1. Introduction
The continuous improvement of human well-being is the main objective for social development and the vision of human society [
1,
2]. Former research on human well-being mainly focused on economics, sociology, and social sciences, while the contribution of the ecological environment to human well-being has not received enough attention [
3,
4]. However, the truth is that improving human well-being in a sustainable way is extremely difficult given the realities of ecological degradation, environmental pollution, and the loss of biodiversity [
5]. The UN Millennium Ecosystem Assessment (MA) proposed a framework for linking ecosystem services and human well-being; 60% of global ecosystem services are declining, while the consumption of over 80% of ecosystem services is increasing, with human wellbeing directly or indirectly affected by these ecosystem services [
6]. Although scholars have conveyed the concept of ecosystem services in a variety of ways for various study contexts and purposes, there is consensus on the basic meaning and connotation of ecosystem services (ESs) as the benefits that humans derive directly or indirectly from the natural world [
7].
The study of the interactions and interlinkages between ESs is one of the core elements of ESs research. For the purpose of encouraging the sustainable management of natural capital, it is crucial to understand the linkages between different ecosystems [
8]. The supply of ecosystem services (ESs supply) depends on the structure, processes, and functions of ESs, which exist objectively rather than according to human will [
9]. The ESs supply is an indicator to measure the potential capacity of ecosystems [
10]. Demand for ecosystem services (ESs demand) refers to the utility that human society obtains through the consumption of ecosystem services in order to meet its own needs for survival and development [
11,
12]. Early scholars focused on the ESs supply, ignoring the ESs demand by human societies [
13]. As human demand for ESs affects the functioning of the whole ecosystem, the need for systematic management of ecosystem services can no longer be met by considering only the ESs supply [
14]. Therefore, more scholars have become interested in the relationship between ESs supply and ESs demand [
15], and they have conducted numerous theoretical [
16], methodological [
17], and practical studies [
1]. Current research focuses on the supply and demand for services of a single ecosystem type, ranging from provision services [
18] to regulating services [
19] and cultural services [
20]. These studies on ESs supply-demand range in scale from small watershed studies to urban [
1], regional [
21], and national [
22] case studies. They mostly focused on ES supply-demand at one particular moment [
23]. Fewer studies have been conducted on the evolution of ecologically fragile areas in watersheds where human-land conflicts are prominent. The ES supply-demand is linked to natural ecosystems and socioeconomic systems [
24]. Research on the long-term evolution of ES supply-demand can help to strengthen ecosystem management and optimize resource allocation, thus, ensuring regional ecological security and sustainable socioeconomic development.
Most studies on the drivers of ESs are based on qualitative analysis and correlation analysis, mostly from the supply-side perspective [
25,
26]. In contrast, there are few studies quantifying the drivers of matching ESs supply and demand [
23]. Moreover, the key influencing factors were mostly revealed by single methods, such as correlation analysis and ordinary multiple linear regression. One of the key challenges in ecosystem management is the lack of comprehensive quantitative studies on the spatiotemporal variability in the influence of various factors on supply and demand relations. It is difficult to reveal, in-depth, the mechanism of the evolution of supply-demand relations under the combined effect of multiple factors. In this study, geographical detector and geographically weighted regression (GWR) models [
14] were used to explore the dynamic evolution of supply-demand relationships under the influence of natural and socioeconomic factors. This has importance for the effective management of regional ESs and related policy formulation.
The Yellow River Basin (YRB) is an important ecological barrier and economic area in China [
27]. It is now facing the situation of a fragile ecological background, a high resource and environmental load, and insufficient economic development. The quality of development in the YRB needs to be improved. The YRB is rich in coal, oil, natural gas, and minerals, and more than 30 resource-based cities have been formed on the basis of resource extraction and processing [
28]. They account for more than 50% of the total number of cities in the basin and about 30% of the total number of resource-based cities in China [
29]. Resource-based cities are some of the regions with the highest concentration of conflicts among population, resources, and the environment. Their ecological background and socioeconomic characteristics have undergone profound changes under the combined influence of mining activities and urbanization [
30]. The imbalance between ESs supply and demand in resource-based cities is a major challenge to China’s major national strategy of “ecological protection and high-quality development of the Yellow River Basin”. Therefore, resource-based cities in the YRB were chosen as the case study. By exploring the matching of ES supply-demand from 2000 to 2020, the spatiotemporal evolution of supply-demand was elucidated. This, in turn, revealed the influence of natural and socioeconomic factors on the evolution of ES supply-demand. This will provide a scientific basis for further optimizing the spatial development pattern, thereby improving the sustainability of regional ecosystems and promoting human well-being.
4. Discussion
4.1. Calculation and Analysis of ESs Supply and Demand
In this study, the characteristics of spatiotemporal variation in ESs supply were derived, which can be used to assess the level of ESs supply and whether it has improved or declined in the counties of the resource-based cities in the YRB. The pattern of supply distribution in the study results was consistent with the distribution characteristics of vegetation cover, and correlated with the distribution of the Yellow River water system. The areas with a high value of ESs supply were mostly located in the upper reaches of the Yellow River and were mostly influenced by the Yellow River water system. The higher supply in these areas may be related to the better ecological background, high water supply, rich vegetation, better ecological functions, and sparse population. Areas with low values of ESs supply were mainly concentrated in the socioeconomically developed areas of the YRB, where urban construction land is predominant. The resource-based cities in the YRB saw a high increase in ESs provisioning capacity over the 20 years period, which was directly related to the implementation of ecological protection policies in the YRB in China.
In this study, we selected three indicators, namely land, population, and economy, to reflect the ESs demand in resource-based cities in the YRB. The spatial distribution of land utilization degree, economic development, and demographic status was consistent. Areas with a high demand for environmental resources tended to be in areas with large populations and developed economies, which were concentrated in the southeast YRB and in the middle and lower reaches of the Yellow River region, with greater regional development. The region’s high economic level and attractiveness to the surrounding population, with increasing urbanization levels and expanding areas of land for urban construction, led to growing ESs demand. Most of the northwestern YRB lacks dynamism in the economy, resulting in a constant exodus of the population and a slower rise in demand. At the same time, previous studies have shown that cities in the central (Shanxi, Shaanxi) and eastern regions (Shandong) have a stronger economic diffusion capacity [
47]. The advantages of cities in resources, technology and labor force should be systematically infiltrated into the surrounding areas and larger areas to improve the economic development level and ability of these areas, thus, increasing ESs demand.
4.2. Analysis of the Spatiotemporal Evolution of ESs Supply-Demand Pattern
The relationship between ES supply-demand is primarily concerned with the coordination of human society and ecosystems [
48]. Regional development facilitates an increasement in ESs demand from human society, which can be met by a greater supply capacity of ecosystems. Recognizing the relationship between ESs supply and demand is a basic prerequisite for resolving the man-land contradiction and achieving regional sustainable development.
Due to the multiple units of measurement used for supply and demand, the spatial relationship between the biophysical supply of ecosystems and the ESs demand from human society is unclear, which is a significant difficulty in the area. To address this issue, this study introduced an ES supply-demand accounting approach to analyze the spatial and temporal characteristics of the ES supply-demand relationships in resource-based cities in the YRB. In order to explore the relationship between ESs supply and ESs demand, a nonlinear curve fitting analysis was carried out using Origin for ESs supply and ESs demand from 2000 to 2020 as shown in
Figure 9. The analysis results yielded the relationship expressed in Equation (11), as follows:
where
x is the ESs supply, and
y is the ESs demand, confirming the significant relationship between ESs supply and ESs demand.
The ESs supply and demand were spatially heterogeneous due to the physical geography and regional differences in socioeconomic development. However, the relationships were largely uncoordinated in most regions. Most of the areas where demand exceeded supply were concentrated in the southeast YRB, where the socioeconomic level is high. The balance between ESs supply and demand in these areas is at risk of becoming imbalanced. The flat topography of these areas, density of the population, production and trade activities, more significant population growth and urban expansion, and massive crowding out of ecological land by construction land have resulted in human demand greatly exceeding ESs supply. Areas with an oversupply of ESs were concentrated in the northwest YRB with a better ecological background. These areas were in the upper reaches of the Yellow River, with better developed ecological functions, a greater ESs supply, and a sparse population. However, China’s economic development strategy put forward the policy of supporting the developed areas in the east to support the backward areas in the west, so as to bring capital investment, talent investment, industrial investment, and other resources to the western region with a backward economic foundation, and to improve the infrastructure construction and industrial development mode in the western region. This policy has led to an increase in the rate of economic development in the west, an increase in the area of land used for construction, and a consequent increase in population. This has caused the area of high regression coefficients for economic factors to expand from east to west over time.
The pattern of the ES supply-demand balance was remarkably consistent over time. Although the supply-demand relationship was uncoordinated and tended to deteriorate overall, the degree of coordination improved between 2010 and 2020. This indicates that, since 2010, with the support of national policies, such as closing mines, returning farmland to forest, returning fields to lakes, afforestation, and ecological transfer payments, the ecological lands, such as water, wetlands, and woodlands in the YRB, have been effectively protected [
49]. However, the balance between ESs supply and demand in resource-based cities in the east remains at risk of becoming unbalanced. The distribution range of areas with a short supply is increasing year by year. This suggests that further efforts are needed to improve the situation.
4.3. Analysis of the Drivers Influencing ESs Supply and Demand Patterns
In this study, the spatial characteristics of the factors influencing ESs supply and demand in the resource-based cities of the YBR were obtained using the geographical detector model. The contribution of socioeconomic factors was significantly higher than that of natural factors, with the interaction between socioeconomic factors being especially prevalent. The degree of supply and demand matching is reflected by the supply and demand index. Urban areas with high population levels in the resource-based cities of the YRB had higher levels of demand for almost all types of ESs, whereas areas with low population levels, such as the Inner Mongolia Autonomous Region, tended to have lower levels of demand. At the same time, population concentration is usually accompanied by the expansion of artificial land surfaces with high ESs demand and low ESs supply, whereas the occupation and destruction of natural ecosystems (e.g., woodlands, grasslands, and wetlands) is accompanied by low ESs demand and high ESs supply.
To further investigate the spatial variation of key influencing factors on the supply-demand relationship, the GWR model was used to analyze the spatial heterogeneity of the influencing factors in different regions. The key factors influencing the relationship between ESs supply and demand in resource-based cities in the YRB were elevation, slope, precipitation, proportion of land used for construction, proportion of woodland, proportion of agricultural land, population density, and GDP per land. Elevation, proportion of land used for construction, population density, and GDP per land exhibited significantly negative effects. Simultaneous positive and negative effects of slope, precipitation, proportion of woodland, and proportion of agricultural land existed on the matching relationship between supply and demand. In terms of spatial distribution, the absolute values of the regression coefficients of socioeconomic impact factors, such as GDP, population density, and the proportion of land used for construction, were greater in the eastern YRB than in the western YRB, but the high-value areas of socioeconomic impact factors tend to expand to the west. The natural impact factors, such as elevation, slope, and precipitation, were more influential in the western YRB than in the eastern YRB. The western region, located in the upper Yellow River region, is an important green ecological barrier with high vegetation cover and low population. The ESs demand is, therefore, lower in these regions compared to the eastern regions. Therefore, for ESs management in the future, different protection approaches should be considered. A method of exploiting soil and water resources that is compatible with the natural conditions and socioeconomic development level of the region should be chosen. In reducing the disturbance of ecosystems by human activities, greater attention should be paid to reducing the negative impacts of climate change on ecosystem services to obtain a stable ESs supply. On the contrary, the socioeconomic level of the eastern region is greater, with more significant population growth and urban expansion, resulting in a greater disturbance of ESs supply than in the western YRB. Therefore, the impact of socioeconomic development on the coordination degree of ES supply-demand in the east is more pronounced than in the west. In the future, sustainable management of the region should focus on adjusting the structure of demand while reducing human interference. Ecosystem restoration and rehabilitation should be promoted using artificial measures as a complement to achieve a sustainable equilibrium between supply and demand for ESs.
4.4. Limitations
There were some limitations to this study. On the one hand, with the aim of reflecting the level of ESs supply and demand, we selected representative ESs indicators that are critical to human well-being. However, the indicators for measuring regional ESs may be richer and more diverse due to the different physical geographic and socioeconomic characteristics of different regions. Hence, a subjective element can be added to the evaluation system in the future. On the other hand, ESs can be generated at different spatiotemporal scales. Differences in the ecological background and socioeconomic conditions at different scales can cause variability in the types, levels, spatial characteristics, and other aspects of ES supply-demand. This study examined the relationship between ESs supply and demand at the county scale. In subsequent studies, ESs supply and demand relationships can be studied at multiple scales to reveal their heterogeneity, with the aim of developing more targeted and implementable regional ecosystem management strategies.
5. Conclusions
This study took the resource-based cities in the YRB as the study area, using multisource data from 2000, 2010, and 2020 to measure the ESs supply and demand and determine the supply-demand degree of coordination. We first used a geographical detector model to explore the main factors influencing the coordination degree of ES supply-demand in resource-based cities in the YRB. Then, the GWR model was used to reveal the extent and mechanism of their influence on the supply-demand match at spatiotemporal scales. The results showed that the total ESs supply and ESs demand gradually increased over the past 20 years with the increase in economic and social development and ecological conservation awareness. In terms of spatial distribution, the relationship between supply and demand was spatially heterogeneous, but the relationship was largely uncoordinated in most regions. Most of the areas where demand exceeded supply were concentrated in the southeast YRB, where the socioeconomic level is higher. Most of the areas where supply exceeded demand were located in the upper Yellow River region, where the ecological background is better. The coordination degree of ES supply-demand in the southeast was mainly influenced by socioeconomic factors, while that in the west was mainly influenced by natural factors.
Although the ecological protection and high-quality development of the YRB have achieved positive results in recent years, resource-based cities in the YRB are facing serious ecological problems, such as surface subsidence, a reduction in agricultural land, land degradation, and soil erosion. The stagnation of green-oriented transformation in the resource-based cities of the YRB will inevitably affect the sustainable development in the YRB. Resource-based cities of the YRB where ESs demand exceeded supply were mainly due to the high level of socioeconomic development and significant urban sprawl. Therefore, we should strike a balance between economic development and ecological protection. The existing ecological space should be protected in strict accordance with the ecological red line by promoting intensive land-use and rational planning, as well as the restoration of ecological space, in order to reduce the imbalance between ESs supply and demand. The areas with surplus ESs in the resource-based cities of the YRB were mainly concentrated in the upper Yellow River region in the west. It is characterized by high levels of ESs supply and low levels of socioeconomic development. Policies that are conducive to population growth should be promoted. Policy should be planned from the following three aspects: socioeconomic development, ecological protection, water-land utilization. A protective approach for water-land utilization can be chosen for future economic development. The optimal allocation of resources is achieved by controlling the total demand for land and water resources, enhancing resource supply ability and maximizing their potential, thus, improving environment and the resource carrying capacity of the region. Green industries can also be introduced as appropriate to promote socioeconomic development. Moreover, an adequate monitoring and early warning mechanism for ecological safety should be established. We should also focus on ecological protection and improve ecological efficiency. Furthermore, we need to avoid pressure on the supply and demand balance of regional ecosystems due to the intensive anthropogenic disturbances.