Predicting Wildlife and Plant Responses to Solar Energy Development in the Desert Southwest
The development of large-scale solar energy facilities is expanding quickly to meet growing electricity generation needs in the U.S. in the coming decades.
USGS conducted a study of wildlife and plant species' responses to solar energy facility construction and operation, developed a framework to predict future responses, and identified ways to mitigate or minimize those effects.
Background
Solar energy is expected to increase in the U.S. and globally, but the development of utility-scale facilities requires large tracts of land. Regions in the hot deserts of the Southwest are increasingly being chosen for utility-scale solar energy development.
The deserts of the U.S. Southwest possess large solar energy potential — the desert sun is bright and intense, with fewer clouds and less rainfall compared to other regions of the country. Large reaches of public lands of the Chihuahuan, Mojave, Sonoran, and San Joaquin Deserts are thus prime locations for new solar facilities.
Despite potential for expansion, the effects of solar energy development on desert wildlife and plants are not well understood, which was also discussed in a USGS review from 2011."
To tackle this knowledge gap, the USGS carried out a review of known responses and predicted (but unstudied) responses using characteristics, or traits, of species and their responses to similar types of development disturbance.
To ensure this assessment was generally applicable, the researchers created a framework that assists land managers in understanding how desert species might respond to future development.
This predictive framework helps guide decision-making.
It includes these elements:
Identifies species’ functional and life history traits: their habitat requirements, biology, structure, functions and processes, seasonal timing of biological events, reproduction, and behaviors.
Groups species into ‘guilds.’ A guild is a group of species that use the same types of resources or have similar ecological roles within an ecosystem. For instance, pollinators, herbivores, or predators are types of guilds.
Identifies a species or guild’s “plasticity,” which is the ability to change and adapt in response to varying conditions or external influences.
Requires context about the site’s history and the type of development. For example, the condition of the land before it was developed and the type of development (such as soil grading, vegetation removal, and fencing).
How do species respond? Case studies:
The USGS reviewed case studies for species in the desert Southwest, including rare and invasive plants, desert shrubs, invertebrates, lizards, desert tortoises, birds, bats, desert bighorn sheep, and kit foxes to evaluate their responses within the framework.
Species respond differently to solar energy development depending on their traits, “response strategies," and the type of construction used.
Known species response strategies were distilled into 3 categories: avoid, tolerate, or exploit the area affected by development.
Traits | Response Strategy | Description of Response |
|---|---|---|
| Narrow niche, such as specialized diet or specific habitat requirements | Avoid the disturbance | Decline in population when faced with disturbance. Avoids the disturbance in space or time. |
| Short-lived | ||
| Plants with persistent budbank or seedbank | ||
| Slow growing | Tolerate the disturbance | Survives disturbance, often at low abundances such that a disturbed area may act as a population sink. May have thresholds for tolerance. |
| Conservative resource use | ||
| Flexibility ("plasticity") to minimize damage from the disturbance | ||
| Rapid resource utilization | Exploit the disturbance | Takes advantage of environmental conditions created by the disturbance. Often concentrated in disturbed areas. |
| Flexible behavior | ||
| Broad niche, such as a broad diet or generalist habitat requirements |
Using the framework, researchers predict that species with behavioral flexibility and broad ecological requirements will be more capable of taking advantage of areas affected by solar development, while species with specific habitat requirements will be more vulnerable and tend to avert or avoid being impacted (see Table above).
The Gemini Solar Project is an example of a facility that uses alternative construction methods (see The Gemini Solar Project | U.S. Geological Survey).
Alternative construction methods that have less environmental impact may mean that some ‘avoidant’ species may be able to ‘tolerate’ and use solar facilities, such as lizards, desert tortoises, or kit foxes.
Avoid:
- These species avoid the disturbance, partially or entirely. They are not persistent in development areas and may have population decline if disturbance cannot be avoided. Avoidant wildlife typically has narrow or inflexible ecological niches that make them vulnerable to disturbance, such as specific habitat requirements and specialized diets. Because of this, they will typically circumvent the disturbance if they can and use alternative more suitable areas.
- Examples are nesting birds, plants such as the endemic Mojave milkweed (Asclepias nyctaginifolia) and white bursage (Ambrosia dumosa), insects including native bees, desert tortoises, bighorn sheep and pronghorn antelope.
Tolerate:
- Tolerant species survive in disturbed areas, though the conditions are not optimal for them to increase in population size. They may be tolerant because they are slow-growing and use resources conservatively, or they are able to modify their traits to minimize damage incurred by the disturbance. They will typically occur at low abundances in and near solar energy development.
- Examples include lizards, burrowing owls, and kit foxes.
Exploit:
- Exploiter species have traits that allow them to rapidly take advantage of the resources available in disturbed areas. These species often have flexible behavior and generalized ecological requirements. For example, species that take advantage of shade provided by PV panels or bare ground resulting from construction are exploiters. These species may be concentrated in habitat patches within the development site.
- Invasive plants such as Mediterranean grasses, coyotes and ravens are good examples.
Opportunities to mitigate effects during solar facility construction and operation:
Large-scale solar energy construction and operation has both direct and indirect effects on species and guilds in the desert Southwest. Direct effects are when the disturbance itself influences the species response, such as fencing that restricts habitat use or movement. Indirect effects are species responses to changes in environmental conditions caused as a result of the construction or the installed infrastructure, like changes in temperature, soil moisture, and erosion (Panel A).
Traditional construction methods (“Blade and Grade”) blade all vegetation, compact the soil, use impervious fencing, and have overhead transmission lines can cause loss of pollinators, invertebrates, desert tortoises, and an increase in bird and bat mortality and invasive species (Panel B).
Alternative construction methods (“Drive and Crush”) drive over vegetation but leave roots and soil intact, and have raised fencing allowing for smaller mammals, birds and reptiles to pass underneath but excludes predators such as coyotes (Panel C).
For more information on the disturbance types (lower case letters in the illustration) and effects on species and guilds (numerals in the illustration), see Predicting the effects of solar energy development on plants and wildlife in the desert southwest, United States.
In addition to alternative construction techniques that reduce habitat disturbance and fragmentation, other actions may be considered that can mitigate impacts.
These actions fit within hierarchical levels – avoidance, minimization, and restoration or offsetting of the disturbance – that were previously developed for the U.S. National Environmental Policy Act and provide a decision-making process.
Scroll down to learn more about these techniques. (Click on the diagram to view it full screen.)
Avoidance:
- Identifying and avoiding the most sensitive or ecologically important areas. This can include constructing facilities in heavily disturbed areas such as urban or agricultural locations.
- Avoid disturbance during sensitive time periods.
Minimization:
- Minimize disturbance to soil, vegetation, and wildlife in all phases of the construction.
- Leave patches or corridors of habitat undisturbed as a buffer for bighorn sheep and pronghorn.
- Alter the infrastructure, adjust panel design, distance between panels, or height, and powerline location, such as burying powerlines.
Restoration and offset:
- Where avoidance and mitigation are not possible or are ineffective, restoration of soils by saving topsoil and creating water catchments, and revegetation of native plants can provide environmental benefits. Offsets that preserve habitat, for instance migration corridors, can help to mitigate loss of habitat at the construction site.
A summary of plant and wildlife case studies indicate both negative and positive effects.
This table summarizes the case studies that USGS reviewed. The disturbance type and species' traits influence how a species or guild responds to the disturbance, and whether the response will be positive or negative or neutral (predicted responses).
It also identifies opportunities that are currently available for mitigation during construction and operation of a solar facility.
The predicted responses (or direction of species' change) are either positive (+), neutral (o), negative (-), or unknown (?). The letters that indicate a species' traits and thus response strategy are: A (avoid), T (tolerate), or E (exploit).
This study is intended to support the Bureau of Land Management and other land managers in decision-making and long-term planning, as well as to encourage additional research.
Karban, C.C., Lovich, J.E., Grodsky, S.M., and Munson, S.M., 2024, Predicting the effects of solar energy development on plants and wildlife in the desert southwest, United States: Renewable and Sustainable Energy Reviews, v. 205, 114823, p. 1-15, https://doi.org/10.1016/j.rser.2024.114823
(If you are not able to access the full paper online, contact mhartwell@usgs.gov)
Downloadable files:
Click here for the Gemini Solar Project Information Brief | U.S. Geological Survey
Click here for the Solar energy in the desert - presentation | U.S. Geological Survey
Related
The Gemini Solar Project
Desert Tortoise Ecology and Renewable Energy Development
Desert Tortoise Ecology
Related
The Gemini Solar Project
Desert Tortoise Ecology and Renewable Energy Development
Desert Tortoise Ecology
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