Forest disturbance threshold is defined as a critical disturbance level (e.g., % of forest cover change) in forested landscapes above which significant hydrological impacts are detected. Determining disturbance thresholds is critically important for supporting forest management to ensure the sustaining of ecological and hydrological functions. However, there are very few quantitative evaluations of forest disturbance thresholds globally. In this study, we applied a well-tested methodology (the modified double mass curve) to derive the long-term, continuous hydrological response curves and then to quantify forest disturbance thresholds on annual streamflow in 42 forested watersheds in British Columbia, Canada. The results show that forest disturbance thresholds for significant and cumulative hydrological impacts vary from 7% to 52% of cumulative equivalent clear-cut area with an average of 17% or from 8% to 52% of disturbed area with an average of 19%. Climate (inter-annual and intra-annual) and watershed properties exert critical controls on forest disturbance thresholds. Watersheds with greater snowfall proportions (more annual precipitation falling as snow), more desynchronizations (temporal mismatching) of energy demand and water supply at the intra-annual scale, less diverse ecosystems, and larger watershed sizes have lower forest disturbance thresholds. Given the present forest disturbance levels in the central interior of British Columbia, about half (53%) of the forested watersheds have already crossed the average disturbance threshold. These results highlight that watershed planning and management using forest disturbance thresholds must carefully consider local climate and watershed properties. The methodology can be effectively and robustly extended elsewhere around the globe.

中文翻译：

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森林干扰阈值和累积水文影响

森林扰动阈值被定义为森林景观中的临界扰动水平（例如，森林覆盖变化的百分比），高于该水平则检测到显着的水文影响。确定干扰阈值对于支持森林管理以确保生态和水文功能的维持至关重要。然而，全球范围内对森林扰动阈值的定量评估还很少。在本研究中，我们应用经过充分测试的方法（修正的双质量曲线）来得出长期、连续的水文响应曲线，然后量化加拿大不列颠哥伦比亚省 42 个森林覆盖流域的年径流量的森林干扰阈值。结果表明，显着和累积水文影响的森林扰动阈值范围为累积当量砍伐面积的 7% 至 52%（平均为 17%）或扰动面积的 8% 至 52%（平均为 19%）。气候（年际和年内）和流域特性对森林扰动阈值具有关键控制作用。降雪比例较大（更多的年降水以雪形式降落）、年内能源需求和供水不同步（时间不匹配）较多、生态系统多样性较低以及流域规模较大的流域，森林干扰阈值较低。鉴于目前不列颠哥伦比亚省中部内陆地区的森林干扰程度，约一半（53%）的森林流域已经超过了平均干扰阈值。这些结果强调，使用森林干扰阈值的流域规划和管理必须仔细考虑当地气候和流域特性。该方法可以有效且稳健地扩展到全球其他地方。