Why some trees are more vulnerable during catastrophic cyclone events in the Sundarbans mangrove forest of Bangladesh

Abstract Mangroves are recognised for their diverse set of ecosystem services, including protection from tropical cyclones and tidal surges. Mangroves are also adapted to withstand disturbances across a range of climatic conditions, and the frequency and severity of disturbances are projected to increase in the coming years due to climate change and sea-level rise. The Sundarbans of Bangladesh and India is one of the most frequently affected mangrove forests in South Asia. We investigated the effect of cyclone disturbance and stand characteristics on the survival of two dominant mangrove tree species – Heritiera fomes and Excoecaria agallocha. Data was collected through field surveys after cyclone Sidr, a category 5 cyclone that struck in the area in 2007, creating substantial forest damage. We used a Generalized Additive Mixed Model to analyse the effect of tree species, stem diameter at breast height (dbh), and tree spatial position in the forest stand on the degree of cyclonic damage. We find that cyclonic damage in the Sundarbans forest is sensitive to species and dbh. At similar tree size, Heritiera fomes was more vulnerable to cyclonic damage than Excoecaria agallocha. In Heritiera fomes the intensity of wind damage during cyclone increase with increasing dbh. In Sundarbans, cyclonic damage also depended on stand factors such as proximity to the riverbank or forest edges. We suggest silvicultural treatments, such as increasing the tapering of crown or decreasing height/dbh ratios of valuable species, could minimise future cyclonic damage in the area. Further investigations are necessary to improve the management of mangroves in the Sundarbans in the face of climate change, sea-level rise, and novel anthropogenic pressures.