Description
The Nature Conservancy has developed a standardised hierarchical system to facilitate the identification and classification of vegetated terrestrial communities (Schneider et al. 1997; NatureServe 2000). The upper hierarchical levels (class and subclass) are based on vegetation structure, height and leaf form; the middle levels (group and formation) are based on climate, hydrology and leaf form; the lowest levels (alliance and association) are based on floristic composition of the uppermost strata (alliance) and total floristic composition (association). An important aspect to the classification is that the community elements are related to a set of environmental factors rather than to a particular site, allowing the classification to have ecological meaning over a broad geographical range. The lowest level of the hierarchy (the plant association) has a definite floristic composition and uniform physiography, and represents uniform habitat conditions. Habitat refers to the...