Document: ALE-3-42-35

The effect of water availability on growth, reproduction, and mortality in Plumeria alba: A field experiment in the dry forest of Puerto Rico.

SLOAN, S.A.*

University of Puerto Rico- Rio Piedras, San Juan, Puerto Rico ¹

Abstract:
This experiment was designed to determine the degree to which a tropical dry forest tree is limited by the amount and seasonality of water availability. This study was conducted in the Guanica Forest Reserve, Puerto Rico, where annual rainfall averages 762 mm and December and April are the driest months. To determine the effect of water availability on Plumeria alba, 8 trees were watered with 19 L of water/tree/month in addition to normal rainfall for a period of 12 months. Results from these trees were compared to 8 control trees receiving normal rainfall and an additional 8 trees in which water availability was reduced by surrounding trees with a plastic sheet 3 m in diameter. Water-limited trees reflushed fewer leaves following the dry season and had higher mortality (75%) compared to either control trees (0%) or trees receiving additional water (0%). Following the dry season, the standing crop of leaves on control trees exceeded that of watered trees due to increased herbivory by sphinx moth larvae. High levels of herbivory caused watered trees to produce significantly fewer flowers and initiate fewer fruit compared to control and water-limited trees. Increased water availability had a significant positive effect on leafing. However, the increase in the number of leaves on watered trees did not translate into an increase in fecundity or growth due to higher rates of herbivory.

Keywords: Herbivory; _Plumeria alba_; resource limitation; Sphingid larvae; tropical dry forest.

This abstract is being presented at: 9:15 AM in session:
Oral Session #44: Terrestrial Invertebrates: Foodwebs and Plant Responses.