Filling empty boxes with hard data: Scientific background for European habitat classification (EUNIS)

Prepared by Milan Chytrý

Examples of EUNIS habitats: N17 Black Sea coastal dune grassland (grey dune) in south-eastern Bulgaria, R1A Semi-dry perennial calcareous grassland (meadow steppe) with Filipendula vulgaris and Salvia nutans in western Ukraine, S33 Lowland to montane temperate and submediterranean genistoid scrub with Cytisus balansae in Catalonian Pyrenees, T3G Pinus sylvestris light taiga in southern Sweden. Photos by M. Chytrý.

This Behind the paper post refers to the article by Chytrý et al. EUNIS Habitat Classification: Expert system, characteristic species combinations and distribution maps of European habitats, published in Applied Vegetation Science (

EUNIS Habitat Classification is a standard international classification of European habitats maintained by the European Environment Agency. It is used as an important tool for conservation planning, monitoring and nature assessment.

The EUNIS Habitat Classification was developed in the 1990s and early 2000s as a comprehensive hierarchical system of European habitats. However, individual habitats were poorly defined, containing just brief text descriptions, with no reference data or exact delimitations. These units were a sort of empty boxes that were difficult to interpret not only for practitioners but also for habitat specialists.

Therefore, the European Environment Agency contracted a group of vegetation ecologists belonging to the IAVS Working Group European Vegetation Survey. I had a privilege to be a member of this group, which also included Joop Schaminée, Stephan Hennekens, John Rodwell, Lubomír Tichý and John Janssen. Other members of the European Vegetation Survey joined later. Since 2012, our group worked systematically on the revision of the terrestrial part of the EUNIS Habitat Classification and exact definitions of individual habitats. Some habitat types were added, others were split or merged. All the vegetated habitats were linked to European phytosociological alliances of EuroVegChecklist (Mucina et al., 2016). Habitat descriptions were improved.

Most importantly, we developed an expert system that contains unequivocal formal definitions of each EUNIS habitat. We call this expert system EUNIS-ESy. The definitions included in EUNIS-ESy are written in the language of formal logic (Tichý et al. 2019) and involve criteria such as plant species composition, the dominance of individual species and geographical location of the site. At the same time, we started the European Vegetation Archive (EVA), an integrated database of European vegetation-plot records (Chytrý et al., 2016). Currently, this database contains more than 1.6 million vegetation-plot records from the whole of Europe. We used the EUNIS-ESy expert system to assign each of the EVA vegetation-plot records to a EUNIS habitat. This assignment was performed using the JUICE program (by Lubomír Tichý). However, it can also be performed using the TURBOVEG 3 program (by Stephan Hennekens) or an R script developed by Helge Bruelheide and Florian Jansen. The use of the formal definitions of habitats guaranteed that the classification of the vegetation-plot records was consistent across the continent.

We used the resulting large continental database of vegetation-plot records classified to EUNIS habitats to extract information about each habitat that was not available before. In particular, we prepared distribution maps and using statistical tools we defined characteristic species combinations including lists of diagnostic, constant and dominant species of each habitat. Appendix S1 of the current paper contains 550 pages of factsheets providing, for each habitat, its brief description, distribution map, corresponding phytosociological alliances and a list of its diagnostic, constant and dominant species.

The version of the expert system described in the current paper contains definitions of 199 coastal, wetland, grassland, shrubland, forest and man-made habitats. In the near future, depending on the progress of revisions of further habitat groups organized by the European Environment Agency, vegetated marine, aquatic and inland sparsely vegetated habitats will be added. Updated versions of EUNIS-ESy and outputs of the analyses will be published in the Zenodo repository (, which currently contains the baseline version 2020-06-08, corresponding to the version published in our Applied Vegetation Science article.


  • Chytrý, M., Hennekens, S. M., Jiménez-Alfaro, B., Knollová, I., Dengler, J., Jansen, F. et al. (2016) European Vegetation Archive (EVA): an integrated database of European vegetation plots. Applied Vegetation Science 19, 173–180.
  • Mucina, L., Bültmann, H., Dierßen, K., Theurillat, J.-P., Raus, T., Čarni, A. et al. (2016) Vegetation of Europe: Hierarchical floristic classification system of vascular plant, bryophyte, lichen, and algal communities. Applied Vegetation Science 19(Suppl. 1), 3–264.
  • Tichý, L., Chytrý, M. and Landucci, F. (2019) GRIMP: A machine-learning method for improving groups of discriminating species in expert systems for vegetation classification. Journal of Vegetation Science 30, 5–17.