Effects of forest harvest, deer herbivory, and tree mortality on nutrient cycling in the Catskill Mountains of New York

I investigated how forest disturbances affect nutrient cycling in the Catskill Mountains (New York). Specifically, I studied effects of forest harvest, herbivory by white-tailed deer, and overstory tree mortality on nutrient cycling in northern hardwood and Tsuga canadensis stands.; I quantified responses of vegetation and stream water chemistry at three sites within a northern hardwood forest after three intensities of timber harvesting: clearcutting, heavy timber stand improvement (TSI), light TSI, and on a reference site. After clearcutting, biomass and nutrient accumulation were initially dominated by regenerating woody stems and herbaceous vegetation, but saplings dominated these processes within three years. I also found that herbivory by white-tailed deer could dramatically reduce biomass and nutrient accumulation by regeneration after clearcutting. After TSI, trees continued to account for practically all biomass and nutrient accumulation while there was little understory response. Clearcutting caused dramatic increases in NO₃− and cation concentrations in stream water for at least three years, but neither level of TSI affected stream water chemistry.; I also monitored soil water chemistry and vegetation in healthy Tsuga canadensis stands and T. canadensis stands subjected to a girdling treatment to simulate mortality due to Adelges tsugae. Girdling resulted in elevated concentrations of NO₃ − and cations in soil water within three months. Concentrations remained relatively high for the duration of the study. Betula alleghaniensis seedling densities and percent cover of understory vegetation more than doubled in the three years after girdling. I also characterized the plant propagule banks in six T. canadensis stands. Betula alleghaniensis seeds, Dryopteris intermedia spores, and Dennstaedtia punctilobula spores were abundant. Understory vegetation and propagule banks indicated potential stand replacement by B. alleghaniensis in the event of hemlock mortality.; Finally, I reviewed known effects of disturbance on nutrient loss to soil and stream water and argue that the relative amount of nutrient loss during and after disturbance is related to disturbance duration and severity. A conceptual model is presented to show that nutrient loss is negatively related to disturbance duration and positively related to severity. I also review and predict the potential for additional disturbances to result in elevated nutrient loss.