12 



of sand are no longer operative. The climatic factors of temperature 

 and rainfall since the time of the amelioration of the climate, have 

 made the forest the dominant plant formation of the region. The 

 forest has developed, in certain places on the sand, to a transitional 

 mesophytic stage, which Gleason has called the mixed forest. This is 

 best developed along the marginal ridge, probably indicating that the 

 forest was established along the river first (PI. V). The forest 

 on both sides of the Black-jack Ditch flat (see PI. I) has not, over 

 most of its area, developed iDeyond the black-jack stage. The forests 

 near Manito and Forest City are largely black oak. The climax as- 

 sociation toward which the forest development is tending is not 

 known, but it is thought from comparison with the forested dunes at 

 the lower end of Lake Michigan, which have reached the climax 

 beech-maple-red oak stage, that the mixed forest will ultimately de- 

 velop into the red oak-hard maple forest. The red oak is present now 

 in small numbers, and the herbaceous plants forming the ground cover 

 are more or less indicative of advancing mesophytism. 



The development of the sand prairie in its gradually firmer con- 

 trol of the environment may be measured by the increasing amount 

 of humus in the soil, and by the decreasing degree of openness of the 

 vegetation. There are all gradations, from the bare, almost pure, 

 sand of the blowout associations to the dense sod-like structure of the 

 black-soil transition stage (p. 80) with its dark brown soil which ap- 

 approaches a sandy loam. When the bunch-grass approaches its opti- 

 mum development, the soil has become dark with humus, the dense 

 tufts of grass have crowded together, eliminating almost entirely the 

 spaces of bare sand between them, and the cactus has been almost en- 

 tirely superseded by grasses. The earlier stages of this successional 

 series take a very long time to complete, and there is constantly the 

 danger of accident resulting in wind control. Over many parts of the 

 sand region the bunch-grass has passed the danger of blowing, and 

 such areas are usually under cultivation at the present time. Much of 

 the country in the neighborhood of the Devil's Neck, among other 

 places, is cultivated, though here and there spots of sand are found 

 which are still subject to wind action. There are a great many hedges 

 in the sand region. These stop the drifting of the sand temporarily, 

 but it soon piles up against the barrier, sometimes even reaching the 

 height of the hedge, burying it and the field beyond. In any event, it 

 does little good to encourage dune fonnation, as sand is much more 

 easily stabilized when level. Agricultural methods should rather favor 

 a gradual modification of the soil by plowing in the straw (only the 

 head of the grain being removed in harvesting) and by top-dressing 



