Forest Migration Outpaces Tree Species Range Shift Across North America

Mounting evidence suggests that geographic ranges of tree species worldwide are shifting under global environmental change. This migration of tree species is causing range shifts of entire forests, but little is known about how much forest migrationthe shift in the geographic ranges of forest typescan differ from individual tree species migration. Here, based on more than 9 million trees measured in situ from 596,282 sample plots, we quantified and compared the migration (in terms of azimuth and velocity) of forest communities and tree species across the conterminous United States, Alaska, and Canada between 1970 and 2019 using machine learning models. We found that forest communities on average are migrating at 205 km per decade across the continent, more than twice the average velocity of tree species migration (96 km per decade). Our findings suggest that the impacts of global change on forest ecosystem functioning and services have been grossly underestimated, because subtle changes in relative abundance and dominance of tree species can aggregate at the forest type level. Our quantification of forest migration patterns may facilitate new adaptive forest management regimes to see the forest for the trees in sustaining ecosystem functioning and services under a paradigm of rapid forest migration.