A new study has shed light on climate change’s effect on trees.
The study, led by Duke biologists and published Wednesday in Global Change Biology, found that many trees aren’t shifting their ranges northward in response to warmer temperatures as quickly as was previously expected. The study looked at 65 different species in 31 eastern states, and found that 80 percent of the species weren’t yet shifting their ranges to higher latitudes. Instead, the trees were speeding up their life cycles, with younger trees replacing older trees at a higher rate.
The study’s findings suggest that most young trees have higher optimal temperature and precipitation levels than older trees, which means they thrive more in warmer, wetter climates than older trees do. That, coupled with longer, wetter growing seasons which encourage growth and competition among older trees are likely reasons why trees are staying put and speeding up their life cycles rather than spreading farther north.
The findings back up results from a 2011 study done by the same team of Duke researchers that found about 58 percent of tree species studied showed a pattern of range contraction rather than expansion in response to climate change, and only about 20 percent of trees are showing a consistent northward shift in range. But at first glance, the study’s findings seem to contradict recent studies done in the western U.S. that have found evidence that desert plants are expanding their ranges upslope as climate warms.
James Clark, a co-author of the Duke study, said the two studies are more compatible than they seem. Temperature gradients are steep in mountains — a region a few miles upslope could be a markedly cooler environment environment than than one at a base of a mountain. So plant migration up mountains can occur quickly, because even if seeds are dispersed a short distance upslope, they could grow up in a much cooler environment. Clark said many regions — specifically in the eastern states, where his study focused — are mostly flat, without much area at high elevation. For that reason, it isn’t surprising that plants in mountainous regions are able to move upslope in response to higher temperatures, while many eastern trees haven’t adapted in that way.
“Small changes in temperature translate to large distances in latitude,” he told ThinkProgress in an email. “For this reason, evidence of migration up mountains does not mean that species can necessarily keep up with climate in flat areas.”
Overall, the Duke study and other research suggests the future looks uncertain for trees. Some, like the giant sequoia and coast redwood, seem to be adapting fairly well so far, but others face major climate-fueled challenges, including expanding regions for pine beetles, wildfires and drought.