Radial growth in mangrove Xylocarpus granatum J. Koenig is driven by salinity in the Sundarbans, Bangladesh

Albeit the Sundarbans provides protection and livelihood supports to ∼ 7.5 million climate vulnerable coastal people in Bangladesh and India, this sentinel mangrove ecosystem has been threatened by anthropogenic disturbances and rapid environmental changes including sea level rise (SLR). In this context, long-term tree growth data are increasingly essential to understand the effects of environmental changes on mangroves and also to formulate their management plans. In this study, we evaluate the nature and periodicity of growth rings in Xylocarpus granatum, an ecologically important mangrove tree species growing in the Bangladesh Sundarbans. In addition, we analyze the influences of climatic variables (i.e., precipitation and temperature) and river discharge on its radial growth. The results reveal that X. granatum forms distinct growth rings which are marked by a layer of parenchyma band consisting of 1–4 cells. The visual crossdating and the quality of chronology statistics indicate that the growth rings are crossdatable. A site-specific chronology was developed spanning from 1973 to 2020 based on the crossdated samples. The annual nature of X. granatum’s growth rings offer an opportunity to estimate tree age and growth rate. The ring width is influenced by salinity which is regulated mainly by freshwater influx through annual precipitation along with river discharge, particularly in July. This study suggests that growth rings could be used as a proxy in exploring X. granatum’s growth dynamics, especially in relation to environmental changes.