Three grasses–Calamagrostis canadensis, Andropogon gerardi, and Koeleria cristata–were grown for 13 months on two soil slopes in a greenhouse. One slope was composed of sand and the other loamy sand; the water table of each was controlled to create equal catenas with sites ranging from dry to wet. All three grasses were seeded uniformly over each tank. Competition was limited as each grass found its own niche above— and below—ground. Some interspecific competition resulted from shading by Koeleria, while the density of Calamagrostis was reduced by intraspecific competition on the better soil (loamy sand) and where the moisture level was most favorable. The density of Andropogon was greatest on the loamy sand and reached its maximum at a very moist site on both soils. Koeleria produced its maximum shoot weight at a greater depth to water table than either of the other two species. During the final month of the study watering was discontinued and a more natural pattern resulted as Calamagrostis died back to the moist sites while Koeleria was able to survive at drier levels. Roots of each species occupied soil stratum, with Calamagrostis having the least flexible root system and Koeleria exhibiting a very flexible root system which readily adjusted to decreasing moisture supply.