The Loobos ecosystem first tower dataset: meteorology, turbulent fluxes and net ecosystem exchange (1996 to 2021)

We describe a 25 years (1996–2021) observational dataset of meteorology, turbulent fluxes and net ecosystem exchange collected from the first tower at the Loobos site, the Netherlands (NL). This is one of the 17 first FLUXNET sites globally. The presented dataset contains six data streams, namely (1) the NL-Loo_BM stream including meteorological data: four-component radiation (radiation balance), air temperature and relative humidity, wind information, precipitation and throughfall, photosynthetic active radiation, bole temperature and soil heat flux), (2) the NL-Loo_Profile stream containing vertical profiles of CO 2 mole fraction, H 2 O pressure, air temperature and relative humidity, (3) the NL-Loo_ST stream derived from the aforementioned two streams including total stored heat flux, H 2 O and CO 2 fluxes below the canopy, (4) the NL-Loo_EC stream including EC measurements of CO 2 flux, sensible heat and latent heat fluxes, (5) the NL-Loo_Soil stream including vertical profiles of soil moisture and temperature and ground water level data, and (6) ancillary data including soil respiration, vegetation properties (i.e., tree height, stem width and dry aboveground biomass, Leaf Area Index, sap flow, needle foliage properties and the associated nutrient analysis) and ground water level. The data quality of these data streams is assured through standard operating procedures. To show the utility of gathering long-term and comprehensive measurements, we present analyses of mean diurnal storage CO 2 flux, the trend of NEE over the last 25 years and the energy balance closure. Being one of the longest datasets of its kind in a temperate forest, this valuable dataset is anticipated to be used for investigating the performance of various gap-filling algorithms, semi-climatological trends including extreme climatic events (such as the heatwave of 2003 and the drought of 2018) and the role of forest ecosystem in the carbon, water and energy cycle. Meanwhile, it is expected to be employed for validating modelled land-atmosphere CO 2 and turbulent exchange fluxes, verifying model assumptions and serving as ground truth for satellite data retrievals. The dataset is accessible at https://doi.org/10.5281/zenodo.15721310 (Zhao et al., 2025) under a CC-BY4 open use license, where it is published as an associated station-like site and the same data will also be available at the European Fluxes Database Cluster. Hence, the data will be committed to the FLUXNET Data System Initiative too. It is noted that in 2021 a second tower was built and equipped with new instrumentation as a replacement of the first tower, which was labelled as an ICOS Ecosystem Class 2 site in 2023. Here we describe the first tower's instrumentation and data processing up to a Level 1 product (derived variables and quality checks, but not gap-filled). The instrumentation and data processing related to the second tower is described in van der Molen et al. (2026).