How does habitat restoration influence resilience of salmon populations to climate change?

Abstract

A pressing question for managing recovery of depressed or declining species is: Can habitat restoration increase resilience to climate change? We addressed this question for salmon populations with varying life histories, where resilience is defined as maintaining or increasing population size despite climate change effects. Previous studies indicate that several interrelated mechanisms may influence salmon resilience to climate change, including improving either habitat capacity or productivity, and ameliorating climate change effects on flood flow, low flow, or stream temperature. Using the Habitat Assessment and Restoration Planning (HARP) model, we first examined the relative importance of each mechanism for increasing salmon population resilience by comparing projected salmon spawner abundance for seven individual restoration action types under current and projected mid-and late-century climates.We found that restoring habitats with the greatest restoration potential most increased resilience for all species, but the most beneficial restoration actions varied among species. Increasing habitat capacity and productivity both contributed to resilience, and ameliorating climate change effects was important in a few subbasins where the restoration opportunity was widespread.Cool-water climate refuges contributed to resilience of some subpopulations by reducing late-century declines in spawner abundance even without restoration. We also modeled more complex habitat restoration strategies comprised of several restoration action types at varying restoration intensities and found that the restoration action types and level of restoration effort needed to increase resilience varied among species. Less vulnerable species such as coho salmon responded well to four restoration actions (floodplain reconnection, wood augmentation, increased shade, and increased beaver ponds) applied at low restoration intensity and over a large area. More vulnerable species such as spring Chinook responded to fewer action types (floodplain reconnection, wood augmentation, and increased shade), but at much higher intensity and over a much smaller area. The analysis also identified important locations for each

Trends in Chinook salmon spawner abundance and total run size highlight linkages between life history, geography and decline

“…While climate‐driven disturbances and novel ecosystem conditions have likely contributed to negative trends across the regions we evaluated, California and Southern Oregon have been further impacted by a prolonged drought affecting freshwater systems (Kogan & Guo, 2015). The negative effects of these disturbances and ecosystem shifts have been precipitated and intensified by more than two centuries of anthropogenic climate change, marine and watershed habitat alterations, and hatchery practices that have eroded the resilience and productivity of Chinook salmon (McClure et al, 2008; Satterthwaite & Carlson, 2015; Dorner et al, 2018; Beechie et al, 2021; Munsch et al, 2022). Chinook salmon are also getting smaller over time, with potentially serious implications for their demographic productivity and ability to support fisheries in the future (Ohlberger et al, 2018; Oken et al, 2021; Xu et al, 2020).…”

“…Restoring natural hydrological and ecological processes and riverine connectivity through dam removal and floodplain reconnection are paramount for Chinook in their migratory corridors, juvenile rearing areas and headwater spawning areas (e.g. Beechie et al, 2021). Dam removal on the Snake River is among the clearest pathways to recovery for Chinook in the Columbia Basin, and recent analyses indicate that unless survival rates are improved for out‐migrating Chinook smolts and returning adults extinction is likely for many of these stocks before the end of the 21st century (Crozier et al, 2021).…”

Restoring freshwater habitat mosaics to promote resilience of vulnerable salmon populations

“…However, there is limited research on the interaction between these ecological concepts-portfolio effect and habitat mosaic-and their potential application in informing restoration efforts. Specifically, little attention has been given to restoring habitat complexity at the landscape or stock complex scale to promote phenotypic diversity and enhance long-term species recovery goals (Beechie et al, 2013(Beechie et al, , 2023Lindley et al, 2007).…”

Variables influencing stream‐type juvenile Chinook Salmon density within floodplain habitat in the Skagit River basin, Washington

“…Most of the river basins draining into the Puget Sound are too small to allow for reproductive isolation, which supports diverse life history types in Chinook Salmon (Waples et al 2008). Phenotypic diversity, including life history diversity, is a key contributor to resilience against environmental disturbance such as climate change (Hilborn et al 2003;Beechie et al 2006Beechie et al , 2013Beechie et al , 2023Thompson et al 2018), which continues to affect salmon recovery efforts. Most watersheds in Puget Sound support ocean-type Chinook Salmon that rear in freshwater for days to months before migrating to estuarine or nearshore habitat; however, few coastal watersheds support the stream-type juvenile (STJ) Chinook Salmon life history pattern, which requires extensive floodplain and side channel rearing habitat (Anderson and Topping 2018).…”

“…2003; Beechie et al. 2006, 2013, 2023; Thompson et al. 2018), which continues to affect salmon recovery efforts.…”