Noncommercial thinning effects on runoff and sediment yield in a mixed conifer New Mexico forest

Abstract

Programs to thin mixed conifer forests have raised concerns about the potential to increase surface runoff and sediment yield. However, there is little research into the effects of noncommercial thinning of mixed conifer forests on surface runoff and sediment yield. The study objective to evaluate influence of thinning on runoff and sediment yield was accomplished through the use of 60 minute rainfall simulations to measure runoff and sediment yield from 64 1 m² (10.75 ft²) rings. The experiment was carried out at two landscape positions (ridge and valley) and two aspects (north and south) on paired treated (noncommercial thinning with scattered slash) and untreated plots of 90 × 90 m (295.2 × 295.2 ft) each. Landscape position (valley vs. ridge) significantly affected runoff ratio and sediment yield. Thus, runoff ratio (0.087 se 0.018) and sediment yield (4.54 se 2.69 g m⁻² [0.014 se 0.00881 oz ft⁻²]) were higher at the valley landscape position than the ridge landscape position with a runoff ratio of 0.016 se 0.008 and a sediment yield of 0.418 se 0.27 g m⁻² (0.00136 se 0.00885 oz ft⁻²). This study did not detect significant effects of thinning on time to peak runoff, time to runoff initiation, runoff ratio, and sediment yield.