6 Illinois Natural History Survey Circular 49 



such as the bluestem grasses and goldenrod, and still later by shrubs 

 and small trees such as the red haws. After perhaps hundreds of 

 years, the deciduous hardwood trees may colonize the small tree com- 

 munities, and eventually the forest may be re-established. 



This Dunesland area that is of such great interest to us repre- 

 sents a set of these colonizing communities. It is no ordinary set. 



The first pioneer plant community growing on newly created 

 sand bars or ridges consists primarily of two annual plants, the wild 

 mustard called Cakile and the cocklebur called Xanthium. This com- 

 munity is soon followed by one dominated by perennial plants, 

 including (alone or in combination) the sand-binding grass called 

 Calamovilfa, fig. 5, the dune willow and the sand cherry, fig. 6, the 

 creeping juniper, and the upright juniper. After the dead roots and 

 leaves of these plants have added a slight amount of humus to the soil 

 or stabilized the shifting sand, the bearberry and some of the bunch 

 grasses can grow on it. The roots and foliage of these plants add 

 more humus to the soil, after which still other plants can grow on 

 the area. This plant succession often results in extensive prairies 

 dominated by little bluestem and big bluestem grasses, intermixed 

 with a wide variety of other herbs, especially species of blazing star 

 or Liatris. In this succession, the later sets of plants crowd out and 

 replace the preceding sets. The process of adding humus to sand is 

 slow, and some botanists estimate that it may take up to several 

 hundred years to progress from bare sand to a black oak forest and 

 over a thousand years more for a black oak forest on sandy soil to 

 change gradually into a deciduous forest typical of the temperate zone. 



The wet swales of the Dunesland, as well as the ridges, have a 

 succession of plant communities, but they have components different 

 from those on the ridges. Although the soil of these swales appears 

 to be mucky, it is chiefly sand. The first pioneer communities on the 

 swales are dominated by sedges, rushes, or marsh grasses. Next come 

 shrubs, such as dwarf birch and roundleaf dogwood. Many of the 

 older swales containing more humus are dominated by several kinds 

 of marsh-inhabiting willows and by cottonwood. Finally, as these 

 areas fill up or become better drained, plants of the deciduous forest 

 gradually invade them, and a black oak forest emerges, fig. 7. 



Looking at this process backwards gives rise to some intriguing 

 questions. If this type of natural change called succession leads 

 always from sand, meadow, and swale communities to forest, some 

 other kind of process must have been operating in order to produce 

 the areas of bare sand that resulted in the present Dunesland strip 

 of sand. Investigation proves these processes to be those that bring 



