Soil Resource Levels and Competition between a Woody and Herbaceous Species

BUSH, J. K. AND 0. W. VAN AUKEN (Division of Life Sciences, University of Texas at San Antonio, San Antonio, TX 78285). Soil resource levels and competition between a woody and herbaceous species. Bull. Torrey Bot. Club 116: 22-30. 1989.-Interspecific competition between Bouteloua curtipendula (Michx.) Torr. (sideoats grama) and Prosopis glandulosa var. glandulosa Torr. (honey mesquite) seedlings was examined in an additive and a replacement experiment, at two resource levels. Bouteloua curtipendula significantly reduced P. glandulosa seedling growth, at every grass density tested. In addition, the growth of B. curtipendula was consistently favored over P. glandulosa, regardless of the proportion of the two species or the soil resource level. Higher nutrient levels increased the total biomass and increased the percent B. curtipendula biomass per pot. Prosopis glandulosa total biomass was highest when grown without B. curtipendula and increased with added nutrients but only in monoculture. Results suggest that intraspecific, rather than interspecific competition, has a greater effect on B. curtipendula growth. However, interspecific competition, rather than intraspecific competition, has a greater effect on P. glandulosa growth. In addition, P. glandulosa seedling establishment and growth in productive B. curtipendula grasslands would probably be severely limited, especially at high levels of soil resources.