An associational study of Illinois sand prairie . irie plants are efficient dune formers,and these species are quite com^ion in the deposit association. Theprincipal species are Rhus canadensis var. illinoensis, Fanicum vir-gatum, and Tephrosia virginiana. A Rhus dune, the side of which isbeing undermined by a large blowout, is shown in Figure 9 (p. 6I) .The process of dune-formation at the lee side of blowouts is now wellshown near the Havana region; the deposit associations are not typi-cal, and so very little study has been given them. A study of theanimals of the association was not even a
An associational study of Illinois sand prairie . irie plants are efficient dune formers,and these species are quite com^ion in the deposit association. Theprincipal species are Rhus canadensis var. illinoensis, Fanicum vir-gatum, and Tephrosia virginiana. A Rhus dune, the side of which isbeing undermined by a large blowout, is shown in Figure 9 (p. 6I) .The process of dune-formation at the lee side of blowouts is now wellshown near the Havana region; the deposit associations are not typi-cal, and so very little study has been given them. A study of theanimals of the association was not even attempted, but the generalcharacter of the assemblage is transitional between the animals ofthe blow-oand and those of the bunch-grass. Future work in the othersand areas should include a study of this association. The deposit association is acted upon by tvro tendencies - thestabilizing action of the vegetation and the destructive action ofthe v/ind. The succession proceeds in either direction, depending uponwhich set of conditions 73 SUCCESSIONAL RELATIONSHIPS IN THE SAND-PRAIRIE. Most of the Illinois River sand area was covered originallyby the tunch-grass. The natural proceee of vegetative developmentcaused a gradual change in part of the area, until the climax stagewae reached. In other places, where the exposure to the wind isconsiderable, the sand between the tufts of grass is blown away, andthe Panicum pseudopubeecens association results. Continued windaction in parts of this association results In the formation ofblowouts. The successions between the basin and the blowsand asso-ciations, and between the blowsand and the deposit associations,may take place in either direction. The confluence of a number ofblowouts may cause the development of large sand wastes. Thesemay also result from accidental causes. Stabilization by thebunch-grass may occur in any association of the blowout formation. The forest formation succeeds the sand-prairie either throughthe b
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