Nonlinear Impacts and Threshold Effects of LULC on Ecological Resilience in the Central Guizhou Urban Agglomeration

Land development inevitably causes disturbances to the ecosystem, leading to instability in ecological functions and abrupt changes in ecological resilience (ER). Previous studies mainly focused on the response of ER to land use but lacked simulations of nonlinear dynamics and quantitative analysis of the threshold effects, especially in mountainous cities with complex terrain. This study applied the boosted regression tree (BRT) model to explore nonlinear land-use effects and threshold features for ecological resilience (ER) across 16 topographic gradients in the Central Guizhou Urban Agglomeration. The gradients derive from four-level classification of elevation, slope, relief amplitude, and terrain position index. Results indicate that forestland shows consistent positive marginal associations with ER, with particularly strong relative contributions at mid-to-high topographic gradients. By contrast, cropland and construction land exert negative marginal effects that intensify under higher topographic constraints, and their suitable intervals narrow markedly in complex terrain. Model-derived empirical reference intervals show that forestland reaches 50–96% at high-elevation gradients; the upper limit for cropland is 7.07% on steep slopes; the suitable upper bound of construction land declines from approximately 50% in low-relief zones to 23% in high-relief zones. Such threshold disparities illustrate the moderating effect of topographic gradients on land-use-ecological resilience relationships, and these insights can offer conceptual references for differentiated territorial spatial governance of karst mountainous urban agglomerations.