Continuous measurements of carbon, water and energy fluxes are performed using the eddy covariance (EC) method in a mixed-beech forest ecosystem in central Germany (52° 5'12N, 11°13'20E, 193 m asl), accompanied by relevant abiotic measurements. The site was established in the Bode catchment as part of the TERENO Harz/Central German Lowland Observatory, a mesoscale water catchment within the Elbe river basin covering an area of approximately 3300 km². The forest area Hohes Holz is the only larger forested area in the otherwise agriculturally intensively-farmed western part of the Magdeburger Börde with an area of about 1500 ha [Wollschläger et al., 2017]. The forest is a protected area with the centre (150 ha) being a nature reserve (Natura 2000) and is dominated by common beech (Fagus sylvatica L.), sessile oak (Quercus petraea) and hornbeam (Carpinus betulus L.) of about 90 years in age, an average tree height of 23.5 m and a stand density of 260 trees/ha. The long term average of annual precipitation is 563 mm and mean annual temperature is 9.1 °C (1981 – 2010 DWD station Ummendorf, #5158). The eddy covariance system consists of a CSAT-3 anemometer (Campbell Scientific Inc., Logan, UT, USA) and a LI-7500 gas analyser (Li-Cor Inc., Lincoln, NE, USA), established in 2014 in 49 m on a scaffolding tower within the research area. Data presented here comprise energy, water (H and LE), and carbon fluxes (NEE) from the EC-system since 2015 as well as gross primary productivity (GPP) and ecosystem respiration (Reco) derived from partitioning of NEE-data. Complimentary data from the turbulence data set and prioritized driver variables as a basis for ecosystem process analysis are added. High-frequency data (20Hz) were acquired with a Campbell data logger and the Eddymeas data acquisition software [Kolle and Rebmann, 2007]. Flux computation from high frequency raw data was performed with the Eddy-Pro® software (v. 7.0.6). After removing physically unrealistic flux values from the time series, subsequent post-processing steps such as estimating the u*-threshold, gap-filling and flux partitioning were performed according to Wutzler et al. [2018] with the REddyProc package. Full details of site instrumentation, metadata information and R-packages used for processing can be found in the supplementary material. Since January 2019 the site is approved as an ICOS ecosystem class 1 station (DE-HoH). ICOS standard procedures required an additional EC-setup consisting of a Gill HS-50 ultrasonic anemometer (Gill Instruments Ltd., Lymington, Hampshire, UK) and a LI-7200 gas analyser which runs in parallel to the above described system (see ICOS carbon portal: https://www.icos-cp.eu/data-products/ecosystem-release).

Eddy-covariance flux data output of processed high-frequency data (including turbulence measures) from CSAT3 ultrasonic anemometer (Campbell Scientific Ltd.) and LI-7500RS gas analyser (LI-COR Biosciences) processed with the Eddy-Pro® software (v. 7.0.6, LI-COR Biosciences) without additional quality assurance (see https://www.licor.com/env/support/EddyPro/topics/introduction.html#EddyPro7Software). '-9999' is indicating missing values.