Effect of plant density and light availability on leaf damage in Manilkara bidentata

Variation in herbivory is often associated with plant density and light environment. To determine the effect of these variables on herbivory we studied leaf production and herbivory on saplings, juveniles and adults of Manilkara bidentata (Sapotaceae) in the Luquillo Experimental Forest (LEF), Puerto Rico. The major herbivore of M. bidentata is microlepidoptera leaf miner (Acrocercopssp.; Gracillariidae). To determine the effect of plant density on herbivory, 24 - 20 x 20 m plots were established and the density of saplings, juveniles and adults were determined. Leaf production, herbivory and growth were measured on all saplings in the plots. In addition, plant density was determined in 8-20 x 20 m plots surrounding the 24 focal plots. The effect of light environment was determined by comparing leaf phenology, leaf quality and herbivory in the vertical and horizontal profile. Sapling density in 60 x 60 m plots was associated with increased levels of herbivory. In the vertical profile, leaf production was continuous in the canopy and synchronous for juveniles and saplings and herbivory increased from the canopy (1.3%) towards the understory (35.6%). In the horizontal profile leaf production was related with the light environmen. Saplings in low light environment produced leaves in June, while plants in gaps had a broader peak of leaf production. Differences in leaf phenology did not result in differences in herbivory possibly because there was high variation in herbivory among leaves. Although many saplings lost more than 80% of new leaf area, there was no detectable effect on plant growth.