Forest Harvest Effects On Soil Nutrient Concentrations and Nitrogen Pools in Ozark Highland Soils.

Mixed hardwood systems at the Missouri Ozark Forest Ecosystem Project (MOFEP) site in southern Missouri are harvested using clearcutting (CC) and single-tree selection (STS) regeneration methods.  Little work has been performed at MOFEP to examine soil nutrient changes that may result from application of different regeneration methods on highly weathered soils present at this site.  The objective of this work is to elucidate the effects of regeneration method on surface soil nutrient pools.  Three soils were selected based on relative nutrient status as indicated by subsoil percent base saturation (BS): low, ≤ 20 % BS; medium, 20 – 50 % BS; and high, ≥ 50 % BS.  Ten years after harvest, samples were collected in 10 cm increments from 0 to 30 cm in each treatment and soil using a paired sampling approach (i.e., samples were collected in treated and nearby non-treated locations).  Treatments sampled included CC, STS, and no-harvest removal (NHR) sites.  Samples were analyzed for pH, extractable base cation concentrations, total organic carbon (TOC) and total nitrogen (TN) content.  Stable and labile nitrogen pools were quantified using extraction and mineralization techniques.  Statistical analyses were performed on concentration difference values developed from paired samples (i.e., treated – untreated concentrations).  Results indicate that exchangeable Ca, TOC and TN are significantly different (α=0.10) between CC and STS sites.  Nutrient concentration difference values are consistently smaller in STS relative to CC treated soils, particularly at the 0 – 10 cm depth.  Statistical analyses also indicate that difference values for stable and labile soil N pools are significantly smaller (α=0.10) in STS sites compared to CC sites, especially in high nutrient status and surface 10 cm soils.  Other parameters followed the same trend, although differences are not always significant. Variations observed between the treated soils are attributed to differences in slash distribution within the treatments.