Response of gross primary productivity to compound drought–heat events in southeast asian rubber plantations

Study Region The Southeast Asian rubber belt (SEA-RB) spans mainland and maritime Southeast Asia (SEA), encompassing approximately 14.2 million hectares of rubber plantations. Study Focus This study quantified compound drought–heat events (CDHEs) across SEA-RB from 2001 to 2020 using a Compound Drought–Heat Index (CDHI) and investigated their impacts on gross primary productivity (GPP) through integrated remote sensing analysis and structural equation modeling (SEM). Novel Hydrological Insights for the Region We identified five major sustained CDHEs that strongly coincided with ENSO phases. Intensification hotspots emerged in mainland SEA (42.72% of plantations), particularly within the northwestern Indochinese Peninsula, whereas maritime regions remained stable. CDHEs caused progressive GPP losses (56% ± 3.2–61% ± 5.2%), significantly exceeding single-stress scenarios. SEM analysis revealed that CDHEs strengthen stomatal regulation as the dominant control on photosynthesis while substantially mitigating direct thermal damage to enzymatic processes. This protective trade-off prioritizes hydraulic safety over carbon assimilation, a mechanism absent under isolated stressors. These findings demonstrate that compound extremes trigger qualitatively distinct physiological responses, highlighting the inadequacy of single-stressor approaches for predicting and managing tropical plantation productivity under future climate scenarios.