Structure and composition of the seaward mangrove forest at the Mai Po Marshes Nature Reserve, Hong Kong

The seaward mangrove fringe at Mai Po Marshes Nature Reserve, Hong Kong, has extended seaward by 7.6 m.yr-1 and possibly increased in relative ground elevation by 1.1 cm.yr-1 since 1949. It is apparently subject to constant deposition of terrestrial sediments. As a result, the area of mangrove forest has trebled since the construction of the Gei Wai ponds and bunds over 50 years ago. Since then, the mangrove fringe has undergone considerable changes in species composition. It apparently began as a forest dominated by Kandelia candel with an undercanopy of Acanthus ilicifolius and Aegiceras corniculatum. Immediately following bund construction, however, newer seaward forests were dominated by Avicennia marina var. marina until around 1969. After this, Kandelia forests again colonized the seaward margin until the present day, producing a curious bimodal distribution of Kandelia. It is proposed that the herbivore which defoliates Avicennia each year has possibly done so for about 20 or 30 years and now retards recruitment success of that species, allowing Kandelia now to dominate the lower intertidal zone.