The cumulative effects of forest disturbance on streamflow in a large watershed in the central interior of British Columbia, Canada

Background/Question/Methods

The Baker Creek watershed (1570 km²) situated in the central interior of British Columbia, Canada has been severely disturbed by both human-being logging and natural disturbance, particularly by a recent large-scale mountain pine beetle (MPB) infestation (up to 2009, 70.2% of the watershed area was attacked by MPB) and subsequent salvage logging. The concept of equivalent clear-cut area (ECA) was used to indicate the magnitude of forest disturbance with consideration of hydrological recovery following various types of disturbances (wildfire, logging and MPB infestation) cumulated over space and time in the studied watershed. The cumulative ECA was up to 62.2% in 2009. A combined approach of statistical analysis (time series analysis) with modified double mass curve was employed to evaluate the impacts of forest disturbance on hydrology. 

Results/Conclusions

Our results showed that severe forest disturbance significantly increased annual mean flow. The average increment in annual mean flow caused by forest disturbance was 48.4 mm/yr, while the average decrease in annual mean flow cased by climatic variability during the same disturbance period was -35.5mm/yr. The opposite change directions and magnitudes clearly suggest offsetting effect between forest disturbance and climatic variability, with the absolute influential strength of forest disturbance (57.7%) overriding that from climate variability (42.3%). Forest disturbances also produced significant positive effect on low flow and dry season (fall and winter) mean flow. Implications of our findings for future forest and water resources management are discussed in the context of long-term watershed sustainability.