We have seen that succession of animal communi- 

 ties in humid climates passes through three terrestrial 

 stages before attaining climax : grass, shrubs and 

 scattered trees (forest-edge), and forest. In arid cli- 

 mates, the climax may be reached at the first or sec- 

 ond stage. It is important for us to examine each 

 community in more detail, therefore, if we are to gain 

 an understanding of the ecology of animals prevailing 

 locally in different parts of the world. 



VEGETATION 



Local Habitats, 



Communities, and 



Succession: 



Grassland, 

 Forests, and 

 Forest-edges 



Grassland vegetation differs from forests in 

 that the above-ground vegetation is completely re- 

 newed each year. Grasses may be divided into three 

 categories on the basis of height: tall grasses (1.5-3 

 meters tall ) , such as big bluestem and slough grass ; 

 mid grasses (0.5-1.3 meters tall), such as little blue- 

 stem and needle grass : and short grasses ( less than 

 0.5 meter tall), such as buffalo grass and grama 

 grass. The taller grasses grow in wet habitats, the 

 short grasses in arid habitats. Most native grasses 

 are bunch grasses in that they grow in clumps with 

 the areas between the clumps either bare ground or 

 occupied by other species. Broad-leaved herbs occur- 

 ring between the dominant grasses are called forbs. 

 A few species are sod formers in that their growth is 

 continuous over the ground surface. The leafy aerial 

 parts of perennial grasses die in the winter or in dry 

 season, leaving the underground stems or rhizomes 

 to propagate the plant the following year (Weaver 

 and Fitzpatrick 1934). 



Forests are composed of trees growing sufficiently 

 close together to dominate the entire area of ground 

 surface. In cold climates, forests are needle-leaved 

 evergreen ; in intermittently warm, moist climates, 

 they are broad-leaved deciduous ; and in continuously 

 warm, moist climates, they are broad-leaved ever- 

 green. In spite of these secondary differences in life- 

 form, the structure and internal dynamics of all forest 

 communities are quite similar. Useful methods for 

 measuring the density of trees per unit area are de- 

 scribed by Cottam and Curtis (1956). 



Between forests and open country, the trees are 

 often widely spaced and do not completely dominate 

 the area : open-country shrubs and grasses become 

 interspersed. This transition area is usually narrow 

 around the margins of a mature forest, but where 

 succession is occurring, large areas of shrubs con- 

 taining small or scattered trees are essentially forest- 

 edge in character. Likewise, in agricultural areas, 

 hedge and fence rows, or narrow strips of trees and 

 shrubs along streams, are really edges without the 

 adjacent forest. Essentially, forest-edges provide, in 

 close proximity, forest, shrub, and open ground habi- 

 tats which animals take advantage of in a variety of 

 unique ways. 



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