The long-term species composition of forests depends upon the successful germination and recruitment of germinants. As anthropogenic activities such as the atmospheric deposition of nitrogen (N) alter the chemical composition of forest soils, seed production and germination patterns of tree species may be affected in unique ways, causing the species composition of forests to shift. To measure the effect of phosphorus (P) and nitrogen availability on the recruitment of sugar maple (Acer saccharum) and American beech (Fagus grandifolia) seedlings, we measured the initial population density of germinants of both species in the context of a long-term, full-factorial N and P fertilization experiment located in three sites within the White Mountain National Forest of New Hampshire. We analyzed cohorts of each species during the summers of 2012 and 2018 following mast years, using 2012 initial density data as a covariate when testing the fertilization effect upon the initial density of germinants in the 2018 cohort.
Results/Conclusions
N additions decreased the initial population density of sugar maple germinants by an average of 28% (p=0.03), and P additions decreased the initial population density of sugar maple germinants by an average of 40% (p=0.01). American beech germinants were affected only by N additions, which increased the initial density of this species by an average of 83% (p=0.001). These findings are consistent with prior research indicating that sugar maple is particularly sensitive to soil chemistry, and they contribute further specificity to our developing understanding of the soil conditions that affect the development of these keystone species.