UBC Theses and Dissertations
The impacts of wildfire and Mountain Pine Beetle disturbance on wood budgets, stability and related sediment storage in low-sediment supply streams of the Okanagan Basin King, Leonora Adele
This thesis presents the Large Woody Debris (LWD) budgets and related sediment dynamics of 12 headwater streams in the Okanagan Basin of British Columbia. The study streams include 3 wildfire (from the recent Okanagan Mountain Park Fire in 2003) sites and 3 control sites in the Interior Douglas-fir (IDF) biogeoclimatic zone, and 3 recent Mountain Pine Beetle (MPB) infestation sites and 3 control sites in the Montane Spruce (MS) zone. The wood budget components were quantified based on repeated annual wood surveys, and represent the first wood budgets produced in the literature. Wildfire was found to significantly increase annual wood recruitment by more than an order of magnitude over undisturbed or control streams. MPB had not significantly increased LWD recruitment, but is expected to increase over the coming decades. Both of the riparian disturbances had shifted the size distribution of recruits to larger wood sizes. Our analysis confirms that the matrix of relative wood size presented by Hassan et al. (2005) is a good predictor of wood stability and export. Wood stability was in turn a primary determinant of wood function and the role of wood in sediment storage. Wood in the study streams stored between 0% and 90% of the sediment in the channels. Sediment stores increased with increasing functional wood loading. This highlights an important role of LWD in sediment storage in spite of large variations. However, in contrast to literature on the role of LWD in supply-rich streams, LWD in our supply-limited streams was found to have no statistical relationship to sediment diversity and was found to be less effective at causing sediment fining. We suggest that LWD-related sediment storage sites in supply-limited streams replace rather than supplement alluvial storage sites as they would in sediment-supply rich streams, and thus do not increase sediment diversity. Furthermore, LWD is a less important roughness element in these step-pool systems compared to pool-riffle systems, and is thus not effective at causing sediment fining under step-pool conditions.
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