Scientists warn that proposed US-Mexico border wall threatens biodiversity, conservation

July 24, 2018, Stanford University
A border fence stretches into the distance. Credit: Matt Clark / Defenders of Wildlife

Borderlands are synonymous with desolation, but the Mexico-U.S. divide is something altogether different. The nearly 2,000-mile-long border traverses some of the continent's most biologically diverse regions, including forests, grasslands and salt marshes—home to more than 1,500 native animal and plant species, according to an analysis published in BioScience on July 24.

The paper, coauthored by Stanford biologists Paul Ehrlich and Rodolfo Dirzo, warns that some of these species face extinction within the U.S. if their movements are cut off by the continuous border wall President Trump has pledged to build.

Physical barriers prevent or discourage animals from accessing food, water, mates and other critical resources by disrupting annual or seasonal migration and dispersal routes. Work on border walls, fences and related infrastructure, such as roads, fragments habitat, erodes soil, changes fire regimes and alters hydrological processes by causing floods, for example.

The potential for ecosystem damage was highlighted more than a decade ago, when the U.S. Congress passed the Real ID Act. The 2005 law gives the Department of Homeland Security (DHS) authority to waive any laws—including the Endangered Species Act and National Environmental Policy Act—that slow the wall's construction.

The paper calls on scientists around the world to support solutions, such as requirements that DHS identify species, habitats and ecological resources at risk from barrier construction and security operations; design barriers for maximum wildlife permeability where possible; and purchase or restore replacement habitat when environmental harm is inevitable. Nearly 3,000 scientists have signed on to endorse the paper's message.

A family of javelinas encounters the wall on the U.S.-Mexico border near the San Pedro River in southeastern Arizona. Credit: Matt Clark / Defenders of Wildlife

Stanford Report spoke with Dirzo, a professor of biology and the Bing Professor in Environmental Science, and Ehrlich, a professor of biology (emeritus) and Bing Professor of Population Studies. Both are also senior fellows at the Stanford Woods Institute for the Environment.

What makes these border regions special?

Dirzo: This area is an ecological theater where evolution has engendered a plethora of plays. A multitude of factors—climatic conditions, topography, geological history, soil types -converge to create an amazing mosaic of ecosystems. A constellation of Northern temperate and Southern tropical lifeforms and lineages coincide with endemic species, as in few areas of the globe. This means these borderlands are a global responsibility.

What impacts have border wall construction had so far on biodiversity?

Ehrlich: Any substantial construction ordinarily forces populations to extinction directly by outright destruction of their habitat or by reducing population size or restricting access to critical areas required seasonally. Every time you see a strip mall, airport or housing development being constructed, you can be sure biodiversity is suffering. Many hundreds of miles of border wall and the accompanying construction and maintenance infrastructure would be a crime against biodiversity.

In this 2007 photo, bulldozers remove a vehicle barrier in Buenos Aires National Wildlife Refuge to make way for the 15-foot wall that will replace it. Credit: Matt Clark / Defenders of Wildlife

What are the ways in which border wall construction specifically threatens one species?

Dirzo: Many species, such as bighorn sheep, are composed of populations of relatively few individuals per unit area and have large home ranges—hundreds of square miles in the bighorn's case. Shrinking that range will lead to local population loss or declines. Smaller population sizes suffer from reduced genetic variation, which reduces their capacity for adaptation. Barriers will impede the bighorn sheep's migrations and movements to track habitats that shift due to a changing climate. Cut off like this, the bighorn and other animals and plants will become zombie species—populations that are demographically and genetically doomed.

You estimate that 17 percent of the species you analyzed risk extirpation within the U.S. if cut off by a border wall. Why should the average person care about this potential loss?

Ehrlich: Aside from effects on water flows and other natural services, the wall could rob us of iconic creatures such as the endangered Peninsular Bighorn sheep and the Sonoran pronghorn antelope. The esthetic value of these magnificent animals, and their cultural meaning to nature lovers, hunters and native American groups, is attested to by great efforts already made to avoid their extinction. There's also an economic loss to consider—the U.S. Fish and Wildlife Service estimated that hunting, fishing and wildlife-watching contributed nearly $26 billion to border state economies in 2011.

Explore further: Proposed border wall will harm Texas plants and animals, scientists say

More information: BioScience (2018). academic.oup.com/bioscience/ar … 0.1093/biosci/biy063

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7 comments

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TheGhostofOtto1923
2 / 5 (4) Jul 24, 2018
Ahaahaaa I think the Rio Grande also threatens biodiversity.

Where have I heard this before? Oh yeah the Alaska pipeline.
JamesG
1.7 / 5 (6) Jul 24, 2018
Exactly. Scientists need to get their politics out of their "science" or lose their jobs.
rderkis
2.3 / 5 (3) Jul 24, 2018
I am guessing here but I imagine wildlife is protected in the USA more than in mexico. Which means with a border wall wildlife can no longer wander across the border into mexico and be slaughtered.
Surveillance_Egg_Unit
2.3 / 5 (3) Jul 25, 2018
I am guessing here but I imagine wildlife is protected in the USA more than in mexico. Which means with a border wall wildlife can no longer wander across the border into mexico and be slaughtered.

says rderkis

Yes, the Environmental Protection Agency (EPA) and other agencies will take the proper steps to ensure that the wildlife that is on the US side of the wall is protected, and the agents will be on the lookout for any likelihood of poaching and other forms of deliberate abuse of any and all species.

The article is also based on the idea that the Mexican government cares nothing for animals on their side of the border and will behave in a callous way and not mitigate any possible harm to them. But all animal species on both sides are always subjected to predation from their natural enemies, and nothing much can be done about it.
barakn
4 / 5 (5) Jul 25, 2018
Ahaahaaa I think the Rio Grande also threatens biodiversity.

Yes. No animals have been observed swimming, wading, or rafting. Ever. We bathe in the glory of your enormous intellect.
rderkis
not rated yet Jul 25, 2018
hhh
TheGhostofOtto1923
1 / 5 (1) Jul 26, 2018
Ahaahaaa I think the Rio Grande also threatens biodiversity.

Yes. No animals have been observed swimming, wading, or rafting. Ever. We bathe in the glory of your enormous intellect.
And no liberal pseudoenvironmentalists have ever been observed concocting spurious studies based on groundless theories about unendangered species with the support of unscrupulous, corrupt, tax-grabbing politicians.

No, thats never happened. Except for the pipeline that is.

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