THE INFLUENCE OF INITIAL SIZE ON THE COMPETITIVE RESPONSES OF 6 PLANT-SPECIES

Plant size may be an important determinant of competitive ability and may affect comparisons of competitive response among species. We exami ned the influence of initial size on plant competitive response in a f ield experiment using transplants in three classes of initial mass (cl ass means: 27, 46, and 73 mg) for each of six species (Agropyron crist atum, Bouteloua gracilis, Elaeagnus commutata, Fraxinus pennsylvanica, Melilotus officinalis, and Potentilla pensylvanica), Transplants were grown for one summer in an old field dominated by the perennial grass Bromus inermis. The transplants were grown with no neighbors present, with shoots of neighbors present, with roots of neighbors present, or with both shoots and roots of neighbors present. The existing Bromus served as neighbors. There were 10 replicates of each factor combinati on. Final transplant mass varied significantly with competition, speci es identity, and initial size. The mass of transplants grown with only neighbor roots was not significantly different from the mass of trans plants grown with both roots and shoots of neighbors, suggesting that competition in the field was primarily belowground. A significant inte raction between species identity and competition indicated that specie s differed in the extent to which they were suppressed by neighbors. T here was no significant interaction between size and competition, howe ver, suggesting that initial size had no influence on competitive resp onse. Further, regressions of final transplant mass against neighbor m ass provided no evidence that initially smaller transplants were weake r competitors. Our results suggest that the competitive responses of t he six species during the first summer of growth were not influenced b y their initial size under conditions of intense belowground competiti on.