2026-03-03 ワシントン大学（UW）
＜関連情報＞
- https://www.washington.edu/news/2026/03/03/forest-thinning-snowpack-snow-drought-wildfire-resilience/
- https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2025.1707812/full
- https://www.frontiersin.org/journals/water/articles/10.3389/frwa.2023.1115264/full
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020WR027926
耐火性森林施業によって積雪量を最大化できるか？米国ワシントン州イースタンカスケード山脈における実験的森林施業からの知見 Can we maximize snow storage through fire-resilient forest treatments? Insights from experimental forest treatments in the Eastern Cascades, WA, USA
Cassie Lumbrazo,Emily R. Howe,Susan E. Dickerson-Lange,Steven Pestana,John Cramblitt,Karen Dedinsky,Kyle Smith,Jessica D. Lundquist
Frontiers in Forests and Global Change Published:03 March 2026
DOI:https://doi.org/10.3389/ffgc.2025.1707812
Abstract
Forest treatments such as prescribed burns, mastication, and thinning are widely implemented across the western USA to reduce fuels and enhance wildfire resilience. These practices also influence snow accumulation and melt, which, in turn, affect snow storage and duration. Since many regions depend on seasonal snow for water resources, it is essential that forest management practices preserve or even enhance snow storage as a buffer against the impacts of climate change. To test the hypothesis that thinning and canopy gap creation can maximize snow storage, particularly on north-facing slopes, experimental forest treatments representing a range of thinning intensities were implemented on Cle Elum Ridge in the headwaters of the Yakima River Basin, Washington, USA. Ground-based snow observations, combined with pre-treatment (2021) and post-treatment (2023) snow-on lidar, show that canopy thinning increased snow depth and storage by 30% on north-facing slopes and by 16% on south-facing slopes. Snow depth was positively related to canopy openness, as measured by sky view fraction and canopy edge metrics, with stronger effects on north-facing slopes. In contrast, there was no clear relationship between snow depth and degree of thinning as measured by forest basal area, a common forestry metric used to plan treatment prescriptions. Using canopy edge metrics and sky view fraction relationships, we estimated the hydrologic benefit of thinning during 2023 at 12.3 acre-feet of water storage per 100 acres of north-facing forest and 5.1 acre-feet on south-facing slopes. These findings highlight the potential to incorporate hydrologic resilience as a co-benefit when planning fuel reduction strategies.
米国ワシントン州東部カスケード山脈の遷移気候における森林ギャップが積雪量に与える影響 Forest gap effects on snow storage in the transitional climate of the Eastern Cascade Range, Washington, United States
Susan E. Dickerson-Lange,Emily R. Howe,Kenna Patrick,Rolf Gersonde,Jessica D. Lundquist
Frontiers in Water Published:20 July 2023
DOI:https://doi.org/10.3389/frwa.2023.1115264
Abstract
Forest thinning and gap creation are being implemented across the western United States of America (USA) to reduce wildfire and forest mortality risk as the climate warms. The Eastern Cascades in Washington, USA, is in a transitional zone between maritime and continental climate conditions and represents a data gap in observations describing the relationship between forest density and snowpack. We collected 3 years of snow observations across a range of forest densities to characterize how forest management efforts in this region may influence the magnitude and duration of snow storage. Observations indicate that peak snow storage magnitude in small gaps ranges from the same to over twice that observed in unburned forest plots in the Eastern Cascades. However, differences in snow duration are generally small. Across all Eastern Cascade sites and years, we observed a median difference of snow storage lasting 7 days longer in gaps as compared to nearby forest plots. A notable exception to this pattern occurred at one north-facing site, where snow lasted 30 days longer in the gap. These observations of similar snow storage duration in the Eastern Cascades are attributed to minimal differences in canopy snow interception processes between forests and gaps at some sites, and to higher ablation rates that counterbalance the higher snow accumulation in the gaps at other sites. At the north-facing site, more snow accumulated in the gap, and ablation rates in the open gap were similar to the shaded forest due to the aspect of the site. Thus, snow storage duration was much longer in the gap. Together, these data suggest that prescriptions to reduce forest density through thinning and creating gaps may increase the overall amount of snow storage by reducing loss due to sublimation and melting of canopy-intercepted snow. However, reducing forest density in the Eastern Cascades is unlikely to buffer climate-induced shortening of snow storage duration, with the possible exception of gap creation in north-facing forests. Lastly, these observations fill a spatial and climatic data gap and can be used to support hydrological modeling at spatial and temporal scales that are relevant to forest management decisions.
森林の積雪への影響のランク付け：森林管理のための意思決定ツール Ranking Forest Effects on Snow Storage: A Decision Tool for Forest Management
Susan E. Dickerson-Lange, Julie A. Vano, Rolf Gersonde, Jessica D. Lundquist
Water Resources Research Published: 21 September 2021
DOI:https://doi.org/10.1029/2020WR027926
Abstract
Forests modify snow accumulation and ablation rates as well as overall snow storage amounts and durations, with multiple processes acting simultaneously and often in different directions. To synthesize complex forest–snow relations and help guide near-term management decisions, we present a decision tree. The framework is based on a hypothesized hierarchy of processes and associated variables that predict forest effects on snow storage. In locations with high wind speeds, forests enhance snow storage magnitude and duration relative to open areas. Where wind speeds are low, and winter and spring air temperatures are colder, forests diminish snow storage magnitude but enhance duration. Where air temperatures are warmer, forests diminish both snow magnitude and duration. Forest structure and aspect are secondary influences. We apply the decision tree framework to map the influence of forests on snow storage under historic climate conditions across the western United States, but this decision tree is applicable in any region with forests and snow. This framework provides practitioners a first-step evaluation to guide management decisions that consider where and how forests can be managed to optimize in situ water storage alongside other objectives, such as reducing wildfire hazard. This framework also articulates geospatial hypotheses, in order of anticipated importance, to be tested in future investigations of forest–snow–climate relations.
Plain Language Summary
Forests affect the amount of snow that accumulates on the landscape and how long it lasts before melting. Thus, the removal of forest canopy via timber harvest, thinning, or fire influences how long water is stored on the landscape as snowpack and summer water availability for soils, instream, and water consumption. However, predicting whether forest cover accelerates or delays snowmelt relative to a nearby open area has proven difficult due to complex forest–snow processes that vary with location. In addition, under-forest observations of snow are sparse. We present a binary decision tree framework to predict how the forest cover affects the amount and duration of snowpack relative to an adjacent open location. The intent is both to articulate a testable hypothesis for future research and to support forest management decisions that strive to balance both water resource considerations and other natural resource objectives, such as reducing wildfire hazard. We utilize publicly available climate and topographic data to present an example application for the western United States. The resulting map illustrates how the effect of forest canopy cover on snow storage varies by region and elevation and has implications for the forest management under current and warming climate conditions.
Key Points
- The net effect of forests on snow storage varies spatially and location-specific studies lack transferability
- We present a decision tree based on a hypothesized hierarchy of processes to predict where forests retain snow longer relative to open areas
- We predict how management actions will affect relative snow storage based on wind speed, winter air temperature, and timing of snowmelt
