The effects of defoliation and competition on regrowth of tillers of two North American mixed-grass prairie graminoids.

Tillers (ramets) of Andropogon gerardi (big bluestem) and Carex filifolia (threadleaf sedge) were subjected to various defoliation regimes under full and reduced competition. Tillers defoliated under conditions of full competition produced significantly less leaf biomass than tillers defoliated under reduced competition. Apparent mortality of tillers defoliated bi-weekly was 95% under full competition and 20% under reduced competition. Andropogon tillers subjected to multiple defoliation under reduced competition produced c3 more leaves per tiller than nondefoliated tillers or tillers similarly defoliated under full competition. All defoliated tillers had substantiated reductions in biomass of storage organs relative to nondefoliated tillers. Tillers defoliated under full competition had stembase biomass reductions comparable to those of tillers defoliated under reduced competition but produced significantly less leaf biomass. Results suggest that the positive aspects of resource sharing among interconnected tillers were outweighed by the negative aspects of intra- and interspecific competition. At the community level, herbivores may mediate competitive interactions among primary producers through the differential defoliation of plants.-from Authors