Eastern White Pine trees have moved more than 80 miles west since the early 1980s in the United States, according to a new study, and they’re likely to continue migrating as the climate changes. But climate change explains only 20% of the movement, and the rest is a mystery. During a recent survey of how tree populations have shifted over the past three decades, ecologists expected to find that cold-adapted species would move northward, and to places that are higher in elevation, in order to survive. But the westward movement was a surprise.
The results of the study, which was published in the Science Advances journal in May, raise more questions than they answer. The West is usual dry, and though rainfall has increased over recent decades, it’s still drier than the East. Forest fires, harvesting and other changes to forest environments likely play a larger role than previously imagined.
According to Phys.org:
Trees, of course, don’t move themselves. But their populations can shift over time, and saplings can expand into a new region while older growth dies in another. The research team compared a tree population to a line of people stretching from Atlanta to Indianapolis: Even if everyone in the line stood still, if you added new people to the end of the line in Indiana and asked others in Georgia to leave, then the center of the line would move nonetheless.
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.
Meanwhile, in Minnesota, scientists from the Nature Conservancy are starting a project to plant 400 acres with cold-loving evergreens – including Eastern White Pines – in places they believe will be cooler, wetter or offering higher quality soil, ensuring their chances for survival as the state grows warmer. They’re hoping to preserve these species and maintain biodiversity. As climate change has progressed, giant pines have disappeared, replaced by more southern species like red maple.
From the Star Tribune:
“Climate scientists predict that, even if global carbon emissions are held to the rates agreed upon in the Paris Climate Accord, average temperatures will rise by 2 to 4 degrees Fahrenheit by the end of this century. That means the pines of northern Minnesota would give way to a hardwood and grass ecosystem, said Lee Frelich, a University of Minnesota professor who studies climate change and forests.
If that’s what happens, then the conifer stronghold will work, he said. But if carbon emissions and climate change continue to accelerate, then in time, northern Minnesota will instead look a lot like Kansas, Frelich said, and no boreal species will survive long-term.”
Image via: Wikimedia Commons