Tree radial growth is projected to decline in South Asian moist forest trees under climate change

Global climate change has been reported to affect tree growth around the world and such impacts are predicted to be intensified under future climate change particularly in the tropics. It is therefore important to study the climate-growth relationships of tropical trees to understand how they have responded to the past climate variability and to predict how they will respond to future climatic changes. We investigated tree radial growth responses to regional climatic changes in Bangladeshi moist tropical forests. We selected three species based on their distinct growth-ring boundaries and their wide distribution around the tropics. First, we simulated growth responses to climate for the past 66 years (1950-2015) based on the climate-growth relationships. Next, we projected tree-growth until the end of current century (2016-2100) under different climate change scenarios (Representative Concentration Pathways, RCP). All the three species produced statistically robust ring-width index chronologies covering the current and the past century. Climate-growth analysis revealed that temperature (monthly, annual and seasonal) significantly negatively affected tree radial growth in all three species. Precipitation prior to the current growing season negatively and current year post monsoon precipitation positively influenced radial growth. Tree radial growth was also influenced by Niño 3.4 region Sea Surface Temperature (SST) anomalies mainly through the modulation of local climate. We projected tree radial growth to be declined in all three species by 20% under high concentration scenario (RCP 8.5) followed by 11.3% and 9% under medium (RCP 6.0) and low-medium concentration scenarios (RCP 4.5). If these species show similar growth responses to climatic changes in other native ranges across the tropics, this could have severe consequences for the carbon balance of tropical forests.