Coupled responses of carbon storage and habitat quality to land use and land cover change in a tropical watershed of Northern Thailand

Land use and land cover change (LULCC) is a major driver of ecosystem service dynamics in tropical watersheds, yet empirical evidence linking carbon storage (CS) and habitat quality (HQ) over long-term trajectories remains limited in Southeast Asia. This study assessed the spatiotemporal responses of CS and HQ to historical (1989, 1997, 2005, 2013), current (2021), and future LULC scenarios (business-as-usual and conservation, 2037) in the Mae Chang watershed, northern Thailand. Using the InVEST model, CS and HQ were quantified for multiple time slices and scenarios. Non-parametric trend analysis (Theil–Sen and Mann–Kendall) was applied to detect monotonic changes, and LULC transition trajectories associated with CS and HQ trends were identified using a trajectory-based overlay approach. CS–HQ interactions were evaluated using Spearman rank correlation and spatial interaction mapping derived from trend classifications. Results indicate a persistent decline in total CS and an expansion of lower HQ classes, primarily associated with transitions involving forest, agriculture, and mining/urban land uses. Scenario projections indicate similar magnitudes of carbon loss under both BAU and conservation scenarios, suggesting that the conservation parameterization applied in this study—limited to protected/restricted areas—does not substantially alter watershed-scale loss trajectories. Despite overall declines in both services, CS and HQ exhibited a consistently strong positive correlation from historical to future conditions. Spatial interaction patterns were dominated by unchanged and weak synergy classes, while localized trade-offs were located among agricultural areas and transition zones. Overall, ecosystem service outcomes were strongly associated with major land transitions These findings suggest strengthening forest protection, promoting diversified agriculture, and considering complementary area-based conservation in vulnerable non-protected transition zones to sustain carbon storage and habitat quality.