Using Ecoregions to Understand Conservation Priorities: The Case of the North American Deserts

North American Deserts biomeOne of the primary tasks of Joint Venture conservation science is to establish linkages between regional and continental conservation goals for migratory birds.

“Setting conservation goals in such a large and diverse region as the Intermountain West is challenging,” says Patrick Donnelly, Spatial Ecologist with the Intermountain West Joint Venture (IWJV), “but when we separate the Intermountain West into ecologically meaningful units—known as ecoregions—we are better equipped to evaluate and rank conservation priorities and create wildlife and habitat models.”

Few North American Joint Ventures can rival the ecological and geo-political diversity of the IWJV. The IWJV encompasses 486 million acres of the Intermountain West, spanning nearly half the northern temperate zone. Within this region, elevational gradients climb from the lowest point on the North American Continent (–282ft) to over 50 of the tallest peaks (>14,000ft) in the continental United States.

The North American Desert Biome covers 57% of the land area in the Intermountain West. © IWJV
The Intermountain West can be divided into three major biomes (also known as ‘Level I Ecoregions’ according to the Commission for Environmental Cooperation): North American Deserts (57% of IWJV land area), Northwestern Forested Mountains (33%), and Temperate Sierras. (4%) These biome designations are useful to describe gross features related to topography, moisture, rainfall, and vegetative cover and the broad ecological processes that persist across the Intermountain West.

Though subdividing these biomes into smaller, more ecologically relevant units (Levels II, III, and IV ecoregions) is useful to develop locally-specific conservation models, understanding these biomes even at a coarse continental scale gives us a greater appreciation of the habitats, ecological threats, and conservation challenges in the Intermountain West.

The North American Deserts ecoregion encompasses the largest land area (278.9 million acres, or 57%) within the Intermountain West by far. While this ecoregion features a mix of physiographic features, it primarily consists of plains with hills and mountains and tablelands of high relief.

In the north, the Columbia and Snake River Plateaus are characterized by flat to rolling topography. In contrast, the Great Basin and its adjacent mountains include ranges (many greater than 10,000 ft) separated by broad, high valleys (many greater 3,000 ft).

The south is characterized by smaller mountain ranges and lower valley floors. Death Valley, for example, has the distinction of being the lowest point in the entire basin (282 ft below sea level) and for having the region’s record highest temperatures, nearing 134°F.

Not surprisingly, aridity is the primary ecological factor defining the North American Deserts. Soils of this ecological region are dry, nutrient poor, and high in calcium carbonate. Playa systems are abundant throughout.

Landscapes here are dominated by low-growing shrubs and grasses. Sagebrush is common in the Great Basin, but shadscale and greasewood occur on more alkaline soils. Tarbush and creosote bush are dominant in the Chihuahuan desert, with warm season grasses intermixed throughout.

In the North American Deserts ecoregion, human activities are generally sparse outside of large population centers, but they often have substantial impacts on the limited resources of the region. Federally-funded reclamation projects have encouraged development of large-scale irrigated agriculture in parts of the Columbia Plateau, Snake River plain, Wasatch piedmont, upper Rio Grande, and San Luis Valley. Although only a small fraction of the region’s land base is cultivated, cattle grazing is common, and irrigated agriculture is the primary consumer of water resources. Interestingly, most of the water within the Intermountain West originates outside the ecological region as winter snow pack.

Growing conservation concerns in the North American Deserts ecoregion include: hydrologic modifications, salinization, sedimentation, pesticide contamination, invasive species, and sufficient water quantity and quality for aquatic biota. The IWJV is keeping its pulse on these threats. The science staff are amassing the data necessary to evaluate and propose models for conservation action. A primary goal is to determine where and how conservation planning will be most effective in maintaining bird population goals. The act of establishing and analyzing the spatial datasets underlying these biomes and the subsequent ecoregions was a significant step in this direction.

Now that the datasets are in place, Patrick Donnelly and the science team will develop and test a variety of bird habitat and population models.

“The data underlying these ecoregional frameworks provide us with a powerful foundation for landscape conservation at all levels,” says Patrick, “We think this work will allow the IWJV and our partners to be more strategic and focused in conservation planning than ever before.”

Laura Kammermeier is Digital Communications Contractor for the IWJV.