The southwestern deserts are criss-crossed by linear structures. Some were built to carry materials and energy along the structure—roads, pipelines, canals and electric lines. Some were built to prevent the flow of materials across the structure—drainage ditches, fences, and now the Border Wall.
Most of these structures were built without regard to nature and have left their imprint on the desert ecosystem. In the early 1980s, I studied the effect of drainage-diversions on the availability of water and the growth of desert shrubs, finding a 50% reduction in plant biomass downslope of these diversions. This unintended consequence extended for as much as a mile from the diversion, altering the structure and function of the desert community. Various studies have also documented the impacts of fences and walls on the movements of the endangered desert tortoise in the Mojave desert of California.
Now, Congress is in heated debate with the POTUS about building a wall to prevent immigration across our southern border. Much has been said about the cost, efficacy, and cultural philosophy of such a project. Little has been said about its potential impact on nature. Indeed, Federal laws exempt projects deemed essential to security from the customary considerations of their impacts on natural habitat. The wall is sure to cross and eliminate the flow of ephemeral streams that maintain desert ecosystems.
The Sonoran desert of Arizona harbors a number of endangered species whose home range will be divided by the wall, limiting access to traditional sources of food and water, limiting home range size, and limiting access to mates and seasonal migration routes. These species include the bighorn sheep and the jaguar, for which the wall may represent the death knell of extinction. Construction of a segment of the wall in South Texas more than a decade ago resulted in population reductions of a number of regional species.
The wall has costs—tangible for materials and construction; indirect economic costs of lost tourism and hunting; and cultural costs for reductions in biodiversity that are the heritage of the desert Southwest. Thoughtful policy makers will consider them all.
References
Flesch, A.D., C.W. Epps, J.W. Cain III, M. Clark, P.R. Krausman, and J.R. Morgart. 2010. Potential effects of the United States-Mexico border fence on wildlife. Conservation Biology, 24: 171-181.
Lasky, J.R., W. Jetz, and T.H. Keitt. 2011. Conservation biogeography of the US-Mexico border: a transcontinental risk assessment of barriers to animal dispersal. Diversity and Distributions 17: 673-687
McCain, E.B. and J.L. Childs. 2008. Evidence of resident jaguars (Panthera onca) in the southwestern United States and the implications for conservation. Journal of Mammalogy 89: 1-10.
Peaden, J.M. and 5 others. 2017. Effects of roads and roadside fencing on movements, space use, and carapace temperatures of a threatened tortoise. Biological Conservation 214: 13-22.
Peters, R. and 17 others. 2018. Nature divided, scientists united: US–Mexico border wall threatens biodiversity and bi-national conservation. Bioscience 68: 740-743.
Schlesinger, W.H. and C.S. Jones. 1984. The comparative importance of overland runoff and mean annual rainfall to shrub communities of the Mojave Desert. Botanical Gazette 145: 116-124.
Wilshire, H.G., J.E. Nielson, and R.W. Hazlett. 2008. The American West at Risk: Science, Myths, and Politics of Land Abuse and Recovery. Oxford University Press.