Seven years of carbon dioxide flux measurements indicate that a ∼90-year-old spruce dominated forest in Maine, USA, has been sequestering 174±46 g C m−2 yr−1 (mean±1 standard deviation, nocturnal friction velocity (u*) threshold >0.25 m s−1). An analysis of monthly flux anomalies showed that above-average spring and fall temperatures were significantly correlated with greater monthly C uptake while above-average summer temperatures… More

in    0

We determined δ13C values associated with canopy gross and net CO2 fluxes from four U.S. sites sampled between 2001 and 2002. Annual mean, flux-weighted δ13C values of net ecosystem CO2exchange (NEE) were estimated for four contrasting ecosystems (three forests and one grassland) by analyzing daytime flask measurements collected at the top of canopies. Combining δ13C… More

in    0

The concentration, contents, and distribution of nutrients, metals, and soil materials were quantified at the Howland Integrated Forest Study (HIFS) site in eastern Maine. The site is a mature, low-elevation spruce-fir forest on Podzolic soils developed from dense basal till. Standard morphologically based soil sampling and quantitative soil pits were both used to characterize the… More

in    0

Carbon dioxide, water vapour, and sensible heat fluxes were measured above and within a spruce dominated forest near the southern ecotone of the boreal forest in Maine, USA. Summer, mid-day carbon dioxide uptake was higher than at other boreal coniferous forests, averaging about – 13 μmol CO2 m–2 s–1. Nocturnal summer ecosystem respiration averaged ≈ 6 μmol CO2 m–2 s–1 at a mean temperature… More

in    0

Over two-thirds of terrestrial carbon is stored belowground and a significant amount of atmospheric CO2 is respired by roots and microbes in soils. For this analysis, soil respiration (Rs) data were assembled from 31 AmeriFlux and CarboEurope sites representing deciduous broadleaf, evergreen needleleaf, grasslands, mixed deciduous/evergreen and woodland/savanna ecosystem types. Lowest to highest rates of… More

in    0

Annual budgets and fitted temperature response curves for soil respiration and ecosystem respiration provide useful information for partitioning annual carbon budgets of ecosystems, but they may not adequately reveal seasonal variation in the ratios of these two fluxes. Soil respiration (Rs) typically contributes 30–80% of annual total ecosystem respiration (Reco) in forests, but the temporal… More

in    0

Whether the goal is to fill gaps in the flux record, or to extract physiological parameters from eddy covariance data, researchers are frequently interested in fitting simple models of ecosystem physiology to measured data. Presently, there is no consensus on the best models to use, or the ideal optimization criteria. We demonstrate that, given our… More

in    0

Soil respiration is an important component of the annual carbon balance of forests, but few studies have addressed interannual variation in soil respiration. The objectives of this study were to investigate the seasonal and interannual variation in soil respiration, temperature, precipitation, and soil water content in two New England forest soils and to develop and… More

in    0

The effects of disturbance history, climate, and changes in atmospheric carbon dioxide (CO2) concentration and nitrogen deposition (Ndep) on carbon and water fluxes in seven North American evergreen forests are assessed using a coupled water–carbon–nitrogen model, canopy-scale flux observations, and descriptions of the vegetation type, management practices, and disturbance histories at each site. The effects… More

in    0