INTERACTIONS BETWEEN CROWN STRUCTURE AND LIGHT ENVIRONMENT IN FIVE RAIN FOREST PIPER SPECIES

Measurements of light variation among leaves within crowns of five Piper species were compared with estimates of spatial variation in light within understory, forest edge, and clearing habitats to estimate the extent to which crown structure contributes to variation in leaf light environment. Daily photon flux density (PFD) varied greatly within and among crowns. Coefficients of variation for daily PFD among sensors within a single crown ranged from 26 to 79%. Within a single crown located in a clearing, the range in daily PFD among leaves was nearly as great as the range over the entire sample of plants. In the understory, localized sunfleck activity contributed to a high degree of spatial variation in instantaneous and total PFD among leaves within individual crowns. Much of the microsite variation in sunfleck activity, however, reflected environmental conditions within the understory habitat. Within an array of sensors placed next to Piper crowns in the understory, correlations were poor for light sensors spaced only 0.2 m apart, and only 8% of the variance in light readings was explained by measurements made 0.5 m away. In the clearing habitats, microsite heterogeneity among leaves was more strongly influenced by leaf positions within crowns and leaf angles than by spatial heterogeneity within the habitat.