Riparian vegetation shade restoration and loss effects on recent and future stream temperatures

Abstract

River temperatures are expected to increase this century harming species requiring cold‐water habitat unless restoration activities protect or improve habitat availability. Local shading by riparian vegetation can cool water temperatures, but uncertainty exists over the scaling of this local effect to larger spatial extents. We evaluate this issue using a regional spatial stream network temperature model with covariates representing shade effects to predict mean August stream temperatures across 78,195 km of tributaries flowing into the Columbia River in the northwestern United States. We evaluate nine scenarios predicting stream temperatures for three riparian shade conditions (current, restored, and no riparian vegetation) within three different climate periods (2000s, 2040s, and 2080s). Results suggest riparian shade restoration (2000s climate) could decrease mean August stream temperatures by 0.62°C across the study network. Under the same restored shade conditions, temperature predictions for tributaries at their confluence with the Columbia River range from 0.02 to 2.08°C cooler than under current shade conditions. The climate warming effect predicted for the 2040s and 2080s, however, is greater than the cooling effect from restoring riparian shade. Streams less than 10‐m bankfull width cooled more frequently with riparian shade restoration. In Oregon, the proportion of fish habitat for salmon and trout rearing and migration that meet temperature numeric water quality criteria could be increased by 20% under restored shade conditions although net habitat declines may still occur in the future. We conclude riparian vegetation restoration could partially mitigate future warming and help maintain cold‐water habitats that function as thermal refuges if implemented strategically.

Contrasting long‐term trends in juvenile abundance of a widespread cold‐water salmonid along a latitudinal gradient: effects of climate, stream size and migration strategy

“…Under a warming climate it is thus important to prevent or decrease any additional stress on trout populations. Restoration of riparian vegetation, especially at the basinwide scale, can help buffer extreme summer temperatures (Broadmeadow et al 2011, Johnson and Almlöf 2016, Justice et al 2017, Turunen et al 2021, Fuller et al 2022, and together with the identification and protection of climate and thermal refugia (Keppel et al 2012, Sullivan et al 2021) should be a priority of climate-smart water management (Elliott 2000, Isaak et al 2015. Furthermore, the increased incidence of summer droughts in small rivers in the southern (warmer) regions points to the negative effects of large-scale irrigation, channelization and loss of wetlands consequent to human practices to gain arable land in the past centuries.…”

Shifting climate conditions affect recruitment in Midwestern stream trout, but depend on seasonal and spatial context

“…For example, in Ash Creek, Wisconsin, Mitro (2016) found that species interactions among brook and brown trout and a brook trout‐specific ectoparasitic copepod under stressful environmental and ultimately climatic conditions (high stream temperature and low stream flows) led to poor brook trout recruitment and thus can be a proximate cause of native brook trout loss in the region. Other local factors like groundwater input (Hare et al, 2021) and riparian habitat (in particular a shaded tree canopy) (Fuller et al, 2022) are also notable for their potential to mitigate regional warming effects on stream temperatures, leading to local deviations from the broader trend that highlight the potential for resiliency to climate change.…”

“…Other actions may be targeted to locations where local factors inhibit resiliency. For example, hot temperatures for brook trout in southern and central Wisconsin may be mitigated through improved groundwater management and channel management for hyporheic exchange, as well as improvements to riparian shading and large wood or log jams (Fuller et al, 2022; Roni & Quinn, 2001). These actions may become increasingly important for brown and brook trout statewide with additional warming.…”

Plasticity of upper thermal limits of Australian Paratya spp. (Decapoda, Atyidae) and considerations of climate-change adaptation

“…Maximum stream temperatures are decreased by shading (Johnson 2004;Fuller et al 2022). Developing resilience in the landscape to reduce in-stream impacts may be important.…”

“…Thermal impacts could be moderately mitigated through increasing shading by riparian vegetation and ensuring natural environmental flows. Restoring riparian vegetation in inadequately shaded streams may counteract some of the influence of projected warming and drying under climate change (Trimmel et al 2018;Fuller et al 2022). However, air temperatures will continue to increase and affect currently well-shaded streams (Fuller et al 2022).…”