Five years of hourly soil water potential monitoring demonstrates forest thinning benefits in the North American Southwest
Semi‑arid forests of the North American Southwest face extreme drought and dense stand conditions, yet the long‑term soil‑moisture effects of restoration thinning remain poorly understood. Using five years of data from 126 soil‑water‑potential sensors, this study examined root‑zone moisture (25–100 cm) in thinned, non‑thinned and edge areas of ponderosa pine forests. Thinned stands were consistently wetter, dried more slowly and spent fewer days under physiological drought thresholds than dense forests, regardless of annual precipitation variability. South‑facing edges dried earliest, indicating heightened vulnerability. Results show that restoration thinning significantly improves water availability and enhances forest resilience under intensifying climate change.
Subject Tags
- Climate resilience
- Forest
- Soils
Abstract
North American Southwest semi-arid forests are experiencing unprecedented stress due to the combination of the 21st century megadrought and abnormally dense, young forest stands. Restoration thinning is being widely implemented across the region with the aim of restoring historical stand structures, improving forest health and decreasing the risk of unnaturally severe wildfire. While restoration thinning likely affects soil moisture as well, it is unknown how significant or long-lasting such effects are. Especially little is known about the influence of thinning on root-zone soil moisture used by mature trees. In this study, we used 5 years of data from 126 soil water potential sensors to examine patterns in root-zone (25–100 cm) soil moisture in thinned and non-thinned dense ponderosa pine (Pinus ponderosa) forests as well as the edge areas (boundary) between them during 1–6 years post-thinning. We focused on the spring dry season and calculated three metrics: mean soil water potential, days to onset of soil drying and days spent under a critical drying threshold beyond which ponderosa pine experiences physiological drought stress. We found that thinned areas were consistently significantly wetter and spent less time under critical drying conditions than either non-thinned edge or non-thinned dense forest. Importantly, the thinned forest also experienced more consistent water availability compared to non-thinned forest, regardless of year-to-year precipitation variability. South-facing non-thinned edge areas dried earlier than either of the other treatments and may be especially vulnerable to drought. Our results strongly suggest that restoration thinning significantly improves forest resilience to climate change.
Citation
Tatum, J., Sankey, T. T., Belmonte, A., Dymond, S. F., & Woolley, T. (2025). Five years of hourly soil water potential monitoring demonstrates forest thinning benefits in the North American Southwest. Ecohydrology, 18(6), e70104. https://doi.org/10.1002/eco.70104
TNC Authors
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Travis Woolley
Forest Ecologist, Arizona
The Nature Conservancy
Email: twoolley@tnc.org