Forest patch geometry and climate regulate the impact of forest thinning on snowpack in the southwest United States
Forest thinning influences snowpack, yet its climate dependence is poorly quantified. Using a high‑resolution snow model validated with extensive field data, this study examines pre‑ and post‑thinning forest geometry under mid‑ and high‑elevation climate conditions in Arizona. A modest 1°C cooling and 20% increase in winter precipitation at higher elevations produced dramatically different snow regimes—longer‑lasting snow, fewer mid‑winter melt events and ~60% larger peak snowpack. Thinning increased peak SWE and liquid‑water input in both climates, reduced sublimation by 10% and shortened snow‑cover duration only at higher elevations. Patch geometry also shaped outcomes, with larger canopy gaps increasing LWI and warm canopy edges reducing SWE. These results highlight the need to consider local climate and forest structure when designing thinning treatments for water‑resource benefits.
Subject Tags
- Forest
- Climate impacts
Abstract
Despite having important implications for water resources, the climatic dependence of forest thinning impacts on snowpack is poorly quantified. In this study, we used a high-resolution snow model to understand the impact of forest thinning on snowpack in Arizona under contrasting climate conditions, leading to ephemeral vs. seasonal snowpack conditions. The model is evaluated using a spatiotemporally extensive set of snowpack measurements and is run for the same set of pre- and post-thinning forest patch geometry using two meteorological forcing datasets representing locally mid- and high-elevation climate conditions. Although the high-elevation climate is only 1°C cooler and has 20% more winter precipitation, it leads to markedly different snowpack conditions, i.e., twice as long-lasting snowpack, less mid-winter ablation events and ~60% larger at its peak. For both climates, forest thinning increased peak snow water equivalent (SWE) and liquid water input (LWI), but it decreased snow cover duration (SCD) only for the high-elevation climate. Total sublimation losses decreased from ~35% of wintertime precipitation pre-thinning to ~25% post-thinning for the high-elevation climate and from ~25% to ~15% for the mid-elevation climate. Generally, a 10% reduction in canopy cover resulted in ~4.5% more snowfall reaching the ground, and a 10-day decrease in SCD reduced the fraction of winter precipitation lost to snowpack sublimation by ~2%. Post-thinning changes in forest patch geometry were also important as larger canopy gaps had more LWI, and areas with warmer canopy edges had lower peak SWE and SCD.
Citation
Broxton, P. D., Biederman, J. A., Dwivedi, R., van Leeuwen, W. J., Sankey, T. T., Woolley, T., & Svoma, B. M. (2025). Forest Patch Geometry and Climate Regulate the Impact of Forest Thinning on Snowpack in the Southwest United States. Ecohydrology, 18(6), e70111. https://doi.org/10.1002/eco.70111
TNC Authors
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Travis Woolley
Forest Ecologist, Arizona
The Nature Conservancy
Email: twoolley@tnc.org