Mechanical thinning impacts on runoff, infiltration, and sediment yield following fuel reduction treatments in a southwestern dry mixed conifer forest

ABSTRACT:

Increasing densities of small diameter trees have changed ecological processes and negatively impacted conservation of soil and water resources in western forests. Thinning treatments are commonplace to reduce stem density and potential fire hazard. We evaluated the impacts of using a specialized heavy piece of equipment to reduce fuel loads on intermediate and steep slopes on surface disturbance, runoff, infiltration, and sediment yield in mixed conifer forests in central New Mexico. Surface disturbance following thinning was similar between slopes, but steep slopes were potentially susceptible to heavy surface disturbance (e.g., deep tire ruts). Rainfall simulations indicated disturbance resulting in exposed bare soil, particularly on steep slopes, increased runoff and sedimentation. However, when surface disturbance was minimized, for example when litter was disturbed but not displaced, regardless of slope, runoff and sedimentation did not exceed non-disturbed sites. Advances in mechanical equipment such as forwarding beds may help reduce surface disturbance. We recommend forest managers focus on minimizing surface disturbance when preparing timber prescription guidelines and on-site priorities.