FORESTRY SURVEY 213 



forested area of map). The effective drainage of the 

 swamp has, no doubt, been the chief factor in allowing the 

 extension of the meadow swamp, which has become the hay 

 land of this region. 



Sherff states that under natural conditions the shrub 

 association would occupy an intermediate place between 

 the swamp meadow or the reed swamp associations and 

 the forest. Most of the shrubs and young trees bordering 

 the Skokie have been killed by the burning over of hay 

 land by many farmers in the late autumn. This would 

 account for the forests rising abruptly from the reed 

 swamp or meadow swamp associations, and also for the 

 recent inability of the forest to encroach upon the better 

 drained areas. 



A reed swamp, in an embayment from the main part of 

 the unforested Skokie area, in X. T. 1, 10 was the only 

 place where a complete and definite shrub association was 

 fotmd bordering the Skokie i^See Figs. 1. 2, and map). 

 Corn us stoloniferoy Cornits a mom urn, Salij^ discolor, 

 Salix (sp. ), Sambiicus canadensis and Tihurniim Jcntago 

 formed a definite zone between the swamp and the forest. 

 These same shrubs were found at the north end of the 

 island in X. T. 1, 23 and 26. 



b. The forested area. — The hydrarch succession of the 

 lowland is represented by two forest associations — the 

 hydro-mesophytic and the hydrarch mesophytic. The 

 former association, as will be seen in Fig. 3, usually 

 forms a zone about the shrub or swamp associations and is 

 characteristic of the wettest part of depressions where 

 trees will grow ; the latter association is found in the bet- 

 ter drained area adjoining the hydro-mesophytic associa- 

 tion. This sticcession probably reaches its fullest expres- 

 sion in the lowland, but it is also found in depressions of 

 the upland. 



The lowland area interpreted three ecological facts very 

 well. First, it exemplifieil how certain factors check the 

 progi-essive development of forests toward the mesophytic 

 climax forest of the region ; second, how other factors 

 hasten the development of pioneer associations toward the 

 mesophytic climax forest of the region ; third, how readily 

 a forest association can be determined by the amount of 

 available soil moisture. 



