SEASONAL FOLIAGE DYNAMICS OF MANGROVE Bruguiera gymnorrhiza (L.) lamk. IN A SUBTROPICAL REGION, MANKO WETLAND, OKINAWA ISLAND, JAPAN

In case of mangroves, little information is available on seasonal crown leaf area growth and leaf survival. Therefore, it is necessary to investigate the dynamics of crown foliage to understand the productivity of mangroves. The present study describes the crown foliage dynamics of Bruguiera gymnorrhiza (L.) Lamk., Okinawa Island, Japan, which is the northern limit of its distribution. This study was carried out from April 2008 to March 2009. The crown foliage dynamics includes the leaf recruitment and survival. The production and fall of leaves were investigated by a direct observation of a sample tree of B. gymnorrhiza as well as by an indirect observation of litterfall measurement. The numbers of surviving and dying new leaves were totaled monthly. Newly flushed leaves occurred successively throughout the year, with a maximum in July and a minimum in January. The highest leaf death was in June, whereas the lowest was in December. The crown leaf area was almost stable throughout the year, having a peak in December. The homeostatic control of the crown foliage area may also be accompanied by the regulation of leaf recruitment and death. Therefore, the present results suggest the existence of integrated mechanisms between the internal and external factors maintain the crown foliage area