@article{92f5fb5f48ba4fa2ba5baa813d3ebef5,
title = "Multi-Decadal Carbon Cycle Measurements Indicate Resistance to External Drivers of Change at the Howland Forest AmeriFlux Site",
abstract = "A long-standing goal of ecology has been to understand the cycling of carbon in forests. This has taken on new urgency with the need to address a rapidly changing climate. Forests serve as long-term stores for atmospheric CO2, but their continued ability to take up new carbon is dependent on future changes in climate and other factors such as age. We have been measuring many aspects of carbon cycling at an unmanaged evergreen forest in central Maine, USA, for over 25 years. Here we use these data to address questions about the magnitude and control of carbon fluxes and quantify flows and uncertainties between the different pools. A key issue was to assess whether recent climate change and an aging tree population were reducing annual C storage. Total ecosystem C stocks determined from inventory and quantitative soil pits were about 23,300 g C m−2 with 46% in live trees, and 48% in the soil. Annual biomass increment in trees at Howland Forest averaged 161 ± 23 g C m−2 yr−1, not significantly different from annual net ecosystem production (NEP = −NEE) of 211 ± 40 g C m−2 y−1 measured by eddy covariance. Unexpectedly, there was a small but significant trend of increasing C uptake through time in the eddy flux data. This was despite the period of record including some of the most climate-extreme years in the last 125. We find a surprising lack of influence of climate variability on annual carbon storage in this mature forest.",
keywords = "AmeriFlux, carbon, forests, inventory, natural climate solution",
author = "Hollinger, {D. Y.} and Davidson, {E. A.} and S. Fraver and H. Hughes and Lee, {J. T.} and Richardson, {A. D.} and K. Savage and D. Sihi and A. Teets",
note = "Funding Information: The findings and conclusions in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy. Funding for this AmeriFlux core site was provided by the U.S. Department of Energy's Office of Science. Additional support was provided by USDA NIFA award #2014‐67003‐22073, the USDA Forest Service Northern Research Station, and the Maine Agricultural and Forest Experiment Station. ADR acknowledges support for PhenoCam through NSF's Macrosystems Biology program (EF‐1702697). The authors wish to acknowledge George Woodwell and Ivan Fernandez for their vision and actions for enabling long‐term ecosystem science studies to be established at the Howland Forest site. Funding Information: The findings and conclusions in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy. Funding for this AmeriFlux core site was provided by the U.S. Department of Energy's Office of Science. Additional support was provided by USDA NIFA award #2014-67003-22073, the USDA Forest Service Northern Research Station, and the Maine Agricultural and Forest Experiment Station. ADR acknowledges support for PhenoCam through NSF's Macrosystems Biology program (EF-1702697). The authors wish to acknowledge George Woodwell and Ivan Fernandez for their vision and actions for enabling long-term ecosystem science studies to be established at the Howland Forest site. Publisher Copyright: {\textcopyright} 2021. American Geophysical Union. All Rights Reserved. This article has been contributed to by US Government employees and their work is in the public domain in the USA.",
year = "2021",
month = aug,
doi = "10.1029/2021JG006276",
language = "English (US)",
volume = "126",
journal = "Journal of Geophysical Research: Biogeosciences",
issn = "2169-8953",
number = "8",
}