Long-Term Spatiotemporal Dynamics of Forest Ecosystem Water Conservation and Management Zoning Based on Coupling Coordination Analysis in the Eastern Dabie Mountains, China

Forest ecosystem water conservation is an important ecohydrological regulating service for sustaining mountain watersheds under climate change. This study assessed water-conservation services in the eastern Dabie Mountains of China by integrating the InVEST Water Yield module under the Budyko framework, a Coupling Coordination Degree (CCD) model, and pixel-scale Theil–Sen, Mann–Kendall, and Ordinary Least Squares analyses. The study covered 1985–2024 through ten benchmark years (1985, 1990, 1995, 2000, 2005, 2010, 2015, 2020, 2022, and 2024). Mean water-conservation capacity across the benchmark-year maps was 362.7 mm. The OLS slope was 1.40 mm/a, while the two-sided MK test was non-significant (Z_MK = 0.54, p = 0.592), indicating a weak positive tendency in the benchmark-year sequence. Year-to-year variation was closely associated with hydroclimatic conditions, with canopy interception, litter storage, soil-water storage, and flow attenuation providing process pathways within the model framework. Water-conservation capacity reached 534.4 mm in the wet 2020 benchmark year, declined to 268.2 mm during the 2022 drought, and recovered to 369.6 mm in 2024. Comparison with area-scaled official bulletin surface-water references for seven overlapping years yielded a mean absolute percentage error of 5.21% and absolute relative errors of 0.00%–17.62%. High-value service areas were concentrated in the central forested massif, whereas low-value and coordination-imbalance areas were more common along agricultural and urbanizing margins. The integrated framework links service intensity, coordination status, and historical tendency to support differentiated watershed management and to identify spatial contrasts together with benchmark-year hydroclimatic responses.