President Donald Trump is allowing the longest government shutdown in US history to drag on because he wants Congress to give him $5 billion for 215 miles of border wall.

But make no mistake, the existing physical wall at the US-Mexico border is about to be extended even without any new funding. That’s because, in the 2018 spending bill, Congress allocated $1.3 billion to build a total of about 33 miles of new border wall and fortify a few existing segments in California and Arizona. The Department of Homeland Security says construction will begin on the first new segment — six miles of reinforced concrete levee wall topped with steel bollards in Hidalgo County — in February.

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 mostly symbolic.

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What’s 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. The existing barrier has cut off, isolated, and reduced populations of some of the rarest and most amazing animals in North America, like the 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.

The new sections of fence under contract are slated for the Lower Rio Grande Valley of Texas and will cut right through a federal wildlife refuge, a state park, Native American grave sites, and the National Butterfly Center. Conservationists and wildlife managers consider this region to be one of the most ecologically valuable areas on the border — home to endangered ocelots and jaguarundis, two beautiful small cat species in the region; plants, and 400 species of birds.

According to internal documents recently made public by the conservation non-profit Defenders of Wildlife through the Freedom of Information Act, US wildlife officials have been raising red flags about the new construction. They think it will further degrade habitat for wildlife, including endangered species like the ocelot and jaguarundi, and further restrict their movement.

“The Service is concerned the levee wall in Hidalgo County could be subject to catastrophic natural flood events, leaving terrestrial wildlife trapped behind the levee wall to drown or starve,” a regional director of the Fish and Wildlife Service wrote in a 2017 letter to a branch chief of the Customs and Border Protection division of DHS. Ecotourism in the region will suffer, they warn.

Meanwhile, local environmental activists have been trying for years to prevent any new wall construction in Texas, precisely because the impacts of the wall are already well-documented.

In 2018, they convinced Congress to exempt the Santa Ana National Wildlife Refuge, a 2,088-acre patch of extraordinary biodiversity on the Rio Grande river, from the new sections of border wall it funded in the spending bill.

“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 wall 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 and Gran Desierto de 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 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.”

In a recent tweet, Rep. Beto O’Rourke (D-TX) asked about where the wall would go and what it would destroy. The responses included a series of stunning photos of the border and its landscapes:

Where would they build the wall? Whose home or ranch or farm are they going to take to build it? Which communities and habitats are they going to destroy? Reply with your best pictures of the border - let the rest of the country see what’s at stake. pic.twitter.com/9ToIXXYKp2 — Beto O'Rourke (@BetoORourke) December 21, 2018

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 wall could have a big impact on still-pristine areas

About two-thirds, or 1,350 miles, of the border remains unfenced. Trump has said that in addition to the 120 miles of new and replacement wall that have already been funded, he wants to build another 215 miles with the $5 billion he’s demanding from Congress.

Environmental activists in Texas who’ve been tracking the wall over the years say they’re concerned that the new wall segment expected to be built starting in February will do significant damage to protected areas, including a section of the Lower Rio Grande Valley National Wildlife Refuge, as well as Bentsen Rio Grande State Park, the National Butterfly Center and the La Lomita Chapel.

A wall would certainly destroy the little remaining butterfly habitat at the center, Jeffrey Glassberg, the president of the National Butterfly Center, told me last year. And it would further erode the region’s ecotourism. Look no further than what happened at Audubon’s Sabal Palm Sanctuary once a border wall was built through it: Visits fell by half because the wall made it a much less pleasant place to be, Glassberg says.

The wall could have a serious, in some cases deadly, impact on other species in the region, including:

Walls and levee walls in this region could pose a serious flooding hazard too, says Millis. “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 worried that CPB intends to act unilaterally and will build new fence in the floodplain of the Rio Grande, despite Mexico’s objections.

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 Millis of the Sierra Club, and has already been impacted by fences. Replacing the fences there, which could happen later this year, could mean more habitat destruction in the estuary.

One unfenced section of the border is precious jaguar habitat

The Trump administration is focused on building new fence in Texas 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 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 only hope for natural re-colonization in the U.S., however remote, hinges on maintaining this core population to the south, and its connectivity,” Alan Rabinowitz, CEO of Panthera, said in a statement. And a fence through the unfenced areas — shown in the illustration above — would clearly destroy that connectivity.

Conservationists say the threat of Trump’s wall also puts a strain on relations with Mexico. “We have a lot of successful conservation partnerships working together with Mexico — monarch butterfly and jaguar, for example,” Avila says. “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.

Will Trump ultimately get to build the additional 215 miles of 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 the agency 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.

Existing US-Mexico border fence data featured in the maps is from Reveal and the Center for Investigative Reporting and OpenStreetMap contributors. This story was originally published in 2017 and was updated in January 2019.

Further reading:

How Donald Trump could actually build the wall — and who would pay the price

Donald Trump’s plan to build a solar border wall, explained with math

Here’s all the land (and water) Trump’s border wall would have to cover.

How Trump’s border policy may already be impacting migration to the US.