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The functional role of Rhus copallina in the tension zone between forests and prairies and the mechanisms which allow clones of this species to replace climax tallgrass prairie were studied in the cross—timbers region of north—central Oklahoma. Measurements and observations indicated that bottomland forest trees were unable effectively to invade climax tallgrass prairie without the prior invasion of R. Copallina or other shrubs. Upland forest tree species, however, were frequently able to invade climax prairie, but these invasions were enhanced by the prior invasion of shrubs. The entry and growth of clones of R. copallina into climax prairie was characterized by a reduction in the density of prairie vegetation and a concomitant increase in tree seedlings, shrubs, and herbs which comprised the nearby hardwood forests. Growth ring counts of nine clones revealed an average rate of encroachment of 1.25 m/yr. The reduced fire frequencies (relative to primeval prairies) on the study area tended to favor the gr...

The root habits of plants of various environments have been investigated by different workers but no one seems to have examined those of a group of woody species which occur very frequently in old fields in southern Indiana. A study of the root systems of the woody plants of such communities seems, therefore, to have promise of interesting and valuable results. In Europe root studies have been attacked rather vigorously. Biisgen and Munch ('29) give an excellent summary of the work done. In this country Cannon ('11) made a thorough study of the roots of desert plants. Weaver ('19) gave another valuable contribution to our knowledge of roots. Weaver and Kramer ('32) described the invasion of trees into grassland in eastern Nebraska. The dry prairie is slowly invaded by shrubs, the three principal species concerned being smooth sumac, Rhus glabra, coralberry, Symphoricarpos orbiculatus, and hazelnut, Corylus americana. Cannon ('11) grouped roots into three types: (1) generalized, with tap root and laterals both well developed; and the specialized; (2) those with prominent tap roots; and (3) those with prominent laterals. This grouping is used in the descriptions of root types in this paper. Formerly almost all of southern Indiana was in deciduous forest. Now few old-age forests are present. After clearing, cultivation of a field results in exclusion of most species formerly present. Later if a field becomes poorer due to inefficient management, it loses much of its usefulness. Cleared places are very often turned into pasture or abandoned entirely. Usually the fields are slowly invaded by species such as Rhus copallina,' Sassafras officicale, Similavx rotundifolia:, and Sympho~ricarpos orbiculatus. They are more able to establish themselves than those of the natural assemblage of more mesophytic woodland plants. It was in this latter group of shrubby species in which the investigations of root habit were made.