Untangling soil factors controlling sugar maple distribution at Hopkins Forest

Background/Question/Methods

Temperate forests play a critical role in battling the effects of anthropogenic emissions on the carbon (C) cycle. Both soils and forest biomass help define the magnitude of C fluxes and storage, so it is important to understand feedbacks between soil chemistry and forest community composition to better understand plant-soil feedbacks to terrestrial ecosystem C cycling. Sugar maple (Acer saccharum) is a dominant hardwood species the northeastern United States, although sugar maple abundance is declining regionally and highly responsive to variation in soil chemistry. We evaluated tree community composition and soil chemistry at Hopkins Memorial Forest (Williams College; Northwestern Massachusetts; 42.7235oN/73.2227oW). Measurements were made in 48 plots, evenly divided between two sites of differing elevation (High Elevation 680 m; Low Elevation 260 m). We characterized plot species richness and Shannon diversity and estimated tree C pool size using measured tree diameter at breast height (DBH) and species-specific allometric equations. We also measured soil base cation (Ca2+, Na+, K+, Mg2+) concentrations, cation exchange capacity (CEC), and pH from samples from each site using standard lab protocols. To evaluate feedbacks between forest litter production and soil base cation concentration, we also characterized cation chemistry in senesced sugar maple litter.

Results/Conclusions

Across both sites at Hopkins Memorial Forest, dominant hardwood species included sugar maple (Acer saccharum), red maple (Acer rubrum), and American Hornbeam (Carpinus caroliniana), with higher species richness and community evenness at the lower elevation site. Base cation pools were dominated by Ca2+, and the lower elevation site maintained significantly higher soil exchangeable Ca2+, with nearly double the concentration present than at the higher elevation site. Across plots, sugar maple relative abundance and biomass increased significantly with soil exchangeable Ca2+ pools. Ongoing analyses of Ca2+ concentration in senesced sugar maple litter seek to determine if these sugar maple trees are enriching surface soil with calcium. Our results help describe the biogeochemical factors controlling the distribution of culturally and economically important tree species at Hopkins Memorial Forest, and inform our understanding of how plant activity responds to and influences soil cation chemistry, which influences a soil’s capacity to store carbon.