INTERACTIONS BETWEEN SEEDLINGS OF AN EARLY AND A LATE SUCCESSIONAL WOODY SPECIES

Replacement experiments between woody seedlings of an early and late s uccessional species (Acacia smallii, huisache, and Celtis laevigata, T exas sugarberry) were conducted using four combinations of two soil ni trogen levels and two light levels. Data indicate that soil nitrogen h ad a greater influence than light level on C. laevigata growth, and li ght level had a greater influence on A. smallii growth than did soil n itrogen. There were few negative effects of seedlings of either specie s on the other. Interactions that were detected were due to a lack of A. smallii growth not interference. High soil nitrogen and high light levels caused greater growth in both species; however, C. laevigata di splayed the greater overall growth stimulation. A stable equilibrium b etween the species existed in the low soil nitrogen-high light treatme nt where the growth of both species in mixture was the same as in mono culture. In the three other treatments, C. laevigata growth was greate r in mixture than in monoculture, but the growth of A. smallii was the same in mixture as in monoculture. During early successional events w hen soil nitrogen is low and soil surface light levels are high, the g rowth of the early successional species, A. smallii, is not reduced by competition with C. laevigata seedlings for soil resources. Late in s uccession, when total soil nitrogen is higher and surface light levels are lower, conditions favor the growth of the shade tolerant C. laevi gata seedlings. Data suggest that the exclusion of A. smallii seedling s late in succession is due to the inability of A. smallii to grow at low light levels below the canopy rather than competition between seed lings of the two species for soil resources.