The influence of coarse woody debris on soil carbon and nutrient pools 15 years after clearcut harvesting in black spruce—dominated stands in northwestern Ontario, Canada

Abstract

This study was designed as a log-scale examination of the influence that decomposing coarse woody debris (CWD in situ for 15 y following harvesting) had on soil carbon and nutrient levels. The study included 4 study sites representing 2 soil types: loamy tills versus sandy outwashes. The mature, fire-origin mixed conifer stands occupying these sites were clearcut harvested in 1994. In 2009, estimates of both total soil carbon and total and available nutrient pools were compared in locations under versus away from CWD. The presence of decaying CWD (now decay classes 3–4) significantly increased soil carbon (+85%) and nitrogen (+49%) pools. Estimates of inorganic N from a fresh soil 2M KCL extraction, however, were lower underneath the logs, suggesting that N immobilization is occurring as part of the decomposition process. In contrast, the presence of CWD had no significant effect on P, K, Ca, or Mg soil pools. Although there were marked differences in soil nutrient pools between the 2 soil types, the patterns associated with the presence of CWD were largely the same, and suggest that the influence of CWD does not extend beyond the bounds of the CWD. The results suggest that it will be important that biomass harvesting guidelines consider and include CWD retention levels to ensure that this important ecosystem component, with its associated functions (e.g., soil fertility, nutrient cycling), is maintained in harvested landscapes.