Date of this Version
This research is the third of a series of investigations of the prairie. The first dealt with the environment of the prairie (Weaver and Himmel, 1931). The second was concerned with the ecology and relative importance of the dominant grasses (Weaver and Fitzpatrick, 1932). The present study treats of the structure of the vegetation in the several types of prairie, the secondary grasses, the ecology of the forbs, together with a general survey of contacts, invasion, and succession. These investigations have resulted from years of intimate association with the great grasslands of North America. They were made in an endeavor to clarify some of the many problems presented by this vast natural unit of vegetation, to better understand the importance and significance of grassland and hence its utilization and to furnish a permanent record of a rapidly vanishing vegetation. It deals with the vegetation as it exists today; nature's yearly productivity unmodified by the hand of man except as he harvests the crop of hay in autumn.