CECROPIA SCHREBERIANA IN THE LUQUILLO MOUNTAINS OF PUERTO-RICO

Cecropia schreberiana Mig. (Cecropiaceae) is a common tree in the Luqu illo Mountains of Puerto Rico because it is a pioneer that establishes abundantly after recurrent hurricanes that damage Luquillo forests. I n these forests C. schreberiana typically reaches about 20 m in height and 60 cm dbh and has few branches, these bearing large, deeply Iobed leaves. The wood is light and weak. Unlike most of its congeners, C. schreberiana in Puerto Rico does not have symbiotic ants. It is dioeci ous and produces wind-pollinated flowers in spikes and abundant minute seeds broadly dispersed by birds and bats. Forest soils contain a hig h density of its seeds, which lie dormant until canopy opening stimula tes germination. With adequate nutrients C, schreberiana grows fast in high light, while nondominant individuals suffer heavy mortality. An individual of the species is thought to live 30 to 50 years. Cecropia schreberiana is uncommon in abandoned pastures in the Luquillo Mountai ns. It colonizes road cuts, landslides, and infrequent, large treefall gaps. Yet these disturbances provide only a limited ''background rege neration,'' which is not sufficient to maintain the species' observed high abundance in Luquillo forests. However, there is widespread and a bundant C. schreberiana regeneration after hurricane damage opens the forest canopy. Despite high mortality among these post-hurricane colon izers, enough survive and grow so that C. schreberiana is generally am ong the ten most common canopy trees in the widespread ''tabonuco'' fo rest type. Post-hurricane colonizers mature, senesce, an decline in nu mber, but C. schreberiana remains abundant as seeds in the soil ready to form tree cohorts after disturbance. The status of the C. schreberi ana population indicates the developmental status of the forest as a w hole. Moreover C. schreberiana performs a key function in the reorgani zation of Luquillo forest ecosystems after disturbance, when its abund ant regeneration and rapid growth capture and store nutrients. Also, i ts colonizing saplings may facilitate succession to mature forest by e xcluding grasses, herbs, and vines that hinder forest development. The biology of this species both reflects and helps drive the dynamics of forests in the Luquillo Mountains.