comprising many species of herbs, lichens, and mosses. This ele- 

 ment is present also in Iceland and Greenland as well as being 

 widely distributed in North America.*'^ 



CLIMAX 



It has been mentioned that the culmination of a directional 

 change is a steady-state, climax community in which no further 

 directional change takes place under the prevailing environ- 

 mental conditions. This is the terminus of habitat and vegetation 

 development. The climax will be discussed because the ability to 

 determine whether a community is a successional or a climactic 

 one is important. 



The criteria of a climax community serve primarily to differ- 

 entiate it from a successional community. The differentiation is 

 both subjective and relative, so that the criteria cannot be highly 

 specific. Each criterion is independent, to a degree, of the other 

 criteria. Furthermore, each may have enough exceptions so that 

 it cannot be employed to the exclusion of the others. The criteria 

 must be used with a degree of subjectivity dependent upon the 

 skill and judgment of the investigator. 



The climax community is in the steady-state with respect to 

 productivity, structure, and population, with the dynamic bal- 

 ance of its populations dependent upon its respective site. The 

 community has a maximum diversity, relative stability, and 

 homogeneity of the species populations within and between the 

 stands of a given climax type. Each stand is self-maintaining 

 and relatively permanent. The stand persists for a long time with 

 little or no change (Figures 5-8 and 5-8A). Any change consists 

 of an interplay of populations, i.e., fluctuation change, even 

 though replacement on a microcommunity basis may be a phasic 

 cycle. There is neither a beginning nor an end of such fluctuation 

 change in time. The given climax type is characterized by its 

 physiognomy or homogeneity in appearance within and between 

 stands. However, a maximum of spatial stratification can be ex- 

 pected, and this balanced structure of several growth-forms and 

 maximum diversity of species provides a system which apparently 



Habitat Patterns, CHanges, and Clinmax • 159 



