Climate Change and Disturbance Are Driving Systematic Shifts in Forest Composition and Cover Across Canada and Alaska

Abstract. Forests in Canada and Alaska are being altered by climate change and disturbance. However, the nature, magnitude, and geography of these changes are poorly understood. Here, we use time series of remotely sensed imagery to show that 9.4 x 10⁵ km² (equivalent to nearly 11 per cent) of Canada and Alaska experienced changes in land cover between 1986 and 2020. The area occupied by needleleaf forests decreased, while broadleaf forests and shrublands expanded. Needleleaf forest loss was most prevalent in taiga forests where shrub cover has expanded, while gains in broadleaf forests were concentrated in warmer and moister regions. Land cover transitions after disturbance reveal climate- and ecoregion-specific recovery patterns that explain the expansion of broadleaf forests and shrubs that we observe. Our results provide evidence that climate change and disturbance are driving systematic shifts in forest and shrub cover across large expanses of Canada and Alaska.