Penetration of Photosynthetically Active Radiation as a Measurement of Canopy Density of Citrus Trees1

Abstract

Citrus trees were defoliated to obtain measurements of radiation penetration at various canopy densities. Tree size measurements were used to calculate the leaf-area index (LAI) and leaf-area to canopy-area ratio (LAC) of trees. Penetration of photosynthetically active radiation (PAR) increased curvilinearly as defoliation increased and LAC decreased. Observed relationships between PAR penetration and LAC were used to estimate LAC values from PAR penetration measurements. Correlations between PAR penetration and LAC were slightly higher than with LAI. LAI and LAC appeared to vary independently from tree size as measured by tree diameter or leaf area.