Soil nitrogen effects on Populus trichocarpa growth rates in the Taneum Canyon hyporheic corridor.

River valleys with porous alluvium have preferential flowpaths called paleochannels that extend the influence of riparian ecosystems away from rivers, creating varying nutrient concentrations in a “hyporheic corridor” where riparian flora can thrive far from the surface influence of the river. Taneum Canyon, an alluvial valley in Kittitas County carved by Taneum Creek, has the characteristics of a hyporheic corridor. In order to identify how nutrient concentrations affected growth rates of Populus trichocarpa, we took ninety-five core samples across four paired sites that were either near or far from the creek within the Taneum Creek hyporheic corridor. Growth rates of each tree were determined by calculating the area of each ring on the tree core for the most recent twenty-two years. We found that growth rates in Populus trichocarpa were related to tree age (p \u3c 0.001) in that older trees accumulated more total biomass when compared to younger trees. Then we related growth rates to nitrogen and phosphorus content of soil samples taken from the base of the tree using regression analysis. Nutrient availability alone was not significantly related to tree growth rate with the exception of one site. However, when tree age is considered as the primary contributing factor affecting growth rates, nutrient availability explains growth rates for the entire sample of Populus trichocarpa (p \u3c 0.001) in the Taneum hyporheic corridor. Subsequent analyses will examine the spatial relationships between nutrient availability and growth rates along the hyporheic corridor