The Grasslands of the Red River Valley

Abstract

The objectives of the study were to provide a documented record of the vegetation of the grassland vegetation of the Red River Valley. The native prairies of this Valley are dominated by various combinations of Andropogon gerardi, Andropogon scoparius, Agropyron smithii, Bouteloua curtipendula, Calamagrostis inexpansa, Calamovilfa longifolia, Koeleria cristata, Muhlenbergia richardsonis, Sorghastrum nutans, Spartina pectinata, Sporobolus heterolepis, Stipa comata, Stipa spartea and Stipa viridula. At present only relicts of these grasslands remain. One hundred and fifty-one stands including 299 species, encompassing a wide range of floristic and habitat variability, were selected for study. The species composition frequency) of each stand was sampled by the use of thirty 0.5 X 0.5 m quadrats. A presence list was prepared for each stand and the dominant graminoid species determined by an estimate of cover contribution to the upper strata. The standing crop of green herbage of .34 stands was sampled by clipping five 0.5 X 0.5 m quadrats, and the material oven dried for weight determination. Environmental measurements were taken to determine physiographic position and soil profile characteristics. Soil samples were collected from the "A" horizon of each stand for textural analysis, field capacity, salinity and pH determinations. An analysis based on indicator species determined by physiographic association, indicated that the various species responded in a continuous manner to a moisture gradient. This was suggested by a gradation of importance from one physiographic habitat to another, with its position of peak performance in association with a specific drainage position. Vegetational types were also associated with physiographic position, but the dominant species and to a lesser degree secondary species showed modification of behavior by soil texture. The total number of species and their levels of importance (frequency) within the various vegetational types was used as a measure of diversity. The mid prairie dominance types with high numbers of species, many with high importance, were the most diverse of all types examined. It was further indicated that mid prairie stands in the northern portion of the area studied had higher diversity than all others. Geographic differences in diversity were related to historical development of the grasslands. The yield of green herbage varied according to prairie division, leading dominant, soil texture and geographic location. A high positive correlation between green herbage yield and length of growing season suggested that geographic location was the most effective determinant in production, with southern stands producing about 100% more green herbage than comparable stands in the north. The species comprising the grasslands of the Red River Valley suggest an amalgamation of species of eastern and western origin. The dominant graminoids, however, are most closely associated with the grasslands to the east and suggest the placement of the Red River Valley grasslands within the True Prairie.