Details

Autor(en) / Beteiligte

• Gronsdahl, Stefan
• Moore, R. Dan
• Rosenfeld, Jordan
• McCleary, Rich
• Winkler, Rita

Titel

Effects of forestry on summertime low flows and physical fish habitat in snowmelt‐dominant headwater catchments of the Pacific Northwest

Ist Teil von

• Hydrological processes, 2019-12, Vol.33 (25), p.3152-3168

Ort / Verlag

Chichester: Wiley Subscription Services, Inc

Erscheinungsjahr

2019

Quelle

Wiley Online Library - AutoHoldings Journals

Beschreibungen/Notizen

• Periods of summertime low flows are often critical for fish. This study quantified the impacts of forest clear‐cutting on summertime low flows and fish habitat and how they evolved through time in two snowmelt‐dominant headwater catchments in the southern interior of British Columbia, Canada. A paired‐catchment analysis was applied to July–September water yield, the number of days each year with flow less than 10% of mean annual discharge, and daily streamflow for each calendar day. The postharvest time series were divided into treatment periods of approximately 6–10 years, which were analysed independently to evaluate how the effects of forestry changed through time. An instream flow assessment using a physical habitat simulation‐style approach was used to relate streamflow to the availability of physical habitat for resident rainbow trout. About two decades after the onset of logging and as the extent of logging increased to approximately 50% of the catchments, reductions in daily summertime low flows became more significant for the July–September yield (43%) and for the analysis by calendar day (11–68%). Reductions in summertime low flows were most pronounced in the catchment with the longest postharvest time series. On the basis of the temporal patterns of response, we hypothesize that the delayed reductions in late‐summer flow represent the combined effects of a persistent advance in snowmelt timing in combination with at least a partial recovery of transpiration and interception loss from the regenerating forests. These results indicate that asymptotic hydrological recovery as time progresses following logging is not suitable for understanding the impacts of forest harvesting on summertime low flows. Additionally, these reductions in streamflow corresponded to persistent decreases in modelled fish habitat availability that typically ranged from 20% to 50% during the summer low‐flow period in one of the catchments, suggesting that forest harvest may have substantial delayed effects on rearing salmonids in headwater streams. Late‐summer flows dropped below preharvest levels about two decades following clear‐cut harvesting in a snow‐dominated catchment. The temporal signatures of the effect of forest harvesting, both within and among years, suggest that the delayed declines in late‐summer flow reflect the combination of persistently advanced snowmelt timing and the ongoing recovery of interception loss and transpiration by the regenerating forest. The declines in late‐summer flow resulted in commensurate reductions in fish habitat availability.