As anybody who's taken a drive through Vermont in the autumn will know, the eastern US has plenty of iconic trees, like maple and oak. But over the past three decades, deciduous tree species in this part of the world seem to be shifting westward, according to new research published on Wednesday. Evergreens, meanwhile, are going north.
Past research has tracked how some tree species are moving north for reasons related to climate change. But in Science Advances, researchers looked at 30 years' worth of tree data from the US Forest Service, including 86 species, reflecting changes between 1980 and 2015—and, to their surprise, saw this westward shift of deciduous trees. "We show that more tree species have experienced a westward shift than a poleward shift (62%) in their abundance, a trend that is stronger for saplings than adult trees," it reads.
This wasn't a modelling exercise that casts forward to something that may happen in the future. Rather, it's tracking changes that are happening now.
This strange shift appears to be linked to climate change and its accompanying effects. Over the last 30 years, the study says, the mean annual temperature in the eastern US has gone up by 0.16 ̊C, on average, and the northern region has seen the highest increase.
Balsam firs showed a northward shift over the last three decades. GIF: Songlin Fei
Precipitation patterns are shifting, too: The central US has seen an increase of more than 150 mm total in annual precipitation, and there's been a reduction in the southeast.
"Broadleaf deciduous species, like maples and oaks, are more responsive to moisture changes related to climate change," study author Songlin Fei of Purdue University told me over the phone. As a result, the composition of forests is shifting.
Those forests are hugely important, not just economically, but for "water purification and carbon sequestration," Fei continued. "You have a system that took [a long time] to get to its current state, and now in a mere 30 years, it is starting to break apart." If species struggle to adapt, "you could be talking about population or species extinction," he said.
Scarlet oaks shifted to the northwest. GIF: Songlin Fei
It's unlikely that the eastern US will become completely devoid of trees, Fei told me, although we'll probably see more drought-resistant species move in. And while he didn't study the specific impacts of this change on Vermont's maple syrup production, for example, it's easy to imagine industries like these being affected—actually, it's already happening.
"There is still some skepticism out there about climate change," Fei acknowledged. With this study, "we're saying, let's look at what's actually happened. We wanted to show the reality, not speculations." Our environment is changing more rapidly than many scientists expected. Fei asked: "Is our society ready to adapt?"
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