With its half-century history of ecological research, the Hubbard Brook (HBR) site has evolved into a model LTER gathering unique and extremely valuable records of long-term biogeochemical cycling in forested watershed ecosystems. The overarching goal of HBR is to increase understanding of the ecological patterns and processes that characterize forested landscapes in the northeastern USA, particularly in response to disturbances. Three types of disturbances are examined: 1) air pollution, 2) catastrophic events (e.g., clear-cutting) and 3) non-catastrophic events (e.g., soil freezing events, ice storms and insect outbreaks). Biogeochemical studies build on a 40-year record of element fluxes and vegetation dynamics in experimental watersheds, focused on construction of quantitative nutrient cycles. Long-term measurements, experiments and process studies are conducted at a variety of scales, ranging from small plots to entire watersheds and forests. Long-term experiments include a whole-watershed calcium fertilization study designed to offset soil Ca losses due to acidic deposition and to track calcium fluxes and cycling throughout the watershed, with particular emphasis on effects on currently declining sugar maple populations. Such experiments and ongoing process studies are to be coupled with new initiatives examining the effects of compounded disturbances on ecosystem structure and function, elemental stoichiometry and hystereses, all in the context of landscape-level variation in ecological state factors. New studies include 1) plot-level fertilization of young and mature forest with nitrogen, phosphorus and calcium, 2) intensive and extensive study of beech bark disease across multiple trophic levels, and 3) detailed study of nitrogen and carbon dynamics in relation to sugar maple decline, forest nutrition and productivity.
Broader Impacts. HBR research is crucially linked with the important societal issues of air pollution and the effects of atmospheric deposition on ecosystem processes. Key HBR scientists are active in regional and national outreach regarding air pollution, acid deposition and their ecological consequences. This outreach is expanded with HBR's generation of newsworthy scientific findings and the production of popularly accessible products. HBR is among the most productive LTER sites in terms of publications in high impact journals, influential synthesis products and theses/dissertations. The new conceptual framework is intended to guide HBR in the future and is likely to influence other LTER research as well. Research at this site has trained more than two generations of prominent ecosystem scientists and will continue this with the training of a high number of new undergraduates, graduate students and postdocs. HBR is actively increasing diversity and the participation of women in science, from the student level to the faculty level. Additional outreach includes the Schoolyard LTER program, public ecological tours and the innovative Science Links feature.
Our long-term research has focused on the responses of forest ecosystems to natural and anthropogenic disturbances. We have demonstrated the patterns and mechanisms of ecosystem responses to and recovery from acid deposition disturbance in order to better inform environmental policy on pollution control. For example, we show why successful reductions in acid deposition translate only slowly to significant improvements in surface water quality. We evaluated long-term changes in the health and productivity of northern hardwood forests in the face of changing environment and disturbance regimes. For example, we demonstrated that experimentally replacing the calcium that was removed by decades of acid rain resulted in correction of health problems for key tree species in the hardwood forest. We continued to build upon the 40+ year record of breeding bird abundance in this forest and the mechanisms influencing changes in bird populations. In particular we showed why some species have increased and others have decreased over this period, and we evaluated the complex interactions among climate/weather, food supply, and predators in regulating bird populations. We expanded and improved our program of information management so that nearly all the long-term data sets collected in the project are available in our data repository. In addition, our sample archive provides for storage and cataloguing of physical samples (ca. 40,000) so that future researchers will be able to utilize new techniques and approaches in their analysis. We conducted a concerted program, Science Links, to translate our scientific information for policymakers at regional and national levels. The Science Links program is serving as a model for efforts to effectively inform appropriate audiences and to improve public policy development on such topics as acid rain, nitrogen and mercury pollution, and regional carbon mitigation. Our research has contributed to the training of students at all levels from K-12 to post-doctoral, including a coordinated program for undergraduates on investigating and communicating change in ecosystems.
