Changes in forest floor and soil nutrients in a mixed oak forest 33 years after stem only and whole-tree harvest

Abstract

Vegetation, forest floor, and soils were resampled at a mixed oak site in eastern Tennessee that had been subjected to stem only (SOH), whole-tree harvest (WTH), and no harvest (REF) 33years previously. Although differences between harvest treatments were not statistically significant (P<0.05), average diameter, height, basal area and biomass were 8–18% lower in the WTH than in the SOH treatment 33years after harvest whereas they differed by 2% 15years after harvest. In contrast to results 15years post-harvest, total forest floor mass and nutrient contents were twofold greater in the WTH than in the SOH treatment at 33years post-harvest, due largely to differences in Oa horizon mass. Soil total C concentrations increased significantly (P<0.05) over the first 15years post-harvest in both harvest treatments. Decreases in soil C between 15 and 33years post-harvest were not statistically significant. Soil total N increased significantly in both harvest treatments over the first 15years post-harvest. Consistent decreases in soil total N occurred in the WTH treatment between years 15 and 33 post-harvest that bordered on statistical significance whereas total N was stable over that time period in the SOH treatment. The increases and decreases in soil N content cannot be explained by any known processes of N inputs or outputs. Harvest treatment effects on both Ca2+ and Mg2+ observed at 15years post-harvest are still observable and significant at 33years post-harvest, although decreases between 15 and 33years were found. Treatment effects and changes in soil exchangeable Ca2+ and Mg2+ are consistent with known inputs from decomposing logging residues, inputs from atmospheric deposition, and increments in forest floor and vegetation. No treatment effects were found for soil extractable P, but steady decreases over time were found. No treatment or time effects were found for soil exchangeable K+.