“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.
These results, among the first to use empirical data to look at how climate change is shaping eastern forests, were published in Science Advances on Wednesday…The results are fascinating in part because they don’t immediately make sense. But the team has a hypothesis: While climate change has elevated temperatures across the eastern United States, it has significantly altered rainfall totals. The northeast has gotten a little more rain since 1980 than it did during the proceeding century, while the southeast has gotten much less rain. The Great Plains, especially in Oklahoma and Kansas, get much more than historically normal.
‘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 Songlin Fei, a professor of forestry at Purdue University and one of the authors of the study.
There are a patchwork of other forces which could cause tree populations to shift west, though. Changes in land use, wildfire frequency, and the arrival of pests and blights could be shifting the population. So might the success of conservation efforts. But Fei and his colleagues argue that at least 20 percent of the change in population area is driven by changes in precipitation, which are heavily influenced by human-caused climate change.
What concerns the team is that—if deciduous trees are moving westward while conifers move northward—important ecological communities of forests could start to break up in the east. Forests are defined as much by the mix of species, and the interaction between them, as by the simple presence of a lot of trees. If different species migrate in different directions, then communities could start to collapse.”