The desert tortoise might be Nevada’s state reptile but rapid changes in fragile desert ecosystems could threaten its very existence. In the last 150 years, non-native animal and plant species, and urban development have infiltrated the Mojave and Sonoran Deserts that are the tortoise’s stomping ground. It’s an evolution that has led to both habitat loss and habitat degradation for this iconic species.
More recently, the construction and deployment of solar power facilities has further fragmented the tortoise’s home and altered the topsoil and land cover disturbing the available food supply. As a first step in mitigating these impacts, School of Life Sciences assistant professor Scott Abella and his team have previously investigated how to reintroduce native plants into the desert environment.
Now they’re determining how desert tortoises use these enhanced environments.
“Our project bridges a gap between the basic ecology of the desert tortoise and the development of practical conservation strategies for enhancing habitat quality in disturbed areas such as near renewable energy facilities,” Abella said.
Focusing on Forage
In 1990, due to the reduced numbers of the desert tortoise, the population in the Mojave and western Sonoran Desert was federally listed as threatened under the Endangered Species Act. Since that date, tortoise numbers not only haven’t recovered, but they’ve gone the wrong way. Between 2004 and 2014 there was a 32 percent decline for desert tortoises in designated recovery areas.
“This decline is considered serious because reproduction is also poor, raising questions as to whether desert tortoise populations can sustain themselves or continue to decline,” Abella said.
In response to the disturbing trend, the U.S. Fish and Wildlife Service prepared a Revised Recovery Plan for the desert tortoise in 2011. In this plan the scientists emphasized habitat conservation, enhancement, and restoration as priority recovery actions.
One of the areas with the greatest potential for enhancing quality of desert tortoise habitats is improving the quality and quantity of forage, Abella says. Currently, non-native annual plants mostly dominate the tortoises’ habitat. In 2012, he specifically targeted the Bureau of Land Management lands just north of the Ivanpah Solar Power Facility for improved forage.
In collaboration with the BLM, Abella and his UNLV team enhanced the habitats of 60, 100-square-meter plots by a variety of techniques such as fencing off the areas to keep large herbivores out.
By the end of the first year, Abella found that pelletized seeding quadrupled the density of some native plants.
“This research showed that augmenting native annual forage plants favored by desert tortoises is feasible,” Abella said. “Desert plantain is a native wildflower nutritionally useful to desert tortoises. The next step of this research would involve evaluating how desert tortoises respond to improvements in forage quality.”
Putting Knowledge to Use
While Abella’s earlier research proved hopeful, scientists have already established that the variation in the availability of such plants over time is key to desert tortoise health, making long-term results important. Abella and his team began to measure the forage conditions and how desert tortoises use these enhanced habitats in the spring.
“This work can help establish for how long restorative actions can augment forage for tortoises,” Abella said. For example, good forage plants might be persistent if their seeds have become stored in the soil enabling them to germinate in future years of good rainfall. “The seeds would not have been there if not for the restoration actions,” Abella said.
The scientists began counting signs of tortoises in the restored habitats and comparing any signs of usage to those in the unrestored areas. These counts and the monitoring of the forage quality are continuing through the spring of 2018.
Abella hopes that the research will help advance scientist’s understanding of how desert tortoises respond to habitat enhancement activities occurring near solar facilities. But the knowledge gleaned from the study could translate to other areas disturbed by construction or road building.
“By linking ecological knowledge of desert tortoise foraging ecology with habitat enhancement actions, this project can help inform conservation planning to ameliorate degradation of desert tortoise habitats,” Abella said.