350 A TEXT-BOOK OF BOTANY 



Following the herb associations, there is a gradual invasion 

 of coarser herbs and shrubby plants, forming thickets; 

 and finally a forest growth may appear again. 



214. Deciduous forests. Deciduous forests are especially 

 characteristic of temperate regions, the deciduous habit 

 being an adaptation to the regular recurrence of winters. 

 How the conifers contrast with the deciduous trees in this 

 regard has been described ( 19). The method of shedding 

 leaves ( 18), the characteristic autumnal coloration ( 18), 

 and the cultivation of the vernal habit by certain asso- 

 ciated herbs ( 27) have all been considered. The decidu- 

 ous forest is known as the climax vegetation of the temper- 

 ate regions, replacing all other associations if the conditions 

 become favorable. Even a forest of conifers is gradually 

 replaced by a deciduous forest when the conditions become 

 mesophytic. 



Deciduous forests may be pure or mixed. A common 

 type of pure forest is the beech forest, which is a dark for- 

 est, the wide-spreading branches of neighboring trees over- 

 lapping so as to form a dense shade (Fig. 315). In such 

 a forest, therefore, there is little or no undergrowth. An- 

 other pure forest, which belongs to drier areas, is the oak 

 forest, which is a light forest, permitting access of light for 

 lower plants (Fig. 316). In such a forest, therefore, there 

 is usually more or less undergrowth. The typical American 

 deciduous forest, however, is the mixed forest, made up of 

 many varieties of trees, such as beech, oak, elm, walnut, 

 hickory, maple, gum, etc. 



Deciduous forests may be roughly grouped also as up- 

 land and flood-plain (river bottom) forests, the former being 

 less luxuriant and containing fewer types, the latter being 

 the highest type of forest growth in its region (Fig. 317). 

 A few general illustrations may be given, which will en- 

 able the student to characterize the forests of his neighbor- 

 hood. 



