BOTANICAL SURVEY— SUGAR GROVE REGION 281 



The uplaiul oak forest originally covered a large part of the coun- 

 try, but it is very much restricted at present. Its boundaries coincide 

 with the limits of arable soil. It has therefore been largely cleared 

 away and is now to be found only in remnants around the borders of the 

 fields. Its composition has, moreover, been greatly modified by the 

 operations of the woodcutter, who has cut out the more valuable timber, 

 leaving behind the inferior sorts to replenish the forest. As a result 

 of this kind of luml)ering the fascies through most of the oak forest 

 has become the worthless black oak {Que reus velutina). 



The two types of upland forest which have been described are the 

 extremes between which are all intermediates. Most of the upland 

 forest seen in the area, indeed, belongs to neither the one nor the other, 

 hut varies in composition, now approaching one now tln^ other. For 

 this reason and because it meets and intergrades with almost all of 

 the other associations of the area, the oak forest is the most difficult 

 of them all to characterize satisfactorily. The most noteworthy of these 

 transitions, perhaps, is to the Liriodendron forest of the lowlands, with 

 which it gradually merges at the heads of the ravines. 



The Talus Asse)eiati(>u. The plant society covering the talus slopes 

 at the bases of cliffs with south exposure is closely similar to the oak 

 forest of the uplands. It should be explained, however, that the talus 

 slope is very different from an ordinary talus slope. It is not made up 

 of fragments of fallen rock, but of sand, which rattles down from the 

 cliffs together with considerable amounts of vegetal)le debris which, 

 on account of the porous character of the soil, are to a large extent 

 oxidized directly without humification. The vegetation of these slopes 

 differs froDi the oak forest principally in an admixture of plants from 

 the rocks. Qaercus prinus is more abundant and is accompanied by 

 Casfanea dentata, Betiila lenta, Mitchella repens, and Gaultheria pro- 

 cumhens. 



THE ROCK DWELLING PLANTS 



Beside the forests, the most considerable body of vegetation is that 

 which occupies the rocks. For the most part, however, the plants of 

 the rocks can be better considered as individuals than as oi-ganized into 

 definite associations. This is not only because the plants are so far 

 apart that they could in any case be understood to form only a very 

 open association, but also because many of the crevice plants are so 

 erratic in their occurrence that there is no very definite composition 



