Effects of treefall gap size and age on carbon and nitrogen biogeochemical cycling in Northern hardwood-hemlock forests.

摘要

In Northern hardwood-hemlock forests, treefall gaps may play a role in biogeochemical cycling. After a gap forms, solar radiation, soil temperature, and soil moisture may be affected. These changes in microclimate can alter biogeochemical cycling by impacting mineral weathering, microbial decomposition, and leaching rates. The size and age of a gap can also affect microclimate and nutrient cycling. Our objective was to determine the effects of gap size and age on carbon and nitrogen biogeochemical cycling in the Northern hardwood-hemlock forest. To study gap size, we identified 12 natural treefall gaps ranging in size from 25--590 m2 and 4 control plots, under closed canopy in the Dukes experimental forest, in Upper Michigan. To study gap age, we identified 12 natural treefall gaps (50--220 m2) ranging in age from 0--12 years (as of 2008) and 4 control plots, under closed canopy at the Huron Mountain Club, in Upper Michigan. At all plots, we analyzed the following fluxes of carbon and nitrogen: leaching losses of ammonium, nitrate, and dissolved organic carbon from forest floor and mineral soil, inputs of ammonium, nitrate, and dissolved organic carbon from throughfall, and carbon and nitrogen mineralization and weathering. In addition, we measured the following nutrient pools: vegetation, mineral soil, forest floor, and microbial biomass. Gap size was positively correlated with vegetative regrowth biomass and throughfall ammonium but negatively correlated with microbial biomass, endomycorrhizal biomass, and soil respiration. Gap size was unrelated to all other parameters measured. Gap age was not significantly correlated with any of the measured parameters. We suspect that the lack of correlation between gap size or age and carbon and nitrogen cycling could be due to the small size of the gaps or that the changes that did occur happened before we began the study. The results of this study imply that in the Northern hardwood-hemlock forest, natural treefall gaps may not significantly alter nutrient cycling.