Sight-based field measurements of tree crown projection area and canopy height are common praxis in forest science but difficult to validate. We quantified their measurement errors based on the virtual representation of an 11-species old-growth forest provided by high-resolution terrestrial LIDAR (light detection and ranging) measurements.

Key message: Aggregated, consolidated, and derived soil physicochemical data of 286 ICP Forests Level II plots were completed with soil hydraulic properties for integrated use with forest monitoring data. Database access should be requested at http://icp-forests.net . Metadata associated available at https://metadata-afs.nancy.inra.fr/geonetwork/apps/georchestra/?uuid=153e599e-6624-4e2b-b862-8124386ea9cd&hl=eng Context: The ICP Forests database is one of the most comprehensive forest ecosystem datasets in Europe and contains the accumulated results of more than two decades of harmonised forest monitoring all over Europe. Aims: The aim of this paper is to share knowledge on the ICP Forests Level II soil data for broader use among forest scientists. Methods: After standard analysis, quality checks, aggregation, and calculation of derived variables (e.g. nutrient stocks, base saturation, C:N ratio, and water retention parameters), data have been gathered into a static database (AFSCDB.LII.2.2), which will be updated to new versions as soon as new measurements become available. Results: The database provides a basis for the combined evaluation of up to 130 unique soil variables of 286 plots with dynamic data on tree growth, ground vegetation, foliar chemistry, crown condition, tree phenology, leaf area index, ozone injury, litterfall, soil solution chemistry, deposition, ambient air quality, and meteorological data assessed on the same plots. Conclusion: The unprecedented comprehensiveness and level of detail in this newly aggregated database may overcome existing restrictions so far impeding the realisation of large-scale forest ecosystem studies in Europe.

Increased deposition of reactive nitrogen (N) since pre-industrial times has dramatically altered the conditions for forest growth and decomposition of organic material in Germany. The second National Forest Soil Inventory (NFSI II, 2006–2008) shows the status of N accumulation in forest soils. A median N stock of 6.3 t ha^–1 has been found in the soil profile down to a depth of maximum 90 cm, whereof 50% is stored in the upper 30 cm of the mineral soil. The high regional variability of N stocks is explained by forest type, parent material, soil acidity, annual mean temperature, and adjacent agricultural land use. C/N ratios of the top soil were on average higher (24.0) than those during NFSI I (22.4, 1989–1992), which may be seen as a first effect of slowly decreasing deposition rates. Observations on limed plots suggest that acidification inhibits soil biological activity and thereby reduces N-storage in the mineral soil. The median annual N balance for German forest soils between NFSI I and II varies between +2.9 and +7 kg ha^–1, depending on the harvest regime assumed. Negative N balances occurred mainly in mountain ranges like the Black Forest or the Rhenish Slate Mountains. N stocks in the upper 30 cm of the soil generally increased, while there are indications for losses of N from deeper soil layers, potentially linked to progressing acidification in these layers. Irrespective of existing measurement uncertainties, the findings indicate the vulnerability of forest N stocks under changing conditions. Further reductions of N deposition should be strived for to reduce the risk of nitrate leaching from forest soils.