Deer are expanding north. That could hurt some species like boreal caribou

White-tailed deer have expanded their range in North America over many decades. Since the early-2000s, these deer have moved north into the boreal forests of western Canada. These forests are full of spruce and pine trees, sandy soil and freezing winters with lots of snow. They're basically your typical winter wonderland in theory — but actually living there can be harsh.

Ecologists haven't known whether a warmer climate in these forests is drawing deer north, or whether human land development might play a bigger role.

"Human land use and climate change are both leading causes of biodiversity loss. But more often than not, those two things are highly intertwined, and it's really tricky to tell which one is the root cause — or if it's both," Melanie Dickie, a wildlife biologist at the University of British Columbia, Okanagan says. "We really need to know which one it is so we can have a better idea of what to do about it.

Dickie described these deer as an "invasive species." Because more deer in these forests can have an impact on other species like boreal caribou. With deer come more predators like wolves. While deer are able to cope with living alongside predators like wolves, caribou are not. Dickie says they've evolved to mostly just avoid areas with lots of predators. And that gets tricky when there are more wolves around.

She also says that deer are really just one piece of the puzzle for boreal caribou — but having more information about what exactly is driving deer expansion helps her and other researchers figure out where to start when it comes to restoring land and protecting wildlife.

Read the study in Global Change Biology.

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Today's episode was produced by Rachel Carlson and Kai McNamee. It was edited by Rebecca Ramirez and Christopher Intagliata. Emily Kwong, Regina G. Barber and Rachel Carlson checked the facts. Patrick Murray and Stu Rushfield were the audio engineers.