Competition between tree seedlings and herbaceous vegetation] support for a theory of resource supply and demand

0 We measured competition intensity "CI# between herbaceous vegetation and tree seedlings "Quercus macrocarpa and Q[ ellipsoidalis# along an experimental moistureÐ light gradient[ Contrasting theories were tested by comparing variation in competition intensity to changes in neighbour biomass and resource supply and demand[ 1 CI based on survival was inversely correlated with net soil water supply "gross supply minus demand by herbaceous vegetation#[ CI was not positively correlated with either gross resource supply or neighbour biomass\ contrary to predictions of Grime|s triangular model for plant strategies[ 2 Many of the inconsistencies and con~icting results that have characterized the recent literature on plant competition could be eliminated if changes in competition intensity along a resource gradient are compared with changes in net resource supply rather than changes in productivity or neighbour biomass[ 3 Tree seedling success in savannas and grasslands may be strongly in~uenced by the intensity of competition from herbaceous vegetation[ Factors that reduce soil water content are likely to increase competition intensity "and reduce seedling success# in these environments\ while factors that increase soil water content will favour seedling success through decreased competition for water with herbaceous vegetation[