Forest Resilience to Wildfire and Harvesting: A Comparison of Microclimate & Understory Plant Diversity in Island Remnants a Decade After Disturbance
Creators: Schneider, Marcel E
Publisher: name: University of Alberta Library
Year: 2023

<p>An important feature of ecosystem-based forest management in the boreal mixedwood of northern Alberta, Canada – and in other forests around the world - is the emulation of natural disturbances such as wildfire. Post-fire landscapes typically include unburned or partially burned patches of forest often referred to as remnants. Remnants are thought to support understory communities and microclimates similar to reference mature forest within a disturbed landscape. While forest managers leave remnant patches within harvest blocks to emulate the structural effects of fire, it is unknown if they are effective analogues. My objective was to examine if harvest and fire remnants are effective at maintaining microclimatic conditions and understory vascular plant communities, similar to those of reference forest, in a post-disturbance landscape, and to establish links between forest structure and understory plant assemblages. I also used a trait-based approach to uncover patterns of plant persistence or colonization within disturbed forest and remnants. I identified three harvested and three burned areas approximately a decade after disturbance, and within each area sampled 3-7 island remnants as well as the disturbed area adjacent to remnants. Each remnant was paired with a nearby “reference”, a mature continuous forest. At each island remnant, disturbed area, and reference, edge and interior plots were sampled to collect data on soil and surface air temperature, tree, and understory vegetation; these were then analyzed using a combination of taxonomic and trait-based approaches.<br><br>
I found that fire and harvest remnants did not support similar understory plant communities; however, they did support communities similar to their respective reference forest. Remnants in both fires and harvests had similar richness, cover and diversity of understory species compared to reference forest. Plant traits associated with plant persistence were more frequent in remnants of both disturbance types and references, while colonization plant traits were more common in the disturbed areas. There were no differences between the understory plant community or traits at edges versus the interiors of remnants of either disturbance type. There were limited positive associations between canopy cover and forest dependent understory plant species abundance and negative associations between canopy cover and early seral species. I did not find any evidence of tree mortality leading to increased abundance of early seral understory species or increases in temperature. While remnants of both disturbance types contained temperatures similar to reference forest, temperatures in fire remnant edges and fire disturbed plots were generally higher than reference forest, unlike the harvest remnant edges/disturbance.<br><br>
These findings support the practice of patch retention within clearcuts, finding them to be similar to fire remnants, with some caveats. I confirm that both fire and harvest remnants are effective at providing a forest structure and microclimatic conditions similar to those of reference forest. I believe this research will help empower forest managers to make harvest decisions that enable the forests of the future to retain biodiversity and function effectively. </p>