Northward expansion of high-stature vegetation reveals net surface-cooling feedbacks in the majority of Canadian Boreal-Tundra ecozones

Climate warming has driven widespread shrub and tree expansion across the Canadian boreal-tundra. This is widely expected to amplify surface warming. However, whether this expectation is supported by observations remains unresolved. Here we show, using satellite observations of vegetation change alongside climate and surface-energy data from 1986 to 2023, that about 70% of central and northern Canadian ecozones exhibit net surface cooling tendencies, driven by interactions between vegetation change and the environment that reduce the energy available to warm the land surface ( -0.003 to  -0.009W m-2 yr-1). Cooling is strongest in landscapes transitioning toward mixedwood forests, broadleaf vegetation and treed wetlands, reducing warming by approximately 0.015-0.028°C yr-1 relative to shrub- and conifer-dominated areas. These findings challenge the view that vegetation expansion at high latitudes uniformly drives warming, showing that its effects depend on vegetation type, moisture and environmental context. They further suggest that the continued spread of mixed vegetation communities may moderate surface warming previously associated with conifer-dominated landscapes.