214 ILLINOIS ACADEMY OF SCIENCE 



The forests in this region are all second growth. The 

 primary factors which caused retrogression were fire, cut- 

 ting and grazing. Aside from the checking of the advance 

 of the forest upon the Skokie region, fire destroyed the 

 dead leaves, thereby preventing the building up of the 

 land and the development of a more mesophytic vegeta- 

 tion. The effect of cutting varied. Where an area was 

 clear cut, the period of recovery has been a long one. In 

 areas where only the larger trees were removed, practi- 

 cally the original type of forest was preserved, if the under- 

 growth was allowed to remain. The pasturing of woods, 

 next to clear cutting, was probably one of the most retro- 

 gressive agencies in this region, because it prevented the 

 reproduction of the forest. Observation seemed to indi- 

 cate that drainage in the region of the hydrarch succession 

 would, if done gradually, hasten the development of the 

 forest toward the mesophitic climax. 



(1) Hydro-mesophytic association. — The area best 

 illustrating the hydro-mesophytic forest was the low 

 swampy depression in N. T. 1, 13 and N. T. 1, 5 and 12, 

 There was one large pond in N. T. 1, 13 and several small 

 ones in N. T. 1, 5 and 12. It is the area to the west of this 

 larger pond which concerns us in the study of the early 

 phases of the hydrarch succession. The slope to the east 

 of the pond was steep and the upland forest came to the 

 very edge of the pond. In October there were a few inches 

 of water in the pond and the growth of aquatic plants in 

 it was quite dense. In the more shallow parts of the pond 

 and toward the outer edge to the west were the reed swamp 

 and the shrub associations. The shrubs found were those 

 typical of undrained depressions, Cephalanthus occiden- 

 talism Salix discolor, Salix (sp.), Rosa Carolina and Vi- 

 hiirnum lentago. These shrubs were the same as those 

 bordering the Skokie. Immediately succeeding the shrubs 

 and forming a border about the west edge of the pond 

 was the forest association represented by Fraxinus nigra, 

 and Fraxinus pennsylvanica. Continuing on the area, 

 rising in places above the level of the swampy area, and 

 west from these were Quercus hicoJor, JJlmus americana, 

 Fraxinus americana, Quercus macrocarpa, Quercus ellip- 

 soidalis, etc. In every case, whether it was in the depres- 

 sions of the upland, or the lowland, these trees occurred in 

 the same order in relation to the amount of available 

 water. 



