Resilience or reassembly: Wildfire–vegetation dynamics in rapidly warming subarctic forests of northwestern Canada

Abstract

Climate-induced shifts in disturbance regimes are reshaping northern forest ecosystems, where tree species are at their geographic range limit. Northern Canada has warmed over twice as much as the mean global increase since 1950, providing a critical context to study climate–fire–vegetation interactions under rapid warming. To fingerprint the changes to northern forest over the past century, we evaluated (1) the extent to which postfire vegetation trajectories return to the prefire composition and structure, and (2) how tree growth is responding to recent climate change under a warming climate. We surveyed 24 sites with a paired design (burned vs. unburned plots) in Nahanni and Nááts'įhch'oh National Park Reserves, Northwest Territories in 2022 and 2023. We compared unburned and burned vegetation structure and composition, and collected 1185 dendrochronological samples to investigate tree growth patterns and their relationships with warming climate. Across all surveyed sites, 88% of them maintained conifer dominance; only one site had over 50% broadleaf dominance after fire, and 8% of sites completely lacked tree recruitment. With the exception of sites where the fire-adapted lodgepole pine was present, postfire recruitment density was generally low compared to unburned paired plots. In contrast to low recruitment, tree growth may have benefited from longer growing seasons in combination with increasing summer precipitation. Despite the variable and generally protracted recruitment, the postfire trajectory has high potential to return to the prefire state in this area, provided fire-free intervals are sufficiently long. While highly site- and species-specific, these forests show resilience to climate change; however, their fate is highly uncertain if projected increases in fire activity are borne out.