FOREST SOCIETIES. 535 



are occupied by an arctic-alpine flora of mosses, lichens, heaths, 

 etc., or the higher ones are snow-clad, while in the southern Alle- 

 ghanies the highest mountains are often clad to the summit with 

 spruces and firs (balsam). Mt. Mitchel, in North Carolina, the 

 highest mountain (6711 ft.) east of the Rockies, is clothed to the 

 summit with spruces and firs, while pines and deciduous trees 

 are on its slope. 



1014. Forests of the Canadian zone. The forests of the Ca- 

 nadian zone are similar, but have some species which do not 

 reach so far north as the spruces and firs, especially some of the 

 pines, the hemlock, spruce, and deciduous trees, but the conifers 

 outnumber the latter. 



III. Austral Forests. 



1015. The forests of the Austral region show greater varia- 

 tions and do not form transcontinental belts because of the barriers 

 presented by the arid interior portion of the United States, the 

 high Rockies, and probably because of the peculiar temperature 

 conditions of the Pacific coast, where a " low summer temperature 

 combined with a high sum total of heat" permits a wider range 

 and mixing north and south of boreal and austral types. 



1016. Deciduous forests of Alleghanian and Carolinian areas. 

 The highest development of the deciduous forest in North 

 America is in the Austral region, principally in the humid Alle- 

 ghanian and Carolinian areas of the same. In the former are the 

 oaks, hickories, chestnuts, locusts, ashes, birches, aspens, the 

 northern spruces, firs, hemlocks, pines, and other coniferous 

 trees found farther south. In the latter are the tulip-tree or 

 whitewood, cucumber-tree, persimmon, sweet gum, sourwood, 

 chestnut oak, Spanish oak, and yellow and scrub pine. 



1017. Autumn colors. One of the striking effects produced 

 by the deciduous forests is that of the autumn coloring of the leaves. 

 It is more pronounced in the forests of the United States than in 

 corresponding life zones in the eastern hemisphere because of the 

 greater number of species. With the disintegration of the chloro- 



