Stream Water Quality and Quantity Effects from Select Timber Harvesting of a Streamside Management Zone

A naturally regenerated, even-aged, mixed pine/hardwood, streamside management zone (SMZ) was selectively harvested in May 2006. The 27.8-ha SMZ buffered an intermittent headwater stream draining a 98-ha watershed. The harvest complied with Texas, US best management practices (BMP) by maintaining a minimum SMZ width of 15 m on either side of the channel, retaining a minimum basal area (BA) greater than 11.47 m2 ha-1, and minimizing forest floor and stream channel disturbance. No changes in soil bulk density were measured with only a slight increase in bare soil. No changes in water quality or quantity were detectable after harvest, in part because of dry posttreatment conditions. The Agricultural Environmental/Policy Extender (APEX) model was used to simulate treatment effects under different harvesting and weather conditions. APEX provided reasonable estimates of water yield, sediment, and nutrient losses and was found to be an effective tool for estimating the relative impacts of alternative BMP scenarios. Results indicate that maintaining a minimum BA of 11.47 m2 ha-01 and SMZ width of 15 m on intermittent streams will protect water quality even in wet years and that not retaining any residual BA can result in over 10 times more sediment loss.