DOES ABUNDANCE REFLECT COMPETITIVE ABILITY - A FIELD-TEST WITH 3 PRAIRIE GRASSES

Two field experiments were conducted in a tallgrass prairie remnant to determine whether the relative abundance of three perennial grasses (Andropogon gerardii > Sorghastrum nutans > Dichanthelium oligosanthes) was directly related to their relative competitive ability. In the first experiment, performance of transplanted seedlings was measured in monocultures (1, 5, 10, 15 and 20 seedlings) and in pairwise species mixtures. Three different planting proportions (2:18, 10:10, 18:2 seedlings) were used for each pairwise species mixture. Neighbours reduced biomass and tiller production of seedlings significantly while survival was largely unaffected. The performance of a species grown in mixture versus in monoculture at an equivalent density did not differ significantly in almost all cases. In the second experiment, neighbours were removed experimentally from a 1 m radius around established target plants of each species. Tiller production increased significantly following neighbour removal. The three species responded about equally to neighbour removal, indicating that common and less common species were about equally suppressed by neighbours. Results of both experiments indicate that competitive ability and abundance are not significantly related for these three grasses.