Effects of riparian forest thinning on resident salmonid fishes in coastal northern California catchments
May 19, 2025
- Resource managers are interested in whether thinning second-growth forests may be a viable restoration strategy for stream and riparian habitats, but may be concerned about the potential impacts that increases in stream temperature associated with riparian thinning treatments may have on cold-water salmonid fishes.
- We evaluated the effects of riparian forest thinning on resident populations of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in coastal northern California catchments using a manipulative field experiment with a replicated before-after-control-impact design (pre-treatment data collected in 2016, thinning treatments occurred in 2017, and post-treatment data collected in 2018). Experimental thinning treatments reduced riparian shade by 20%–30% along five 150–200 m stream reaches. To provide a process-based evaluation of the implications of riparian thinning for coastal cutthroat trout, we combined seasonal observations of trout density, biomass, and growth with bioenergetics modelling.
- Cutthroat trout density increased by 8%–31% and biomass increased by 27%–111% in thinned reaches 1 year post-treatment, but responses varied widely across sites and seasons so did not always differ statistically. Growth rates of cutthroat trout varied more among seasons than among reach types (upstream reference, thinned, and downstream), peaking in spring and overwinter relative to summer.
- Bioenergetics modelling indicated that cutthroat trout responded to thinning-induced increases in stream temperature and shifts in prey energy density via higher consumption rates (i.e., fish fed more frequently) in thinned reaches. Additionally, reach-scale consumption estimates indicated that the energy intake of cutthroat trout increased at the population level in thinned reaches. However, thinned reaches exhibited relatively small changes in consumption, suggesting that riparian thinning was unlikely to enhance growth opportunities for cutthroat trout, supporting our empirical growth observations.
- Collectively, our field experiment suggests that salmonid fishes may be resilient to thinning second-growth riparian forests when treatments do not substantially increase water temperatures. Moreover, our results highlight that pairing empirical data with bioenergetics modelling can provide valuable insights into the mechanisms driving fish responses to riparian forest restoration.
Citation Information
| Publication Year | 2025 |
|---|---|
| Title | Effects of riparian forest thinning on resident salmonid fishes in coastal northern California catchments |
| DOI | 10.1111/fwb.70040 |
| Authors | David A. Roon, Jason B. Dunham, Joseph R. Benjamin, Bret C. Harvey, James R Bellmore |
| Publication Type | Article |
| Publication Subtype | Journal Article |
| Series Title | Freshwater Biology |
| Index ID | 70267320 |
| Record Source | USGS Publications Warehouse |
| USGS Organization | Forest and Rangeland Ecosystem Science Center |
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Jason B Dunham
Supervisory Research Ecologist
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Joseph R Benjamin
Research Biologist
Research Biologist
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Related
Jason B Dunham
Supervisory Research Ecologist
Supervisory Research Ecologist
Email
Phone
Joseph R Benjamin
Research Biologist
Research Biologist
Email
Phone