How much is too much? How do biomass harvesting, site preparation intensity, and wood ash applications alter plant community recovery of a second growth boreal jack pine forest?

More intensive forest management practices have been suggested as a means to meet increasing demands for forestry products, particularly those for renewable energy. In this study, we compare plant community composition, structure, and function in response to a gradient of silvicultural practices in a second growth jack pine forest (Pinus banksiana Lamb.) in northern Ontario, Canada. Five combinations of biomass harvest and site preparation disturbance intensities, including landings (wood processing area) from the previous harvest were compared six years after planting. Additionally, two wood ash amendment treatments were included to explore the ameliorative effects of ash application. We found more intensive treatments that had large amounts of biomass harvested, forest floor removal, and high soil compaction, changed plant community composition. The plant communities of the intensive treatments had low taxonomic and functional diversity, and were characterized by low vegetation cover, a high prevalence of short, shade intolerant species, and an underdeveloped vertical structure. The less intensive treatments, including Tree-length harvest and the two ash amendment treatments, had similar taxonomic and functional composition to the Full-tree harvest treatment and were comprised of vascular and non-vascular plant species typically associated with mature boreal forest communities. These findings underscore the importance of establishing biomass harvest guidelines that preserve ecologically significant conditions and attributes to safeguard biological legacies and facilitate ecosystem-level recovery, including minimizing forest floor disturbance and maintaining a balance of fine and coarse woody debris.