The Harvard Forest LTER program (HFR) is a two-decade strong, integrated research and educational program that collects and uses long-term data to investigate the pace and pattern of forest responses to human and environmental change across New England. During LTER-IV (2006-2012), HFR engaged more than 30 researchers, 200 graduate and undergraduate students, and dozens of institutions in research that incorporates social, biological, and physical sciences. Scientists conduct this work across multiple time scales: investigating the present, looking back thousands of years, and using that knowledge to calculate future change. HFR is committed to strong education and outreach programs. Our K-12 Schoolyard LTER program reaches more than 3,000 students at 50 schools each year. We work to strengthen the scientific basis for environmental stewardship by connecting scientists and long-term ecological data with news media and decision makers at multiple levels of society.

Key outcomes of HFR LTER-IV include:

• Synthesis of century-long studies document persistent legacies of human and natural history in shaping modern forest ecosystems. Ancient land-use practices and prior forest conditions continue to influence a forest’s potential to grow trees, respond to disturbance and stress, and support diverse plants and animals. 
• Data collected from the world’s longest continuously operating forest-atmosphere exchange measurement system and permanent forest measurement plots revealed that old forests at Harvard Forest can store carbon at rates higher than previously documented. These results imply that allowing forests to mature can be an important strategy for mitigating climate change, and suggest a major paradigm shift in forest management strategies. 
• Results from 20-year climate-change experiments have illustrated that warming soils release more carbon dioxide to the atmosphere and accelerate the pace of climate change, and nitrogen deposition leads to increased soil carbon storage. The composition and function of the soil microbial community largely controls observed responses to both warming and nitrogen deposition.
• Connecting data from Harvard Forest with regional field sampling, imaging spectroscopy, remote sensing, and tower-based carbon flux measurements revealed strong linkages among canopy carbon, nitrogen and albedo. The results raise the possibility of an unrecognized feedback in the Earth’s climate system involving the nitrogen cycle as a key factor influencing surface energy exchange.
• Researchers at Harvard Forest and six other LTER sites introduced the concept of a “foundation species” into terrestrial ecology. Individual foundation species disproportionately influence biodiversity and modulate ecosystem dynamics. In LTER-IV, Harvard Forest scientists used a network of permanent forest plots, a large-scale, long-term experiment, analyses of fossil pollen, and modeling forecasts of regional carbon budget response to explore the consequences of losing eastern hemlock, a forest foundation species of northeast North America.
• The discovery that some invasive plants release chemicals belowground that disrupt the relationship between native tree seedlings and beneficial, co-occurring fungi. With native plants suppressed, the invasive plants are able to expand aggressively in forest understories.
• Advancement of new approaches that link landowner behavior, land use practices, forest dynamics and the consequences of future scenarios of climate and land use change on forest habitat, wood and carbon in the Northeast. This research already is playing a pivotal role in guiding forest stewardship and policy throughout New England. 
• Publication of the Wildlands and Woodlands vision, which call...

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