Summer stream temperature changes following forest harvest in the headwaters of the Trask River watershed, Oregon Coast Range

Abstract

The Trask River Watershed Study in the northern Oregon Coast Range was designed to examine physical, chemical, and biological effects of contemporary forest management practices on aquatic ecosystems. We measured stream temperature for 11 summers in 15 small watersheds, eight of which were harvested in 2012. Three riparian buffer treatments, which varied by landowner, were implemented. Using half‐hourly data, we characterized summer water temperature distributions with five percentiles: 5th, 25th, 50th, 75th, and 95th. Each percentile was analysed as a separate response variable using a linear mixed model. After harvest, streams without overstory buffer requirements showed shifts in all the percentiles of the temperature distribution; the largest increase (3.6°C) occurred at the 95th percentile. Sites with narrow riparian buffers showed little to no change. We also calculated changes in duration of thermal exposure above 15°C and 16°C for two species of native stream amphibians; these temperatures occurred 4.7% and 1.3% of the time postharvest in the sites clearcut with no buffer. Analysis of distributions of summer temperatures preharvest and postharvest enabled us to more fully characterize site‐to‐site variability and responses to forest management.

Stream Temperature Response to 50% Strip-Thinning in a Temperate Forested Headwater Catchment

“…Bladon et al [53] showed that streams with 15-m-wide riparian buffers did not increase in daily mean stream temperature after forest harvesting in Needle Branch, Oregon Coast Range. Reiter et al [54] showed that a headwater stream with a 15.2-m-wide buffer had no apparent stream temperature increases after forest thinning in the Trask River Watershed Study, Oregon Coast Range.…”

Restoring local climate refugia to enhance the capacity for dispersal-limited species to track climate change

“…Restoring climate refugia by reducing environmental stochasticity might be difficult to manage on a large scale, but it might be possible in a few situations. Canopy cover can affect temperature extremes, acting as climate refugia on forest floors and riparian environments (Davies 2010;De Frenne et al 2013;Reiter et al 2020). Clear-cut areas experience a greater range in temperatures than deciduous or mixed forests (Barbier et al 2008).…”

Spatiotemporal patterns of emergence phenology reveal complex species‐specific responses to temperature in aquatic insects

“…Furthermore, the topographical complexity of mountain landscapes coupled with interannual heterogeneity of weather results in thermal conditions in one year that are rarely predictive of thermal conditions in the next (Bales et al, 2006;Reiter et al, 2020). As such, mountain stream networks should be useful settings for documenting phenological response along thermal gradients, both spatially and temporally, while controlling for photoperiod and other local/ regional-scale environmental cues.…”

“…Mountain stream networks in particular contain a mosaic of local, reach‐scale thermal environments thanks to elevational gradients, shading, substrate, and heterogeneity of hydrological sources to headwaters (Hotaling et al, 2017; Rupp et al, 2020; Ward, 1994). Furthermore, the topographical complexity of mountain landscapes coupled with interannual heterogeneity of weather results in thermal conditions in one year that are rarely predictive of thermal conditions in the next (Bales et al, 2006; Reiter et al, 2020). As such, mountain stream networks should be useful settings for documenting phenological response along thermal gradients, both spatially and temporally, while controlling for photoperiod and other local/regional‐scale environmental cues.…”