President Donald Trump‘s plan to build a wall along the U.S. border with Mexico has been greeted with cheers from his supporters but skepticism and outright resistance from those who fear it will do little to ensure national security. Many worry that the wall will harm relations with Mexico while costing taxpayers billions of dollars.

But conservationists and other scientists are raising a separate issue with the wall: It poses a threat to the local environment and ecosystems, they say. A wall would inhibit movement for animals that need to travel for food and water. It would also divide the mating pool of several animals, potentially leading to a decline in genetic diversity.

“The wall is a disruptive, artificial boundary in the natural world,” says Jamie Rappaport Clark, CEO of the Defenders of Wildlife conservation group. “Wildlife must be able to move freely across connected landscapes to survive.”

Much of the border is already fenced, which inhibits animal movement to a degree, but Trump’s promise of a concrete wall as high as 55 feet would essentially stop movement for every local species expect birds.

The wall would affect a wide range of animals, but a few vulnerable species including jaguars, Mexican gray wolves and ocelots would be particularly hard hit, according to a Defenders of Wildlife report. Black bears, spotted owls and deer are also common in the region.

Trump’s executive order does not mention an environmental review process for the wall, so it’s unclear whether the administration would weigh these concerns, but Trump said this week that he wanted to begin construction within “months.” In other contexts, Trump has denounced many environmental reviews as unnecessary bureaucratic requirements. A 2006 federal law also gives the Secretary of Homeland Security the authority to waive environmental reviews for such border projects when there is a national security interest.

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Write to Justin Worland at justin.worland@time.com.