75% of eastern tree species moving west
White oaks, sugar maples, American hollies and other common trees have been shifting their population centers west since 1980.
The western side of the United States has been luring escapees from the east since before the temptation of gold in the hills and Horace Greeley’s advice to “Go west, young man, and grow up with the country.”
And now it appears that even trees are not immune to the allure.
A new study looking at how tree populations have shifted over the past 30 years finds that they are decidedly moving west. As The Atlantic reports, “About three-quarters of tree species common to eastern American forests – including white oaks, sugar maples, and American hollies – have shifted their population center west since 1980. More than half of the species studied also moved northward during the same period.”
How the center of tree populations moved from 1980 to 2015. (Fei et al./Nature Advances) /CC BY 2.0
Since trees don’t just pick up their things and take a few steps to the left, a shifting population happens over time as saplings expand in a new direction and the older growth fades behind it.
As climate change settles in, ecologists have correctly predicted that cold-loving animal and plant species will move northward to escape warmer temperatures. So it was little surprise to see that trees shifting north, but the westward expansion caused some head-scratching.
The researchers, however, believe that it may have to do with rainfall.
“Different species are responding to climate change differently. Most of the broad-leaf species – deciduous trees – are following moisture moving westward. The evergreen trees – the needle species – are primarily moving northward,” said one of the study authors and Purdue University forestry professor, Songlin Fei.
Other possibilities nudging the trees westward could include changes in land use, wildfires, and the arrival of pests – as well as conservation efforts. But Fei and his colleagues argue that at least 20 percent of the change in population area, notes The Atlantic, is driven by changes in precipitation, which are heavily influenced by human-caused climate change.
For data, the team relied on the U.S. Forest Service’s Forest Inventory and Analysis Program, a tree census that tracks everything from the great national forests to patches of trees near highways, in city parks and suburban developments.
“This is not a modeling exercise, there are no predictions, this is empirical data,” says Fei. “This study is looking at everything everywhere in the eastern United States.”
And while this all might be lovely for the deciduous trees heading west and their conifer cousins heading north, what fate does it spell for the east? The researchers say that important ecological communities of forests could start to fracture. Forests are the sum of their different species and the interplay between them all; switching up the mix could signal a collapse of that special dynamic.
“If you have a group of friends, and people move away to different places – some go to college in different places, and some move to Florida – the group is … probably going to fall apart,” Fei says. “We’re interested in whether this tree community is falling apart.”
See the full study in Science Advances.