Publication

Understanding the effects of forest timber harvests on soil chemistry is essential to manage for a sustainable yield of timber from forests. Yet few studies have examined the long-term effects of timber harvesting on the soils of temperate hardwood forests. We use a 25-year chronosequence of post-regeneration irregular shelterwood harvests in an oak-hardwood forest in Connecticut, USA to examine the impacts of timber harvesting and subsequent forest regeneration on soil and leaf litter chemistry. Soil and leaf litter samples were collected across 34 stands ranging in age from one year to 25 years since harvest. Using hierarchical, linear mixed effects models, we analyzed trends in soil and leaf litter properties over time in the harvested stands and compared these values to undisturbed reference sites. Soil chemistry from two depths (0–10 and 10–20 cm) revealed that surface and sub-surface soils respond differently through time, with the shallow soils being more responsive to harvest and regeneration, but both increasing in fertility with increasing time since harvest. In shelterwood soils, time since harvest had a positive effect on macronutrient concentrations and a negative effect on the carbon (C) stable isotope ratio (δ13C), with the latter indicative of recovery of faster-cycling soil C pools. In leaf litter, time since harvest had a positive effect on nitrogen (N) concentrations and a negative effect on δ13C, with the latter again suggesting build-up of more recent litter inputs. Relative to eight unmanaged reference sites, harvested stands were lower in some soil nutrients (magnesium, phosphorus, percent C, as well as cation exchange capacity), but these differences were recovered over time within the 25-year chronosequence. Post-hoc t-tests (α = 0.10) showed no significant difference in percent nitrogen by 11–15 years post-timber harvest as compared to the undisturbed sites. Likewise, potassium, phosphorus and percent carbon showed no difference by 16–20 years, and magnesium showed no difference by 21–25 years. Calcium never varied significantly between shelterwood and uncut reference sites. Overall, our results suggest that decomposing organic matter acts quickly to promote macronutrient recovery in surface soils following irregular shelterwood harvests.