Tree mortality and snag dynamics in North American boreal tree species after a wildfire: a long-term study

Abstract

Temporal patterns of tree mortality and snag dynamics after fire were investigated over 10 years in a permanent plot design established immediately after a wildfire in an eastern boreal forest landscape of north-western Quebec, Canada. Post-fire tree mortality, snag persistence, tree fall patterns and variables influencing snag dynamics were assessed in deciduous, mixed and coniferous stands that experienced low- and moderate-severity fires. Temporal patterns of tree mortality for the three species revealed that mortality was delayed through time. Most post-fire tree mortality occurred within 2 years following fire but continued until the end of the 10-year observation period. Jack pine was the most persistent snag species, followed by trembling aspen and black spruce. Factors influencing the persistence of snags were multi-scaled and generally species-specific. Fire severity was the only common factor influencing snag persistence among all species, with snags located in severely-burned stands being less susceptible to falling. Trembling aspen snag persistence increased with basal area and diameter. Salvage logging in the vicinity affected black spruce. Fall patterns also differed among species. Bypasses of the snag stage (i.e. when a living tree falls directly to the forest floor) as well as uprooting of snags were common.