Prediction of recovery pathways of cyclone-disturbed mangroves in the mega delta of Myanmar

Mangroves in the Ayeyarwady Mega Delta of Myanmar are crucial for the ecology, society and economy of this country. At the beginning of May 2008, a severe cyclonic storm, Cyclone Nargis, struck the Ayeyarwady mangroves. Since that time, the present long-term study has been exploring the dynamics of post-cyclone mangrove vegetation. Every year since the 2008 cyclone, a census has been taken of 60 permanent plots (each measuring 10 m × 10 m) in six mangrove communities in order to predict trends in their long-term recovery. Each selected mangrove community was dominated by either Avicennia officinalis, Bruguiera sexangula, Excoecaria agallocha, Heritiera fomes, Rhizophora apiculata, or Sonneratia caseolaris. Mortality among the Rhizophoraceae group, including B. sexangula and R. apiculata adult individuals, was more than 90%, whereas for other species belonging to the non-Rhizophoraceae group, it was less than 20%. Based on the 5-year assessment, the mangroves showed considerable resilience after the catastrophic cyclone disturbance. However, the recovery potential of specific species varied. In particular, communities where R. apiculata dominated demonstrated slow recovery processes. The reasons for the vulnerability of this species of Rhizophora to cyclone disturbance is assumed to be the result of three indirect post-cyclone consequences: high mortality caused by limited sprouting ability after wind-induced disturbance; erosion that occurred in the stressful habitat on riverbank mud flats with frequent tidal inundation; and delayed phenology after the catastrophic disturbance. The attempt to generalise the recovery rate of mangroves based on the crown closure of the six dominant mangrove communities explored in this study showed a recovery rate of 61.06% during the 4 years after Cyclone Nargis. The demonstration of these patterns and processes among the most dominant mangrove species after the cyclone disturbance should therefore provide reliable information to forest managers, ecologists and local people, helping them make management decisions regarding measures for mangrove restoration.