Reexamining forest disturbance thresholds for managing cumulative hydrological impacts
Xiaohua Wei, Yiping Hou, Mingfang Zhang, Qiang Li, Krysta Giles‐Hansen, Wenfei Liu
Abstract
Abstract Forest disturbance thresholds, defined as those at or above which significant hydrological impacts are caused, are important guides to support forest and watershed management decisions for protecting hydrological functions and minimizing negative environmental impacts. Our literature review suggests that despite their significance, the research on this topic is surprisingly limited (<20 publications), where the paired watershed experiments (PWEs) primarily designed for detecting hydrological responses to forest cover change at the small watersheds were used to derive the thresholds. However, the widely used thresholds (e.g., 20%) based on the PWEs were identified from visual interpretation rather than determined from hydrological response curves, suffering from methodological shortcomings, and thus, may lack reliability. To advance this topic, we provided a robust technique (the modified double mass curve, MDMC) for quantitatively determining forest disturbance thresholds on annual mean flow as it allows the development of a hydrological response curve between cumulative hydrological effects and forest disturbance over time at the watershed scale. We applied this robust technique in eight large watersheds in British Columbia, Canada, and found that the forest disturbance thresholds ranged from 12 to 25%. We highly recommend that the widely used forest disturbance thresholds must be reexamined, and more studies are needed with rigorous methods and in consideration of other hydrological variables in forested watersheds.