From Soil to Canopy: Using Moisture Data From Soil and Tree Sensors to Predict Live Fuel Moisture and Guide Forest Management in a Mediterranean Coastal Woodland

ABSTRACT Ecosystem response to forest management and disturbance is governed by many factors and their interactions. This has historically made it difficult for practitioners to reach consensus on ideal management prescriptions and restoration activities. Forest management to decrease wildfire susceptibility and improve water supply is often informed by estimates of live fuel moisture (LFM). However, ecosystem response to environmental conditions and management treatments is dependent to a large degree on soil moisture. Soil moisture has been used as a surrogate to estimate LFM, but tree‐based sensors have not been applied in the same manner. In this paired watershed study, coupled soil and tree moisture probes were installed to study the relationship between soil and tree moisture and to examine soil moisture–tree–ecosystem relationships in Sonoma County, CA, USA. We found that (1) there were statistically significant effects on soil moisture and evapotranspiration (ET) from mechanical tree thinning and prescribed burns compared to an untreated watershed, (2) soil moisture decreased at the surface and increased in the root zone post‐treatment, relative to an untreated watershed, and (3) ET decreased by 90 mm in the post treatment year for the treated watershed. To investigate regional generalizability of these results, the soil moisture surrogate was applied at a nearby station within the Pepperwood Preserve to look at wildfire danger for large historical fires and was found to be relevant to the surrounding area. These results suggest that in situ soil and tree moisture sensors can be used as a surrogate for discrete and time‐consuming LFM measurements and that soil moisture thresholds can be used to help identify wildfire susceptibility and drought conditions. Information on the hydrologic response to forest treatment in different locations is valuable to land and resource managers and improving real‐time wildfire danger and drought conditions using existing or low‐cost in situ sensors can improve situational awareness and planning.