Community, Population, and Growth dynamics of Alnus tenuifolia: Implications for nutrient cycling on an Interior Alaskan floodplain

Abstract

This study describes the community, population, and growth dynamics of Alnus tenuifolia (thinleaf alder) and implications for nutrient cycling on the Tanana River floodplains. Through symbiotic N-fixation inputs, alder contributed to soil N accumulation with time. N-fixation itself was likely limited by soil P. Soil N was positively related to alder stem density in early successional stands. Community structure varied along a temporal gradient of changing environmental characteristics, but variations in successional patterns were found. Landscape scale alder recruitment varied temporally and was apparently linked to interactions between geofluvial processes, seed production and dispersal, and herbivory. A widespread stem canker outbreak has resulted in high alder mortality and likely reductions in N-fixation inputs. Disease incidence and mortality were positively related to stem density. Alder radial growth was sensitive to drought during June and August. Alder growth was positively related to river level, suggesting that fluctuation in hyporheic flow is important to alder water balance, especially on lower terraces. The sensitivity of alder growth to meteorological drought was heightened with increasing terrace elevation. Long-term climatic trends suggest that drought will become more common and severe, resulting in reductions in alder-mediated ecosystem N inputs.