MANGROVE COLONIZATION - MANGROVE PROGRESSION OVER THE GROWING PAK-PHANANG (SE THAILAND) MUD FLAT

A combination of remote sensing techniques and ill situ measurements a long a chronosequence was used to elucidate the rate of progression of the mangrove forest in the Pak Phanang Bay (SE Thailand), a large bay with an extended and rapidly accreting mud flat. The examination of b lack and white aerial photographs of the forest in 1966, 1974, 1989 an d 1995, and satellite images in 1985, 1990 and 1994 revealed that the mangrove forest located in the eastern bank of the bay was progressing over the mud flat. The rare of progression was estimated, from examin ation of changes in the position of the forest edge with time in the s eries of images, to average 38.6 m year(-1) over the 28-year interval encompassed by the images. Mangrove progression rates were fastest bet ween 1966 and 1974 and slowest between 1974 and 1985, remaining unifor m at about 30 m year(-1) thereafter. The in situ examination of vegeta tion along transects in the area of fastest mangrove progression showe d an average progression rate of 53.12 +/- 5.86 m year(-1), quite simi lar to the estimate (48.4 m year(-1)) derived from remote sensing tech niques for the area where the transects were surveyed. Avicennia alba was found to dominate the vegetation at the progressing edge of the ma ngrove, followed by Sonneratia caseolaris, with Rhizophora apiculata b eing present only occasionally. The fast colonization of A. alba over the mud flat was supported by a large export flux of mangrove propagul es from the channels draining the mangrove forest, which averaged 3715 +/- 920 and 1900 +/- 808 fruits day(-1) in each of the channels exami ned. Extrapolation of the long-term mean mangrove progression rate obs erved along the eastern bank of the Pak Phanang Bay suggested that thi s mangrove forest will increase by 33 ha year(-1). These results provi de evidence that natural mangrove colonization can be a rapid process if sufficient propagules of the pioneer species (A. alba and S. caseol aris) are available, and point, therefore, to alternative management p lans to promote and enhance natural colonization processes. (C) 1998 A cademic Press.