Objective The interplay of natural and anthropogenic factors has led to significant spatial heterogeneity in vegetation distribution across the Beijing-Tianjin-Hebei region. Vegetation conditions are a critical determinant of regional ecosystem service (ES) and functioning. Nevertheless, the threshold effects of vegetation changes on ecosystem services across different functional zones remain unclear, and whether such thresholds vary spatially lacks quantitative identification. This study aims to systematically analyze the spatiotemporal dynamics of fractional vegetation cover (FVC) and key ES in various functional zones (the northwestern ecological conservation zone, central core functional zone, southern functional expansion zone, and eastern coastal development zone) from 2000 to 2020, and to quantify the threshold effects of FVC on ES.
Methods Based on data availability and assessment feasibility, this study focused on the importance of ecological security in the Beijing-Tianjin-Hebei region and its correlation with vegetation changes, and selected four key ecosystem services: habitat quality, water yield, soil conservation, and carbon sequestration. The specific methods were as follows. First, the habitat quality and water yield modules of the integrated valuation of ecosystem services and trade-offs (InVEST) model were utilized to assess habitat quality and water yield; the revised universal soil loss equation (RUSLE) model was used to assess soil conservation services, and the Carnegie-Ames-Stanford approach (CASA) model was used to assess carbon sequestration services across different functional zones of the Beijing-Tianjin-Hebei region. Second, FVC in each functional zone was estimated based on NDVI data. Subsequently, the biophysical values of the four ecosystem services were normalized into dimensionless values, which were then summed to obtain the total ecosystem service (TES), representing the overall level of ES in the Beijing-Tianjin-Hebei region. Finally, a combination of the quantile segmentation method and elasticity coefficient was applied to identify the FVC thresholds that influence TES across different functional zones.
Results The spatiotemporal dynamics of ES in the Beijing-Tianjin-Hebei region was significant from 2000 to 2020. From the perspective of functional zones, habitat quality decreased by 2.98% in the northwestern ecological conservation zone, by 11.32% in the central core functional zone, and by 8.14% in the southern functional expansion zone. Notably, habitat quality in the eastern coastal development zone showed an increasing trend during this period, with an increase of 10.62%. Soil conservation increased most significantly in the eastern coastal development zone, rising by 91.84%. It also increased in the northwestern ecological conservation zone (61.01%), the central core functional zone (55.22%), and the southern functional expansion zone (28.63%). Regarding water yield, the eastern coastal development zone exhibited the largest increase (132.13%), followed by the northwestern ecological conservation zone (127.36%), the central core functional zone (119.40%), and the southern functional expansion zone (43.19%). In terms of carbon sequestration, the northwestern ecological conservation zone and the southern functional expansion zone showed the most substantial increases, with rises of 65.46% and 65.99%, respectively, while the central core functional zone and the eastern coastal development zone increased by 1.26% and 24.12%, respectively. FVC showed an overall increasing trend. By functional zone, the northwestern ecological conservation zone exhibited a relatively pronounced increase (14.60%), followed by the eastern coastal development zone (2.66%), the central core functional zone (1.49%), and the southern functional expansion zone (0.37%). Furthermore, this study elucidated the differentiated impacts and thresholds of FVC on ES across functional zones. The thresholds, in descending order, were: northwestern ecological conservation zone (0.946), central core functional zone (0.824), eastern coastal development zone (0.775), and southern functional expansion zone (0.772).
Conclusion This study shows that the effects of FVC on ES in different functional zones exhibit regional threshold characteristics. Accordingly, differentiated ecosystem management pathways were proposed based on the ecological conditions and FVC threshold characteristics of each functional zone. For the northwestern ecological conservation zone, which has an overall high FVC, management priorities should shift from quantity expansion to quality improvement. The central core functional zone should focus on the comprehensive enhancement of ecosystem quality rather than merely increasing vegetation area, promoting ES improvements within limited spaces through optimized urban green space landscape patterns. For the southern functional expansion zone dominated by agricultural ecosystems, efforts should enhance the multifunctionality of agricultural ecosystems, scientifically regulate FVC in agricultural systems, and promote water-saving irrigation and ecological agriculture to synergistically improve provisioning ES alongside biodiversity and hydrological regulation functions. The eastern coastal development zone requires the synchronised improvement of vegetation quality and stress resistance, avoiding monoculture vegetation planting, emphasizing saline-alkali tolerance, and constructing structurally stable and functionally diverse ecosystems. These findings provide scientific support for precision ecosystem management and the realization of ecological product value and sustainable development in the Beijing-Tianjin-Hebei region.
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