SUCCESSIONS ON CLAY OR CLAY-GRAVEL 223 



(Rhvs), the pin cherry and choke cherry (Prwms pennsylvanica 

 and P. virginiana), sassafras (Sassafras variifolium), and the maple- 

 leaved haw (Viburmim acerifolium) . There are also many her- 

 baceous plants such as goldenrod (Solidago sijeciosa and S. hisjnda) , 

 the milkweed and butterfly weed (Asclepias syriaca and .1. tnherosa), 

 the prickly pear (Opuntia Rafinesquii), and the false Solomon's seal 

 (Sviilacina racemosa and S. steUata). 



The black oak community may persist for a rather long time but 

 is gradually replaced by a more mesic oak community in which the 

 red oak (Quercvs rubra) is a prominent dominant. Finally the 

 habitat reaches the highest degree of mesism, a thick layer of humus 

 has formed over the sand, the water-holding capacity of the soil has 

 greatly increased, the evaporation rate has decreased, and the 

 climax forest, dominated by the beech (Fagus grandifolia) and the 

 sugar maple {Acer saccharum), appears and persists indefinitely 

 unless destroyed by one means or another. 



136. Successions on Clay or Clay-gravel.— The clay-gravel suc- 

 cessions that are best known are those that take place on glacial 

 deposits. These have been studied in various places in the north- 

 eastern quarter of the United States and in southeastern Canada. 

 The glacial deposits throughout these regions are very variable, 

 some areas being almost pure clay and others consisting of more or 

 less complex mixtures of clay, gravel and other materials. They 

 are practically all occupied by plants at the pres^ent time so that 

 opportunities for actually observing primary successions in the early 

 stages are extremely rare. The best that are available for this pur- 

 pose at present are the striplands of Illinois, Indiana and Ohio where 

 the vegetation has been completely destroyed in the process of 

 surface coal-mining. 



As a result of stripping the soil is left as bare alternating ridges 

 and furrows, the ridges varying from 3 or 4 feet to 30 or 40 or more 

 feet in height (Fig. 100). In many cases these areas are left undis- 

 turbed for a long term of years and their revegetation takes place 

 without any artificial interference. In Vermilion County, Illinois, 

 these striplands are mostly on bottomland areas along streams. 

 Here the pioneer plants are usually annual and perennial herbs. 

 In the bottoms of the furrows the knotweeds {Polygonum aviculare 

 and P. pcrsicaria) arc often the dominant and sometimes the only 

 plants. In the more shallow furrows the barnyard grass ( Eckinochloa 

 crvsgalli) takes the place of the knot weeds or occurs along with 

 them, and often scattered individuals of the giant ragweed {Ambrosia 



