Land sparing and sharing: Understanding the relationship between different construction land strategies and land functions in karst areas

Land multifunctionality requires integrated strategies to reconcile diverse human needs within finite resources. Conventional land sparing and sharing (LSS) frameworks, primarily applied to agricultural trade-offs between food production and biodiversity, inadequately address the non-agricultural production and living functions associated with construction land development. This study extends the LSS framework to holistically assess production, living, and ecological functions under construction land intensification. Focusing on China's karst region, we employed the Development Intensity Index (DII) as a quantitative strategy indicator. Using sub-basins in the Southwest China karst belt as analytical units over 2010–2019, we integrated land function measurements with the DII, nonparametric tests, Locally Weighted Scatterplot Smoothing (LOWESS), and Bayesian Change Point (BCP) analysis to precisely delineate spatial strategy differentiation and nonlinear functional responses. Significant nonlinear relationships and critical threshold effects were revealed between land use strategies and functions. As DII increased, production function exhibited an inverted U-shaped trend, peaking at a DII of 6.2 then declining significantly. Living function maintained a continuous positive correlation, with its growth rate accelerating slightly beyond an intensity of 10.5. Ecology function remained negatively correlated, declining sharply at a DII of 0.65 followed by a slower decrease rate. The comprehensive land function index reaches an inflection point at a DII of 6.35, beyond which its growth rate diminishes until eventually turning negative. The research quantifies key functional response thresholds, broadens the LSS framework's applicability to multifunctional land systems encompassing construction land. This finding facilitates the scientific selection of land-use strategies and promotes the transition of territorial spatial development toward coordination and sustainability.