Primary Article: Eichenwald, A. J., M. J. Evans, & J. W. Malcom. (2020). US imperiled species are most vulnerable to habitat loss on private lands. Front Ecol Environ; doi:10.1002/fee.2177.
Featured Image: Poster from the Environmental Protection Agency. Source: Wikipedia.
Biodiversity loss causes a reduction in ecosystem services, a loss of potential medical substances, and a less secure food supply chain. Habitat loss is the top reason for biodiversity loss as it reduces the size of populations and hinders reproductive success.
The Endangered Species Act (ESA) is one of the strongest pieces of legislation in the world for protecting biodiversity. However, it may not provide equal protection for all species and all habitat.
The Endangered Species Act (ESA) is a success story of an environmental law supported by bipartisan unity, and is one of the most effective environmental policies in the U.S. and in the world. Threatened and endangered species of plants and animals can be listed under the Act, which then prevents “the destruction or adverse modification of designated critical habitat of such species” and prohibits the taking ( meaning “to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct) of any listed species.
The Red List by the International Union for Conservation of Nature (IUCN) also provides a compilation of endangered and threatened species. Although this list is available for the use of government NGOs, agencies, and other stakeholders worldwide, it is not legally enforced in the United States.
The Endangered Species Act: what does it do, and what are its limitations?
Enforcing the Endangered Species Act is more complicated than it sounds on paper. Although suitable habitat may look good to an endangered species no matter who owns it, the politics of land ownership and rights of use are more complicated. The Endangered Species Act is enforced differently depending on who controls the land in question.
Various federal agencies (e.g. the US Forest Service, Army Corps of Engineers, Department of Transportation) and non-federal entities (e.g. state agencies, private companies, and citizens) can get exceptions which allow “incidental take” of threatened or endangered species; for example, through a construction project that would cause the loss of some individuals or a reduction in population size. However, the process by which federal agencies receive this exception is visible to the public. The process for non-federal agencies is different and more difficult to enforce; therefore, we can’t be sure how often they incidentally take species while avoiding enforcement of the Endangered Species Act altogether.
Data-driven analysis of policy efficacy
Adam Eichenwald, Michael Evans, and Jacob Malcolm, associated with Tufts University, George Mason University, and the Center for Conservation Innovation noted this policy discrepancy and wanted to learn more about its effects. Specifically, the team wanted to find out whether there were measurable differences in the ESA’s effectiveness on federal versus non-federal lands. They predicted that federal lands may provide stronger protections for threatened and endangered species.
To test their prediction, the researchers chose 24 vertebrate species (see figures for examples) whose ranges (the land they inhabit) had been estimated by the U.S. Geological Service (USGS). In order to be part of this list, species’ ranges needed to include both federal and non-federal land and have habitat that could be seen in satellite images. As a group, the 24 species ranges included all 12 of the major ecoregions in the continental U.S. Sixteen of the included species were listed under the Endangered Species Act, while eight were included on the International Union for Conservation of Nature (IUCN) Red List, which lists threatened or endangered species but does not provide legal protection for them. The researchers could therefore differentiate between patterns exhibited by endangered or threatened species with legal protection versus those without legal protection.
The researchers analyzed satellite images over 30+ years, from 1986-2018. Image pixels were categorized based on vegetation type. Habitat loss for a particular species was defined by changes per year in the natural vegetation that it called home. Some types of land were difficult to analyze, and therefore excluded from the study. For example, agriculture crop rotations can be difficult to distinguish from other causes of vegetation change, and areas burned by fire are difficult to distinguish between natural burns and those prescribed for land management purposes.
The Endangered Species Act provides measurable protection for listed species
From scouring over satellite images, researchers found that lower annual habitat losses occurred after species were added to the ESA list compared to before they were listed. Additionally, there were lower rates of habitat loss for ESA-listed species compared to the Red List species, which lack legal protection. These patterns suggest that the Endangered Species Act does successfully reduce losses in endangered and threatened species’ habitat.
Additionally, most habitat loss occurred on private lands, while the least occurred on federal lands. This trend suggests that although the ESA does effectively protect habitat, it doesn’t protect all parts of a species’ range equally. Rather, the Endangered Species Act provides unique and more effective protection for habitat that happens to be on federal land.
Why do these trends occur, and why do they matter?
Individual property rights are culturally and legally valued in the U.S., so the Endangered Species Act provides certain special exemptions for private lands.
This may be a problem for some threatened and endangered species, because they don’t know the difference between federal and non-federal lands! They can’t make the decision to limit themselves to federal lands to stay safe. Additionally, the majority of ESA-listed species’ ranges are made up of private lands.
These trends mean that the majority of the habitat used by ESA-listed species isn’t being protected as fully as it could be if it were federally managed. This may prevent the ability of endangered and threatened species to expand their range outside of better-protected federal lands if populations recover and grow.
Implications for policy
Although the ESA does improve protection of listed species’ habitat, it is limited by a gap in enforcement on private compared to federal lands.
In order to more effectively protect endangered and threatened species’ habitat, no matter who owns and manages it, the authors suggest that the application of the ESA should be strengthened on private lands. This could occur through more consistent enforcement, conservation incentives for landowners, and assistance from the federal government to landowners who want to learn how to voluntarily comply with the ESA.
Moving forward: what research questions should come next?
This study used methods that resulted in the identification of trends over long periods of time over large geographic scales. This type of data is difficult to come by but can be the most useful for improving federal environmental policies.
However, there are some limitations to the study which mean that we shouldn’t overgeneralize the results and implications. The study only included a few of the 1,600 ESA-listed species, and excluded some land types (agricultural lands and areas burned by fire).
It also included only one threat: habitat loss. While this threat causes the majority of biodiversity loss, some species are more vulnerable to other threats.
Future research may employ similar methods to this study to gain knowledge of the long-term trends in habitat for multiple types of species facing multiple types of threats. The more we know, the better we can manage!