Vegetation plays a central role in controlling terrestrial carbon (C) exchange, but quantifying its impacts on C cycling on time scales of ecological succession is hindered by a lack of long-term observations. The net ecosystem exchange of carbon (NEE) was measured for several years in adjacent ecosystems that represent distinct phases of ecological succession in… More

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We combined Eddy-covariance measurements with a linear perturbation analysis to isolate the relative contribution of physical and biological drivers on evapotranspiration (ET) in three ecosystems representing two end-members and an intermediate stage of a successional gradient in the southeastern US (SE). The study ecosystems, an abandoned agricultural field [old field (OF)], an early successional planted… More

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This study explores the complexity (or disorder) in mapping energy (Rn) forcing to land surface fluxes of sensible heat (Hs), water vapor (LE), and carbon dioxide (or net ecosystem exchange, NEE) for different soil water states (θ). Specifically, we ask, does the vegetation act to increase or dissipate statistical entropy injected from Rn? We address… More

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Free-air CO2 enrichment (FACE) technology was used to expose a loblolly pine (Pinus taeda L.) forest to elevated atmospheric CO2 (ambient + 200 µl l–1). After 4 years, basal area of pine trees was 9.2% larger in elevated than in ambient CO2 plots. During the first 3 years the growth rate of pine was stimulated by ~26%. In… More

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Increasing atmospheric CO2 concentration decreases stomatal conductance in many species, but the savings of water from reduced transpiration may permit the forest to retain greater leaf area index (L). Therefore, the net effect on water use in forest ecosystems under a higher CO2 atmosphere is difficult to predict. The free air CO2 enrichment (FACE) facility… More

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Soil CO2 efflux is a major component of net ecosystem productivity (NEP) of forest systems. Combining data from multiple researchers for larger-scale modeling and assessment will only be valid if their methodologies provide directly comparable results. We conducted a series of laboratory and field tests to assess the presence and magnitude of soil CO2 efflux… More

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Increased canopy leaf area (L) may lead to higher forest productivity and alter processes such as species dynamics and ecosystem mass and energy fluxes. Few CO2 enrichment studies have been conducted in closed canopy forests and none have shown a sustained enhancement of L. We reconstructed 8 years (1996–2003) of L at Duke’s Free Air… More

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Responses of forests to changes in environmental conditions reflect the integrated behavior of their constituent species. We investigated sap flux-scaled transpiration responses of two species prevalent in upland eastern hardwood forests, Quercus alba in the upper canopy and Acer rubrum in the low to mid canopy, to changes in photosynthetically active radiation above the canopy… More

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