Influence of gap size on carbon and nitrogen biogeochemical cycling in Northern hardwood forests of the Upper Peninsula, Michigan

Abstract

The objective of this study is to determine the effect of treefall gap size on carbon and nitrogen biogeochemistry in the Northern hardwood forest. The size of the gap controls the microclimate, particularly solar radiation, soil temperature, and soil moisture, which can alter nutrient cycling. However, in Northern hardwood forests, our understanding of the relation between biogeochemistry and gap size is incomplete. Twelve natural treefall gaps ranging in size from 27 to 590 m2 and four control plots located under closed canopy were identified in Upper Michigan in May 2008. Concentrations of ammonium and nitrate were measured in throughfall and soil leachates; soil respiration rates were measured in soil; and nutrient pools were measured in vegetative biomass, forest floor (Oe, Oi horizons), mineral soil, and microbial biomass. Gap size was positively correlated with sapling biomass density and throughfall ammonium concentration but negatively correlated with microbial biomass, endomycorrhizal biomass, and soil respiration. Gap size was unrelated to all other parameters measured. The results of this study suggest that in the Northern hardwood forest, vegetative recovery and a reduction in microbial biomass may limit the influence larger gaps have on nutrient cycling.