When scientists talk about “migrating trees,” it’s not because they’ve watched The Lord of the Rings too many times. Individual trees may not be able to hop, run or fly, but tree species can take advantage of favorable conditions by moving into new habitats. On the flip side, tree species may disappear from their historical habitats when conditions deteriorate. Take, for example, spruce trees in North America, which are now more abundant but farther north than during the last ice age.

Conventional scientific understanding suggests that many tree species will shift or expand northward and to higher elevations as the climate warms. A new study, however, challenges that understanding with an analysis of 92 species across the eastern U.S. Despite a strong warming trend and a clear link between temperature and tree occurrence, the range of more than half the species studied appears to be shrinking.

It’s not clear from this study why trees aren’t keeping pace with temperature change. Perhaps geographical boundaries, like coastlines, are getting in the way. Perhaps the species on the move are being out-competed in the new habitats. It’s even possible that tree seedlings are responding to climate change differently than adults.

According to the authors, however, one thing is clear: “Climate change has already been large — we do not have to wait decades to evaluate whether or not climate change is affecting migration.”

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