There are few whole-canopy or ecosystem scale assessments of the interplay between canopy temperature and photosynthesis across both spatial and temporal scales. The stable oxygen isotope ratio (δ18O) of plant cellulose can be used to resolve a photosynthesis-weighted estimate of canopy temperature, but the method requires independent confirmation. We compare isotope-resolved canopy temperatures derived from… More

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The 14CO2 composition of plant and soil respiration can be used to determine the residence time of photosynthetically fixed carbon before it is released back to the atmosphere. To estimate the residence time of actively cycled carbon in a temperate forest, we employed two approaches for estimating the Δ14CO2 of ecosystem respiration (Δ14C-Reco) at the… More

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Ecosystem fluxes of energy, water, and CO2 result in spatial and temporal variations in atmospheric properties. In principle, these variations can be used to quantify the fluxes through inverse modelling of atmospheric transport, and can improve the understanding of processes and falsifiability of models. We investigated the influence of ecosystem fluxes on atmospheric CO2 in… More

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Turbulent fluxes of carbon, water vapor, and temperature were continuously measured above an upland forest in north central Wisconsin during 1999 and 2000 using the eddy covariance method. Maple (Acer saccharum), basswood (Tilia americana), and green ash (Fraxinus pennsylvanica) species found in this forest also comprise a substantial portion of the landscape in the northern… More

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Soil temperature and moisture influence soil respiration at a range of temporal and spatial scales. Although soil temperature and moisture may be seasonally correlated, intra and inter-annual variations in soil moisture do occur. There are few direct observations of the influence of local variation in species composition or other stand/site characteristics on seasonal and annual… More

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The climate sensitivity of plant seasonal life cycles, or phenology, may impart significant carbon cycle feedbacks on climatic change. Analysis of interannual ecosystem carbon exchange provides one way to assess this climate sensitivity. Multiyear eddy covariance carbon dioxide flux observations from five different ecosystems (deciduous forest, northern hardwood mixed forest, old-growth forest, shrub wetland, and… More

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We measured component and whole-system respiration fluxes in northern hardwood (Acer saccharumMarsh., Tilia americana L., Fraxinus pennsylvanica Marsh.) and aspen (Populus tremuloides Michx.) forest stands in Price County, northern Wisconsin from 1999 through 2002. Measurements of soil, leaf and stem respiration, stem biomass, leaf area and biomass, and vertical profiles of leaf area were combined… More

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We present the annual patterns of net ecosystem-atmosphere exchange (NEE) of CO2 and H2O observed from a 447 m tall tower sited within a mixed forest in northern Wisconsin, USA. The methodology for determining NEE from eddy-covariance flux measurements at 30, 122 and 396 m above the ground, and from CO2 mixing ratio measurements at 11, 30,… More

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The biosphere–atmosphere exchange of methane (CH4) was estimated for a temperate/boreal lowland and wetland forest ecosystem in northern Wisconsin for 1997–1999 using the modified Bowen ratio (MBR) method. Gradients of CH4 and CO2 and CO2 flux were measured on the 447-m WLEF-TV tower as part of the Chequamegon Ecosystem–Atmosphere Study (ChEAS). No systematic diurnal variability… More

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