Many species would face local extinction in the US if they couldn't travel back and forth between habitats and resources on either side of the border.
The US-Mexico border is nearly 2,000 miles long and peppered with marshes, deserts, and grasslands. The construction of a continuous wall could therefore harm species who are, of course, not on the administration’s immigration radar.
More than 1,500 species of flora and fauna, like the bighorn sheep shown above, make their homes along this biologically diverse strip of North America. Sixty-two of these species are considered vulnerable, endangered, or critically endangered by the International Union for Conservation of Nature (IUCN). And many of those species would face extirpation — meaning local extinction in the US — if they were unable to access habitats and resources on either side of the border, according to a study from Stanford University.
The Stanford analysis showed that 346 species that would lose access to half of their habitat because of a border wall.
Of those species, 17% would be stuck living in an area of roughly 7,700 square miles or less — elevating their risk of extirpation according to IUCN guidelines. According to the study, which was published in the journal BioScience in July 2018, some of these at-risk species include the endangered jaguar and ocelot.
The two Stanford biologists behind the study, Paul Ehrlich and Rodolfo Dirzo, explained that physical barriers — whether they be rivers, mountains, or a human-made wall — can deter or prevent animals from finding mates, fresh water, and necessary food.
Animal migration patterns, even those of birds, would be disrupted.
Dirzo and Erhlich noted the border wall could also impede flying species that enjoy riding currents close to the ground. Examples include the endangered Quino checkerspot butterfly or the ferruginous pygmy owl.
Echoing those concerns, the National Audubon Society, the National Resources Defense Council, and more than 170 conservation groups penned a letter to Secretary of Homeland Security Kirstjen Nielsen in November.
The letter elaborated on the impact of a wall on “environmentally sensitive conservation areas” like the Lower Rio Grande Valley area, which has a plethora of butterfly and bird fauna. Bruce Stein, chief scientist at the National Wildlife Federation, wrote, “barriers like border walls can interfere with the ability of animals to meet their daily needs, make seasonal migrations or disperse to new areas.”
Rising temperatures and extreme weather are already altering certain regions' ecology, leading animals to shift their behavior in order to survive and find food. A wall could prevent creatures from successfully adapting. Stein also pointed this out in the letter to Neilson.
One of the greatest potential environmental impacts of a border wall would be almost invisible at first: it would lead species to become less resilient to stress.
A wall that cuts animals' habitat into pieces would consequently force their populations into smaller subgroups that are effectively unable to interact and mate with one another.
That would make each remaining subgroup more vulnerable to diseases and natural disasters. Plus, less gene flow between individuals within a species means less genetic diversity, and a higher possibility of inbreeding. Overall, these consequences would increase a species' overall risk for extinction.
Conservationists are particularly concerned about the future of the Mexican gray wolf.
According to Vox, fewer than 200 total Mexican gray wolves remained in the wild in the US and Mexico in 2016. A report from the Center for Biological Diversity in July 2018 noted that the US population of Mexican gray wolves increased by only four individuals between 2014 and 2017. In the report, Bryan Bird, Defenders of Wildlife's southwest program director, said that the “Mexican gray wolves are in a race with extinction, and the clock is ticking.”
A wall separating the some three dozen wolves in Mexico from their counterparts in the US could therefore be a deadly blow for the world's most endangered wolf.
A border wall would also change the flow of major rivers.
Impacts on wildlife aside, the proposed border wall could also impact the quotidian movements of three major rivers and their tributaries.
The wall would need to bisect the Rio Grande, Colorado, and Tijuana Rivers. Bob Irvin, president of the environmental group American Rivers, told News Deeply that between 100 and 500 rivers and streams would be affected.
The wall would “undoubtedly change the flow of those rivers and streams, and it would also impair the water quality in them,” he said.
Irvin added that “when you change the flow of a river, you’re changing the natural cleansing mechanisms of that river. So you certainly could see a buildup of pollutants — both solid and chemical — as a result of that.”
Depending on where and how a wall were erected — in the middle of a river, say — it could even act like a dam.
If the border wall wound up acting as a 2,000-mile dam, debris could pile up any time there was a storm, impeding the flow of the river. Irvin told News Deeply that’s already happening along some sections of wall that already exist in Arizona.
According to a report by the Sierra Club, such walls have contributed to severe flooding and flood damage before when constructed across natural drainage points.
One example of such flooding was a 2008 disaster that happened along the US-Mexico border in Nogales, Arizona.
During a seasonal rain storm, that wall acted as a dam, flooding the sister cities of Nogales and Sonara in 6 feet of water. The disaster caused $8 million in property damage and two deaths. Six years later, a similar flood happened again in Nogales, when debris blocked a 60-foot section of the border.
There’s little evidence that the designs for the proposed continuous border wall would account for mitigation of possible flood risks. Quartz even reported that 8 miles of the planned wall in Texas would be built on a floodplain.