Relationships Between Characteristics of Plant Communities and Climatic Conditions at Qara Soo Catchment Area, Gorgan.

In order to understand the relationships between climatic factors and the biological variables of plant communities in the qara soo catchment area, a systematic sampling of natural plant community variables such as crown closure, diversity, reproduction rate and crown height has been taken. information about physical components of the ecosystems such as climatic elements, soil properties and topographic characteristics was also collected for each plant community. by using the numerical taxonomy model suggested by sneath and sokal (1963), the plant communities were classified and sorted according to a “development index” which indicates the plant community development toward the climax stage of ecosystem. then the relationships between ecosystem physical components and the biological variables of communities (development index) were understood by using a multiple regression model. it was concluded that climatic elements are the dominant factor affecting on the formation, distribution, reproduction and stability of plant communities in the area. it was further concluded that the numerical taxonomy model, which has been commonly used by social scientists, is a suitable tool for system analysis in plant communities and natural ecosystems.