By Nick Atkinson
The line marking the transition between Vermont’s northern hardwood and boreal trees has moved around 100 meters uphill in just 40 years, according to a study published in Proceedings of the National Academy of Sciences. In 2004, researchers at Yale University and the University of Vermont, led by the latter’s Brian Beckage, revisited sites first mapped in 1964 that stretched between 550 and 1160 meters above sea level. As they climbed higher, they noted changes in the species composition of the trees they found. Disease, acid rain (or snow), and an increase in freeze-thaw events have conspired to make life tougher for some species, easier for others. However, the observed elevation change was only around half of that predicted through climate change models, suggesting that the northern hardwood trees will continue their ascent, even if warming stops overnight—which, of course, it won’t. Disturbances such as those caused by insect outbreaks likely make this upward progression swifter; the question is whether the Green Mountains of Vermont are high enough for the boreal species to survive.
Beckage, B. et al. 2008. A rapid upward shift of a forest ecotone during 40 years of warming in the Green Mountains of Vermont. Proceedings of the National Academy of Sciences 105(11):4197-4202.
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