Increased Instream Wood Loading Attributed to Mountain Pine Beetle Outbreak in Subalpine Watersheds
Abstract
Many lodgepole pine (Pinus contorta) forests in North-Central Colorado have undergone recent widespread infestation by mountain pine beetle (Dendroctous ponderosae), causing high levels of mortality over substantial areas. The reach of this epidemic, thought to be related to increased temperatures and sustained drought conditions, continues into previously unaffected watersheds, including areas of the Fraser Experimental Forest (FEF), CO. Widespread forest loss from beetle outbreak may potentially increase water yield and rates of sedimentation from steep hillslopes. Several watersheds within FEF have extensive records of water and sediment yield, providing an opportunity to evaluate changes in flow and sedimentation following the outbreak. However, perhaps the most immediate impact to streams will be increased instream wood loading as beetle-killed trees begin to fall from steep hillslopes. Many of the small streams on FEF are directly adjacent to steep hillslopes and up to one third of current load of instream wood can be traced to hillslope origins. Baseline information on volumes, sources, and geomorphic influences of large wood in these systems indicate that much of the wood is relatively immobile and often becomes incorporated into the channel form (e.g., steps, banks, and small falls) rather than being transported. Typical numbers of pieces of large wood vary from 0.5 to 0.8 pieces per meter channel length, with most reaches falling in the 0.7 to 0.8 range. Large wood in streams can both increase and decrease local channel stability so the net effect of increases in wood loading are uncertain. Conceptual models of potential changes in wood loading and its impacts on channel form are addressed in this presentation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.H41H..04R
- Keywords:
-
- 0483 Riparian systems (0744;
- 1856);
- 1825 Geomorphology: fluvial (1625);
- 1856 River channels (0483;
- 0744);
- 1879 Watershed