SEEDLING ESTABLISHMENT IN ADULT NEIGHBORHOODS INTRASPECIFIC CONSTRAINTS IN THE REGENERATION OF THE BUNCHGRASS BOUTELOUA-GRACILIS

1. In order to determine the effect of conspecific adult neighbours and opening size on the process of seedling establishment in Bouteloua gracilis, seeds were added to naturally occurring openings of bare soil, and water was provided up to and beyond the time of adventitious root development of seedlings. Exclusion of roots of neighbours was accomplished using steel tubes sunk in the soil of openings. 2. Adult neighbours affected emergence, survival and performance of seedlings in the whole observed range of opening sizes (10, 20 and 30 cm in diameter). With neighbours present (no root exclusion), seedlings produced few tillers regardless of opening size, and had higher survival only in the 30-cm-diameter openings. 3. The number of adventitious roots of seedlings was reduced when growing in the presence of active roots of established conspecifics. 4. Root density of established plants in undisturbed openings did not increase significantly due to the experimental watering, suggesting that the negative effect of neighbours was associated with extant roots. 5. Root exclusions provided a favourable environment for seedling establishment. The results strongly suggest that below-ground competition by adult B. gracilis plants negatively influences establishment even after the development of adventitious roots of seedlings.