Impact assessment of urbanization on vegetation net primary productivity: A case study of the core development area in central plains urban agglomeration, China

Response of agroecosystem services to urbanization based on social-ecological networks: A case study of the Guanzhong Plain Urban Agglomeration

Deeply understanding the impact of urbanization on agroecosystems and their services is a key scientific issue in the field of human-land coupling system. In current studies, less attention has been paid to the complicated interrelation between the natural and socio-economic factors, and the properties of agroecosystem, being insufficient to systematically describe their influence of urbanization on AES, with a gap in deeply understanding the complicated intrinsic influence mechanisms between them. Taking Guanzhong Plain Urban Agglomeration (GPUA) as an example, the correlation networks of AES and vegetation, climate, landscape, geomorphology, and agricultural practices under different urbanization gradients were constructed by network analysis, and revealed how urbanization changes the impact of agroecosystems on AES. The results indicate that during the study period, habitat quality decreased by 1 % in GPUA, the water yield first increased and then decreased, with a change range of 27.86 %, and carbon sequestration and oxygen release, soil conservation, economic production, and tourism and leisure increased by 23 %, 67.34 %, 80.47 % and 5 % respectively. The supply of AES is strongly related to the structural features of urban and agricultural networks. With urbanization increased, the network structure became looser, and the network complexity and stability decreased by 16.27 % and 40.83 % respectively, while, and the links between network components weakened. The network transitivity and density have significant positive effects on AES. Totally, network structural properties accounted for 81.62 % of the variation of AES across the urbanization gradient in GPUA. Furtherly, these suggested that urbanization weakens AES by reducing the complexity and stability of agroecological networks. This study has significant implications for sustainable AES management and planning, and could provide a new perspective for investigating the maintenance mechanism of AES in complex agroecosystems.

From city to countryside: Unraveling the long-term complex effects of urbanization on vegetation growth in China

The urban environment is the "natural laboratory" of the global ecosystem, and it has complicated effects on vegetation growth, including direct effects (land use transformations) and indirect effects (climatic environment changes). However, the long-term responses of vegetation to urbanization and its associated controlling factors across different spatial scales, from pixels to regions, remains unknown. Here, we unraveled the dual influence of urbanization on vegetation growth and its potential drivers along the urban development gradients in China with satellite observations of leaf area index (LAI) during 2000-2020. The results showed that 65.68 % of pixels in whole China exhibited an increasing trend in vegetation growth, with prominent greening (as indicated by LAI increases) in rural background areas (0.198/10a), significant greening in urban core areas (0.0343/10a), and significant browning in suburban areas (-0.0391/10a). As the process of urbanization intensified, the relationship between urbanization and vegetation growth became increasingly complex, transitioning from linear to non-linear interaction. The overall direct effects of Chinese cities were negative and increased annually. Meanwhile, the positive indirect effects of urban environments on vegetation growth initially declined and then recovered. Cities with high urbanization level (urbanization rate, ULp >70 %) had higher indirect effects (0.24 %) and growth offsets (0.98 %) than that with moderate (ULp = 60 %-70 %) and low urbanization levels (ULp <60 %) (0.18 %, 0.10 %). In economically developed cities, land use changes from construction to vegetation, influenced by urban policies and management strategies, positively impacted urban greening. Overall, more urbanized cities (ULp >70 %) experienced vegetation growth enhancement due to more intense land use changes, whereas less urbanized cities (ULp <70 %) showed the opposite trends. Understanding the direct and indirect effects of urbanization on vegetation growth is crucial for devising effective urban planning and environmental conservation policies. It can help guide future urbanization processes and minimize adverse effects on the natural environment.

Urbanization weakens vegetation resilience in the Pearl River Delta, China

Rapid urbanization has introduced increasingly complex social-ecological processes, intensifying the impacts on vegetation growth. Assessing urban vegetation resilience is critical to understanding urban vegetation growth. However, the current understanding of vegetation resilience in highly urbanized areas, especially regarding the influence of human activities, remains limited, constraining efforts toward sustainable urban vegetation management. In this study, we identified the spatiotemporal heterogeneity of urban vegetation resilience in the Pearl River Delta (PRD) using the lag-one autocorrelation coefficient (AC1) of the enhanced vegetation index (EVI) derived from Landsat imagery. Referring to the general conceptual framework for quantifying the impacts of urbanization on vegetation growth, we assessed the impacts of urbanization on vegetation resilience in the PRD urban agglomeration from 1998 to 2022. Results revealed that 21% of the urban area experienced one to five vegetation loss events, primarily lasting 1-2 years. Although vegetation growth was enhanced along the urbanization intensity gradient, a significant (p < 0.05) downward trend in vegetation resilience was observed, indicating that urbanization restricted the stability and sustainability of urban vegetation. By distinguishing between direct and indirect impacts, we found that the indirect impacts of urbanization on vegetation resilience gradually outweighed the direct impacts over time. Our findings further demonstrate that while intensive management can promote regreening in urban settings, maintaining the prevalent stability of urban vegetation remains challenging. These findings contribute to a better understanding of the human impact on vegetation resilience and offer significant implications for seeking directions to improve urban vegetation resilience.

Detecting and attributing the impact of human activities on grassland aboveground biomass in China's Loess Plateau

Human activities significantly influence grassland ecosystem functions, particularly plant biomass. However, the direction and magnitude of these effects remain insufficiently explored. Herein, we quantitively assessed both the positive and negative effects of various human activities on grassland aboveground biomass (AGB) in China's Loess Plateau from 2000 to 2022. The results indicated that the magnitudes of positive effects increased by 0.29 g m-2 per year, whereas the negative effects decreased by 0.31 g m-2 per year. Spatially, 32 % of the grasslands experienced significant positive effects, whereas the rest grasslands faced negative effects. Notably, only 20 % of the areas with negative effects showed worsening trends mainly due to ecological restoration, sustainable agriculture, and population migration. Agricultural production activities and population changes emerged as dominant factors, with some activities, like livestock farming, exhibiting dual effects (i.e., positive and negative effects) on AGB. These findings underscore the complexity of human activities in affecting the grassland production function and highlight the necessity for balanced management strategies to sustain grassland productivity and resilience.

Monitoring and predicting development of built-up area in sub-urban areas: A case study of Sleman, Yogyakarta, Indonesia

Monitoring built-up areas in the previous year and possible predictions for the following year are important in planning regional development and controlling the expansion of built-up areas. This study detects changes in the built-up area (2018-2022). It predicts the future (2026) using Landsat satellite imagery in the Sleman Regency, Yogyakarta Special Region, Indonesia study area. Mapping built-up areas is identified using the Normalized Difference Built-Up Index (NDBI). Vegetation conditions were analyzed using the Normalized Difference Vegetation Index (NDVI). Changes in the built-up area are predicted using the CA-Markov chain model for 2026. The prediction is calibrated by comparing the simulated map with the results of the classification of built-up areas in 2022. The research findings show that the built-up area has increased by 12.84 % from 2018 to 2022 and is predicted to increase by 15.48 % in 2026. The existence of built-up areas has an influence on land surface temperatures where the analysis results show a moderate correlation between NDBI and LST, namely 2018 (R2 = 0.401), 2019 (R2 = 0.323), 2020 (R2 = 0.401), 2021 (R2 = 0.415), and 2022 (R2 = 0.384). The higher the NDBI value, the higher the LST value, and vice versa. Therefore, regional development planning, mainly built-up areas, is an important recommendation for decision-makers in the study area.

Impacts of urbanization on ecosystem carbon cycle: a case study of land use change in Tianjin metropolitan area

For the sustainable development of the city, in a study of Tianjin's rapid urbanization, we explore the complex interplay between land use change and the ecosystem carbon cycle from 2000 to 2020. Spatial analysis and profit-loss matrix calculations reveal contrasting ecological impacts: expansion of woodlands and grasslands enhances Net Primary Productivity (NPP) and reduces carbon emissions, while urban construction shows the opposite effect. Over 20 years, Tianjin's urban transformation led to a 16.91 GgC decline in NPP amidst a construction boom. However, post-2015 ecological policy shifts resulted in a significant net carbon uptake of 0.85 Gt, demonstrating the potential of policy interventions in mitigating environmental impacts of urbanization. This study underscores the importance of sustainable urban planning and ecological conservation strategies in highly urbanized settings.

Dual effects on vegetation from urban expansion in the drylands of northern China: A multiscale investigation using the vegetation disturbance index

Drylands contribute roughly 40 % of the global net primary productivity and are essential for achieving sustainable development. Investigating the effects on vegetation from urban expansion in drylands within the context of rapid urbanization could help enhance the sustainability of dryland cities. With the use of the drylands of northern China (DNC) as an example, we applied the vegetation disturbance index to investigate the negative and positive effects on vegetation from urban expansion in drylands. The results revealed that the DNC experienced massive and rapid urban expansion from 2000 to 2020. Urban land in the entire DNC increased by 19,646 km2 from 8141 to 27,787 km2, with an annual growth rate of 6.3 %. Urban expansion in the DNC imposed both negative and positive effects on regional vegetation. The area with negative effects reached 7736 km2 and was mainly concentrated in the dry subhumid zones. The area with positive effects amounted to 5011 km2 and was comparable among the dry subhumid, semiarid, and arid zones. Land use/cover change induced by population growth significantly contributed to these negative effects, while the positive effects were largely caused by economic growth. Therefore, it is recommended to strike a balance between urban growth and vegetation conservation to mitigate the adverse effects on vegetation from urban expansion in drylands. Simultaneously, it is imperative to expand urban green spaces and build sustainable and livable ecological cities to facilitate sustainable urban development.

Asymmetric response of vegetation GPP to impervious surface expansion: Case studies in the Yellow and Yangtze River Basins

Terrestrial gross primary production (GPP) changes due to impervious surfaces significantly impact ecosystem services in watersheds. Understanding the asymmetric response of vegetation GPP to impervious surface expansion is essential for regional development planning and ecosystem management. However, the asymmetric response of vegetation GPP to the impacts of impervious surface expansion is unknown in different watersheds. This paper selected the Yellow River and Yangtze River basins as case studies. We characterized the overall change in GPP based on changes in impervious surface ratio (ISR), determined impervious surface expansion's direct and indirect impacts on GPP in the two watersheds, and further analyzed the asymmetric response of the compensatory effects of indirect influences on the impervious surface expansion in different watersheds. The results showed that: (1) The vegetation GPP decreased with increasing ISR in the Yangtze River Basin, while that in the Yellow River Basin first increased and then reduced. (2) The direct impacts of increased ISR reduced vegetation GPP, while the indirect impacts both had a growth-compensating effect. Growth compensation stabilized at approximately 0.40 and 0.30 in the Yellow and Yangtze River Basins. (3) When the ISR was 0.34-0.56, the growth compensation could offset the reduction of GPP due to direct impact and ensure that the background vegetation GPP was not damaged in the Yellow River Basin. In contrast, the background vegetation GPP was inevitably impaired with increased ISR in the Yangtze River Basin. Therefore, this study suggests that the ISR should be ensured to be between 0.34 and 0.56 to maximize the impervious surface of the Yellow River Basin without compromising the background vegetation GPP. While pursuing impervious surface expansion in the Yangtze River Basin, other programs should be sought to compensate for the loss to GPP.

The impact of climate change and human activities to vegetation carbon sequestration variation in Sichuan and Chongqing

Exploring the vegetation carbon cycle and the factors influencing vegetation carbon sequestration in areas with complex plateau-basin topography and fragile ecosystems is crucial. In this study, spatial and temporal characteristics of carbon sequestration by vegetation in Sichuan and Chongqing from 2010 to 2020 and the influencing factors were investigated through simulations of net primary productivity (NPP) using the modified Carnegie-Ames-Stanford approach (CASA) and the Thornthwaite Memorial (TM) model and using chemical equations of photochemical reactions. The results indicated that: The spatial distribution of carbon sequestration capacity (CSC) trends showed an increase in the east (the most prominent increased trend along the mountainous areas of the basin) and a decrease in the west (western Sichuan plateau). Differences exist in the impact factors of CSC in different regions. In the basin margins and mountainous areas, where the proportion of forests was high, a combination of climate change and human activities contributed to the increase in CSC. The relatively warm and humid meteorological conditions in the hinterland of the basin were more conducive to the increase in CSC, and climate change also affected the region more significantly. In contrast, in the relatively high altitude of western Sichuan, controlled human activities were the key to improving CSC. The results of the study contribute to the understanding of the basic theory of vegetation carbon cycle in areas with complex plateau-basin topography and fragile ecosystems, as well as to provide suggestions for ecological shelter construction and ecological restoration in the upper Yangtze River.