Deep-seated landslides and Salmon

To what extent do extensive deep-seated landslides, a phenomenon that's ubiquitous in the Oregon Coast Range, influence Coho Salmon habitat?

harvey condon_landslide vs debris flow m

Read the paper published in JAWRA here.

Our objective was to investigate how the presence of deep-seated (bedrock) landslides influences the quantity and connectivity of potential seasonal Coho salmon habitat, including spawning, summer-rearing, and winter-refuge habitat.

We used a published map of deep-seated landslides to locate subbasins within the Umpqua River Basin that are influenced by extensive deep-seated landsliding. We then used published stream survey data from 5 streams with extensive deep-seated landsliding and 5 streams with uniform valley-ridge topography and calculated the quantity of seasonal habitat types and the minimum distances to each type, from which we calculated metrics of connectivity between types.

We show that median fractions of stream length identified as spawning, summer-rearing, winter-refuge habitat, and as having high connectivity among seasonal habitat types are greater in streams with deep-seated landslides and that distances between units of each seasonal habitat type are significantly lower in deep-seated landslide terrain.

Declines in populations of Pacific salmon have prompted extensive and costly restoration efforts, yet many populations are still in peril. An improved understanding of landscape-scale controls on salmon habitat should help focus restoration resources on areas with the greatest potential to host productive habitat. Our results suggest that deep-seated landslides promote connectivity among seasonal habitat types for Coho Salmon and that prioritizing restoration projects in streams in deep-seated landslide terrain could improve the effectiveness of salmonid recovery programs.