During the campaign, it was easy to scoff at President Donald Trump’s promise to build a “big, beautiful” concrete wall along the US-Mexico border.
It sounded, well, preposterous.
But now the prospect of a border wall is quite real. Trump intends to request $4.1 billion over the next two years to build it. The Department of Homeland Security is reviewing proposals for designs that are “physically imposing in height” and “aesthetically pleasing in color.”
There’s a long debate over whether physical barriers on the border actually curb the illicit flow of people and drugs. The Border Patrol, which is backing Trump’s plan, says they’re a “vital tool.” Migration experts say they’re more symbolic than effective.
But what is undeniable is that the 654 miles of walls and fences already on the US-Mexico border have made a mess out of the environment there. They’ve cut off, isolated, and reduced populations of some of the rarest and most amazing animals in North America, like the jaguar and ocelot (also known as the dwarf jaguar). They’ve led to the creation of miles of roads through pristine wilderness areas. They’ve even exacerbated flooding, becoming dams when rivers have overflowed.
And while we don’t yet know exactly what path Trump’s new wall would take, DHS has been eyeing unfenced areas in a Texas wildlife refuge that conservationists consider some of the most ecologically valuable areas on the border — home to armadillos and bobcats. If a wall were to slice through these ecosystems, it could cause irreversible damage to plants and animals already under serious threat.
“We’ve been dealing with all these negative environmental impacts of fences on the border for more than a decade,” says Dan Millis of the Sierra Club Borderlands project. “And Trump’s proposal would make it worse.”
The border region is ecologically rich because a lot of it has been federally protected
The political boundary between the US and Mexico stretches 2,000 miles from the Gulf of Mexico to the Pacific Ocean. Along the way, there are three mountain chains, the two largest deserts in North America, vast cattle ranches, a handful of cities and their sprawling suburbs, and the southern section of the mighty Rio Grande river.
Much of the region has never been heavily populated, and over the years, several large swaths of land have been designated as protected areas. Today there are 25 million acres of protected US public lands within 100 miles of the line. That includes six wildlife refuges, six national parks, tribal lands, wilderness areas, and conservation areas — all of them managed by various federal agencies and tribal governments.
On the Mexican side, meanwhile, sit protected areas like El Pinacate y Gran Desierto Altar, which abuts the US Cabeza Prieta National Wildlife Refuge and parts of the Organ Pipe National Monument and Barry M. Goldwater Range in Arizona.
These protected areas have been established, in part, to protect wildlife and plants that span both countries. In the case of the El Pinacate and Cabeza Prieta, desert species like the Sonoran pronghorn (an antelope relative) have been able to migrate back and forth. But in recent years, that’s gotten harder with the construction of long sections of vehicle barriers and fences, as you can see from the map.
“People think of deserts as barren lands and flat sand dunes with nothing there,” Sergio Avila, a conservation scientist at the Arizona-Sonora Desert Museum, says. “But deserts are very diverse and rich in life.”
The protected areas on the border harbor an incredible array of wildlife and plants
When you trace the border from west to east (as this Story Map project by Krista Schlyer did), you find shrinking pockets of remarkable biological abundance. At the far west is the Tijuana Estuary, a key salt marsh habitat for some 400 species of migrating birds. At the far east, birds and butterflies stop through the Lower Rio Grande Valley, which is also a permanent home for colorful mammals, reptiles, and amphibians.
“There are tropical animal species in some of these canyons that are not found anywhere else,” says Jesse Lasky, a biologist at Penn State who has studied the impact of border fences on border species. “They inhabit these little slices of tropical ecosystem that creep up into the US near the Gulf coast.”
Not many scientists have measured the border’s biodiversity in its totality — or the full impact of fences. One of the few studies to tackle these questions was written by Lasky and co-authors in 2011. They estimated that 134 mammal, 178 reptile, and 57 amphibian species live within about 30 miles of the line. Of those, 50 species and three subspecies are globally or federally threatened in Mexico or the United States. And they survive only because people on both sides have worked hard to conserve them.
Probably the most biologically impressive region on the border, according to Avila, is the sky islands, a range of mountain “islands” that extend from Arizona and New Mexico into Mexico and host a greater variety of life than almost anywhere else in North America. Most are part of the Coronado National Forest, the most ecologically diverse national forest in the country. The Coronado also hosts the greatest number of threatened and endangered species of any national forest in the US.
Living in those sky islands are spotted owls, jaguars, thick-billed parrots, barred tiger salamanders, Mount Graham red squirrels, and many more unusual species. But as with all of the protected areas on the border, these populations are dwindling fast. Climate change and urbanization are factors. But the biggest threat of all, according to Lasky, Avila, and other conservationists in the border region, are the fences that have been built along the border in the past couple of decades.
Border fences have been terrible for wildlife and plants
Since 1994, the US government has been erecting barriers to keep people and drugs from Mexico and beyond out. By 2010, about one-third of the border had been fenced with materials ranging from barbed wire to steel, bollard to wire mesh, and chain link. In addition, the Department of Homeland Security has built hundreds of miles of roads to allow the Border Patrol to access remote regions, both fenced and unfenced.
All of this construction has sliced and diced a lot of protected land along the border. And ever since the passage of the Real ID Act of 2005, DHS has had the power to waive most environmental reviews in the name of national security.
So, unlike most federal infrastructure projects, these fences have received little or no input from the public, land managers, conservation groups, or other agencies. Experts had no chance to assess beforehand what impact the fence might have on wildlife, plants, and rivers. Only after the fact have researchers documented instances where fences have interrupted wildlife corridors, and caused erosion and other damage to fragile ecosystems, as well as flooding.
But what evidence we do have is alarming. For instance, Lasky and his co-authors found that the biggest risk comes when fences bisect the range of a small population of a species with a specialized habitat, leaving the majority of the population on one side and the others adrift. His paper found 45 species and three subspecies that the current fence has affected this way.
Cutting off animal populations in this fashion leads to reduced gene flow and inbreeding — leading to a greater risk of extinction. Conservation groups are particularly worried about the Mexican gray wolf; in 2016, there were just 113 in the US and about three dozen south of the border. A wall between them could make the recovery of the population unsurmountable.
Fences also can also restrict animals’ access to water sources — particularly problematic in the drought-prone Southwest. And they can make it harder for animals to adapt to climate change. “A lot of species do best in northern Mexico, but with changes in precipitation patterns, they would need to disperse across the border,” says Lasky. “This is something we should be thinking about a lot more — how fast organisms are responding to climate change.”
The wall structures hurt animals and insects in other ways too. Some sections have lights that attract and zap pollinators, like the monarch butterfly, that migrate across the border. And the taller the fence, the more impassable it is for some bats and birds, like the cactus ferruginous pygmy owl.
Based on this research, leading groups like the Sierra Club, the Center for Biological Diversity, and Defenders of Wildlife have strongly recommended against any further construction of fences on the border.
Trump’s proposed wall could have a big impact on still-pristine areas
About two-thirds, or 1,350 miles, of the border remains unfenced. It will be exceedingly difficult for Trump to build a wall across this entire area. (Cost estimates for doing so range from $21 billion to $40 billion.)
But it’s plausible that Trump will try to build barriers along a significant portion of this unfenced region. According to CNN, the administration’s first request is for $1 billion of funding to cover 62 miles of border wall — for “14 miles of new border wall in San Diego, 28 miles of new levee wall barriers and six miles of new border wall in the Rio Grande Valley region and 14 miles of replacement fencing in San Diego.”
San Diego is a sprawling urban center, but just south of it is the Tijuana Estuary, where the Tijuana River meets the Pacific Ocean. It’s one of the most biodiverse areas in the entire state of California, according to Willis, and has already been impacted by fences. Replacing the fences there could mean more habitat destruction in the estuary.
Activists in Texas who’ve been tracking fence construction over the years say they think part of the 28 miles of new levee wall will bisect the Lower Rio Grande Valley National Wildlife Refuge — a collection of dozens of tracts of habitat stretching from Brownsville by the Gulf of Mexico to Rio Grande City, about 100 miles west.
This area is a refuge for 19 federally threatened and endangered species, and 57 state protected species, including the ocelot and other species in the illustration below. And a wall could have a serious, in some cases deadly, impact on these species:
Walls and levee walls in this region could also pose a serious flooding hazard, says Dan Millis of the Sierra Club. “They are particularly problematic because they would be the first walls built inside the Rio Grande floodplain, and thus are likely to cause floods in the populated areas where they are planned,” he says.
Building fence where there is a flood risk has already caused chaos on other parts of the border: Flash floods in Nogales and Organ Pipe Cactus National Monument in Arizona have caused millions of dollars in damage and two deaths because of floodwaters that built up along the fence.
“Flood water always has debris in it,” Millis says. “That’s how you got these damming events that blew out chunks of wall. Damming also causes erosion — it creates the situation we saw in Arizona where debris backs up the water and then the sediment building upstream created a waterfall that causes more erosion. This is liable to happen in Texas.”
Current walls in Texas are not in the floodplain — in part because a binational commission that oversees the Rio Grande River has refused to allow CPB to build there, fearing flooding in towns on both sides. But Scott Nicol, with the Sierra Club in McAllen, Texas, says he’s concerned that DHS intends to act unilaterally and will build new fence in the floodplain of the Rio Grande, despite Mexico’s objections.
One unfenced section of the border is precious jaguar habitat
The Trump administration is focused on building new fence in Texas and San Diego for the moment. But one day it could turn its sights on other unfenced sections — and one of the most troubling possibilities would be the miles of protected areas in Arizona and New Mexico where jaguars occasionally roam.
Jaguars are critically endangered in North America; the populations that once prowled New Mexico, Arizona, Texas, and Southern California were essentially hunted to extinction in the 20th century. The northernmost breeding population in the Americas — some 80 to 120 individuals — is in the Northern Jaguar Reserve in the Mexican state of Sonora.
Like wolves, jaguars like to ramble widely, with ranges anywhere from 10 to 50 square miles. And since 1996, seven males have been spotted in the US, giving conservation groups hope that they may be trying to reestablish a population on this side of the border. The Fish and Wildlife Service, along with several conservation groups, have tried to encourage them by establishing six critical habitat areas under the Endangered Species Act to allow the jaguars to enter the US.
“The only hope for natural re-colonization in the U.S., however remote, hinges on maintaining this core population to the south, and its connectivity,” said Alan Rabinowitz, CEO of Panthera, in a statement. And a fence through the unfenced areas in the illustration above would clearly destroy that connectivity.
Conservationists say the threat of Trump’s wall also puts a strain on binational relationships. “We have a lot of successful conservation partnerships working together with Mexico (monarch butterfly and jaguar, for example),” says Avila. “But these policies are putting a dent on those partnerships and pitting people against each other. They could sour the relationships.” For instance, he says, changes in immigration policies are making it harder for him to bring Mexican officials to meetings in the US.
When it comes to protecting jaguars and other big cats threatened on the border, he says the solution is pretty simple: Just don’t build a wall.
“We don’t have to do that much. We have to leave them alone and allow them to move freely and their populations would move freely,” he says. “If we create a wall for these species north or south of the border, it doesn’t matter; they’re blocked.”
Will Trump ultimately get to build the border wall he’s promised his supporters? We don’t know if Congress will give him the money. But DHS’s record of building fences whenever it can — with the anachronistic but still powerful argument that walls work for national security — suggests it will fight hard for it. And the tragedy for conservationists is that they have next to no legal leverage — when it comes to the border, security trumps just about every other law of the land.