The FLUXNET2015 dataset provides ecosystem-scale data on CO 2 , water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

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AbstTactWater vapour and CO2 fluxes were measured using the eddy correlation method above and below the overstorey of a 21-m tall aspen stand in the boreal forest of central Saskatchewan as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). Measurements were made at the 39.5-m and 4-m heights using 3-dimensional sonic anemometers (Kaijo-Denki and Solent, respectively) and closed-path gas analysers (LI-COR 6262) with 6-m and 4.7-m long heated sampling tubing, respectively. Continuous measurements were made from early October to mid-November 1993 and from early February to lateSeptember 1994. Soil CO2 flux (respiration) was measured using a LI-COR 6000-09 soil chamber and soil evaporation was measured using lysimetry.The leaf area index of the aspen and hazelnut understorey reached 1.8 and 3.3, respectively. The maximum daily evapotranspiration (£) rate was 5-6 mm d^^ Following leaf-out the hazelnut and soil accounted for 22% of the forest £. The estimated total £ was 403 mm for 1994. About 88% of the precipitation in 1994 was lost as evapotranspiration.During the growing season, the magnitude of half-hourly eddy fluxes of CO2 from the atmosphere into the forest reached 1.2 mg CO2 m'^ s^* (33 |imol C m~^ s"^) during the daytime. Downward eddy fluxes at the 4-m height were observed when the hazelnut was growing rapidly in June and July. Under well-ventilated night-time conditions, the eddy fluxes of CO2 above the aspen and hazelnut, corrected for canopy storage, increased exponentially with soil temperature at the 2-cm depth. Estimates of daytime respiration rates using these relationships agreed well with soil chamber measurements. During the 1994 growing season, the cumulative net ecosystem exchange (N££) was -3.5 t C ha"^ y"^ (a net gain by the system). For 1994, cumulative NEE, ecosystem respiration (K) and gross ecosystem photosynthesis (GEP = R-NEE) were estimated to be -1.3, 8.9 and 10.2 t C ha"^ y~^, respectively. Gross photosynthesis of the hazelnut was 32% of GEP.

Both species showed a decrease in canopy conductance as the saturation deficit increased and both showed an increase in canopy conductance as the photosynthetic active radiation increased. There was a linear relationship between forest leaf area index and forest canopy conductance. The timing, duration, and maximum leaf area of this deciduous boreal forest was found to be an important control on transpiration at both levels of the canopy. The full-leaf hazelnut daytime mean Priestley and Taylor [1972] a coefficient of 1.22 indicated transpiration was largely energy controlled and the quantity of energy received at the hazelnut surface was a function of aspen leaf area. The full-leaf aspen daytime mean c• of 0.91 indicated some stomatal control on transpiration, with a directly proportional relationship b6tWeen forest leaf area and forest canopy conductance, varying c• during much of the season through a range very sensitive to regional scale transpiration and surface-convective boundary layer feedbacks. IntroductionThe boreal forest represents one of the world's largest yet least understood ecosystems. Of the estimated 48.5 million km 2 total land area of the world's forests, 12.0 (25%) is covered by boreal forest, second only to the 17.0 (35%) covered by tropical rain forest. Boreal forest net primary productivity (ex---1 pressed as dry matter) accounts for an estimated 9.6 Gt yr (13%) of the world's forests 73.9, exceeding both temperate deciduous 8.4 (11%) and temperate coniferous 6.5 (9%) forests [Salisbury and Ross, 1978].•University of British Columbia, Vancouver, Canada. 2Atmospheric Environment Service, Downsview, Ontario, Canada.•Yale University, New Haven, Connecticut. Continuing with the work presented by Black et al. [1996], the objectives of this paper are (1) to describe the diurnal and seasonal patterns of the aspen overstory and hazelnut understory energy balance, (2) to describe the diurnal and seasonal patterns of canopy water vapor conductances for both the aspen and the hazelnut, and (3) to relate the canopy conductances to the ambient meteorological conditions at both the canopy and the regional levels. Site DescriptionThe study site (

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