Migration Models for Grasses in the American Midcontinent.

This paper uses graphic and geographic migration models to examine the relationship between present dominance patterns and presumed source areas for six important native grass species in the Midcontinent Plains. The study has five parts: (1) describing the theoretical migration patterns of grasses as they spread out from a source area: (2) determining the dominant grasses on medium-textured, well-drained, upland range sites in a large sample of counties: (3) fitting trend surfaces to these dominance patterns in order to evaluate the degree to which the distributions are spatially systematic: (4) comparing these trend surfaces with climatic boundaries that are presumed to be significant in limiting the distributions of grasses: and (5) evaluating the relative importance of climatic limits and migration patterns in “explaining” the present distributions of the grasses. The geographic patterns summarized by the trend surface maps appear to favor a migrating-wave hypothesis of grass species dominance: they do not support the idea that grass species distributions are controlled primarily by climatic factors. [ABSTRACT FROM AUTHOR]