A FLOOD-PLAIN PALM FOREST IN THE LUQUILLO MOUNTAINS OF PUERTO-RICO 5 YEARS AFTER HURRICANE-HUGO

Long-term studies are needed to understand the dynamics of tropical fo rests, particularly those subject to periodic disturbances such as hur ricanes. We studied a flood plain Prestoea montana palm forest in the Luquillo Mountains of Puerto Rico over a 15-yr period (1980-1995), whi ch included the passage of Hurricane Hugo in September 1989. The passa ge of the hurricane caused the dominant species to become more dominan t and created low instantaneous tree mortality (1% of stems) and reduc tions in tree biomass (-16 Mg/ha/yr) and density, although not in basa l area. Five years after the hurricane, the palm flood plain forest ha d exceeded its prehurricane aboveground tree biomass, tree density, an d basal area. Aboveground tree biomass accumulated at a rate of 9.2 Mg /ha/yr, 76 percent of which was due to palms. Before the hurricane thi s rate was on the order of 3 Mg/ha/yr. Forest floor litter decreased t o prehurricane levels (6.7 Mg/ha), within 5 yr, mostly due to the disa ppearance of woody litter. Thirteen tree species not represented in th e canopy entered the forest by regeneration, and 2 species suffered al most 20 percent/yr mortality over a 5-yr period after the storm (flood plain average of 2%/yr). Delayed tree mortality was twice as high as i nstantaneous tree mortality after the storm and affected dicotyledonou s trees more than it did palms. Regeneration of dicotyledonous trees, palms, and tree ferns was influenced by a combination of factors inclu ding hydroperiod, light, and space. Redundancy Data Analysis showed th at the area near the river channel was the most favorable for plant re generation. Palm regeneration was higher in locations with longer hydr operiods, while regeneration of dicotyledonous trees was higher in are as with low risk of flooding. This study shows how a periodic disturba nce provides long-term opportunities for species invasions and long-te rm ecosystem response at the patch scale of <1 ha.