The horizontal and vertical distribution of plant biomass was examined by Milchunas and Lauenroth, on shortgrass steppe communities that were heavily grazed or protected from grazing for 47 years. Community characteristics such as aboveground and belowground biomass were compared between swales and upland sites in heavily grazed and ungrazed areas. 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. 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. In conclusion, the grazing-lawn concept which is a widely used term to describe the short-statured, prostrate growth forms resulting from repeated heavy grazing by large herbivores in some grasslands, is extended to belowground plant community and discussed in terms of possible herbivore mediated plant-plant interactions rather than as an aboveground grazing avoidance mechanism.
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