Three-Dimensional Distribution of Plant Biomass in Relation to Grazing and Topography in the Shortgrass Steppe

The horizontal and vertical distribution of plant biomass was examined on shortgrass steppe communities that were heavily grazed or protected from grazing for fortyseven years. Uplands and swales were sampled along the gently rolling topograhy. Three-dimensional distributions of plant biomass were generated by direct side-byside coring whereby 0.5 mx0.5 mx20 cm deep volumes were completely sampled. Long-term grazing had no effect on total biomass of surface crowns and only small effects on total biomass of roots at 0-10 cm and 10-20 cm depths. The effect of grazing on the vertical distribution of crown and root biomass was also smaller than the difference between topographical positions. In contrast, grazing had a large influence on the horizontal distributions of all vertical components of the plant community by producing smoother more uniform horizontal distributions. This was most evident for the more heavily grazed swale communities. The grazing-lawn concept is extended to the belowground plant community and discussed in terms of possible herbivore mediated plant-plant interactions rather than as an aboveground grazing avoidance mechanism.