Effects of Large Wood and Log Jams on Eastern Slope Rocky Mountain Trout Populations

Western U.S. rivers are currently influenced by legacy effects of reduced in-stream large wood (LW) loading, leading to an alternative stable state characterized by loss of stream channel and valley complexity and changes in nutrient dynamics.  We compared trout populations in streams along a gradient of wood loading on the eastern side of the Rocky Mountains.  Trout population densities appear positively related to LW, increasing number of pools, and standing stock biomass of aquatic insects.  Yet, at different scales (square-meter vs valley-length) different variables are better at predicting population density, with insect biomass being more important at the square-meter scale and number of pools predicting trout density better at the valley scale.  Individual trout growth rates were negatively affected by population density in age-1 fish, but density did not affect growth in age 2 or 3 fish.  LW did not appear to affect insect community structure or standing stock biomass of aquatic insects at the square meter scale, however, at the valley scale, standing stock insect biomass increased.  Scaling our results up to the valley scale (as opposed to the habitat scale) indicates a potential loss in fish production at sites of reduced channel and valley complexity.