MESOPHYTE SOCIETIES. 2-±3 



171. Thickets. — The mesophyte thickets are not so 

 abundant or impenetrable as the xerophyte thickets. 

 They seem to be developed usually as forerunners of forest 

 vegetation. An illustration of this fact may be obtained 

 by noting the succession of plants which appear on a 

 cleared area. After such an area has been cleared of its 

 trees, by cutting or by fire, it is overrun by herbs which 

 develop rapidly from the seed. Sometimes these herbs are 

 tall and with showy flowers, as the so-called fire-weed or 

 great willow herb. Following the herb societies there is a 

 gradual invasion of coarser herbs and shrubby plants, 

 forming thickets, and finally a forest growth may appear 

 again. 



In arctic and alpine mesophyte regions the willow is 

 the great thicket plant, often covering large areas, but in 

 temperate regions willow thickets are confined to stream 

 banks and boggy places, being the characteristic hydro- 

 phyte thicket form. 



The upland and flood-plain mesophyte thickets of tem- 

 perate regions are different in character. For example, 

 the upland thicket of the Northern States very commonly 

 contains hazel, birch, and aspen as dominant plants ; while 

 the flood-plain thicket is apt to contain, in addition to 

 these, prominent growths of haws and wild crab-apples. 

 In this same region pure thickets frequently occur — that 

 is, thickets in which a single form is the prevailing type, 

 as pure hazel thickets on uplands, or pure haw thickets on 

 flood-plains. 



In the Southern States the plants enumerated above 

 may not be the characteristic mesophyte thicket plants. 

 For example, in Kentucky and Tennessee the dominant 

 thicket plants are persimmon, locust, redbud, and 

 sassafras. 



172. Forests of temperate regions. —Deciduous forests 

 are especially characteristic of temperate regions. The 

 deciduous habit, that is, the habit of shedding leaves at a 



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