Identifying land use thresholds for ecosystem service balance through supply-demand assessment in Hainan Island

Against the backdrop of accelerating urbanization, the imbalance between ecosystem services (ESs) supply and demand has become a major concern for regional sustainable development, particularly in geographically isolated islands, where spatially confined land resources limit the self-regulatory capacity of terrestrial ESs and amplify their vulnerability to supply-demand imbalance. Using Hainan Island as a case study, we integrated the InVEST model, random forest algorithm, and weighted linear regression to quantify the spatiotemporal supply-demand dynamics of five core ESs from 2010 to 2020, identified key land-use thresholds governing ESs balance, and established a dual-scale analytical framework at county and grid levels. The results revealed a pronounced spatial dichotomy of “coastal degradation versus central stability”. Central forests sustained surpluses in regulating services (Habitat Quality (HQ), Soil Retention (SR) and Carbon Sequestration (CS)), while deficit zones clustered in coastal towns. Contribution analysis of land-use types to the ecological supply-demand ratio (ESDR) identified built-up land as the primary negative driver of imbalance. Built-up expansion contributed to supply-demand deficits in Water Retention (WR), with mean ESDR values of − 0.0090 in 2020 and induced imbalance risks for Grain Production (GP) in half of the counties at the county scale. At the 500 m grid scale, 87.71% of the island maintained simultaneous supply-demand balance across all five services. Threshold analysis identified a structural land-use dilemma: attempting to achieve GP balance through forest-to-cropland conversion triggers a “denominator effect”, mechanically increasing built-up land proportions and pushing locally bound regulating services beyond their critical thresholds. This reflects an asymmetry in compensability, as GP deficits can be mitigated via external trade networks whereas regulating services are difficult to compensate externally. At the county scale, five management zones (“maintained zone”, “GP promoted zone”, “CS promoted zone”, “GP-CS promoted zone”, and “GP-CS-WR promoted zone”) were delineated to safeguard ecological cores and address spatially differentiated deficits; at the grid scale, 87.71% of the study area currently maintains ESs balance across all five services, with the identified land-use thresholds serving as early-warning indicators to guide timely regulation of built-up expansion. The integrated analytical framework established in this study is potentially transferable to other tropical islands facing land resource constraints, while the empirical threshold values necessitate site-specific calibration for regional adaptation. This threshold-based governance paradigm offers a practical and quantitative reference for alleviating structural trade-offs in ESs and optimizing ecological management strategies for land constrained island regions.