FOREST RECOVERY IN ABANDONED TROPICAL PASTURES IN PUERTO-RICO

The conversion of tropical forests into pastures has increased dramati cally in the last 20 years. Once these lands are abandoned it is not c lear if they will recover to forest or if they will become permanent g rasslands. Economic changes in Puerto Rico have led to the abandonment of agricultural lands over the last 60 years, providing an opportunit y to assess the longer term patterns of forest recovery following huma n disturbance. This study focuses on the changes in vegetation in aban doned pastures ranging in age from 0 to 60 years or more in two replic ate chronosequences. Species richness and density of woody species wer e very low during the first 10 years following abandonment and woody b iomass did not increase substantially until approximately 15 years pos t-abandonment, Recovery in pastures is greatly delayed in comparison w ith forest recovery following other types of human and natural disturb ance. The successional trajectory is quite different in comparison to those following natural disturbances in the nearby Luquillo Mountains. In particular, the initial colonizing species are not 'typical' pione er species (e.g. Cecropia sp., Scheffleria morotononi), but a group of shrubs and treelets in the Rubiaceae, Melastomataceae, and Myrtaceae. The presence of grasses and the rapid colonization and growth of fern s and herbaceous species in the abandoned pastures appears to be a maj or factor inhibiting the establishment of secondary forest and imparts a selective barrier on the colonizing woody species.