Forest disturbance induced changes in the coupling of forest carbon and water have important implications for ecosystem functioning and sustainable forest management. However, this is rarely investigated at the large watershed scale with cumulative forest disturbance. We used a combination of techniques including modeling, statistical analysis, and machine learning to investigate the effects of cumulative forest disturbance on water use efficiency (WUE, a proxy for carbon and water coupling) in the 19,200 km2 Chilcotin watershed situated in the central interior of British Columbia, Canada. Harvesting, wildfire, and a severe Mountain Pine Beetle (MPB) infestation have gradually cumulated over the 45-year study period, and the watershed reached a cumulative equivalent clear-cut area of 10% in 1999 and then 40% in 2016. Surprisingly, with the dramatic forest disturbance increase from 2000 to 2016 which was mainly due to MPB, watershed-level carbon stocks and sequestration showed an insignificant reduction. This resilience was mainly due to landscape-level carbon dynamics that saw a balance between a variety of disturbance rates and types, an accumulation of older stand types, and fast growing young regenerated forests. Watershed-level carbon sequestration capacity was sustained, measured by Net Primary Production (NPP). A concurrent significant decrease in annual evapotranspiration (ET), led to a 19% increase in WUE (defined as the ratio of NPP to ET), which is contrary to common findings after disturbance at the forest stand-level. During this period of high disturbance, ET was the dominant driver of the WUE increase. We conclude that disturbance-driven forest dynamics and the appropriate scale must be considered when investigating carbon and water relationship. In contrast to the stand-level trade-off relationship between carbon and water, forested watersheds may be managed to maintain timber, carbon and water resources across large landscapes.

中文翻译：

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在大森林流域规模上，随着累积的森林扰动，水资源利用效率显着提高

森林扰动引起的森林碳水耦合变化对生态系统功能和可持续森林管理具有重要意义。但是，很少在大流域规模上对这种情况进行调查，并且有累积的森林干扰。我们使用了包括建模，统计分析和机器学习在内的多种技术，研究了位于森林中心内部19,200 km2 Chilcotin流域中累积森林扰动对水分利用效率（WUE，碳与水耦合的代表）的影响。加拿大不列颠哥伦比亚省。在为期45年的研究期内，收获，野火和严重的山地松甲虫（MPB）侵扰逐渐累积，分水岭的累计净砍伐面积在1999年达到10％，然后在2016年达到40％。令人惊讶的是，从2000年到2016年，森林扰动急剧增加，这主要是由于MPB的影响，流域级碳储量和封存量显示出微不足道的减少。这种复原力主要归因于景观水平的碳动态，该动态在各种干扰率和类型之间，旧林分类型的积累和快速生长的年轻再生森林之间取得了平衡。用净初级生产（NPP）衡量，流域一级的固碳能力得以维持。每年蒸散量（ET）的同时显着减少，导致WUE（定义为NPP与ET的比率）增加19％，这与森林林位水平受到干扰后的常见发现相反。在此高干扰时期，ET是WUE升高的主要驱动力。我们得出的结论是，在调查碳与水的关系时，必须考虑扰动驱动的森林动态和适当的规模。与碳和水之间的标准权衡关系相反，森林流域可以通过管理来维持大景观中的木材，碳和水资源。