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.

Windthrow after group and dispersed tree retention in eastern Canada

“…However, such information has rarely been collected in similar ecosystems. Angers et al (2011) monitored windthrow after fire in the Abitibi region. Our level of mortality was higher than that observed in their study, even though it was likely increased by salvage harvesting that was conducted close to their sample plots.…”

Detecting regional differences in within-wildfire burn patterns in western boreal Canada

“…Most of the photo scales were 1:15 840 or better, although we allowed some photos up to 1:30 000 if they were large-format plates, and supplementary photos were available. For all but 15 fires, post-fire photos were available within two years, reducing the possibility of bias associated with short-term mortality (Angers et al 2011). The quality of the photos and negatives was such that individual trees, and their condition, could be easily identified.…”

Vegetation Mortality within Natural Wildfire Events in the Western Canadian Boreal Forest: What Burns and Why?

“…We had hoped to overcome this challenge by using more accurate and precise mortality data based on high resolution photographic negatives, the results suggest that there are other factors involved in predicting vegetation mortality levels. One possibility is that mortality continues over several years post-fire [60] which means that all post-fire "snapshots" (including those used in our study) represent just one of several remnant vegetation patterns over time. Another possibility is that moderate mortality is associated with areas that experienced less severe fire conditions, such as overnight fires and/or the back or flanks of a fire where the relative influence of fire weather, topography and fuel-type may change, or even reverse [25].…”