This research will continue investigations of air-land-plant- water-human interactions in aggrading and disturbed northern hardwood forest ecosystems. Historically, the Hubbard Brook Ecosystem Study has coupled long-term investigation of ecosystem biogeochemistry and forest growth with detailed experimentation, including laboratory and plot-level studies, whole ecosystem manipulations, as well as the development and application of computer models. Studies of precipitation inputs, ecosystem pools and stream outflow will be continued. This long-term biogeochemical research will be integrated with ongoing and proposed process-level studies through the development of proton budgets and analysis of element cycle interactions. Plot-level chemical manipulations using (NH4)2SO4, H2SO4, Na2SO4 and CaSO4 will investigate present-day, anthropogenically-induced changes in hydrogen ion, sulfur, nitrogen and metallic cation cycles. Research on northern hardwood forest ecosystems at Hubbard Brook is a multi-investigator-/multi-institutional effort. Most work will be conducted at the Hubbard Brook Experimental Forest, NH, yet the concepts and processes to be investigated are generally applicable to many types of ecosystems. This research will, as in the past, contribute to the fundamental understanding of forest ecosystems and yield information useful to the better management of their valuable natural resources. The project team is excellent and comprises proven collaborative performers. USDA/Forest Service collaboration is quite positive. Institutional accommodations are first-rate. The Ecosystem Studies Program confidently recommends that this collaborative, four-year continuing award be made.
