i 9 2o] CLAY BERG— UPLAND SOCIETIES 47 



especially where the soil is stirred up or the humus destroyed. It 

 has been said (3, g, 10) that this new association is not "lower" 

 than a forest, since it is new, but regression can be conceived as 

 meaning return to a stage where less use is made of the space and 

 light available. Furthermore, forest will finally replace such a 

 society, just as it blots out any naturally formed clearing. The 

 change here is toward a physically and physiographically youthful 

 aspect (rejuvenation of Cowles, 6). The surface soil gives the 

 prevailing tone to the society, being gray or yellow, powdery, and 

 nearly free of available water, radiating intense heat on a warm day. 



Into this xerophy tic habitat comes a clearing flora showing but a 

 limited number of species, among which Epilobium angustifolium L. 

 is dominant. Other species of importance are Sisymbrium altissi- 

 mum L., Erigeron canadensis L., Cirsium arvense Scop., and Ver- 

 bascum Thapsus L. Besides these occur also Sisymbrium canescens 

 Nutt., Lactuca scariola L., L. canadensis L., L. spicata Hitch., 

 Ambrosia artemisiifolia L., Gnaphalium polycephalum Michx., 

 Erechtites hieracifolia Raf., Sonchus as per Hill., S. arvensis L., 

 Erigeron annuus Pers., and E. ramosus BSP. 



Most of these species have a profusion of wind-borne seeds, and 

 they take possession by having seeds there, by resistance to harsh 

 conditions, by rapid growth, and by seeding profusely over the area 

 when once started, thus getting ahead of competitors. They are 

 finally shaded out by saplings. Certain species of Lactuca were 

 observed 3-4 m. tall, and while in "young" dry areas a society as 



\ 



scattered as in a desert may be found, in full development this 

 flora can form a positively impenetrable jungle, particularly on 

 hilly ground with a dirty terrain. Few societies in this region can 

 show such a wide variation of form corresponding with as wide a 

 range of environmental conditions. 



Thorn society. — Its species are natives of the region. This 

 society occurs much in natural clearings, but because artificial 

 clearings and cutovers are so much more numerous in this region 

 at present, the thorn flora is found mostly in such places. It is 

 dominated first by Rubus idaeus L., which is commonly succeeded 

 in turn by R. allegheniensis Porter. The latter can hold a patch for 

 years against saplings when pickers are numerous enough to 



