HR: 14:40h
AN: B52D-04    [PDF]
TI: Old and Not-So-Old: Examining Changes in Forest Ecosystem Carbon Exchange With Stand Age in the Upper Midwest U.S.
AU: * Desai, A R
EM: adesai@essc.psu.edu
AF: Pennsylvania State University - Department of Meteorology, 503 Walker Building, University Park, PA 16802 United States
AU: Cook, B
AF: Pennsylvania State University - Department of Meteorology, 503 Walker Building, University Park, PA 16802 United States
AU: Davis, K J
AF: Pennsylvania State University - Department of Meteorology, 503 Walker Building, University Park, PA 16802 United States
AU: Bolstad, P
AF: University of Minnesota - Department of Forest Resources, 1530 Cleveland Ave N, St Paul, MN 55108 United States
AU: Carey, E
AF: University of Minnesota - Department of Forest Resources, 1530 Cleveland Ave N, St Paul, MN 55108 United States
AU: Martin, J
AF: University of Minnesota - Department of Forest Resources, 1530 Cleveland Ave N, St Paul, MN 55108 United States
AU: Kreller, L
AF: University of Minnesota - Department of Forest Resources, 1530 Cleveland Ave N, St Paul, MN 55108 United States
AU: Wang, W
AF: University of Minnesota - Department of Forest Resources, 1530 Cleveland Ave N, St Paul, MN 55108 United States
AB: Forest stand age is an important determinant of ecosystem carbon uptake. Though there are biometric measurements and ecological models for forests of all ages, there are few stand-scale eddy-flux measurements of net carbon exchange in older forests, though the number is increasing. In order to scale carbon fluxes from sites to regions, where stands of multiple ages may exist, it is necessary to measure to the effect of stand age on carbon exchange. Measuring the effect of stand age on carbon exchange is also necessary when trying to predict future or past carbon exchange (scaling across time). Many researchers have noted that site disturbance history is the fundamental factor in determining carbon uptake by forests over time scales of decades to centuries. The 8,500 ha Sylvania Wilderness in the upper peninsula of Michigan is one of several large tracts of old-growth forest in the Midwest. Trees range from 0-350 years old. Primary species are sugar maple, eastern hemlock and yellow birch. Catastrophic disturbance is rare. A research plot near the wilderness was established in late 2001 to measure the net ecosystem exchange (NEE) of carbon and water using eddy-flux, component flux and biometric methods. This site is part of the Chequamegon Ecosystem Atmosphere Study (ChEAS, http://cheas.psu.edu), a loose affiliation of researchers conducting carbon and water research in northern Wisconsin and upper Michigan. Another similar research plot within ChEAS and not far from Sylvania is the Willow Creek mature uplands site. This forest is about 70 years old and the primary species are sugar maple, basswood and green ash. The site had presettlement old-growth vegetation similar to what is currently seen in the Sylvania Wilderness. Thus, the carbon exchange seen at Sylvania may be representative of carbon uptake at Willow Creek had it not been logged in the early 20th century, and may also represent the future (or past) carbon uptake for similar forests in northern Wisconsin/upper Michigan. Initial results from 2002 show that both Sylvania and Willow Creek were sinks of carbon, though the annual NEE of carbon at Sylvania was only -72 gC/m2/yr, while it was -447 gC/m2/yr at Willow Creek. The lack of carbon balance at the old-growth site may be caused by growth enhancement due to carbon/nutrient fertilization, climate warming, or recent local-scale disturbances. A standard moving-window Arrenhius-style temperature-nighttime NEE relationship was used to separate total ecosystem respiration from gross ecosystem production (GEP). Total annual respiration was much greater at Sylvania (965 gC/m2/yr) than Willow Creek (667 gC/m2/yr), while GEP at Sylvania (1045 gC/m2/yr) was only slightly smaller than Willow Creek (1136 gC/m2/yr). The largest differences in respiration between the two sites occurred in early summer, whereas the largest difference in GEP occurred in late summer. The observed differences between the two sites matches well with theory. Ecosystem respiration is expected to increase steadily with stand age while gross ecosystem production is expected to increase rapidly as new species are established, but eventually level off. Current ongoing component flux measurements will help determine the mechanisms for the observed differences in carbon uptake at the two sites and provide insight on the causes of declining carbon exchange with stand age.
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
DE: 3322 Land/atmosphere interactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting