160-9 Snow, Wind, and Fire: Volumes, Characteristics, and Geomorphic Impact of Large Wood Derived from Large-scale Forest Disturbances

Session: Advances in Fluvial Processes and Sediment Transport, Part I

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Abstract:

It is well understood that large-scale forest disturbance events are capable of substantially increasing wood supply to stream channels, but the particular quantities of wood delivered by these mechanisms – along with the characteristics and geomorphic impact of that wood – remain relatively unknown. Given that such events may potentially generate elevated wood loading compared to background supply processes, better understanding of the degree to which forest disturbances drive increases in wood volume, and the geomorphic impacts that wood exerts on stream channels in disturbed catchments, is necessary to predict stream response following disturbance. Here, we quantify these particulars for three different forest disturbance mechanisms: snow avalanches, blowdown, and fire. Results suggest that avalanches and blowdown substantially increase wood volumes over background (85~500%) at both the reach and watershed-scale, demonstrating their outsized impact on in-stream wood loadings. Fire, on the other hand, may drive elevated loading at the watershed-scale (~80% of individual wood pieces and ~90% of jams in study sites were comprised of burned wood), but increased wood supply at the reach-scale may be mitigated by local characteristics including valley morphology and burn severity.  In terms of geomorphic impact, large-scale disturbances such as these do appear to supply wood with an observable impact on stream morphologic processes, with 30~80% of pieces and jams found to either store sediment, form pools, or deflect flow. Together, results indicate that while forest disturbances are capable of driving increased loading, heterogeneity in both volume and geomorphic impact exists among mechanisms, driven in part by disturbance type, time since disturbance, and site-specific factors such as valley morphology, geomorphic setting, forest type, and watershed history. Overall, results will help to inform recovery-focused management decisions such as wood addition to streams following disturbance and provide managers and decision makers with improved perspective regarding post-disturbance stream trajectories.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9277

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