An Ecological Analysis of Conservation Priorities in the Apache Highlands Ecoregion

Date Published or Written


Rob Marshall, Dale Turner, Anne Gondor, Dave Gori, Carolyn Enquist, Gonzalo Luna, Rafaela Paredes Aguilar, Susan Anderson, Sabra Schwartz, Chris Watts, Eduardo Lopez, Pat Comer


Executive Summary

A bi-national team worked from August 2001 through February 2003 to systematically analyze the best scientific information available for the 30-million acre (12-million ha) Apache Highlands ecoregion. The objective was to identify a network of conservation areas that, with proper management, would ensure the long-term persistence of the ecoregion’s biological diversity. The technical team included staff from The Nature Conservancy, Instituto del Medio Ambiente y el Desarrollo Sustentable del Estado de Sonora (IMADES), and the Arizona Game and Fish Department. A companion study initiated to fill a critical data gap - on the status of the ecoregion’s grasslands – was completed with the assistance of the Natural Resources Conservation Service, University of Arizona, Bureau of Land Management, U.S. Forest Service, and Instituto Naciónal de Investigaciónes Forestales, Agricolas y Pecuarias (INIFAP). To generate awareness of the project and attract assistance we initiated an outreach program with more than a dozen presentations made to public agencies, tribes, private entities, and regional conferences and symposia.

The Apache Highlands ecoregion comprises portions of four states in two countries: Arizona and New Mexico in the U.S., and Sonora and Chihuahua in Mexico. It is bounded on the north by the Mogollon Rim (the southern edge of the Colorado Plateau), to the west by the Sonoran and Mojave deserts, to the south by the Sierra Madre Occidental, and to the east by the Chihuahuan Desert. We selected a representative sample of the ecoregion’s species and ecological systems to serve as the focal units of analysis, or conservation targets. In total, 223 species of amphibians, birds, fish, mammals, reptiles, invertebrates, and vascular plants were selected with special emphasis given to imperiled, endemic, or keystone species, or those which are limited by area, dispersal, or particular ecological processes. Twenty-six terrestrial ecological systems were identified and incorporated into the analysis as conservation targets.

We developed numerical conservation goals for all targets as a quantitative basis for guiding analyses and evaluating outcomes. Conservation goals also serve as a hypothesis for evaluating two critical questions in conservation - How much is enough? How many discrete populations and in what spatial distribution are needed for long-term viability? The combination of selecting a representative suite of conservation targets and setting quantitative goals for targets are two attributes, in particular, that distinguish this regional conservation planning effort.

We used a variety of spatial and traditional data sets to assist in the identification of conservation areas, including species’ population data housed in Natural Heritage programs, Conservation Data Centers, and museums throughout North America, and spatially-referenced data on vegetation, land use, land management, hydrography, topography, infrastructure, and protection status. In addition, we developed three new spatial data sets: a literature review to develop a complete spatial coverage depicting the location of the ecoregion’s ciénegas; a 14- month field study done in conjunction with agency partners to delineate and characterize the status of the ecoregion’s remaining grasslands; and a linear mapping of native fish distributions in streams.

We used the computer algorithm, SITES, to identify the network of conservation areas. SITES selects areas to meet established conservation target goals while balancing objectives of efficiency, defined as the greatest number of goals met for the lowest “cost” or least amount of suitable land. The capability of the program to integrate multiple data sets in a repeatable process enabled rapid evaluation of alternative conservation area configurations. We developed and evaluated 27 different scenarios before settling on a draft conservation area network. The

draft network was reviewed by regional experts to identify omissions of areas that are important to conservation targets as well as commissions of areas where conservation is no longer feasible.

The final network consists of 90 conservation areas encompassing just over 12.5 million acres (5 million hectares), about 40% of the ecoregion. Conservation areas range in size from 1,235 to 1.9 million acres (500 to 757,500 ha), with an average of 138,967 acres (56,239 ha). Individual conservation areas captured from 1 to 119 conservation targets, with an average of 17 targets. The network captured 2,118 miles (3,408 km) of perennial streams, 86% of the perennial stream length in the ecoregion. Aquatic or riparian targets occur in 69 (77%) of the conservation areas.

Conservation goals were met for 83% of the targets, including 189 species and 12 ecological system targets. We came close to meeting goals (90% or more) for an additional 24 targets. Some conservation areas incorporate a continuous area from valley bottom to mountaintop; others span continuous areas from mountain range to mountain range. The former approach, if fully protected, should buffer conservation targets against the impacts of climate- induced changes in habitat, while the latter approach is needed to maintain dispersal areas and connectivity for wide-ranging, forest-dwelling species such as black bear.

Nearly 3.7 million acres (1.4 million ha) were identified for conservation in the Mexico portion of the ecoregion, while the remaining 8.8 million acres (3.6 million ha) of the conservation network was identified in the U.S. An analysis of protected status using a modified Gap classification revealed that only 5% of the ecoregion is in Gap categories 1 and 2, the highest levels of protection afforded. Twenty-seven percent of the ecoregion is in Gap category 3, where protection of natural land cover is balanced with extractive uses (e.g., federal multiple- use lands in the U.S.). Nearly 60% of the ecoregion, however, permits intensive land uses and lacks mandates preventing the conversion of native vegetation cover by anthropogenic uses.

We used two measures to rank the biodiversity value of the 90 conservation areas; target richness, or the number of targets found in each conservation area, and a measure of the uniqueness or “irreplaceability” of each area. Of the 10 highest-ranking conservation areas identified in the two analyses, 8 areas were the same across analyses. In both the richness and irreplaceability measures the Huachuca Mountains Grassland Valley Complex (#66) and Sierra San Luis/Peloncillo Mountains (#67) were the first- and second-ranked areas, respectively. Both conservation areas straddle the U.S.-Mexico border region. The Upper Verde Watershed (#9) ranks 3rd in richness and 4th in irreplaceability, while the Chiricahua Mountains (#58) ranks 3rd in irreplaceability and 4th in richness.

Several key stressors will continue to challenge our collective ability to grow sustainably and promote conservation of the region’s biological diversity. Growth in urban, ex-urban and rural areas that does not consider the region’s biological diversity will continue to foreclose opportunities and will result in the extirpation of more species. With increasing residents region- wide comes increasing demands on our limited surface and groundwater supplies. Again, a lack of planning that effectively integrates the needs of our aquatic and riparian fauna and flora will needlessly limit options for conservation and will likely result in expensive, crisis-driven recovery programs as more species receive protection under the Endangered Species Act. The effects of altered fire regimes in our forests are now more widely appreciated by the public after several years of catastrophic fires. But awareness is still low on the importance of fire in maintaining the region’s dwindling grasslands. Finally, invasive species, particularly in our aquatic systems, have placed some native species and native vegetation communities at a competitive disadvantage.

Proactive conservation efforts, such as Pima County’s Sonoran Desert Conservation Plan, need to be replicated throughout the ecoregion before conservation issues reach crisis proportions, at which time it will be far more costly to develop effective solutions. Such efforts will not only require the best available scientific information, as presented here, but also commitments by community leaders to engage the public in a focused dialogue about balancing future growth with conservation of the natural heritage we have inherited. The results of this analysis and the data developed for this study, collectively, provide a scientific basis for decision-making by federal, state, county and municipal agencies in planning for land and water conservation