CAREER: Fire management effects on Sierra Nevada ecohydrology - a dynamical systems approach

森林覆盖的山地流域为美国西部提供了大部分的水，从根本上来说是容易发生火灾的生态系统。当前的干旱和预计的未来气候变化，同时加剧了内华达山脉的火灾风险，并威胁到供水的可持续性。迫切需要能够同时减少火灾风险和保障供水的管理办法。这项研究利用了内华达山脉的一对独特的流域，在20世纪70年代之前，这里已经实施了近一个世纪的灭火措施，从那时起就开始实施有管理的野火。将对这些盆地进行研究，以确定植被覆盖、积雪和土壤水分行为以及水量如何响应变化的火灾状态。研究结果将在一个建模框架中进行综合，该框架可用于评估内华达山脉其他地区类似火灾变化的潜在后果。研究结果将为激励内华达山脉的新火灾管理提供证据基础，降低火灾风险，加强该地区的水安全，该地区为加州3800万居民中的60%提供水。这些结果将通过与加州消防科学联盟开发的外展计划共享。该项目还将包括一个公民科学项目，让中学生参加由约塞米蒂国家公园NatureBridge运营的户外环境教育项目。从森林山地生态系统中去除火是一个长达一个世纪的、大规模的、知之甚少的实验，它改变了森林的组成、人口、异速生长和演替动态，对生物地球化学、水文和生态系统功能产生了假定的影响（尽管在很大程度上没有量化）。本研究项目利用了一个独特的机会，通过检查内华达山脉仅有的两个流域的植被、火灾和水文的变化来探索这些影响，这两个流域故意减轻了灭火措施，并允许重新建立自然火灾制度。历史和当代航空摄影将用于重建研究流域的植被历史。由此产生的植被图将作为在整个研究流域进行的提高分布土壤湿度和燃料湿度测量的基础，并作为分布式水文模型的输入。气象站、雪摄影机和土壤湿度观测站将在火灾后不同植被演替的地点安装，以描述植被变化对当地气象和水文条件的影响。将进行实验室实验，以评价在反复冻融循环下土壤疏水性的持久性，这是内华达山脉雨季的特征。通过这些实地观察获得的过程见解将用于开发、参数化和测试代表火、植被和水的动态相互作用的概率模型。该项目将有助于对雪主导景观中火与水文相互作用的新过程理解，特别是火灾历史如何影响积雪动力学（如拦截、升华和融化时间），以及冻融过程如何影响火后土壤疏水性。它将产生独特的空间、时间和历史数据集，揭示灭火和减轻火灾对山地森林植被和水文的共同影响。

Forested mountain watersheds supply the majority of water to the western United States, and are fundamentally fire-prone ecosystems. Contemporary drought, and projected future climate change, simultaneously exacerbate fire risks in the Sierra Nevada and threaten the sustainability of the water supply. Management approaches that could simultaneously reduce fire risks while safeguarding water supplies are sorely needed. This research takes advantage of a unique pair of watersheds in the Sierra Nevada where fire suppression was practiced for almost a century prior to the 1970s, and managed wildfire has been practiced since then. These basins will be studied to determine how vegetation cover, snow and soil moisture behavior, and water yields have responded to the changed fire regime. The results will be synthesized in a modeling framework that can be applied to evaluate the potential consequences of similar shifts in fire regime elsewhere in the Sierra Nevada. Results of the research will provide an evidence basis to motivate new fire management in the Sierra Nevada, reducing fire risk and enhancing water security in a region that supplies 60% of California's 38 million residents. These results will be shared through an outreach program developed with the California Fire Science Consortium. The project will also include a citizen-science project involving middle-school students participating in outdoor environmental education programs run by NatureBridge at Yosemite National Park. The removal of fire from forested mountain ecosystems represents a century-long, massive, and poorly-understood experiment, altering the composition, demography, allometry and succession dynamics of forests, with presumed (although largely unquantified) effects on biogeochemistry, hydrology and ecosystem function. This research project leverages a unique opportunity to explore these effects by examining changes in vegetation, fire and hydrology in the only two watersheds in the Sierra Nevada where fire suppression has been deliberately alleviated and the natural fire regime allowed to re-establish. Historical and contemporary aerial photography will be used to reconstruct vegetation histories in the study watersheds. The resulting vegetation maps will be used as a basis for upscaling distributed soil moisture and fuel moisture measurements made throughout the study basins, and as input into distributed hydrological models. Weather stations, snow cameras and soil moisture observations will be installed in sites with distinct post-fire vegetation successions to characterize the effects of vegetation change on local meteorological and hydrological conditions. Laboratory experiments will be undertaken to evaluate the persistence of soil hydrophobicity under repeated freeze-thaw cycles, characteristic of the Sierra Nevada wet season. The process insights obtained through these field observations will be used to develop, parameterize and test a probabilistic model representing the dynamic interactions of fire, vegetation and water. The project will contribute new process understanding about the interaction of fire and hydrology in snow dominated landscapes, specifically how fire history impacts snowpack dynamics (such as interception, sublimation and melt timing), and how freeze-thaw processes impact post-fire soil hydrophobicity. It will generate unique spatial, temporal and historical datasets that will reveal the joint consequences of fire suppression and its alleviation on vegetation and hydrology in montane forests.