Dispersal, establishment and survival of Ceriops tagal propagules in a north Australian mangrove forest

Studies of the ecology of mangroves show that a wide variety of factors, including salinity, desiccation, disturbance, competition and predation, may affect the distribution and abundance of species. Field studies were done to examine the relative importance of several of these factors in the establishment and early survival of Ceriops tagal, a species common in mid- to high-shore regions of mangrove forests in northern Australia. The fate of marked and tethered propagules was followed to estimate the range of dispersal and the intensity of predation. Propagules were artificially planted under different thicknesses of shade cloth (none, 30%, 80%) and in different habitats (clearing, forest, clearing-forest fringe) to examine the effects of light and soil conditions on survival and growth. Results suggested that dispersal was very limited: only 9% of marked propagules were ever found more than 3m from the parent tree. Losses to predators were great, with 83% of tethered propagules being damaged or consumed within 3 months. On average, 56% of planted propagules survived for at least 6 weeks and 76% of these initiated growth. Survival in clearings was lower than in other habitats, with 29% fewer surviving six weeks and 48% Fewer surviving 15 months. The growth of seedlings was correlated with soil temperature, but the effects of treatments were complex. Overall, results indicated that poor dispersal and establishment were the main factors likely to limit the colonisation and population growth of this species.