Intra-specific patterns of δ13C, growth and wood density variation at sites of contrasting precipitation with implications for modelling carbon sequestration of tropical tree species

Tropical agroforestry practices play a crucial role in mitigating global climate change by absorbing CO2 from the atmosphere through photosynthesis and storing carbon in their biomass. Assessing the effects of water stress on carbon sequestration as well as uncertainties in measurement, are important for implementing the Reducing Emissions from Deforestation and Forest Degradation (REDD+) programs and carbon trading. This study aims to understand how precipitation influences carbon sequestration of Tectona grandis, Acacia mangium and Eucalyptus camaldulensis growing in agroforestry (woodlot) plantations in Bangladesh. Wood cores were collected at two different sites with contrasting (low vs high) annual precipitation and analysed for radial growth, carbon isotope abundance (δ13C) of cellulose and wood density. Site- and species-specific variation in δ13C was observed with higher values (less negative) detected at the low precipitation site. Trees at the low precipitation site showed lower growth rate and higher wood (basic) density compared to the trees at high precipitation site. Trees at the low precipitation site also showed significantly lower carbon sequestration rate (CSR) than those of the high precipitation site. δ13C reflects site- and species-specific water stress conditions. This study characterises intra- and inter-specific CSR variations in contrasting sites and confirms the importance of considering site-specific radial variation of wood density to render more accurate accounting of carbon sequestration and storage in tropical forests.