Northern expansion is not compensating for southern declines in North American boreal forests

Abstract

Climate change is expected to shift the boreal biome northward through expansion at the northern and contraction at the southern boundary respectively. However, biome-scale evidence of such a shift is rare. Here, we used remotely-sensed tree cover data to quantify temporal changes across theNorth American boreal biome from 2000 to . 2019. We reveal a strong northsouth asymmetry in tree cover change, coupled with a range shrinkage of tree cover distributions. We found no evidence for tree cover expansion in the northern biome, while tree cover increased markedly in the core of the biome range. By contrast, tree cover declined along the southern biome boundary, where losseswere related largely towildfires and timber logging. We showt hat these contrasting trends are structural indicators for a possible onset of a biome contraction which may lead to long-term carbon declines.