Effects of above- and below-ground competition of shrubs and grass on Calophyllum brasiliense (Camb.) seedling growth in abandoned tropical pasture

Early-successional vegetation is often a major factor that limits recovery of tropical forest in abandoned pastures by outcompeting seedlings of forest trees. The goal of this study was to compare the effects of above- and below-ground competition of pasture grasses and shrubs on the growth of tree seedlings in abandoned tropical pasture in Costa Rica. Seedlings of Calophyllum brasiliense were planted in areas of dense pasture grass and below shrub patches. In each vegetation type seedlings were subjected to one of four treatments: control, root trenching, above-ground clearing, or trenching and clearing. Seedling height was measured and above- and below-ground biomass was harvested after one year. Seedling height and biomass were higher for seedlings grown under grass than under shrubs. Above-ground clearing had a strong positive effect an seedling height and all biomass measurements (stem, leaves, tap root, and fine roots). Trenching had a significant effect on height and all biomass measurements except tap root mass; however, trenching had a weaker effect on plant growth than above-ground clearing. Root:shoot ratios were significantly affected by trenching. These results suggest that both pasture grasses and early-colonizing shrubs may slow succession of forest in abandoned pasture. Moreover, the results highlight the importance of reducing above-ground competition to improve the success of reforestation efforts. (C) 1998 Elsevier Science B.V.