Principles concerned in the formation and classification of communities

Characteristics of species that are important in the formation of plant groupings are classified as basic principles, as follows: Every species has certain relations to the physical environment: (a) essential requirements, (b) range of ecological amplitude, (c) capacity to utilize available resources. Every plant has relations with other organisms: (a) competition, (b) association of species, (c) reproduction and dispersal, (d) changes in relations because of grazing, mowing or other disturbance, (e) parasitism, (f) mutualism and commensalism. The ecological success of a species or a population depends upon its capacity to cope with its physical environment and associated organisms in relationships, such as those stated in these principles. Groupings of species in stands or communities are formed because of similarities and differences among them with regard to these principles and because of similarities and differences in habitats. The best descriptions are based upon analysis which reveals intrinsic characteristics of the stands. The more detailed and accurate the analysis, the more valuable is the description. Stands that show the greatest number of characteristics in common may be grouped into community types or abstract communities of various kinds. Precise similarity of stands in each kind of type is not essential. Various classifications of stands and community-types may be made, depending upon the purpose to be served. Some of the bases of classification are: similarities and differences in composition and structure, or in complexity of communities; relations to habitat, succession or geographic distribution; physiognomic appearance; and economic values. Each of these is discussed with examples.