Proceedings of the National Academy of Sciences of the United States of America
Environmental Studies Program
Nitrogen (N) availability, defined here as the supply of N to terrestrial plants and soil microorganisms relative to their N demands, limits the productivity of many temperate zone forests and in part determines ecosystem carbon (C) content. Despite multidecadal monitoring of N in streams, the long-term record of N availability in forests of the northeastern United States is largely unknown. Therefore, although these forests have been receiving anthropogenic N deposition for the past few decades, it is still uncertain whether terrestrial N availability has changed during this time and, subsequently, whether forest ecosystems have responded to increased N deposition. Here, we used stable N isotopes in tree rings and lake sediments to demonstrate that N availability in a northeastern forest has declined over the past 75 years, likely because of ecosystem recovery from Euro-American land use. Forest N availability has only recently returned to levels forecast from presettlement trajectories, rendering the trajectory of future forest N cycling uncertain. Our results suggest that chronic disturbances caused by humans, especially logging and agriculture, are major drivers of terrestrial N cycling in forest ecosystems today, even a century after cessation.
McLauchlan KK, Craine JM, Oswald WW, Leavitt PR, Likens GE. Changes in nitrogen cycling during the past century in a northern hardwood forest. Proc Natl Acad Sci U S A. 2007 May 1;104(18):7466-70. doi: 10.1073/pnas.0701779104. Epub 2007 Apr 19. PMID: 17446271; PMCID: PMC1863457.
Dartmouth Digital Commons Citation
McLauchlan, Kendra K.; Craine, Joseph M.; Oswald, W. Wyatt; Leavitt, Peter R.; and Likens, Gene E., "Changes in Nitrogen Cycling during the Past Century in a Northern Hardwood Forest" (2007). Dartmouth Scholarship. 1425.