EFFECTS OF LIGHT, MOISTURE, TEMPERATURE, AND LITTER ON THE REGENERATION OF 5 TREE SPECIES IN THE TROPICAL MONTANE WET FOREST OF PUERTO-RICO

Field experiments were conducted to investigate the effects of light, moisture, temperature, and litter on the regeneration of two early-, o ne mid-, and two late-successional tropical tree species. High light a nd litter seem to be universally good cues for regeneration, increasin g seed/seedling survival for al species except for Cecropia (an early- successional species) whose small seeds may not be able to penetrate t he litter layer. In addition, the high temperature environment in both artificially shaded and nonshaded areas of a natural gap exhibits les s seed loss, an increase in the percent and rate of germination, and a n increase in seedling survival for Dacryodes (a late-successional spe cies), than the lower temperature environment under an intact canopy. Low soil water is also a good cue for Dacryodes germination as it is f or Prestoea and Cecropia. Finally, the lower temperature environment f ound under the forest canopy (compared to the natural gap) leads to le ss seed loss and more germination for Guarea (a mid-successional speci es). Our results suggest that a good patch for regeneration of many sp ecies in this forest, early- as well as late-successional species, wou ld have high light and a litter layer that moderates temperature and m oisture extremes. The substantial variation in suitability among regen eration filters and species could: (1) contribute to low establishment success, i.e., most dispersed propagules do not become trees, (2) mak e it difficult to group species into germination strategies, and (3) m ake it hard to generalize about a net effect of any specific environme ntal variable on establishment. We suggest that tropical disturbances should be viewed in terms of their impact on a variety of environmenta l cues, which may signal germination and impact subsequent growth and survival.