Human Influence on Desert Tortoise Habitats

Science Center Objects

The deserts of the Southwest are under increasing pressure from growing human communities. The spread of cities, agricultural fields, grazing livestock, power plants, and other forms of human development in the past and present have affected the region’s natural resources, including its wildlife. WERC’s Dr. Kristin Berry is studying the response of threatened desert tortoises to changing habitats in the Mojave and Sonoran deserts.

Historic Land Use Patterns and Effects on Desert Tortoises

Dr. Kristin Berry is studying historic land uses and their effects on Agassiz’s desert tortoises (Gopherus agassizii) in the Mojave and western Sonoran desert ecosystems. Land uses include but are not limited to paved and dirt roads and trails, vehicle use off road and off trails, livestock grazing, feral burros, mining, and trash. All these activities can have detrimental effects on Agassiz’s desert tortoises and their habitats. For example, trash attracts ravens, which prey on juvenile and adult tortoises. Tortoises can also be threatened by livestock grazing on native plants that provide food and shelter from the harsh environment. In a recent publication, Dr. Berry and co-authors compared tortoise populations and habitat in three adjacent areas with different management. Tortoise populations and habitat were in better condition inside a protected area without vehicle use and livestock use, compared with critical habitat and private lands. Dr. Berry’s studies provide government managers with new research tools and information on current threats to tortoise populations.

 

Vegetation of the Mojave and Sonoran Deserts

Desert Marigold WERC

(Credit: Elizabeth Moore, Western Ecological Research Center. Public domain.)

The Mojave and Sonoran Deserts have experienced both urban development (aqueducts and other structures) and invasions of non-native, annual plants.

1. Dr. Kristin Berry and partners are examining the effects of invasive plants on desert ecosystems and, in turn, on the ecology of Agassiz’s desert tortoises. Non-native, invasive plants are often opportunistic and hardy species, and can quickly take over a new landscape. In the Mojave, invasive cheatgrass and Mediterranean grass have altered natural wildfire patterns, destroying habitat for native wildlife. Dr. Berry has documented rapid invasion and expansion of Sahara mustard, a non-native species, in the Colorado Desert.

2. Dr. Berry collaborates with BLM staff at the Desert Tortoise Research Natural Area, which preserves key habitat for desert tortoises, to study the Mojave’s native flora. This protected area is home to more than 250 native plants.  Dr. Berry and colleagues have prepared more than 500 herbarium specimens from the Research Natural Area for a permanent collection.

3. As part of a third project, Dr. Berry monitors changes in Mojave and western Sonoran Desert vegetation. Over time, Dr. Berry can monitor changes in and recovery of vegetation in previously disturbed areas, as well as track natural changes in plant communities over time. Monitoring is achieved using “rephotography,” i.e., comparing historical and current photographs, conducting site visits, and measuring changes in vegetation. Through this project, land and resource managers can learn more about natural changes and recovery processes in desert ecosystems. Dr. Berry recently published a study of natural recovery of annual and perennial plants along the Los Angeles aqueduct in the Mojave Desert.