Multiscale processes drive formation of logjam habitats and use by juvenile Chinook salmon across a boreal stream network in Alaska

Boreal forest streams are characterized by large volumes of instream wood, yet the relationship between logjams and Pacific salmon productivity remains underqualified. We located logjams (n = 427) within the distribution of Chinook salmon (Oncorhynchus tshawytscha) in the Chena River, Alaska (Yukon River tributary) and measured dimensions, classified formative process, and snorkel-sampled a subset (n = 189) of logjams to detect and count juvenile salmon relative to multiscale variables and a dam. Logjam size increased downstream, whereas logjam density and large wood recruits declined (upstream = 6 logjams/km, 33 recruits/km; downstream = 0.3 logjams/km, 6 recruits/km), particularly below a dam that reduced downstream wood transport and log-trapping locations (i.e., bars). Juvenile salmon occupied 68% of logjams; mid-network logjams had the highest densities (mean = 0.85 fish/m²). We modeled juvenile salmon counts with logjam-, stream reach-, and neighborhood-scale (> 1 km) predictors. Covariates that best predicted juvenile salmon densities included bankfull flow and stream power at reach scales in addition to growth potential, spawning habitat quality, and logjam area within 1 km of the focal logjam at neighborhood-scales. Multiscale perspectives that link landscape characteristics, wood dynamics, and instream modifications with juvenile salmon production will be important to facilitate conservation and management of boreal streams.