FORESTRY SURVEY 219 



elevation would mean better drainage, and hence a pro- 

 gression in the forest association which would evolve. 

 Contrasting the few large trees of Uhnus am erica na^ Tilia 

 ai)icrica)ia, and Qurrcus cJJipsoidalis, which were on a 

 slightly lower part of land adjacent to the island in X. T. 

 1, S, with the upland hydraich mesophytic trees which 

 were dominant on the island, these conclusions regarding 

 the retrogression of the forest by cutting and the progres- 

 sion of associations by drainage seem justitied. 



The small bit of hydrarch mesophytic woods in X. T. 1. 

 29 is of special interest, first, because it is the only place 

 in the newly acquired forest preserve in which the native 

 shrubs and herbs have been allowed to grow practically 

 unmolested, and thus where the forest is replacing itself; 

 second, because its tree population represents well the 

 transition from the lower hydrarch mesophytic forest type 

 to the higher upland hydrarch mesophytic type of forest. 

 All of the trees and practically all of the shrubs enumer- 

 ated under the typical hydrarch mesophytic forest were 

 piesent here. This forest ditfered from the typical 

 hydrarch mesophytic forest in having Qiierciis rubra and 

 Qiiercus aVba as the dominant tree species. Most of the 

 trees here were quite large. They were the trees remain- 

 ing after the removal of the larger trees from the virgin 

 forest. 



The hydrarch mesophytic forest northwest of Lincoln 

 Avenue in X. T. 7. 9 and 27 presented quite a different 

 aspect. It consisted almost entirely of second growth 

 trees from eight to fourteen inches in diameter. This for- 

 est consisted of an almost pure sand of Qucrcus cUipsoi- 

 dalis. 



The study of the lowland forests has indicated qtiite 

 clearly that the forest type is very closely associated with 

 the moisture content of the soil. It has also illustrated 

 how cutting, grazing and fire have caused retrogression in 

 the development of the forest successions toward the 

 climax mesophytic type ; and how drainage may cause the 

 hastening of hydrarch successions towards this mesophytic 

 type of forest succession. 



The diagram (see Fig. 5j well illustrates the approxi- 

 mate order in which trees were found in the hydrarch 

 succession of the lowland. 



