Phytosociology

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Phytosociology is a subset of vegetation science that deals with extant plant communities and puts particular emphasis on their classification. As a tribute to the originator of its founding ideas, phytosociology is also termed the Braun-Blanquet approach. The basic data record of phytosociology is the relevé, which lists all plant taxa, their occurrence in vertical strata, and their cover-abundance for a plot representing a vegetation stand. Supplementary data on geographic position, environmental factors, and vegetation structure are also recorded in the relevé. Vegetation units (syntaxa) are classified according to their species composition into a hierarchical system consisting from bottom-up of four principal ranks: association, alliance, order, and class. These units are given scientific names derived from the names of typical species and regulated by the International Code of Phytosociological Nomenclature. Traditional classification based on manual table-sorting is nowadays largely replaced by numerical algorithms that allow classifying large sets of relevés in a repeatable manner. The crucial concept is fidelity, which describes the concentration of a species in a particular syntaxon and which is used both in the classification procedure and in the characterization of syntaxa. Besides mainstream phytosociology, which deals with whole plant communities, synusial approaches classify partial communities and symphytosociological approaches focus on spatial assemblages of plant communities. Phytosociology’s major applications are in ecological assessment (e.g., Ellenberg indicator values), vegetation mapping, monitoring environmental change, and nature conservation inventory.