Professor University of British Columbia (Okanagan) Kelowna, British Columbia, Canada
Abstract: Forest disturbance threshold is defined as a critical disturbance level in forested landscapes above which significant hydrological impacts are detected. Determining disturbance thresholds is challenging but critically important for ensuring hydrological functioning and ecosystem stability and resilience. This calls for quantitative evaluations of forest disturbance thresholds regionally or globally. In this study, a well-tested framework combining dynamic forest disturbance history (cumulative equivalent clear-cut area, CECA) and hydrological response curve (the modified double mass curve, MDMC) was applied to determine disturbance thresholds on annual streamflow in 42 Montane forested landscapes in the interior of British Columbia, Canada. The results show that the average forest disturbance threshold for significant and cumulative hydrological impacts is 17.28% of CECA ranging from 7.20 to 51.67%. Climate (inter-annual and intra-annual) and watershed properties exert critical controls on forest disturbance thresholds. Watersheds with smaller snowfall proportions, more synchronization of energy demand and water supply, greater ecosystem diversity, smaller watershed sizes, greater water retention capacities, and more gentle slopes have higher forest disturbance thresholds. Given the present forest disturbance levels, more than half (53%) of the montane forested watersheds have already crossed the disturbance thresholds in the central interior of British Columbia. These results have important implications for maintaining hydrological functions, and ecological stability and resilience.
