Does spruce budworm herbivory alter nitrogen cycling in forest soils?

Spruce budworms (Christoneura occidentalis) are widespread forest defoliators among coniferous trees in western forests. Central Washington currently has a widespread outbreak that has concerned state and federal land managers because of the threat to forest health. When budworms feed upon trees, they affect soil nitrogen processes by returning nitrogen to the forest floor and causing more nitrogen to remain in forest soils. I predict that frass (solid excrement) deposition by spruce budworms increases the soil nitrogen pool, thus increasing the chance that nitrogen runoff will affect stream systems. I will study three sites in the upper North Fork Teanaway River and a control site with no budworms in summer 2013 when spruce budworm activity is highest. I will collect replicate soil cores from each site and extract them with KCl to measure initial NH4+ and NO3-. Net mineralization (N release from biomass) and nitrification (NH4+ conversion to NO3-) will be measured by deploying soil cores with ion-exchange resins and sampling through time. Mineralization rate is calculated as the net change in NH4+ per unit time and nitrification rate is calculated as the net change in NO3- per unit time. I will compare N transformation rates among sites using one-way ANOVA, and positive net nitrification will indicate susceptibility of N loss to streams. If spruce budworm feeding leads to greater nitrogen export from forest soils, it would enrich nearby stream systems with nitrogen and potentially cause excessive algae growth, which could affect endangered species in the streams that drain this region