An associational study of Illinois sand prairie . mer arid condiiionftook place; the xerophytic prairie formation of the sand hills there-fore v;aG changed little if at all. This partial history of the east-ern prairies is supported by a mass of evidence v/hich does not proper-ly belong in this account. This evidence is taken from the distri-bution of relict colonies of western and northern plants, from thepresent successional tendencies of our vegetation, and from our know-ledge of glacial and climatic history. If we accept this explanation of vegetational changes in the j past, we see at onc
An associational study of Illinois sand prairie . mer arid condiiionftook place; the xerophytic prairie formation of the sand hills there-fore v;aG changed little if at all. This partial history of the east-ern prairies is supported by a mass of evidence v/hich does not proper-ly belong in this account. This evidence is taken from the distri-bution of relict colonies of western and northern plants, from thepresent successional tendencies of our vegetation, and from our know-ledge of glacial and climatic history. If we accept this explanation of vegetational changes in the j past, we see at once that after and during the Wisconsin glaciation,the xerophytic grassland, which was then at its maximum development,must have covered most of Illinois south and west of the conifer mar- I gin, which never extended far beyond the terminal moraine. But itv/as at about the time that the sand deposits of the IllinoisRiver,and similar deposits of the Rock River and the Llississippi,were left uncovered by the diminishing streams. The xerophytic. 14 prairie vms therefore the original vegetation of the sand deposits,for it v;as the only vegetation near enough at hand for prairie v;as continuous in distribution front its present locationin the sand hills of the Y/est to central Illinois and much farthereast. It has persisted in the west because the arid climate has re-mained unchanged. It has persisted in the sand deposits of Illinoisbecause physical conditions of the soil, evaporation,and exposurehave been such as to keep out invaders not adapted to these conditionsThe kinship between the sand-prairie of Illinois and the sand-prairieof the west is shown in the pla,nts and in the animals. Many animalsreach the eastern limit of their range in the Illinois sand are not continuous in distribution, but occur in the sandareas and also in the west. Others may have been isolated in theIllinois area, and have become distinct geographic varieties. Zlnoughhas bee
Size: 1332px × 1875px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookidassocia, booksubjecttheses
