INFLUENCE OF THE MOUNTAIN PINE BEETLE INFESTATION ON WOOD LOADS IN HEADWATER STREAMS OF THE MEDICINE BOW NATIONAL FOREST, ROCKY MOUNTAINS USA

Disturbance regimes are important determinants of both terrestrial and aquatic ecosystem structure and function. Disturbances may linger in the landscape and lag temporally, influencing stream ecosystem form and function for decades, if not centuries. The recent anthropogenically enhanced Mountain Pine Beetle (MPB) infestation in pine forests of the Rocky Mountain region has resulted in extensive tree mortality, producing the potential for significant increases in carbon supply to stream channels in the form of MPB-killed trees. To better understand MPB impacts on in-stream large wood, we conducted a wood census in 30 headwater streams within the Medicine Bow National Forest, Wyoming across the temporal spectrum from early- to late-stage MPB-infestation. The results show that wood loadings correlate strongly with stage of MPB infestation, with loads increasing with time since infestation. However, even in latter-stage infestation streams, many of the fallen trees bridge the channel and have yet to break down sufficiently to enter the channel. Wood loads are likely to further increase in the future as these bridging pieces decompose, break, and enter the channel, eventually being transported by streamflow. Although forest infestation has peaked in the study area, the streams are still early on a curve of rapidly increasing wood loads that have the potential to dramatically increase the carbon base of regional stream ecosystems.