Investigating the connections between soil, fire, and ecosystem recovery in the Western US: The role of soil water repellency in essential ecosystem processes

Abstract:

As climate change alters the frequency and severity of wildfires, exploring the mechanisms behind ecosystem recovery becomes a crucial component in predicting the future of Pacific Northwest forests. One of the most complex and least understood factors exists in the foundation of the forest is the soil. Fire provokes dramatic changes in the soil environment, particularly the relationship between soil and water. Organic matter and microbial by-products often contain hydrophobic compounds which can create natural water repellent layers (WPLs). During a fire, these compounds are released and redistributed, condensing onto soil particles as they cool resulting in WPL formation. This can have serious repercussions, including limiting available water in rooting zones, impeding the establishment of new biotic communities, and initiating erosion. This study examines the effects of fire in two recently burned areas in the Western US that have naturally-occurring WPLs. Determining the horizontal and vertical spatial heterogeneity of WPLs and understanding the role it plays in succession across a range of burn severities is essential to limiting erosion and ensuring lasting soil health. Post-fire recovery often depends on micro-scale conditions. Can the environment support a germinating seed? Will water infiltrate or run off, carrying valuable nutrients with it? The spatial variation in soil hydrophobic properties has an enormous influence over soil-water relationships including plant water availability, the ratio between infiltration and runoff, and erosion on micro- to macro-scales. In areas where WRLs occur naturally, the dynamic becomes even more complex. This project aids in the ongoing work to quantify how the patterns in soil hydrophobicity vary across spatial scales and if they vary in a predictable way. Answering this question allows managers to target specific areas of focus for erosion prevention and replanting. Using these relationships between soil properties and wildfire disturbance, managers could rely on readily available data (e.g. soil burn severity maps developed by U.S.F.S. Burned Area Emergency Response teams) to define potential zones of interest. This project provides key insights into wildfire recovery and will improve our understanding of the future of forests in a changing world.