plant association (association) A term loosely applied in the classification of vegetation communities and given varying interpretations in different phytosociological traditions, with resulting confusion. The current most widely accepted usage follows the Zurich–Montpellier school. In this, the association is the basic vegetation unit, an abstract entity, floristically defined from field data or relevés. Each association has a distinctive faithful species and a group of high-presence or constant species which give the community or association a cohesive structure. Often these companion species of the association form the faithful species of the next and succeeding hierarchical levels, alliances, and orders into which similar associations are grouped. In British and American traditions, ‘association’ has tended to imply a community with physiognomic as well as floristic unity, usually a climax community in which the species dominants are those of the upper vegetation layer. In this tradition an association usually has several co-dominant species. The term ‘consociation’ is reserved for single-species dominance. See also FORMATION and PHYTOSOCIOLOGY.

plant association(association)
1. In the Zurich–Montpellier school, the basic unit of vegetation, an abstract entity that is defined floristically from field data or relevés. Each association has a distinctive faithful species and a group of constant (i.e. high-presence) species which give it a coherent structure. The companion species of the association often form the faithful species of the next and succeeding hierarchical levels, alliances, and orders into which similar associations are grouped.

2. In the British and American phytosociological traditions (see phytosociology), a community that is united physiognomically as well as floristically; commonly it is a climax community in which the species dominants are those of the upper vegetation layer. There are usually several co-dominant species; if there is only one dominant the community is called a ‘consociation’. See also formation.