of-view. We are, in this book, using the biome 

 system, the various parts and concepts of which will 

 unfold as we proceed. We will consider the com- 

 munity as being at least analogous to an organism in 

 being a functional unit of interacting parts and hav- 

 ing some degree of structural uniformity. Although 

 community-types are certainly not highly discrete and 

 absolute units, recognition and naming of them is one 

 way of indicating positions in the continua along en- 

 vironmental gradients that are occupied by particular 

 aggregations of plant and animal species. 



Physiognomy 



The gross structure of a community or its phys- 

 iognomy is an important basis for its recognition. In 

 terrestrial communities, physiognomy is determined 

 by the life forms of the dominant plant species and 

 their spacing. The life forms that prevail in a given 

 area depend on the climate and sometimes the sub- 

 strate or other special features of the habitat and give 

 character to the landscape. The distribution of ani- 

 mal communities is closely correlated with the struc- 

 ture of the vegetation, hence these vegetation-types 

 need to be recognized and defined : 



Desert : hot, arid habitats with scattered scrubby 

 or thorny vegetation or, in extreme cases, 

 none. 



Steppe, plains : semi-arid grassland covered with 

 short grasses. 



Prairie : semi-humid grassland covered with mid- 

 and tall grasses. 



Chaparral: semi-arid areas covered with bushes 

 and shrubs, usually broad-leaved evergreen. 



Savanna : grassland with scattered groves of trees 

 or shrubs. 



Woodland: open stand of small deciduous or 

 evergreen trees with undergrowth of grass- 

 land or desert vegetation. 



Forest-edge : mixture of trees, shrubs, and open 

 country, ordinarily occurring as a narrow belt 

 on the margin of forests. 



Forest : closed stand of trees forming a continu- 

 ous canopy over most of the area. 



Deciduous forest : broad leaves fall during cold 

 or dry seasons. 



Broad-leaved evergreen forest : no regular sea- 

 son of leaf fall, leaves often sclerophyllous, 

 warm climates. 



Rain forest : tall luxuriant forests, often with sev- 

 eral strata of trees, foliage retained through- 



FIG. 3-4 A mixed deciduous-coniferous plant community (after Dansereau 1951). Above, a semi-realistic diagram of the community; 

 below, symbolic structure of the community depicting life-form, size, function, leaf type, and texture. 



"WWW Um^ 



28 Background 



