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A Global Boom in Fences Is Harming Wildlife

This story originally appeared on Yale Environment 360 and is part of the Climate Desk collaboration.The most famous fence in the United States is the expanded border wall pushed by former president Donald Trump. Intended to prevent illegal immigration, the barrier also keeps wildlife from moving between the United States and Mexico.“The main threat of the border wall is not the localized area of habitat loss and habitat degradation,” said Aaron Flesch, a wildlife biologist at the University of Arizona, who has studied the wall’s impacts. “It’s the landscape-level impacts of curtailing or completely precluding wildlife movement and eliminating landscape connectivity at large scales.”Bighorn sheep or jaguars, for example, are cut off from others of their kind on the opposite side of the border. This means that the genetic interaction needed to keep small populations of jaguars or ocelots healthy may be affected. It also means bighorn sheep in Mexico may not be able to migrate north to escape a hotter and drier climate.These are the kinds of impacts caused by the many millions of miles of barriers around the globe that slice and dice the natural world. It’s a rapidly growing problem, with fence projects expanding worldwide. In Europe, nations are building new fences to keep migrants from illegally crossing borders in isolated areas. In East Africa, livestock fencing is interrupting the migrations of the region’s storied wildlife. A new fence between Mongolia and China has blocked the movement of gazelles. And the list goes on.

Until recently, the study of fences and their role in conservation biology has been scattershot. Half of the studies were done in just five countries, with many focused on the effects on medium-sized animals. And fences are still not part of the Human Footprint Index, a database of human changes to the earth used by researchers to measure the cumulative impact of human development.

But that is changing. Several years ago, biologists in the Northern Rockies published a paper titled “A fence runs through it: A call for greater attention to the influence of fences on wildlife and ecosystems.” In 2020, a meta-analysis in BioScience looked at all the studies of the effects of fences and found that their profound impacts are often ignored or greatly underestimated.

Photograph: LAKRUWAN WANNIARACHCHI/Getty Images