Biogeochemical Effects of Silvicultural Management on Intermittent Streamside Management Zones in the Coastal Plain of Alabama

Abstract

Three experimental intermittent watersheds in the Coastal Plain of Alabama were subjected to varying Streamside Management Zone (SMZ) silvicultural treatments in 2000: reference, partial cut, and clearcut. Biomass and carbon (C), nitrogen (N), and phosphorus (P) dynamics in litterfall, leaf litter decomposition, and herbaceous vegetation were measured for pre-harvest baseline values and post-harvest responses. Changes in aboveground primary productivity and herbaceous vegetation composition, regarding speciation and distribution of stratum, also were evaluated. Pre-harvest comparisons of litterfall and mass loss rates indicated the reference SMZ exhibited the highest productivity with no significant differences between the partial cut and clearcut SMZs. General assessments of pre-harvest measurements of nutrient dynamics across all response variables and all 3 SMZs revealed no significant differences. Post-harvest comparisons of productivity demonstrated a significant treatment response of herbaceous vegetation in the clearcut SMZ, specifically regarding the forb and grass strata. Analysis of nutrient dynamics suggested that P was limited in all 3 SMZs. Reductions in decomposition rate among the partial cut and clearcut SMZs indicate a possible loss of P to the intermittent stream system. Observed levels of P content in the herbaceous vegetation of the treatment SMZ likely did not account for the loss of aboveground woody biomass as it relates to nutrient assimilation and storage. My results suggest that herbaceous vegetation responses to silvicultural treatments within SMZs do not buffer adverse effects to nutrient allocation, ultimately resulting in possible nutrient loss from the site and, thus, impacting site productivity and downstream water quality. Modification of best management practices to reflect the sensitivity of intermittent watersheds to silvicultural operations would benefit site productivity and water quality.