CHAPTER XVI 



PLANT CO]\BIUNITIES 



Plants do not ordinarily live alone like hermits but are found 

 growing along with other plants in communities that usually con- 

 sist of many individuals (Fig. 80). When an ecologist goes into a 

 forest he does not see merely a number of trees, shrubs, and her- 

 baceous plants with no relations one to another except that they 

 happen to be growing in close proximity. What he sees is a plant 

 community which is just as simple and understandable but with its 

 multitude of activities just as complex, just as inevitable in its 

 structural make-up but with its succession of life problems just as 

 intensely interesting as any city or other community dominated by 

 the genus of bipeds to which we belong. 



The kinds of plants that one may expect to find in any com- 

 munity depend upon the factors of the environment, for just as we, 

 in order to live and be healthy, must have homes that are adequately 

 supplied with heat, light, water and food, so the plants in their homes 

 are affected by these same factors of the environment. For this 

 reason various kinds of plants that require the same type of environ- 

 ment are habitually found living together in the same community. 

 So true is this that often when an experienced field man sees a cer- 

 tain species of plant he almost instinctively looks for other species 

 that he has learned are usually associated with this one. 



The ecology of plant communities is called synecology and will be 

 discussed in this and the following five chapters. 



114. The Plant Community an Organism.— The individual plants 

 that make up a plant community are living together in a state of 

 social disjunctive symbiosis but they are so intimately associated 

 that the community as a whole may be considered as an organic 

 entity; that is, an individual organism. Ecologists are not in com- 

 plete agreement that it should be so considered but the idea has 

 slowly but steadily grown in favor during the past quarter of a 

 century and we shall see that it is perfectly logical. As an individual 

 the plant community is born, it grows and develops, it matures, 

 reproduces, and may finally die like any other organic individual. 



If we consider the plant community as an individual organism 

 then we recognize three distinct types of individuals. The first of 

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