Chapter XI 



MAIN HABITATS, SUCCESSIONS, 

 AND CLIMAXES 



Whereas originally the term ' habitat ' referred simply to the place 

 (locality or station) in which an organism or community lived, 

 ecologists nowadays take it to mean rather the kind of place, involving 

 the sum of effective conditions (operative influences) characterizing a 

 particular type of area or inhabited by a particular species or com- 

 munity. Thus as a scientific term it involves all the conditions 

 affecting an individual or community that are incidental to the place 

 in which that individual or community lives, and we have to dis- 

 tinguish between the general habitat of a community and the partial 

 habitats of its component species, etc. These partial habitats may 

 vary greatly within the orbit of a single example of a single general 

 habitat. Thus with a Beech forest growing on a calcareous soil 

 under certain climatic conditions, there may be rather similar general 

 factors of soil and climate under which the dominant trees flourish 

 in different spots within the same area or even in different areas in 

 the same region. Very different may be, for example, the ' micro- 

 habitats ' of Mosses or Algae growing on their boles or branches, and 

 of herbs upon the forest floor. In the present treatment of the main 

 different types of plant habitats that are discernible, we shall have to 

 confine ourselves largely to general terms in showing how the factors 

 of the environment dealt with in the last chapter constitute the 

 habitats of the various types of vegetation to be treated in the next 

 five chapters. 



The habitat is thus made up of the many and various environmental 

 factors having any kind of influence upon life within it, and them- 

 selves interacting complicatedly. The sum of effective ecological 

 conditions has many widely different manifestations which range 

 for instance from dry land to open water : and indeed water con- 

 ditions seem to provide the best criterion for the primary subdivision 

 of habitats. But even as most biological pigeon-holing is notoriously 

 imprecise, involving many an arbitrary cut-off across a more or less 

 complete line of gradation, so is it with any of the main types of 



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