134 -^ ^' Clements 



To obtain a glimpse of the hardwood dimax that covered the 

 region before this time, it is desirable to turn to the outposts or, 

 better, the rear guards of the great deciduous forest of the East 

 as they exist today. Of the dominants of the three associations, 

 only a few fail to reach eastern Nebraska and Kansas on the 

 north and Texas on the south, and most of them belong to the 

 more eastern oak-chestnut community, namely, Castanea den- 

 tata, Quercus fn-inus, and Liriodendron. By contrast, 25 are 

 found today at the edge of the oak-chestnut association and 

 some of these extend well beyond it in relict areas. In this list 

 are Acer saccharum and Fagus americana, 10 species of Quercus, 

 6 of Hicoria, 2 of Tilia, and one each of Magnolia, Per sea, Pru- 

 nus, Aesculus, and Nyssa. The sugar maple still persists in the 

 l^ cool recesses of Caddo Canyon in central Oklahoma, Quercus 

 texana and acuminata linger in the mountain ranges of western 

 Texas, minor grows as a shrub in the sandy plains of the Pan- 

 handle region, macrocarpa survives around the Black Hills as 

 well as in northeastern Wyoming, and Liquidambar occurs 

 south of Texas to the highlands of Guatemala. 



Among the important subdominants of layers or margins, 

 nearly all are to be found from eastern Nebraska to Texas, 

 namely, Carpinus, Ostrya, Asimina, Cornus, Diospyrus, Morus, 

 Sassafras, Ilex, Rhamnus, Madura, Crataegus, and Malus. Car- 

 pinus caroliniana persists as a relict in the mountains of southern 

 ^ Mexico and Central America; Ostrya virginiana is represented 

 by a single outpost, 0. \nowltoni, at the Grand Canyon; Morus 

 celtidifolia occurs in southern New Mexico and Arizona, stretch- 

 ing southward in the mountains from Mexico to Peru; and 

 Ulmus reaches northwest Nebraska as the species thomasi and 

 western Texas as crassifolia. Such important serai dominants as 

 Ulmus, Celtis, and Fraxinus follow the rule in persisting far 



