EARLY WOODY INVASION UNDER TREE PLANTATIONS IN COSTA-RICA - IMPLICATIONS FOR FOREST RESTORATION

The role of tree plantations as facilitators of tropical forest restor ation in degraded lands has been explored recently, but there are few data on the effect of different tree species on invasion of the plant understory. We evaluated early patterns of understory composition in t hree-year-old native tree plantations in lowland Costa Rica using two pure-species treatment (Jacaranda copaia and Vochysia guatemalensis) a nd one mixed-species treatment (J. copaia, V. guatemalensis, Stryphnod endron microstachyum, and Calophyllum brasiliense). We also monitored woody invasion in unplanted control areas dominated by grasses. The un derstory of the different plantation treatments differed in light envi ronment, woody-plant growth and recruitment, and quantity and quality of woody regeneration. Forest tree invasion appeared to be enhanced un der Vochysia, while shrubs were more abundant under the Jacaranda and mixed-species treatments. Woody plant growth, herbaceous cover, and un derstory light availability were highest under Jacaranda, intermediate under mixed species, and lowest under Vochysia. Soil-stored seeds see med an important source for woody plant recruitment in Jacaranda and m ixed species and of minimal importance under Vochysia, probably due to light suppression. It appears that competition from grasses is a majo r factor influencing early woody invasion in our study area. We found no woody recruitment after one year in the unplanted controls. We sugg est that to promote the use of plantations as tools of forest restorat ion, there is a need to gather basic ecological information on how dif ferent tree species may influence patterns of plant understory coloniz ation.