Headwater stream temperature response to forest harvesting: Do lower flows cause greater warming?

Abstract

This study addressed two hypotheses regarding the relationship between stream temperature response to shade removal and streamflow: (a) that temperature response increases as flow declines and (b) that the relationship can be complicated by shifts in dominant streamflow sources and pathways during low‐flow periods. The study was based on a paired‐catchment design in rain‐dominated headwater catchments in the southern Coast Mountains of British Columbia, Canada, and focused on the effect of a 50% thinning treatment on daily maximum temperature in June, July and August for three sites within the harvest treatment. At the two upstream sites, the treatment response exhibited a negative relationship with daily mean streamflow, especially for days with high incident solar radiation. This result suggests that the effectiveness of forest practice rules for protecting cold‐water habitat may be reduced under future climatic conditions characterized by more frequent extended drought. However, stream temperature response at the most downstream site exhibited a pronounced inverted‐U‐shaped relationship with streamflow measured at a weir. It is hypothesized that the response at the most downstream temperature logger was controlled by the existence of a stable, relatively cool inflow just upstream of the logger, which represented an increasing fraction of flow as streamflow generated higher up in the catchment declined through time. There was a lack of convergent surface topography upstream of the logger, and it is hypothesized that localized inflow may have been controlled by the topography of the soil‐till interface and/or originated as hyporheic discharge.

JAMES BUTTLE REVIEW: Quantifying the influence of forestry and forest disturbance on stream temperature: Methodologies and challenges

“…Moore, Sutherland, et al (2005) introduced the use of time series regression to address issues with temporal autocorrelation of the residuals when using sub‐annual time series. An advantage of using sub‐annual time series is that it allows analysis of the temporal variability of stream temperature response to forest cover changes in relation to seasonal and weather‐related effects (Gomi et al, 2006; Moore et al, 2023; Oanh et al, 2021), which may be important when considering the potential for impacts on different life‐history stages for a species of concern.…”

“…Decades of research in a range of forest ecosystems have demonstrated that reductions in riparian shade by logging, vegetation management or natural disturbance result in summertime warming by increasing the amount of solar radiation reaching the stream (Bladon et al, 2018;Brown, 1969;Isaak et al, 2010;Leach et al, 2022;Leach & Moore, 2010;Lynch et al, 1984;Raulerson et al, 2020;Rex et al, 2012;Rishel et al, 1982;Rowe & Pearce, 1994;Rowe & Taylor, 1994;Stott & Marks, 2000). The magnitude of post-harvest warming depends not only on the amount of shade reduction, but also factors such as catchment area, channel morphology and substrate, weather conditions, and the quantity and source components of stream discharge (Beyene & Leibowitz, 2024;Coats & Jackson, 2020;Gomi et al, 2006;Janisch et al, 2012;Miralha et al, 2024;Moore et al, 2023;Oanh et al, 2021). Post-harvest stream warming has historically been of concern in relation to the potential degradation of thermally suitable habitat for cool and coldwater aquatic species such as salmonids (e.g., Cunningham et al, 2023) and some amphibians (e.g., Jackson et al, 2001).…”