Johnson, BrittanyWeatherholt, Jalene Ann2021-08-262021-08-262021-08-262021Weatherholt_washington_0250O_23152.pdfhttp://hdl.handle.net/1773/47562Thesis (Master's)--University of Washington, 2021Land area burned annually in the western US has risen in association with shifting climatic conditions as a result of global climate change. Successional processes greatly rely on soils as a foundational medium for the establishment of new plant communities following disturbance. During a wildfire, the combustion of organic materials releases hydrophobic compounds that contribute to the formation of water repellent soils below the surface. Soil water repellency (SWR) can greatly increase erosion risk and overland flow events in an already vulnerable, post-fire system. The myriad of environmental and burn conditions that contribute to the formation, destruction, and perseverance of SWR result in extremely heterogeneous spatial patterns across a landscape. Managers could benefit from a clearer understanding of SWR properties to best aid in successional management practices. This document reports not only the findings of my thesis research work but also explores the journey to my current understanding of SWR in the Pacific Northwest (PNW). Seed data collected in 2018 throughout post-fire ecosystems 1 year following disturbance in the PNW was reflective of the heterogeneous nature of soil water relations. Largely indistinguishable variation of SWR across burn severity classes and naturally occurring hydrophobicity patterns did not provide any clear differences across the landscape. We hypothesized that the scale used to assess relationships between burn severity metrics and SWR from this field design, consisting of four measurement locations per plot across multiple fires was not appropriate to the process itself. Learning from this work, a new protocol measuring 81 locations within a 44x20m rectangle was adapted to explore spatial scales and environmental factors that managers can use to predict SWR behavior on their post-fire forests. This adapted protocol was implemented on the Green Ridge fire that burned in the summer of 2020 in the Deschutes National Forest in Oregon state. Soils within this forest were found in the 2018 data to experience both natural and fire-induced SWR as a process of this mixed-conifer system. We found that soil burn severity is a significant factor in predicting the variability of SWR conditions compared to unburned areas but does not identify a clear pattern across management-relevant distinctions of burn severity. While SWR density significantly diminishes with depth into the soil horizon, little evidence of management-relevant scalable spatial patterns of SWR horizontally throughout a stand were identified. The influence of environmental factors on SWR density will be a key component in the ability to predict post-fire conditions through satellite inputs for landscape level modelling. The future of SWR research will rely on advancements made in remote sensing products of soil qualities and wildfire severity in addition to improved SWR sampling standards.application/pdfen-USnoneerosionPacific NorthwestPost-fireSoilSoil water repellencyWildfireSoil sciencesForestryThesis