All four of North America’s deserts can be found in Arizona, three of which are considered “warm” deserts (Sonoran, Chihuahuan, Mohave) and one is considered a “cold” desert (Great Basin). Although all four share the common factor of aridity, each has a unique set of physical characteristics with distinct suites of plants and animals (Brown 1994). As a result, this habitat group contributes significantly to Arizona’s exceptionally high biodiversity. Together, these habitats make up approximately 45% of the landscape in Arizona and each provides important habitat for fish and wildlife species.
Upper and Lowland Sonoran Desertscrub
The most biodiverse of all North American deserts, the Sonoran Desert spans the south-central and southwestern portions of Arizona and extends into Sonora, Mexico and southeastern California. Much of the Sonoran Desert landscape is characterized by low mountain ranges separated by large open valleys (Basin and Range topography). Vegetation composition is generally more diverse here than the Mohave or Chihuahuan deserts, with leguminous trees, shrubs, and cacti, including the iconic giant saguaro cactus, covering the desert valleys and foothills. Typical climate consists of hot, dry summers and mild winters with precipitation occurring in a bimodal pattern with two “wet” periods: July to September (monsoon season) and December to February (Bradley and Colodner 2019). Warm winters are a distinguishing characteristic of the Sonoran Desert, where winter frosts are rare. Approximately 60 species of mammals, 350 bird species, 20 amphibians, 100 reptiles, and 30 species of native fish make their home in the Sonoran Desert for at least a portion of their life cycle. In addition, an estimated 2,000 species of plants and more than 200 species of native bees also occupy the Sonoran Desert region (Nabhan 2015).
The Phoenix and Tucson metropolitan areas lie within the Sonoran Desert and continue to expand as more and more visitors and new residents are drawn to the area’s warm climate, beautiful landscape, outdoor recreational activities, and economic opportunities. The population growth and corresponding development are threatening the biodiversity and overall health of natural communities in the Sonoran Desert region.
The Sonoran Desert comprises two distinct desertscrub types, the lower Sonoran desertscrub and upland Sonoran desertscrub, characterized by different topography and vegetative communities (Dimmit and Fusari 2015). See lower Sonoran desertscrub and upland Sonoran desertscrub habitat profiles for further details.
The Mohave Desert in Arizona occurs in the northwestern and north-central portions of the state, covering much of Mohave County as well as portions of Yavapai County. The Mohave Desert also covers a large area of southeastern California and extends into southern Nevada and the extreme southwestern corner of Utah. Elevation is a bit higher than the Sonoran Desert and the climate is generally cooler with more winter precipitation (USGS 2005). Winter frosts are common. Basin and range topography characterizes the Mohave Desert with desertscrub habitat throughout the broad valleys. Other than the Joshua tree and soaptree yucca, smaller shrubs, grasses, and annual forbs dominate lower elevation areas.
In Arizona, the Mohave Desert is sparsely populated. Kingman is the largest city with a population of approximately 31,000 in 2020. A large portion of the land is State Trust or owned by BLM, where livestock and wild burro grazing, along with outdoor recreational activities such as off-highway vehicle use, have impaired undeveloped areas and altered the desert plant community composition. Specifically, abundance and diversity of native grasses have been reduced with a subsequent increase in shrub density and non-native annuals (Zuliana et al. 2021). In recent years, the expansion of irrigated farmlands in Mohave County has caused concern regarding increased groundwater pumping. The depletion of groundwater from the desert aquifers could create serious issues for the citizens of Kingman and surrounding areas and would further stress parched Mohave Desert habitats (Burrell 2020). See the Mohave Desertscrub habitat profile for further details.
The Chihuahuan Desert occurs primarily in Mexico, however, it also extends into portions of Texas, New Mexico, and a small portion of southeastern Arizona. Although the topography consists of the same Basin and Range pattern as the Sonoran and Mohave deserts, the Chihuahuan Desert climate differs, in that it generally receives more of its precipitation during the summer monsoons (Briggs et al. 2019). Winters are generally colder due to the higher elevation compared to the Sonoran Desert. Overall climate in this habitat type is characterized by hot summers and cool, dry winters. Biodiversity is rich in the Chihuahuan Desert with many endemic species, a result of long-term isolation by mountain ranges to the east and west. This geographic isolation also increases vulnerability to threats such as climate change, livestock grazing, agriculture, and sand and gravel mining (Hruska et al. 2017). The combination of habitat degradation, barriers to wildlife movement, pollution, and invasion of non-native species from these anthropogenic sources is taking a toll on this region (Poulos et al. 2013).
A rare and important desert riparian area, the undammed San Pedro River and riparian corridor, provides high quality habitat for many species of migrating birds as well as many other native fish and wildlife species (Brand et al. 2010, Stromberg and Tellman 2009). Today, more than one-third of the river corridor is protected, thanks to collaborative conservation efforts between AZGFD and our partners like TNC and BLM. Several wildlife SGCN, including the loach minnow, desert pupfish, and spikedace have been reintroduced to waters in the San Pedro watershed.
About 30% of the Chihuahuan Desert in Arizona is owned and managed by BLM. An additional 40% of this desert is State Trust land, where livestock grazing and recreational activities including off-highway vehicle use are common. State Trust land also has the potential to be developed, contributing to additional habitat loss and fragmentation. See the Chihuahuan desertscrub habitat profile for further details.
Great Basin Desertscrub
Portions of Great Basin desertscrub habitat occur on the plateaus of northern Arizona. Here, lower, drier, and sparsely-vegetated areas exist adjacent to more topographically diverse cliff-bench complexes where higher elevations and more annual moisture bring greater abundance and diversity in vegetation. Blackbrush, ephedra, rabbitbrush, white ratany, and broom snakeweed are typical shrubs found in the relatively shallow, sandy soils. Livestock grazing and altered fire regimes are major sources of impacts to Great Basin desertscrub habitat. Many of these areas that once supported native shrubs are now invaded by non-native annual grasses. See the Great Basin desertscrub habitat profile for further details.
Arizona’s desertscrub systems are as varied as they are unique to one another. However, they all share specific biotic and abiotic characteristics that make them highly susceptible to environmental change. Low annual precipitation rates, lack of fire-tolerant vegetation, and invasive species make all of Arizona’s desertscrub habitats highly vulnerable to the many threats facing us today. One of the most critical threats to all of Arizona’s desertscrub systems is climate change. Slight temperature changes as well as changes to the timing and amount of precipitation that occurs could have substantial and long-lasting impacts to these habitats and species. Habitat fragmentation and loss due to urban and suburban sprawl is also having increasingly adverse effects to these systems, especially in the Sonoran Desert regions that surround growing urban areas of Tucson and Phoenix.
Currently, there are several local, state, and national initiatives that have implemented public/private partnerships to accomplish desertscrub conservation in Arizona:
The Central Arizona Conservation Alliance (CAZCA) brings together public and private entities under the guidance of the goals of the Regional Open Space Strategy (ROSS). Mostly focused on the Sonoran Desert region, partners in the Alliance include Desert Botanical Garden, Pinal and Maricopa counties, AZGFD, and others.
Founded in 1995, the non-profit Altar Valley Conservation Alliance works to conserve productive working landscapes in the Sonoran Desert west of Tucson. The Alliance is primarily made up of many ranchers and private landowners in collaboration with other private and public entities, including AZGFD, Pima County, University of Arizona, the Arizona Land and Water Trust, TNC, and several others.
The Desert Bird Conservation Plan is a project of California Partners in Flight and Point Blue Conservation Science (formerly Point Reyes Bird Observatory) that was developed to guide conservation policy and action on behalf of desert habitats and wildlife. The geographic scope of this plan includes the Mojave Desert in California, southern Nevada, and western Arizona, as well as the Sonoran Desert in California, western Arizona, and Sonora and Baja California Norte, Mexico. There are many federal, state, university, private and public entities associated with this plan.
Some of the broader and most relevant plans to desertscrub habitats and species (with web links) can be found in each of the habitat profiles, such as: