September 13, 2019
Michael Evans

Finding Ways to Balance Energy Development and Species Conservation on Public Lands

Desert Tortoise
Justin Ennis / Flickr user Averain

Increasingly, we are confronted with the ways that climate change contributes to the looming sixth mass extinction. Historically, the Mojave Desert tortoise (Gopherus agassizii) has been threatened by changes in land use that destroy its habitat - like urbanization, road construction and off-road vehicle trails. But today, this species is facing an ever more difficult road to recovery, with the prospect of rising temperatures and decreasing rainfall due to climate change threatening to reduce the availability of food, facilitate the spread of invasive plants, and shift the ratio of males to females.

Solar Panels at Topaz Solar 2
Sarah Swenty/USFWS

To combat climate change, Defenders of Wildlife is committed to the development of renewable energy sources like solar power as a replacement for fossil fuel and we are working to find approaches that do not compromise wildlife conservation. The desert tortoise is a challenging case because its range in the Mojave desert is in some of the most productive and important areas for solar energy development. Any utility-scale energy development creates unique challenges for the desert tortoise. Not only can power generating facilities impair tortoise habitat, transmission lines can increase tortoise mortality. These tall structures provide nesting, roosting, and perches for ravens – one of the tortoise’s main predators. So how do we balance renewable energy development with tortoise conservation?

Clouds with Mojave yucca in Pinto Basin
Lian Law/NPS

At the Center for Conservation Innovation (CCI) our mission is to find new and improved ways to protect species that are close to the brink of extinction. We use science and technology to inform policy – in this case by developing tools that federal land management agencies can use to prioritize the lands they manage for wildlife conservation. CCI is working with Defenders’ Landscape Conservation program and others to create a transparent, objective, and replicable approach to making decisions about where to prioritize solar development that minimizes impacts to desert tortoise. The online tool we have built helps decision makers decide how they value tortoise habitat suitability and connectivity before seeing how much habitat is available or where. These valuation decisions are then translated to a map to define areas of high, medium, and low conflict with tortoise habitat.  By making these subjective judgements explicit and up-front, this approach helps avoid cherry picking areas for development or conservation that correspond to pre-existing preferences. In the Mojave Desert, Defenders of Wildlife is working with the Bureau of Land Management (BLM) southern Nevada district, which encompasses roughly 1/3 of the Mojave Desert tortoise’s range, to make more informed land management decisions through better science. One of the main issues under consideration is the designation of areas of critical environmental concern and solar development zones - designations that determine where solar energy projects can and cannot be cited. To guide these decisions, the BLM wants to identify areas that are in high, medium, and low conflict with tortoises based on where suitable tortoise habitat is found.  

The tortoise and the solar panel graphic

So what level of habitat suitability qualifies as high conflict? And how do we account for small areas that connect highly suitable habitat patches? This process often involves subjective judgments made using maps of suitable habitat and habitat connectivity. As you might imagine, different stakeholders often have different opinions and motivations for different designation. Using our prioritization approach, a decision maker first decides how they theoretically value Mojave Desert tortoise habitat suitability and connectivity by identifying an appropriate curve that converts habitat suitability or connectivity to a standardized ‘Importance.’  For example, the left curve above (orange line) indicates that we think even low suitability habitat is relatively important.  In contrast, the right curve (blue line) shows the ’Importance’ of an area increasing steadily as habitat connectivity increases.  Whatever function is selected, the way that desert tortoise habitat is being valued will be transparent and unbiased by where habitat is found.

Solar Panels
Tom Witham/USDA

Once the relationships between habitat suitability/connectivity and importance are defined, our tool calculates the value of all possible combinations of connectivity and suitability. This range of values is fixed between 0 and 2, allowing us to consistently define high, medium, and low conflict categories by splitting this range into thirds. The transformed ‘Importance’ values will be distributed amongst these fixed categories differently depending on how a user has decided to value habitat suitability and connectivity. To see how this works, check out our public, online tool that lets users experiment with different valuation functions and see the high, medium, and low conflict designations. Finally, now that we have defined the ‘Importance’ of all possible combinations of habitat suitability and connectivity, we can map those scores back onto the landscape based on where tortoise habitat occurs.

Desert Tortoise Joshua Tree NP
Kurt Moses/NPS

We are excited about this approach because it provides a quantitative, objective decision support tool that the BLM can use to protect tortoises while increasing solar energy production in southern Nevada. And beyond tortoises, we are working to make this prioritization tool generic, such that it could serve as a replicable model for environmental prioritization and decision-making in any context where information about species habitats are being used to inform and designate protected areas. Florida panthers, red-cockaded woodpeckers, Sonoran pronghorn, Mexican gray wolves, and many other species could benefit from this strategy. 


Michael Evans headshot

Michael Evans

Conservation Data Scientist
Mike Evans works with a variety of biological, and administrative data to improve the implementation of the Endangered Species Act.  

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