Abstract
Seedling survival and growth of the 3 common SE Asian mangrove speciesAvicennia alba,Rhizophora mucronataandSonneratia caseolariswere quantified experimentally along 2 spatial gradients of shelter: (1) between 2 stations, at the inner and outer end of the sheltered Pak Phanang Bay (SW Thailand); and (2) for each station, among plots across a gradient of vegetation density from the mangrove forest edge inwards. Exposure to water movement, quantified as gypsum clod card weight loss, was found to vary more than 5-fold between seasons, which contributed most of the variance accounted for (73%). Variation between plots was higher than that between the 2 stations: clod card loss ranged between 3.0 and 4.6 g d–1in the plots, whereas the grand means of the 2 stations were 3.4 and 3.7 g d–1, respectively. These differences between stations and plots were comparable to the patterns found for mangrove seedling survival. Survival was high (80 to 93%) in most treatments inR. mucronata, with the exception of the most exposed plot (30%). In the other 2 species, overall survival was significantly less but was highest in the outermost plots with the lowest tree density. This pattern confirms the successional status of these 3 mangrove species. Seedling growth, expressed as height increase, was significantly reduced with increasing neighboring tree density forA. albaandS. caseolaris, whereasR. mucronatashowed an opposite pattern. Internode production of all 3 species was highest in the most exposed plots. Overall, relative growth rate, expressed as height increase, declined with the age of the seedlings.