Interception of photosynthetic photon flux density in a mangrove stand of Kandelia candel (L.) Druce

The canopy structure and interception of photosynthetic photon flux density (PPFD) in a 10-year-old Kandelia candel (L.) Druce stand were investigated before and after artificial defoliation. Leaf and wood areas for different layers were measured through area-weight relationships of subsamples. PPFD was measured at specified heights before and after leaf clipping. The leaf area index (LAI) and wood area index (WAI) were 4.501m2m−2 and 1.412m2m−2, respectively. There was a strong linear relationship between the cumulative wood area (C) and leaf area (F) densities from the top down to a given depth of the canopy, C = aF (r 2 = 0.950), with a proportional constant a of 0.096 ± 0.008 (mean ± SE). The PPFD relative to that above the canopy (relative PPFD; I R) at a given depth of the canopy was assumed to be given by the equation I R = e−(KCC+KFF ) = e−KF , where the apparent light extinction coefficient K (= K F + aK C , where K F and K C are respectively the light extinction coefficient of leaves and woody organs) was calculated to be 0.502 ± 0.041 (mean ± SE) m−2 m2 before leaf clipping. After leaf clipping, $I_{R_C } = e^{ - K_C C} $ is satisfied. As a result, the value of K C was estimated to be 0.785 ± 0.046 (mean ± SE) m−2 m2. The light extinction coefficient of leaves K F was calculated to be 0.427 m−2 m2 using the indirect method, K F = K − aK C, and 0.432 ± 0.026 (mean ± SE) m−2 m2 using the direct method, $I_R /I_{R_C } = e^{ - K_F F} $ . Of the total PPFD intercepted by the canopy, the fraction K F/K due to leaves alone was estimated to be 85.0%–86.1% and the rest was contributed by woody organs.