Gustaf Du Rietz and Communities of Plants

Braun-Blanquet and his colleagues founded one school of phytosociology, but there were others. Professor Teodor Lippmaa (1892–1943) established an Estonian school in 1934 at the University of Tartu, and its first task was to map the plant distribution throughout the country. This was completed in 1955. The plant communities were then grouped into associations on the basis of soil type, and the associations were grouped according to the predominant plant species and the amount of water available to them, so the grouping proceeded from the most arid to the wettest environments.

The principal rival to the Zurich–Montpellier School was founded in 1921 by Gustaf Du Rietz (1895–1967) at the University of Uppsala, Sweden. The Uppsala School based its studies on observations that Du Rietz had made. He found that some combinations of plant species occurred more frequently than other combinations; he called these associations. There was usually a distinct boundary or narrow transition zone between an association defined by one dominant species and its neighbors. Patches of different associations sometimes occurred within the same habitat. Species that were not dominant occurred in some associations but not in others. In a word, the distribution of species appeared somewhat random. Du Rietz explained this as the result of competition between dominant species in adjacent associations. Competition led to the elimination of one of the species, but which would win depended on their relative abilities at reproducing in the surrounding associations where neither was dominant.

This implied that competition between plants could produce stable, long-lasting associations with quite different compositions. The Uppsala ecologists sampled areas of habitat by measuring out areas, called quadrats, commonly one square meter in area but larger in woodland, and counting every plant within the quadrat. Quadrats were marked out in random locations.

For a time the Zurich-Montpellier and Uppsala Schools offered alternative phytosociological systems, each with its own technical terms. This was obviously confusing, and the two approaches were eventually reconciled. The two schools still exist, but now they differ only in the emphasis they place on different aspects of their classifications. The Nomenclature Commission of the International Association for Vegetation Science now regulates the vocabulary used in phytosociology.

Gustav Einar Du Rietz was born on April 27, 1895, at Sandvik, Stockholm. He studied at the University of Uppsala, where he received his Ph.D. In 1934 he became professor of plant ecology at Uppsala. He died in Uppsala on March 7, 1967.