Adam Coble

M.S. Candidate, Northern Arizona University

Conference Travel Grant Type 2 (Society of Wetland Scientists)

Effects of River Regulation on Establishment and Growth of Native Riparian Trees along the Lower Dolores River, Colorado

“Our study is evaluating the downstream effect of McPhee Dam on the establishment and annual radial growth of native riparian tree species (Populus deltoides subsp. wislizenii, Populus angustifolia, and Acer negundo). We sampled trees ranging from 0 to 70 cm in base diameter growing at three sites: the floodplains of the regulated Dolores River below McPhee Dam, the unregulated Dolores River above McPhee Dam, and along its tributary, the unregulated San Miguel River. We evaluated relationships between standardized annual radial growth of P. angustifolia and seasonal climate and streamflow at regulated and unregulated sites during pre-dam (1961-1984), post-dam (1985-2008), and all years (1961-2008). For all years, growth at the unregulated reach above McPhee Dam was negatively correlated with mean winter streamflow, whereas growth at water-diverted and regulated reaches was positively correlated with mean spring streamflow. The construction of McPhee Dam had no detectable effect on growth-streamflow relationships. The only significant relationship between growth and climate variables occurred during the pre-dam period at water diverted sites where growth was positively correlated with total winter precipitation. Our future work will extend the analysis of relationships between tree growth, streamflow, and climate variables to P. deltoides subsp. wislizenii, and Acer negundo, and will evaluate the impact of streamflow regulation on recruitment years.“