Riverside Solar Zone Tortoise Habitat Too Widespread to Avoid

Desert tortoise ready for its closeup | Photo: US Fish and Wildlife Service/Flickr/Creative Commons License

Solar development in the revised Riverside East Solar Energy Zone (SEZ) may harm as much as 14% of the region's habitat for the threatened desert tortoise, and such habitat is too widespread within the SEZ to be avoided by solar developers. That according to the Final Programmatic Environmental Impact Statement for Solar Energy Development in Six Southwestern States (PEIS), released by the departments of Energy and the Interior in July.

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The Riverside East SEZ contains 147,910 acres of land the federal government deems potentially suitable for solar development. It extends across eastern Riverside County from the east end of Joshua tree National Park to the city of Blythe, on the Colorado River.

According to the PEIS's discussion of desert tortoises in the Riverside East SEZ, 136,800 acres of suitable tortoise habitat could be directly affected by construction and operation of solar energy facilities built in the SEZ -- about 3.3% of such habitat in the region. Indirect effects of solar development, such as habitat fragmentation, could impair another 442,000 acres of tortoise habitat in the area, another 10.5% of the region's habitat. All in all, according to the PEIS, almost 900 square miles of tortoise habitat could be affected by development in the SEZ.

Based on U.S. Fish and Wildlife Service (FWS) surveys of tortoises in similar habitat in nearby Joshua Tree National Park, the PEIS estimates that an 80% build-out of suitable lands on the SEZ for solar development could directly affect up to 2,865 desert tortoises.

Though the boundaries of the SEZ were redrawn after comment from environmental groups on the wildlife impacts of the original, 202,89-acre version, the redrafted SEZ still contains crucial wildlife connectivity corridors, and adjoins areas of tortoise habitat of sufficient value to have been protected as Desert Wildlife Management Areas (DWMAs) by the BLM. As the PEIS says;

Information provided by the USFWS since the publication of the Draft Solar PEIS has identified the SEZ as being situated in an area that provides habitat and genetic connectivity between areas with greater habitat suitability north and south of the SEZ where desert tortoise densities are presumably higher. The USFWS has also determined that some portions of the SEZ are within high-priority connectivity areas, which are necessary to facilitate natural processes of gene exchange between populations in order to maintain population viability. Solar energy development on the Riverside East SEZ, therefore, may isolate and fragment these tortoise populations by creating impediments to natural migration patterns. The SEZ is situated between the Chuckwalla and Pinto Mountains DWMAs (these DWMAs also contain USFWS-designated critical habitat for desert tortoise), and the SEZ may provide important connectivity for desert tortoise movements between the DWMAs.Therefore, development on the SEZ may disrupt desert tortoise population dynamics in nearby DWMAs and designated critical habitat. Fragmentation would be exacerbated by the installation of exclusionary fencing at the perimeter of the SEZ or individual project areas.

The California Department of Fish and Game describes DWMA designation as "the central strategy for saving the tortoise."

The PEIS further says that making adjustments to site design of solar installations, or excluding development from tortoise habitat with the SEZ, probably won't work:

[I]mplementation of programmatic design features alone is unlikely to substantially reduce these impacts. Avoidance of all potentially suitable habitats for this species is not a feasible means of mitigating impacts, because these habitats (desertscrub) are widespread throughout the area of direct effects

Instead, the PEIS suggests mitigation -- buying and protecting tortoise habitat elsewhere -- and moving tortoises from construction sites as their best solution. The document states:

Despite some risk of mortality or decreased fitness of the desert tortoise, translocation is widely accepted as a useful strategy for the conservation of this species (Field et al. 2007). [Link added.]

Translocation of desert tortoises is indeed widely accepted, but it is not universally accepted. A year after "Field et al. 2007" was published, a tortoise relocation program at Fort Irwin was called to a halt when half the moved tortoises died. A study published this year by USGS biologist Ken Nussear and colleagues indicates that translocations may work well if done carefully, but the authors caution that no thorough scientific peer review of the practice exists, and that habitat conservation should always be the first priority.

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