Date of this Version
Destruction of a portion of one plant association and its replacement by another has just been completed. This has occurred not as the result of man's interference with the vegetation nor the effect of his grazing animals. It has been due to a dry climatic cycle and has been accomplished within a period of seven years. The scene of action was the broad area on the western edge of true prairie in central Kansas, eastern Nebraska, and eastern South Dakota. It is distinctly east of the mixed prairie in the central portion of these states. Although the phenomenon was general over hundreds of square miles of grassland, it has been studied in detail from year to year in only a few widely separated places. Three of these have been selected to illustrate this remarkable transition in grassland populations and structure and the manner in which it occurred, as well as the time relations and the causal factors.