Detection of long-term trends in carbon accumulation by forests in Northeastern U. S. and determination of causal factors: Final report

J. William Munger ; Steven C. Wofsy ; David R. Foster

关键词: carbon flux;    NEE;    forests;    eddy flux;   

DOI  :  10.2172/1033926
RP-ID  :  er64358-1
PID  :  OSTI ID: 1033926

学科分类：环境科学（综合）

美国|英语

来源: SciTech Connect

【 摘 要 】

The overall project goal was to quantify the trends and variability for Net ecosystem exchange of CO{sub 2}, H{sub 2}O, and energy by northeastern forests, with particular attention to the role of succession, differences in species composition, legacies of past land use, and disturbances. Measurements included flux measurements and observations of biomass accumulation using ecosystem modeling as a framework for data interpretation. Continuation of the long-term record at the Environmental Measurement Site (EMS) Tower was a priority. The final quality-assured CO{sub 2}-flux data now extend through 2010. Data through 2011 are collected but not yet finalized. Biomass observations on the plot array centered on the tower are extended to 2011. Two additional towers in a hemlock stand (HEM) and a younger deciduous stand (LPH) complement the EMS tower by focusing on stands with different species composition or age distribution and disturbance history, but comparable climate and soil type. Over the period since 1993 the forest has added 24.4 Mg-C ha{sup -1} in the living trees. Annual net carbon uptake had been increasing from about 2 Mg-C ha{sup -1}y{sup -1} in the early 1990s to nearly 6 Mg-C ha{sup -1}y{sup -1} by 2008, but declined in 2009-2010. We attribute the increasing carbon uptake to a combination of warmer temperatures, increased photosynthetic efficiency, and increased influence by subcanopy hemlocks that are active in the early spring and late autumn when temperatures are above freezing but the deciduous canopy is bare. Not all of the increased carbon accumulation was found in woody biomass. Results from a study using data to optimize parameters in an ecosystem process model indicate that significant changes in model parameters for photosynthetic capacity and shifts in allocation to slow cycling soil organic matter are necessary for the model to match the observed trends. The emerging working hypothesis is that the pattern of increasing carbon uptake over the early 2000's represents a transient pulse that will eventually end as decomposition of the accumulated carbon catches up.