COS 255-1 - Tree mortality in post-fire and post-harvest residual patches: are fire skips different than retention patches 12 years following disturbance in aspen-dominated forests?
As forests are put under compounding stresses because of climate change and demand for resources, industries must develop innovative ways to harvest forests sustainably. In the boreal forests of Alberta, Ecosystem Based Management is implemented to mimic natural disturbances by leaving behind patches of intact forest during harvesting, called island remnants. These island remnants are crucial to the resilience and recovery of forests following disturbance—they provide important habitat, preserve heterogenous forest structure and help mitigate environmental impacts. Previous studies have compared the rates of post-disturbance tree mortality in island remnants created by harvest to reference forests and clearcuts, but not against those created by wildfires. This study aims to examine the effects of different disturbances (fire and harvest) and edge influence within references and island remnants on tree survival through dendrochronological analysis of tree cores. We determined the year of death for snags following each disturbance and quantified tree mortality rates to verify if harvest-created island remnants are functioning similarly to wildfire-created island remnants with respect to tree survival. We hypothesize that tree mortality will be similar in island remnants created by both fire and harvest but elevated compared to reference stands.
Results/Conclusions
The results of an ANOVA on both fixed and mixed effects linear models revealed that almost all explanatory variables did not result in significant differences seen in tree mortality, which supports our hypothesis. In fact, the interaction between disturbance and location was found to be the only treatment combination to result in different observed tree mortality rates. Fire island remnants had somewhat higher tree mortality than harvest islands, as well as higher mortality than reference forests. However, harvest islands did not show elevated mortality compared to reference forests. Mortality rates between forest edge and interior sites were not different, and island size was not correlated with tree mortality amounts. Intra-species mortality rates were not explained by treatments. These results are evidence to support the continued implementation of retention forestry and creation of island remnants because elevated retention tree mortality was not observed following the harvest compared with reference forests, and this can help to promote forest recovery and resilience following the disturbance.
