Soil communities following clearcut and salvage harvest have different early successional dynamics compared with post-wildfire patterns

Abstract

Understanding the impacts of harvest and subsequent silviculture practices at stand scales on the below-ground biota, and their associated nutrient cycling processes, is needed to more fully evaluate the sustainable management of boreal forest systems. While stand replacing wildfire is the primary natural disturbance mechanism in jack pine-dominated boreal forest systems; clearcut harvest also results in stand renewal so is sometimes used in silvicultural systems to emulate natural disturbance and renewal processes. In this study, we simultaneously assessed the successional trajectories of three major taxa of the below ground soil community, bacteria, fungi, and arthropods using DNA metabarcoding. The objectives of this study were to use a chronosequence framework to: 1) assess whether the soil communities following clearcut harvest and wildfire converge along a successional gradient, 2) assess when the soil community recovers following clearcut harvest to the pre-disturbance, mature, wildfire reference condition, and 3) assess the effects of cumulative disturbance on soil community succession (i.e., wildfire followed by salvage harvesting of fire-killed trees). We found that richness (alpha diversity) did not illustrate any clear patterns of convergence and could, therefore, underestimate recovery times, especially for soil arthropods. Comparisons of the underlying community composition (beta diversity) proved to be more informative. In this case, we found that different soil taxa following clearcut harvest recovered on different timelines compared with succession following stand-replacing wildfire. In general, bacteria appear to be the first to converge to post-wildfire conditions followed by arthropods, however, fungi did not converge within the time frame of the chronosequence. This suggests that more extended periods are required to achieve complete recovery of the soil fungal community to the pre-disturbance condition. The cumulative disturbance associated with salvage harvest appeared to have a greater (compounded) effect on soil communities when compared with wildfire or clearcut harvest. This work showcases the performance of a scalable method for monitoring a diverse arrange of soil biota using DNA metabarcoding. In future work, tracking fungal and arthropod soil communities may provide more insights into the longer-term effects of current forest management practices and provide guidance when comparing alternative approaches.