Scatter plots of daily GPP vs. GCC for all deciduous broadleaf forest (DBF) evergreen needleleaf forest (ENF) and grassland (GRS) sites, listed by plant functional type.

Leaf area and its spatial distribution are key canopy parameters needed to model the radiation regime within a forest and to compute the mass and energy exchange between a forest and the atmosphere. A much larger proportion of available net radiation is received at the forest floor in open-canopy forests than in closed-canopy forests. The proportion of ecosystem water vapor exchange (lambda E) and sensible heat exchange from the forest floor is therefore expected to be larger in open-canopy forests than in closed-canopy forests. We used a combination of optical and canopy geometry measurements, and robust one- and three-dimensional models to evaluate the influence of canopy architecture and radiative transfer on estimates of carbon, water and energy exchange of a ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forest. Three-dimensional model simulations showed that the average probability of diffuse and direct radiation transmittance to the forest floor was greater than if a random distribution of foliage had been assumed. Direct and diffuse radiation transmittance to the forest floor was 28 and 39%, respectively, in the three-dimensional model simulations versus 23 and 31%, respectively, in the one-dimensional model simulations. The assumption of randomly distributed foliage versus inclusion of clumping factors in a one-dimensional, multi-layer biosphere-atmosphere gas exchange model (CANVEG) had the greatest effect on simulated annual net ecosystem exchange (NEE) and soil evaporation. Assuming random distribution, NEE was 41% lower, net photosynthesis 3% lower, total lambda E 10% lower, and soil evaporation 40% lower. The same comparisons at LAI 5 showed a similar effect on annual NEE estimates (37%) and lambda E (12%), but a much larger effect on net photosynthesis (20%), suggesting that, at low LAI, canopies are mostly sunlit, so that redistribution of light has little effect on net photosynthesis, whereas the effect on net photosynthesis is much greater at high LAIs.

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A mathematician may say anything he pleases, but a physicist must be at least partially sane.Josiah Willard Gibbs, The Scientific Monthly, December 1944

Significance This article defines ecosystem functional properties, which can be derived from long-term observations of gas and energy exchange between ecosystems and the atmosphere, and shows that variations of those cannot be easily explained by classical climatological or biogeographical approaches such as plant functional types. Instead, we argue that plant traits have the potential to explain this variation, and we call for a stronger integration of research communities dedicated to plant traits and to ecosystem–atmosphere exchange.

A quantitative study of the architecture of both a stand and individual plant with its organs constitutes a fundamental task of phytometry.. . . solar radiation in a plant stand is a highly complicated process dependent both on incident radiation and on the optical and geometrical properties of the vegetation.For this reason a more specified and generalized concept of a turbid medium was proposed, according to which a stand was treated as a plate turbid anisotropic medium homogeneous in horizontal plane in terms of statistics.Juhan Ross (1981)

Abstract Restored wetlands are a complex mosaic of open water and new and old emergent vegetation patches, where multiple environmental and biological drivers contribute to the measured heterogeneity in methane (CH 4 ) flux. In this analysis, we replicated the measurements of CH 4 flux using the eddy covariance technique at three tower locations within the same wetland site to parse the spatiotemporal variability in CH 4 flux contributed by large‐scale seasonal variations in climate and phenology and short‐term variations in flux footprint movement over a mosaic of vegetation and open water. Using a hierarchical statistical model accounting for site‐level environmental effects, tower‐level footprint and biological effects, and temporal autocorrelation, we partitioned the key drivers of the daily CH 4 flux variability among the three replicated towers. The daily mean air temperature and mean friction velocity, a measure of momentum transfer, explained a significant variability in CH 4 flux across the three towers, and the abundance and spatial aggregation of vegetation in the flux footprint along with the daily gross primary productivity explained much of the tower‐level variability. This statistical model captured 67% of the total variance in the daily integrated growing season CH 4 fluxes at this site, which bridged an order of magnitude from 80 to 480 mg C m −2 d −1 during the measurement period from 10 May 2012 to 24 October 2012.

The Central Valley of California is home to a variety of fruit and nut trees. These trees account for 95% of the U.S. production, but they need a sufficient amount of winter chill to achieve rest and quiescence for the next season's buds and flowers. In prior work, we reported that the accumulation of winter chill is declining in the Central Valley. We hypothesize that a reduction in winter fog is cooccurring and is contributing to the reduction in winter chill. We examined a 33 year record of satellite remote sensing to develop a fog climatology for the Central Valley. We find that the number of winter fog events, integrated spatially, decreased 46%, on average, over 32 winters, with much year to year variability. Less fog means warmer air and an increase in the energy balance on buds, which amplifies their warming, reducing their chill accumulation more.

A partir d’une hauter variable avec la situation atmospherique (de 8 km à 12 km) commence une zone caractérisée par lá très faible décroissance de température ou même par une croissance légère avec des alternatives de refroidissement et d’echauffement. Nous ne pouvans préciser l’épaisseur de cette zone; mais, d’après les observations actuelles, elle pataît atteindre au moins plusieurs kilometers.[At some variable height in the atmosphere (between 8 km and 12 km) there begins a characteristic decay of the low temperature trend, or even a slight increase in temperature with alternating heating and cooling. We can specify the thickness of this zone and from the current observations it appears to be at least several kilometers.]Leon Philippe Teisserenc de Bort (1902)

At the leaf scale, it is a long-held assumption that stomata close at night in the absence of light, causing transpiration to decrease to zero. Energy balance models and evapotranspiration equations often rely on net radiation as an upper bound, and some models reduce evapotranspiration to zero at night when there is no solar radiation. Emerging research is showing, however, that transpiration can occur throughout the night in a variety of vegetation types and biomes. At the ecosystem scale, eddy covariance measurements have provided extensive data on latent heat flux for a multitude of ecosystem types globally. Nighttime eddy covariance measurements, however, are generally unreliable because of low turbulence. If significant nighttime water loss occurs, eddy flux towers may be missing key information on latent heat flux. We installed and measured rates of sap flow by the heat ratio method (Burgess et al. 2001) at two AmeriFlux (part of FLUXNET) sites in California. The heat ratio method allows measurement and quantification of low rates of sap flow, including negative rates (i.e., hydraulic lift). We measured sap flow in five Pinus ponderosa Dougl. ex Laws. trees and three Arctostaphylos manzanita Parry and two Ceanothus cordulatus A. Kellog shrubs in the Sierra Nevada Mountains, and in five Quercus douglasii Hook and Arn. trees at an oak savanna in the Central Valley of California. Nocturnal sap flow was observed in all species, and significant nighttime water loss was observed in both species of trees. Vapor pressure deficit and air temperature were both well correlated with nighttime transpiration; the influence of wind speed on nighttime transpiration was insignificant at both sites. We distinguished between storage-tissue refilling and water loss based on data from Year 2005, and calculated the percentage by which nighttime transpiration was underestimated by eddy covariance measurements at both sites.

Fluxes of trace gases, water and energy - the 'breathing of the biosphere' - are controlled by a large number of interacting physical, chemical, biological and ecological processes. In this interdisciplinary book, the authors provide the tools to understand and quantitatively analyse fluxes of energy, organic compounds such as terpenes, and trace gases including carbon dioxide, water vapour and methane. It first introduces the fundamental principles affecting the supply and demand for trace gas exchange at the leaf and soil scales: thermodynamics, diffusion, turbulence and physiology. It then builds on these principles to model the exchange of water, carbon dioxide, terpenes and stable isotopes at the ecosystem scale. Detailed mathematical derivations of commonly used relations in biosphere-atmosphere interactions are provided for reference in appendices. An accessible introduction for graduate students and a key resource for researchers in related fields, such as atmospheric science, hydrology, meteorology, climate science, biogeochemistry and ecosystem ecology.

The Journal of Geophysical Research: Biogeosciences covers a wide range of scientific disciplines. JGR-Biogeosciences papers investigate topics that range from the mechanisms and processes responsible for the fluxes and exchange of biogeochemically relevant materials (e.g., energy, water, carbon, and nutrients) across key interfaces (e.g., land-atmosphere-ocean) to factors affecting the productivity and ecology of terrestrial and aquatic (freshwater and marine) ecosystems and to feedbacks and interactions between the biosphere and climate. Given such broad and multidisciplinary focus, JGR-Biogeosciences relies on a committed team of Associate Editors and a large number of dedicated, rigorous, and thoughtful reviewers from a variety of fields and backgrounds to maintain the highest level of scientific integrity and quality in the papers we publish. In 2014, the papers published in JGR-Biogeosciences benefited from 522 reviews provided by 455 individual referees. The dedication and thoughtfulness of our reviewers is critical to ensure high quality; cutting edge research is effectively communicated through our publication process. We thank all those who contributed their time and knowledge to the peer review process in our journal. Because many of the topics covered by JGR-Biogeosciences have direct and significant societal implications, their dedication not only benefits the advancement of science but also has a positive impact on future policy based on sound science. Individuals in bold italics provided three or more reviews during the year