Assessing tree-related microhabitat retention according to a harvest gradient using tree-defect surveys as proxies in Eastern Canadian mixedwood forests

Tree-related microhabitats (hereafter TreMs) play a key role in forest biodiversity. However, harvesting may cause their erosion. In North America, knowledge about TreMs is still lacking but defect surveys are largely available in managed forests. The objectives of our study were: (1) to demonstrate that defect surveys can be a reliable resource to identify TreMs; and, (2) to evaluate the capacity of silvicultural treatments to maintain TreM abundance and diversity according to a harvest gradient. To achieve these objectives, we identified TreMs from a defect survey performed the year a harvest gradient was applied to 20 plots, including uncut control, shelterwood treatments removing 50%, 43% and 36% of basal area, and clearcut (4 plots/treatment). The density and composition of TreMs were then compared based on treatments. Overall, 38% of defects actually corresponded to TreMs, confirming that tree-defects can be used as TreM proxies. Bark loss was the most abundant TreM. While there was practically no TreM in clearcuts, all shelterwood treatments initially maintained TreM diversity and density at the same values found in uncut control plots. Shelterwood systems, especially those maintaining a continuous cover, could therefore prove helpful to sustain TreMs and their biodiversity in managed forests.