Water and carbon balance of rubber trees modelled under changing climate and management-driven disturbances

Abstract. Rubber plantations play a critical role in the economy of Southeast Asia, yet their productivity is increasingly exposed to environmental variability and climate change. Process-based models able to represent the interactions between water and carbon dynamics are essential for assessing their current functioning and anticipating future responses. In this context, we adapted the CASTANEA-MAESPA model to simulate the biophysical functioning of mature rubber plantations in Thailand. We included in that model a newly developed module for latex production which takes into account management practices and links tapping-related processes to overall carbon allocation and growth. The model results were compared to water and carbon fluxes and stock data at a flux tower experimental site in the central-east Thailand (CRRC) and water fluxes and latex yield data at a research station in southern Thailand (SKRS). Good agreement is found between the simulated model outputs and the measured water and carbon fluxes and stocks at both sites. The model estimated at CRRC a gross primary productivity (GPP) of 25.95 t C ha^-1 yr^-1 for a 25-year-old rubber plantation, close to the observed 26.98 t C ha^-1 yr^-1. Simulated latex yield was 1.64 t C ha^-1 yr^-1 versus 1.80 t C ha^-1 yr^-1 observed, and simulated wood biomass was 117.96 t C ha^-1 compared with 123.15 t C ha^-1 observed, at CRRC. Overall, this work provided scientifically grounded results to understand latex production in Southeast Asia, while also identifying key knowledge gaps, particularly regarding the determinants of rubber leaf phenology.