CANCELLED - Wildfire residuals and harvest residuals exhibit similar characteristics for coarse woody debris a decade after a disturbance in deciduous dominated stands

Background/Question/Methods

Although the management practice of retaining forest structural elements is modelled on the propensity for fires to leave behind a variety of biological legacies or structural elements, the comparison of post-fire and post-harvest residual forest structure and diversity has received little attention. We compared coarse woody debris (CWD) attributes to determine the similarity between anthropogenically created residuals to wildfire residuals. During the spring of 2021, 30 sites (15 harvest and 15 fire) in northern Alberta were selected that experienced a harvest or fire between the years of 2009-2011 and left residuals that possessed a patch size >0.45 ha and was >70% deciduous. Each site included a reference (larger matrix of forest bordering the same disturbance) area and a disturbance area. Within these 3 areas of a site an interior (location not bordering another area) plot and an edge (location bordering another area) plot were surveyed. CWD data was gathered during the summer of 2021 from an 11.28 radius plot containing 6 overlapping transect lines at every 60 degrees. Using the line-intercept method CWD ≥7.5 cm in diameter was counted, assigned a decay classification and identified by species (if possible): the same information was gathered for standing dead ≥9.1 cm.

Results/Conclusions

Post-fire island edge, disturbance edge and disturbance interior plots expressed higher recent (decay classes 1 and 2) CWD volumes. The CWD attributes of reference edge, reference interior and island interior plots were similar between post-fire and post-harvest sites. Decay class distribution, also, presented similarities between the disturbance types. The wildfire sites contained a larger proportion of small CWD (≥7.5 cm < 20 cm) but showed no significance in other size categories. The disparity in the disturbances was to be expected due to the strategy of harvesting being vastly different from a wildfire. The greater volume in wildfire island edges is likely due to the edge gradient that is present compared to a definite harvest edge. It is probable that sampling bias influenced these results. Overall, it appears that harvesting companies have been able to effectively mimic the retention patches created by natural disturbances.