relatively few species with wide-spreading, umbrella-shaped 

 crowns as much as 80 ft in diameter that do not touch one an- 

 other. The middle layer at 50 to 120 ft contains many species 

 with small, rounded crowns up to 33 ft in diameter that occasion- 

 ally come into contact. The lowest stratum, as high as 50 feet, is 

 limited in the number of trees that are restricted to this level, but 

 contains many young individuals belonging to species character- 

 istic of the two upper layers. The crowns are often small and 

 conical with larger leaves than the taller trees, and they form a 

 closed canopy bound together by climbing plants. The shrub 

 layer, containing mostly young trees and a few shrubs, is poorly 

 defined. The herb layer, not over 3 ft high, is even more poorly 

 deliniated and in places is missing. The ground layer is missing 

 entirely.^ ''° 



In the Mixed Mesophytic Forest region of the Cumberland 

 Mountains, and in the southern Allegheny Mountains and adja- 

 cent territory, the top layer of trees varies in composition in dif- 

 ferent areas. The dominants in this region total about 25 species 

 and include the beech (Fagus grandifolia), tulip tree {Linodendron 

 tulipifera), basswood {Tilia heterophylla, T. Jlondana, T. neglecta), 

 sugar maple {Acer saccharum), sweet buckeye {Aesculus octandra), 

 and white oak {Quercus alba). In the lower tree layer are found 

 dogwood {Comus florida), magnolia {Magnolia tripetala, M. macro- 

 phylla), redbud {Cercis canadensis), blue beech {Carpinus caroliniana), 

 hornbeam {Ostrya virginiana), holly {Ilex opaca), striped maple {Acer 

 pennsylvanicum), and others. Many species are found in the shrub 

 layer, such as Lindera benzoin, Hamamelis virginiana, Asimina triloba, 

 Hydrangea arborescens, and Cornus alternifolia. The field layer is very 

 rich in herbs which are favored by the mull humus developed 

 from leaf litter of the trees, and the spring aspect is noted for 

 conspicuous flowering plants such as Trillium grandiflorum, T. erec- 

 tum, Viola spp., Sanguinaria canadensis, and Erythromum americanum. 

 In late summer and autumn, the fall asters {Aster cordifolius, A. 

 divaricatus) and goldenrods {Solidago caesia, S. lalifolia) come into 

 bloom. 22 



Stratification in a jack pine community in Quebec, a stage fol- 

 lowing a forest fire, consists of four layers. The upper layer 



Analytic CHaBracteiristics of the Community • 83 



