ORIGINAL ARTICLE J For Res (2004) 9:205–210 © The Japanese Forestry Society and Springer-Verlag Tokyo 2004 DOI 10.1007/s10310-003-0074-7 Md. Nabiul Islam Khan · Rempei Suwa · Akio Hagihara Kazuharu Ogawa Interception of photosynthetic photon ﬂux density in a mangrove stand of Kandelia candel (L.) Druce Received: November 10, 2003 / Accepted: December 26, 2003 M.N.I. Khan · R. Suwa · A. Hagihara (*) Laboratory of Ecology and Systematics, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan Tel./Fax +81-98-895-8546 e-mail: amyh@sci.u-ryukyu.ac.jp K. Ogawa Laboratory of Forest Ecology and Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan Abstract The canopy structure and interception of photo- synthetic 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 rela- tionships of subsamples. PPFD was measured at speciﬁed heights before and after leaf clipping. The leaf area index (LAI) and wood area index (WAI) were 4.501 m 2 m -2 and 1.412 m 2 m -2 , respectively. There was a strong linear rela- tionship 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 -(K C C+K F F ) = e -KF , where the apparent light extinction coefﬁcient K (= K F + aK C , where K F and K C are respec- tively the light extinction coefﬁcient of leaves and woody organs) was calculated to be 0.502  0.041 (mean  SE) m -2 m 2 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 m 2 . The light extinction coefﬁcient of leaves K F was calculated to be 0.427 m -2 m 2 using the indirect method, K F = K - aK C , and 0.432  0.026 (mean  SE) m -2 m 2 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. Key words Apparent light extinction coefﬁcient · LAI · Light extinction coefﬁcient of leaves · PPFD, WAI Introduction Canopy structure, i.e., spatial distributions of leaf and wood areas, plays a signiﬁcant role in the interception of photo- synthetic photon ﬂux density (PPFD) by leaves, which strongly affects the gas exchange between forests and the atmosphere (Kurachi et al. 1993; King and Maindonald 1999; Sterck and Bongers 2001; Law et al. 2001). The pio- neer study by Monsi and Saeki (1953) assumed that light interception by plant canopies is caused by leaves alone, and their model for estimating plant photosynthetic produc- tion was based on the apparent light extinction coefﬁcient, K. In forest canopies, however, PPFD is intercepted not only by the leaves, but also by the woody organs. Some studies had been performed on the light interception by forest canopies (Yim et al. 1969; Kurachi et al. 1986; Hagihara and Yamaji 1993; Maass et al. 1995; Chen et al. 1997; Levy and Jarvis 1999; Green et al. 2001). Among these studies, only a few considered the contribution of woody organs to the light attenuation by the canopy (Yim et al. 1969; Kurachi et al. 1986; Hagihara and Yamaji 1993; Chen 1996). Some modiﬁcations of the Monsi–Saeki model (Kurachi et al. 1986, 1993; Hagihara 1987), which incorpo- rated not only the K but also the light extinction coefﬁcient of leaves K F , suggested that canopy photosynthetic produc- tion of a Larix leptolepis (Sieb. et Zucc.) Gordon stand based on K showed approximately 30% overestimation in comparison with their model based on K and K F (Kurachi et al. 1986). Therefore, the estimation of K and K F became an important issue for forest ecophysiologists. The knowl- edge of PPFD interception not only by the canopy as a whole, but also by the leaves and woody organs separately, is very important in understanding the structural and func- tional characteristics of forest canopies. So far, information regarding the light extinction coefﬁcients of leaves K F and of woody organs K C remains inadequate. In addition, similar studies in mangrove forests have not been conducted. Therefore, the aim of this study was to elucidate the canopy structure of a Kandelia candel (L.) Druce stand and to evaluate the pattern of PPFD