores Monterrey (ITESM) - we invited over 100 experts to participate in a prioritysetting workshop to test the proposed approach to ERBC. Sixty of the 100 invitees attended, representing a wide array of taxonomic experts with extensive personal knowledge of the ecoregion. A subset of those unable to attend the workshop provided peer review for this assessment. We devised a method for Chihuahuan experts to provide data on species occurrences and distributions, natural communities, ecological processes, and intact habitat areas (Chapter 2). The first activity at the workshop was to map important sites for conservation of six indicator taxa - birds, mammals, herpetofauna, invertebrates, obligate freshwater species, and plants - and distinct habitats. These 299 locations became known as nominated sites for an ERBC strategy. The second activity was to synthesize the data layers of the overlapping nominated sites to create a smaller subset of 61 terrestrial candidate priority sites. Unfortunately, it is impossible to act immediately at all 61 sites. Thus, the terrestrial experts adopted a matrix and ranking system to prioritize terrestrial sites based on the integration of two powerful variables: biological distinctiveness and landscape integrity (Chapter 2, Figure 2.2). The freshwater experts designed a similar matrix, based on biological distinctiveness and habitat intactness (Chapter 2, Figure 2.3). Biological distinctiveness estimates the relative rarity of biological features at global, continental, and ecoregion scales (Chapter 4). Classification of this variable ranged from sites that supported high levels of endemism, rare communities, or important ecological and evolutionary ix processes - the highest ranked features - to multiple sites that support similar species and communities in the lowest ranked category. Landscape integrity estimates the probability of long-term persistence of ecological processes, species assemblages, and other important elements of biodiversity (Chapter 5). It is divided into categories based on the size of habitat blocks and their condition: intact or relatively intact, degraded, or highly degraded but still restorable. Habitat intactness, the variable used in the freshwater matrix, is similar to landscape integrity but does not take into account the size of habitat blocks, as this measure is not as relevant or easily measured for freshwater systems. The cells of the matrix were consolidated into five ranks, but only the top four ranks were considered as part of the conservation portfolio for terrestrial sites. Only the top two ranks were considered in the freshwater analysis.
Date: 2000

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Observatorio Ambiental de El Colegio de Chihuahua (COLECH)
Biblioteca Virtual Ambiental del Estado de Chihuahua (BVA)
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