Ranking forest effects on snow storage: a decision tool for forest management

Forests modify snow accumulation and ablation rates, and 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 model 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 magnitude and duration. Forest structure and aspect are secondary influences that shift the net effect of forest on snow storage. We apply the model to map the influence of forests on snow storage under historic and warming climate conditions across the western United States, but this model is applicable in any region with forests and snow. The decision tree model 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 fuels. This framework also articulates geospatial hypotheses, in order of anticipated importance, to be tested in future investigations of forest-snow-climate relations. The data and code included herein are described in Dickerson-Lange, et al. 2021, Ranking forest effects on snow storage: a decision tool for forest management, Water Resources Research. The repository contains all input data, model code, and results.森林会改变积雪积累与消融速率，以及整体积雪储量与存留时长，多种过程同时发生且作用方向往往存在差异。为综合解析复杂的森林-积雪相互关系，为近期森林经营决策提供参考，我们基于一套假设的过程层级与关联变量，构建了可预测森林对积雪储量影响的决策树模型（decision tree model）。在风速较高的区域，相较于开阔无林地带，森林可提升积雪储量与存留时长；当风速较低且冬春气温较低时，森林会降低积雪储量，但延长其存留时长；而当气温较高时，森林会同时降低积雪储量与存留时长。森林结构与坡向（aspect）为次要影响因素，可改变森林对积雪储量的净效应。我们将该模型应用于美国西部历史气候与变暖气候情景下的森林对积雪储量影响制图，不过该模型同样适用于任何存在森林与积雪的区域。该决策树模型可为从业者提供初步评估工具，辅助其制定管理决策，考量森林的经营位置与方式，以在优化原位储水的同时兼顾其他目标，例如降低林火可燃物载量。该框架还按照预期重要性排序，梳理出可用于未来森林-积雪-气候关系研究的地理空间假设，以待后续验证。本文所附数据与代码的详细说明参见Dickerson-Lange等人2021年发表于《水资源研究》（Water Resources Research）的论文《积雪储量的森林影响排序：森林管理决策工具》。该仓库包含全部输入数据、模型代码与最终结果。