Relationships among forest age, composition and elemental dynamics of Adirondack northern hardwood forests

We conducted a biogeochemical analysis of four Adirondack northern hardwood forests (two old-growth and two maturing second-growth) to elucidate correlations among stand age, site conditions and several nutrient cycling processes. One each of the old-growth and maturing forests were located on base-rich sites, while the other two were on base-poor sites. At each site we analyzed soil solution chemistry and estimated nutrient flux rates; measured annual litter production, and nutrient and lignin content; measured annual N mineralization and nitrification rates; and characterized herb- and canopy-layer vegetation, and coarse woody debris volumes. Vascular plant communities of the two base-rich sites were dominated by several rich-site indicator species, while such indicators were lacking at the base-poor sites. Tree basal areas and annual litter production did not differ among the study sites, but the old-growth stands contained 3-fold more coarse woody debris than the maturing stands. Foliar litter N concentrations did not differ among the study sites, but foliar litter from the base-rich sites had higher Ca²⁺ and lower lignin concentrations than the base-poor sites. Differences in foliar litter quality among the sites were due, in part, to intraspecific variation in litter chemistry. There were no consistent differences between the old-growth and maturing stands in soil solution nutrient concentrations or fluxes. Soil solution H⁺ concentrations were higher and Ca:Al ratios lower at the two base-poor sites. Annual, net N mineralization rates did not differ among the sites, but net nitrification rates in the organic soil horizons at the rich old-growth site were more than twice those at the other sites. High levels of net nitrification and N leaching were observed only in the base-rich old-growth site. Our data suggest that net forest nutrient retention may be a function of interacting mechanisms associated with forest developmental stage, community composition and site conditions.