Wednesday, May 28, 2008 - 3:45 PM
480

Increased inputs of large wood to streams due to mountain pine beetle outbreak

Kathleen A. Dwire1, Sandra E. Ryan1, Erica L. Bishop2, and Michael K. Young1. (1) USDA Forest Service, Rocky Mountain Research Station, 240 West Prospect Road, Fort Collins, CO 80526, (2) Department of Geography, University of Wyoming, 1000 E. University Avenue, Laramie, WY 82071

Pine-dominated forests in the interior western USA are undergoing widespread infestation by mountain pine beetle (MPB), which is causing high levels of tree mortality.  Although models predict that such large-scale forest disturbance can result in the pulse delivery of large wood (LW) to streams, they have not been validated by empirical data.  At the Fraser Experimental Forest, north-central Colorado, we are studying LW dynamics to assess the impacts of MPB-caused canopy mortality on instream wood loading.  In four subalpine watersheds, we measured instream LW pieces (length, end diameters), and evaluated fall direction, distance from source, probable recruitment process, and geomorphic function.  The number of LW pieces averaged 0.8 per meter channel length; most pieces were relatively immobile and had become incorporated into the channel form (e.g., steps, banks, small falls).  Approximately 45% of the pieces were traced to sources within 30 m of the channel and attributed to chronic tree mortality and bank erosion, with less than 1% directly due to MPB.  We will combine instream LW data with estimates of tree mortality from upland and riparian plots to present conceptual models of potential changes in wood loading and impacts on channel form over different time scales. 


Web Page: riparian, forest disturbance, channel form

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