The YEB is a major national strategic development area in China with the Yangtze River basin as the main trunk, which contains three national strategic urban agglomerations: YRD, MRYRU and CCU ( Figure 1 ). YEB involves 130 prefecture-level cities in 11 provinces and municipalities, including Shanghai, Jiangsu, Zhejiang, Anhui, Jiangxi, Hubei, Hunan, Chongqing, Sichuan, Yunnan, and Guizhou (Chen et al., 2023). This study takes the YEB as the case study, with 130 cities within it as the research sample. The Yangtze River basin, with its warm climate, abundant rainfall, numerous tributary lakes and rich species resources, is a concentrated distribution area for rare and endangered wildlife in China. The per capita GDP of Yangtze River Economic Zone increased from 7506.25 yuan to 71,102.70 yuan from 2000 to 2020, an increase of 8.472 times, and the population density increased from 454.65 person/km² to 490.6 person/km², an increase of 7.907%. Despite the Chinese government’s initiative of “Grasping the big protection, not big development”, the conservation and restoration of forest and ecological space in the YEB has achieved significant achievements. However, the rapid growth of economic scale and population size, as well as the significant disparities between provinces and cities in socio-economic and natural contexts have led to the continued contradiction between human urban activities and ecological environmental protection in the region. Therefore, it is important to study the impact mechanism of urbanization on NPP in the YEB for the construction of ecological resilience and sustainable development in the region.

Combining GIS zoning statistics tools and spatial interpolation techniques to measure the dynamic trend of NPP in the YEB, as shown in Figures 3 , 4 . The investigation shows that the average NPP in the YEB increased from 592 g*c/m² to 670 g*c/m² at a rate of 0.621% from 2000 to 2020 ( Figure 3A ). Among them, the NPP growth of CCU is the most significant, with an increase of 39.387% from 2000 to 2020, followed by MYRYU and YRD, with increases of 14.867% and 6.495%, respectively. In terms of spatio-temporal dynamics, the NPP level in the YEB shows a clustering pattern of “high in the south and low in the north, high in the west and low in the east” ( Figure 4 ), both in terms of remote sensing images and distribution based on administrative districts. The three major low-value clusters (NPP<450 g*c/m²) in the eastern, central and western parts of the study area in 2000 gradually developed toward dispersion in 2020, and the high-value clusters, mainly in Yunnan Province, spread further in 2020. In terms of the change trend, the average NPP of the YEB shows a general pattern of change of “increased in the north and decreased in the south”. The NPP degraded cities with 13.178% of all cities are mainly located in the southeastern and southern part of the YEB. The most prominent NPP degradation is Xishuangbanna and Lishui, with decreases of 9.787% and 4.575%, respectively. The cities with high values of NPP growth are mostly distributed in the CCU and northern areas of the MYRYU, especially Suining and Ziyang with increases of 84.486% and 78.810%, respectively.

The overall average UL index of the YEB grew from 22.485% to 23.652% with an average annual growth rate of 0.253% from 2000 to 2020 ( Figure 5 ). Among them, the UL index of the MYRYU has the most significant growth, with an increase of 17.455% from 2000 to 2020, followed by CCU and YRD, while the UL index of YRD is usually the highest, with a UL index of 42.982% in 2020. In terms of spatio-temporal dynamic distribution, the level of urbanization in the YEB gradually changes from “high in the east and low in the west” to a distribution pattern with urban agglomerations as the regional core. In 2000, it was presented as the eastern UL high-value group with Shanghai as the core. By 2010 and 2020, the UL indexes of Wuhan, Changsha, Chongqing and other central cities in the central and western regions grew rapidly, gradually forming a pattern of UL high-value distribution led by the core cities of urban agglomerations. In terms of the change trend, 37.984% of the cities in the YEB have a decreasing trend in UL index, mainly in the northwestern cities represented by Aba and the northeastern cities represented by Bozhou. However, this does not imply a degradation of the urbanization process, as the UL index is performed based on a standardized formula (Eq. 2), the variation of the UL index mainly shows the degree of difference in urbanization levels and the change in the rank order among cities in the YEB. The cities with significant UL index growth are mainly located in the eastern part of the MYRYU and the southern part of the YRD. In particular, the UL indexes of Jiujiang, Suzhou and Changsha increased by 17.747%, 14.900% and 15.444%, respectively.

Figure 6 shows the change trend of bivariate global autocorrelation and local autocorrelation of UL index with NPP in YEB from 2000 to 2020. The global Moran’s I for UL and NPP in 2000, 2010 and 2020 are −0.350, −0.380 and −0.419 (p-value = 0.001), respectively, which indicate an overall increasingly significant negative spatial autocorrelation between urbanization and NPP in the YEB. In terms of bivariate local autocorrelations, UL and NPP negatively correlated cluster cities (containing both High-Low and Low-High cluster types) are dominant, and the share increases from 24.806% to 33.333% during the study period. This validates the increasingly significant negative spatial autocorrelation between urbanization and NPP in the YEB, and confirms the urgent need to adjust urbanization pathways in the region to reduce the negative impacts on vegetation ecosystems and carbon cycle functions. “High-Low” is the dominant cluster type in the bivariate spatial correlation, and the number of cities increased from 13.178% to 20.930%, followed by “Low-High” clusters, whose overall share also increased from 11.628% to 12.403%. In terms of spatio-temporal evolution, the distribution pattern of bivariate local spatial autocorrelation cluster types is relatively stable during the study period. Specifically, the “High-Low” negative correlation clusters are mainly located in Bozhou, Huai’an and other cities in Anhui and northern Jiangsu. The prominent scale of population, arable land, and construction land in these cities ( Figure 1 ) generates significant encroachment on vegetated ecosystems, resulting in relatively high levels of urbanization and relatively low NPP in the region.

The “Low-High” negative correlation clusters cities are generally located in the southwestern region, such as Xishuangbanna, Lincang and Pu’er. These cities are located near the “Hu Huanyong population density line” in China, where the human footprint is relatively sparse and the terrain is complex, with many forested and mountainous areas off the beaten path. The excellent natural ecological background and the low intensity of urban development have contributed to the low level of urbanization but high quality plant ecosystems in the area. The “High-High” positive correlation clusters are mainly located in Kunming, reflecting the high quality ecological environment and the strong “siphon effect” of population, industry and resources in the region. The “Low-Low” positive correlation agglomeration is mainly laid out in Huanggang, Jingzhou and Jingmen and other cities in the middle reaches of the Yangtze River. Combined with the performance of multidimensional urbanization, these cities have low levels of land and economic urbanization, have significant gaps in urban development intensity compared to Wuhan, and are subject to significant resource siphoning. At the same time, due to the location in Jianghan Plain, organic matter produced by photosynthesis of grassland vegetation is more disadvantaged than that of mountainous woodlands in humid climate, resulting in relatively disadvantaged urbanization level and vegetation ecosystem productivity in this region.

The direct effect of urbanization on NPP has been confirmed in previous studies, which emphasize the substantial conversion of ecological spaces such as grasslands and woodlands to production-living spaces during urbanization, resulting in the derogation of vegetation cover systems and leading to a decrease in regional NPP levels (Yang et al., 2021). Our study considers urbanization as a unified system, integrating urbanization elements such as population urbanization, economic urbanization, and land urbanization, providing an comprehensive perspective for investigating the impact of urbanization on NPP (Chen et al., 2020). The findings emphasize that the negative effect of urbanization on NPP is not only in the local area, but more widely a spillover effect that goes far beyond the local effect. The former may be related to the inherent resource-consuming activities of cities (Sharma et al., 2022; Zhong et al., 2021; Chen et al., 2023). Urban population migration and industrial boom increase the demand for natural resources and production-living space, while land urbanization implies the conversion of a large amount of ecological space to artificial impervious surfaces. These urbanization processes have, to some extent, directly or indirectly enhanced the encroachment on native vegetation cover systems and challenged the carbon cycling capacity of vegetation. The latter may have some connection with the regional integration construction of the Yangtze River Economic Belt. As a national strategic development region in China, the Yangtze River Economic Belt forms an integrated cooperation space with Shanghai as the leader and urban agglomerations along the route as the core. The region has gradually built synergistic channels in technological innovation, data integration, and industrial chain construction (Tian and Pang, 2022). With the support of regional integration, ecological product consumption actions can influence neighboring urban markets through the integrated “land, water, and air” channel, thus indirectly causing cross-regional ecological consumption of vegetation (Wang et al., 2022).

The spatial heterogeneity of the impact of UL on NPP in urban agglomerations in the YEB is verified in this study, which complements previous studies based on individual urban agglomerations or the YEB as a whole. For example, Qiao and Huang (2022) assessed the ecosystem health of the YRD and evaluated the impact of land urbanization on ecosystem health. Chen et al. (2022) based on NDVI index explored the ecosystem health level of the MYRYU, and pointed out a U-shaped relationship between urbanization and ecosystem health. Our investigation finds that the NPP of the CCU is most strongly influenced by UL, especially the negative influence of western cities is significantly stronger than that of eastern cities such as Chongqing. The reason for this phenomenon may be that the western part of the CCU is surrounded by mountains and hills, with a high quality forest ecological substrate and carbon sequestration capacity, and urban development activities have modified the local forest ecosystem to a more obvious extent. In contrast, most of the eastern cities such as Chongqing are located in the plains and have relatively more homogeneous NPP of grassland ecosystems, which, together with more modern urban planning and green economy construction, contribute to the ecological resilience of these cities to resist urbanization (Li et al., 2023; Luo et al., 2023). The distribution pattern of UL effects in the MYRYU remains relatively stable, but it is noteworthy that the UL of cities in the eastern part of the urban agglomeration is positive in 2020. This may have some synergistic relevance to urban ecological planning in the region (Chen et al., 2022; Liu et al., 2023; Ma et al., 2023). At the end of 2009, China released the “Poyang Lake Ecological Economic Zone Plan”, which tries to build the Poyang Lake area into an advanced and efficient ecological industrial cluster and gradually build a new urban agglomeration with ecological livability. This promotes the ecological restoration of vegetation and the sustainable construction of urbanization in the area. The driving effect of UL on NPP in the YRD turns from negative to positive, which may be related to the implementation of ecological co-protection planning in the region. By proliferating green production processes, circular economy technologies and energy saving and emission reduction standards of the core cities of Shanghai, Nanjing, Hangzhou and Hefei, the overall ecological restoration governance and urban sustainability of the YRD urban agglomeration can be promoted (Luo et al., 2021; He et al., 2023).

Our study confirms that widespread significant negative ecological effects of urbanization exist in the YEB, where vegetation carbon cycle function and ecological stability were challenged, and ecological resilience building strategies based on optimal urbanization management perspectives should receive attention. In terms of land urbanization, constraints on the rough expansion of production-living space should be strengthened, and more attention should be paid to the vegetation protection and land development approval in new urban areas. The renewal of urban parks, corridors, green space construction and intensive and optimal use of land in old urban areas should also be mentioned more often. In terms of population urbanization, a concept that focuses on green and low-carbon living and consumption should be mentioned more often, with attention to people-centered vegetation and ecological restoration efforts. In terms of economic urbanization, we will strengthen the breakthrough of circular economy and green production process, and accelerate the transformation of low carbon and green industry for alleviating the plundering of vegetation and ecological resources by urban economic development. Moreover, our study confirms that the negative ecological effect of urbanization has a significant spillover effect, which actually provides fundamental evidence for the joint regional ecological management of the YEB. More improved communication channels on information technology, greening industrial chains and pollutant emission standards should be established between cities. Meanwhile, the sharing of information related to ecological monitoring, pollution emission and climate change should be enhanced to optimize the urbanization paths and patterns of the YEB from an overall perspective. From the direction of urban agglomeration optimization, the CCU needs to strengthen the ecological restoration of vegetation in western cities and formulate gradual construction of human settlements and resource extraction activities. The MYRYU should pay more attention to the ecological conservation work in the western Hunan region, and strengthen the protection of mountainous forests and grassland management. The YRD should further improve urban ecological planning policies and enhance urban livability, focusing on the transmission of urban ecological resilience construction ideas and the diffusion effect of green production technologies. In this way, to promote the YEB to form a green development path guided by urban agglomerations.