{"type": "FeatureCollection", "features": [{"id": "10.1016/j.agrformet.2006.01.007", "type": "Feature", "geometry": null, "properties": {"updated": "2026-05-25T16:15:19Z", "type": "Journal Article", "created": "2006-02-25", "title": "A Multi-Site Analysis Of Random Error In Tower-Based Measurements Of Carbon And Energy Fluxes", "description": "Measured surface-atmosphere fluxes of energy (sensible heat, H, and latent heat, LE) and CO2 (FCO2) represent the \u2018\u2018true\u2019\u2019 flux plus or minus potential random and systematic measurement errors. Here, we use data from seven sites in the AmeriFlux network, including five forested sites (two of which include \u2018\u2018tall tower\u2019\u2019 instrumentation), one grassland site, and one agricultural site, to conduct a cross-site analysis of random flux error. Quantification of this uncertainty is a prerequisite to model-data synthesis (data assimilation) and for defining confidence intervals on annual sums of net ecosystem exchange or making statistically valid comparisons between measurements and model predictions. We differenced paired observations (separated by exactly 24 h, under similar environmental conditions) to infer the characteristics of the random error in measured fluxes. Random flux error more closely follows a double-exponential (Laplace), rather than a normal (Gaussian), distribution, and increase as a linear function of the magnitude of the flux for all three scalar fluxes. Across sites, variation in the random error follows consistent and robust patterns in relation to environmental variables. For example, seasonal differences in the random error for H are small, in contrast to both LE and FCO2, for which the random errors are roughly three-fold larger at the peak of the growing season compared to the dormant season. Random errors also generally scale with Rn (H and LE) and PPFD (FCO2). For FCO2 (but not H or LE), the random error decreases with increasing wind speed. Data from two sites suggest that FCO2 random error may be slightly smaller when a closed-path, rather than open-path, gas analyzer is used.", "keywords": ["Random error", "Flux", "550", "carbon", "Uncertainty", "0207 environmental engineering", "AmeriFlux", "Eddy covariance", "02 engineering and technology", "15. Life on land", "01 natural sciences", "Carbon", "flux", "Measurement error", "13. Climate action", "Natural Resources and Conservation", "Data assimilation", "eddy covariance", "Ameriflux", "uncertainty", "random error", "data assimilation", "measurement error", "0105 earth and related environmental sciences"]}, "links": [{"href": "https://doi.org/10.1016/j.agrformet.2006.01.007"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Agricultural%20and%20Forest%20Meteorology", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "10.1016/j.agrformet.2006.01.007", "name": "item", "description": "10.1016/j.agrformet.2006.01.007", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.1016/j.agrformet.2006.01.007"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2006-01-01T00:00:00Z"}}, {"id": "10.1073/pnas.1905912116", "type": "Feature", "geometry": null, "properties": {"updated": "2026-05-25T16:18:00Z", "type": "Journal Article", "created": "2019-08-06", "title": "Disentangling the role of photosynthesis and stomatal conductance on rising forest water-use efficiency", "description": "

Multiple lines of evidence suggest that plant water-use efficiency (WUE)\uffe2\uff80\uff94the ratio of carbon assimilation to water loss\uffe2\uff80\uff94has increased in recent decades. Although rising atmospheric CO 2 has been proposed as the principal cause, the underlying physiological mechanisms are still being debated, and implications for the global water cycle remain uncertain. Here, we addressed this gap using 30-y tree ring records of carbon and oxygen isotope measurements and basal area increment from 12 species in 8 North American mature temperate forests. Our goal was to separate the contributions of enhanced photosynthesis and reduced stomatal conductance to WUE trends and to assess consistency between multiple commonly used methods for estimating WUE. Our results show that tree ring-derived estimates of increases in WUE are consistent with estimates from atmospheric measurements and predictions based on an optimal balancing of carbon gains and water costs, but are lower than those based on ecosystem-scale flux observations. Although both physiological mechanisms contributed to rising WUE, enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to species that experienced moisture limitations. This finding challenges the hypothesis that rising WUE in forests is primarily the result of widespread, CO 2 -induced reductions in stomatal conductance. Multiple lines of evidence suggest that plant water-use efficiency (WUE)\uffe2\uff80\uff94the ratio of carbon assimilation to water loss\uffe2\uff80\uff94has increased in recent decades. Although rising atmospheric CO 2 has been proposed as the principal cause, the underlying physiological mechanisms are still being debated, and implications for the global water cycle remain uncertain. Here, we addressed this gap using 30-y tree ring records of carbon and oxygen isotope measurements and basal area increment from 12 species in 8 North American mature temperate forests. Our goal was to separate the contributions of enhanced photosynthesis and reduced stomatal conductance to WUE trends and to assess consistency between multiple commonly used methods for estimating WUE. Our results show that tree ring-derived estimates of increases in WUE are consistent with estimates from atmospheric measurements and predictions based on an optimal balancing of carbon gains and water costs, but are lower than those based on ecosystem-scale flux observations. Although both physiological mechanisms contributed to rising WUE, enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to species that experienced moisture limitations. This finding challenges the hypothesis that rising WUE in forests is primarily the result of widespread, CO 2 -induced reductions in stomatal conductance.