forest
May 19, 2017

Climate change causing US trees to ‘migrate’

It’s a well-known fact that many species of birds fly south for the winter and return north once spring arrives, but migrating trees? That’s a new one, and the authors of a new study published this week in the journal Science Advances believe that climate change is to blame.

In the new study, Purdue University professor Dr. Songlin Fei and his colleagues explained that the warming temperatures and changes in precipitation patterns resulting from human activity are causing trees in the eastern United States to slowly shift north and west, said USA Today.

Warmer, drier conditions have caused the trees to move an average of 20 miles to the north and 25 miles to the west, and while the study authors explained to the Associated Press that the move northward in search of cooler conditions was expected, the shift westward came as a surprise.

Of course, the trees themselves aren’t exactly moving, per se – no Lord of the Rings-style trees uprooting themselves and changing location here. Rather, new trees are tending to sprout farther north and west while those located more to the south and east are dying off.

Fei’s team looked at 86 different species of trees over a 30 year period and discovered that the warmer temperatures in the southern states and the lack of rainfall (particularly in the southeast) was responsible for the shift of their geographical center. These changes could ultimately result in the extinction of some species of trees, the researchers revealed in their report.

Lack of moisture, not heat, the primary reason for the shift

As part of their study, the authors examined abundance data for the affected groups and species of trees across the eastern US, and found that 73 percent of them were shifting to the west while only 62 percent of them had been moving to the north in terms of their overall density.

The trend was “stronger for saplings than adult trees,” they explained, adding that “the observed shifts are primarily due to the changes of subpopulation abundances in the leading edges and are significantly associated with changes in moisture availability and successional processes.”

Furthermore, they found that many of the species affected by the shifts have similar characteristics (such as drought tolerance, seed weight, and wood density) and that, in general, most angiosperms moved westward while most gymnosperms moved northward. The researchers also reported that changes in moisture availability tended to affect the trees than changes in temperature.

“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,” Fei said to The Atlantic. “The results seem to show that moisture plays a much more significant role in the near-term, which is very intriguing.”

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Image credit: Chelsea Bock/Unsplash