Growth, crown architecture and leaf dynamics of saplings of five mangrove tree species in Ranong, Thailand

Abstract

We investigated the regeneration pattern of mangrove forests, considering the corre- spondence between growth strategies (i.e. sapling growth, crown architecture, leaf dynamics) of 5 canopy-dominant species and the disturbance regime in Ranong, Thailand. Individual canopy gap size and percent gap area were greater in the Sonneratia alba-Avicennia alba (SA) zone, which is located on the most seaward fringe, than in the other inland zones. In canopy gaps, the seaward species S. alba and A. alba showed a higher relative height growth rate than the inland species Rhizophora apiculata, Bruguiera gymnorhiza and Xylocarpus granatum. Under closed canopies, the seaward species showed greater mortality, presumably due to their low shade tolerance, while the inland species demonstrated a net growth in spite of the dark conditions. Leaf longevity of sunlit saplings increased from seaward to inland species. The 2 seaward species had well-branched, slen- der and deeper crowns, while R. apiculata and B. gymnorhiza had wider and flatter crowns, and X. granatum had less-branched, smaller crowns. Phenotypic traits were correlated with each species' growth strategy (potential growth rate and shade tolerance), which corresponded to the disturbance regime in each vegetation zone. Many large gaps may enhance the abundance of S. alba and A. alba in the SA zone, and a few small gaps may prevent establishment and growth of light-demanding species in the inland zones. Accordingly, the correspondence of disturbance regime and growth strategies of canopy-dominant species provides an advantage for successful regeneration, and may contribute to the maintenance of the present species composition in each vegetation zone.