1. Introduction
The Since China’s reform and opening up, rapid industrialization and urbanization have accelerated economic development and bolstered international influence. Concurrently, these processes have significantly impacted the transformation of urban-rural relations [
1]. This shift is characterized by trends towards urban-rural integration and equity [
2]. These changes have brought about notable transformations in factors such as population density, land use patterns, and industrial structures [
3], particularly in ecologically vulnerable regions like mountainous areas and the Yellow River basin. This transformation has led to a range of problems, including reduced vegetation cover, fragmented ecological corridors, increased environmental pressures, and spatial fragmentation [
4,
5]. At the county level, which serves as the fundamental unit for advancing urban-rural integration, optimizing development models and enhancing developmental capacities are critical for fostering ecological civilization [
6]. Therefore, examining the coupled dynamics of urban-rural transformation (URT) and the ecological environment at the county scale, and diagnosing environmental challenges arising from this transformation across different regions, is imperative for achieving sustainable development in counties.
From the perspective of geographical human-land systems science, urban-rural territorial systems emerge from complex interactions among humanities, economics, resources, and environment [
7]. Central to these systems are population dynamics, land use patterns, industrial activities, and ecological conditions, which constitute essential elements not only within social, resource, and ecological systems, but also at the core of URT [
8]. Population dynamics play a pivotal role during this transformation, impacting food security and exerting ecological pressures, while also influencing other elements through individual behaviors [
9,
10]. Human needs, fundamental to fostering harmonious human-environmental interactions, significantly shape the ecological environment [
11]. Land serves as a spatial framework for rural populations and industrial elements, providing essential support for the development of other components [
12]. Industry acts as an internal driving force for rural development, ensuring both rural development and sustainable ecological environments. Furthermore, industrial upgrades influence the efficiency of land utilization [
13]. Changes in the ecological environment exert significant economic impacts [
14], influenced by shifts in population and land use, alongside investments in green technologies within industries [
15,
16,
17]. In summary, the coordinated development of urban-rural populations, land use, industry, and ecological environments is indispensable for achieving URT and sustainable ecological development. Hence, understanding the mechanisms and driving forces behind their integration remains crucial [
18].
From the perspective of the relationship between URT and the ecological environment, the core of URT lies in promoting fundamental changes in industrial, agricultural production, and urban-rural dynamicss [
19,
20]. Major challenges facing China’s urban-rural development in the new era include exacerbated contradictions in land resource allocation, widening disparities in regional urban-rural development, and increasingly prominent urban-rural environmental issues [
21,
22,
23]. Environmental challenges associated with URT have commenced to affect the daily lives of local inhabitants, including farmers and villagers, and are impeding the healthy progression of industrialization processes, informatization, urbanization, and agricultural modernization, thereby jeopardizing future economic and social sustainability [
24,
25]. Existing research primarily explores the interactions between population, land, industry, and the ecological environment. Studies on population and environment reveal that population growth drives urban expansion. Analyzing factors influencing urban green spaces, it is found that population development positively affects urban green spaces, while human density has a negative impact. Socio-economic variables also influence the environment [
26,
27]. In studies on land and environment, observations during urban expansion show rural land transitioning from productive landscapes, cultural hubs, and ecologies into tangible entities supporting commerce and social security [
26]. Deforestation and agricultural expansion continue to reduce global forest cover, with the speed and extent of land use change affecting socio-economic development and the ecological environment to varying degrees [
28,
29]. In terms of optimization paths, managing green infrastructure supports ecological environments, alleviating adverse impacts caused by artificialization of land, ecological fragmentation, and reduced resource availability in urban-rural development [
30]. In studies on industry and the environment, it is discovered that changes in environmental climate impact economic production. The existing economic and social challenges posed by the climate today are akin in scale to the projected impacts stemming from human-induced climate change [
14]. Both domestic and international subsystems of URT have significant impacts on the ecological environment. Research explores the mutual relationships between various subsystems and the ecological environment from perspectives of environmental and socio-economic impacts, land changes, and climate geography. This lays the foundation for studying the coupling mechanisms between internal elements of URT and the ecological environment. From the perspective of coupling coordination, research focuses primarily on provincial and watershed scales, emphasizing the coupling relationships between development and ecology. This includes the coordination and development relationships between ecological civilization and urbanization [
31,
32], the resilience and interactive coupling degrees between urbanization systems and ecological systems [
12,
33,
34,
35], the coordinated development of economic-ecological environment-tourism industry couplings [
36], the coupling relationships between ecological conservation and high-quality development [
37], and the coupling analysis of ecological environment and socio-economic system coordinated development [
38]. Overall, domestic research has highlighted environmental issues during URT, interpreting the environmental effects triggered by various subsystems such as population, land, and industry. The application of coupling coordination models has matured relatively, addressing the coupling coordination relationships between urban-rural development and ecological environments at a macroscopic scale.
Existing research on theories and evaluation methods of URT and the application of coupling coordination models has matured. However, research into the specific coupling mechanisms linking county-level URT with ecological environments is somewhat limited. The lack of clarity in understanding the internal and external driving forces, as well as the optimization pathways, between URT and ecological environments at the county level has impeded the resolution of sustainable development challenges pertinent to urban-rural development and ecological conservation. The coupling coordination model is crucial for studying the intensity of interactions and coordination relationships among various systems [
39]. Utilizing this model can elucidate the coupling coordination relationships between URT and ecological environments. Therefore, this study uses the coupling coordination model to comprehensively analyze the relationship between URT and ecological environment in Lingbao City. Additionally, geographic detectors are utilized to explore the degree of influence of each factor. Ultimately, this study aims to (1) Reveal the spatiotemporal evolution characteristics of county-level URT and ecological environment, (2) Analyze the coupling coordination and influencing factors between county-level URT and ecological environment, (3) Rnvestigate the coupling mechanisms and pathways for high-quality development of county-level URT and ecological environment. The findings will provide insights for the URT and ecological environment protection in mountainous and hilly urban areas.
3. Result
3.1. Characteristics of the Spatiotemporal Evolution of the Urban-Rural Transformation
From 2000 to 2020, the level of URT has been greatly improved, Rural-urban transition shows an upward trend on the whole. In 2000, the degree of URT of administrative villages was relatively low. A total of 76.54% belong to the low, relatively low and medium administrative villages, concentrated in the southern area of Lingbao City, there are 106 administrative villages with low index value and 128 administrative villages with relatively low index value. There are 41 administrative villages with high index, accounting for 9.34% of the total. In 2005 and 2010, the number of administrative villages with low, relatively low and medium index values was 72.44% and 63.33%, respectively, showing a decreasing trend. The number of administrative villages with high index values was 49 and 72, respectively, showing a significant increase, and all of them were distributed in the northern and central areas of Lingbao City. In 2015 and 2020, the number of administrative villages with high URT index values increased significantly, the number are 100 and 121, respectively, accounting for 22.78% and 27.56% of the total, while the number of administrative villages with low, relatively low and medium index values decreased significantly, accounting for 54.44% and 51.71%, respectively (
Figure 2).
From the perspective of spatial pattern, the URT of Lingbao City has undergone great changes from 2000 to 2020. In 2000, the difference between the URT in Lingbao City was obvious from north to south, and then the high-value area of URT showed a trend of expansion, while the low-value area showed a spatial contraction. In 2000 and 2005, the spatial heterogeneity of URT was obvious, showing a typical north-south differentiation and cluster distribution pattern. Along the Yellow River, a development belt with relatively high URT is formed in the northern part, and form a cluster with a relatively high URT in the central region. In 2010 and 2015, the number of administrative villages with relatively high URT increased significantly, and most of the administrative villages along the Yellow River in the north were above the middle level. The high-value area in the central region showed an obvious outward expansion trend, while the low-value area in the south showed a significant spatial decrease. In 2020, the high-value areas of URT continue to expand, but the formed villages with relatively high and medium indexes show a spatial contraction trend, which is more obvious in the southwest region.
3.2. Characteristics of the Spatiotemporal Evolution of NDVI
From 2000 to 2015, the NDVI level increased significantly, with the average rising from 0.144486 to 0.172192, but the average decreased to 0.127715 in 2020. In 2000, the overall NDVI level of all administrative villages was low, with 57.63% belonging to low, relatively low and medium administrative villages, concentrated in the central and northern areas of Lingbao City. There were 98 administrative villages with low index value, 84 administrative villages with relatively low index value, accounting for 22.32% and 19.13% of the total, and 81 administrative villages with high index value. It accounts for 18.45% of the total, mainly distributed in the southwest region. The average value of NDVI in 2005, 2010 and 2015 was 0.153191, 0.167655 and 0.172192, respectively. The number of administrative villages with high index increased from 89 in 2005 to 98 in 2010. The increase in administrative villages is mainly concentrated in the southeastern region. Between 2010 and 2015, the number of administrative villages with a low NDVI index decreased from 102 to 70, with the decrease mainly concentrated in the northern region. In 2020, the average NDVI dropped to 0.127715, in which the proportion of administrative villages with low, relatively low and medium NDVI index increased from 50.80% in 2015 to 66.29%, and the number of administrative villages with high and relatively high indices decreased by 35 and 33 respectively (
Figure 3).
From the perspective of spatial pattern, the NDVI system of Lingbao City has undergone great changes from 2000 to 2020. In 2000, the difference of NDVI between the north and the south is obvious, and the low-value area of NDVI is mainly concentrated in the northeast and central areas. In 2005, 2010 and 2015, the NDVI low value area showed a spatial contraction phenomenon in the central region, and the low value area continued to decrease. In 2010, there was an east-west NDVI low value zone in the northern part of Lingbao City, and the north-south differentiation phenomenon was more prominent, showing a spatial “high in the south and low in the north”. In 2020, the low-value NDVI area showed spatial expansion in the central and northern regions, and the low-value cluster area appeared in the southwest region, and the southwest still maintained a high value cluster phenomenon. On the whole, the administrative villages with relatively low NDVI value over the years are located in the northern region, while the high NDVI value area is located in the southwest region.
3.3. Characteristics of the Spatiotemporal Evolution of CCD
From 2000 to 2020, the mean of URT and NDVI coupling coordination degree (CCD) of each administrative village in Lingbao City first increased and then decreased, from 0.276 in 2000 to 0.322 in 2015, and then to 0.308 in 2020. In 2000, the CCD of each administrative village was at a relatively low level, the low and relatively low CCD values accounted for 13.44% and 28.47% of the total, respectively, concentrated in the southeast of Lingbao City, there are 125 administrative villages with low CCD, 87 administrative villages with relatively low CCD. From 2005 to 2015, the average CCD was on the rise, respectively 0.288, 0.297 and 0.322. The number of low-value administrative villages was 48, 36 and 17, respectively, and gradually decreased over the years. The number of high-value and relatively high-value administrative villages was 80, 102 and 160, and gradually increased over the years. In 2020, the mean CCD decreased to 0.308, in which the low value of administrative villages increased from 3.87% in 2015 to 8.43% in 2020, and the high value and relatively high value of administrative villages decreased from 59.45% to 52.16% (
Figure 4).
From the perspective of spatial pattern, the CCD in most administrative villages of Lingbao City is at a disordered level, and the spatial distribution is high in the west and low in the east. In 2000, the area of low CCD is mainly located in the southeastern area of Lingbao City, showing a spatial agglomeration phenomenon, and there is a diagonal belt composed of low CCD and relatively low CCD in the southeastern area of Lingbao City. From 2005 to 2015, the number of administrative villages with high CCD and relatively high CCD increased continuously in the northern and central areas of Lingbao City, while the number of administrative villages with low CCD decreased gradually in the southeastern area of Lingbao City. The spatial differentiation between north and south is significant, and the zonal distribution along the Yellow River is obvious. In 2020, the high-value and relatively high-value administrative villages show a shrinking trend in space, the high-value and relatively high-value spatial agglomeration phenomenon is weakened in the north, and the low-value CCD administrative villages show a spatial agglomeration in the southeast of Lingbao City.
3.4. The Changes in the Proportion of Different CCD Types of Lingbao City
Based on the population, land, industrial development level, and NDVI index of each administrative village, Lingbao City’s administrative villages were divided into 76 coupling coordination types according to CCD, divide the administrative villages in Lingbao City into 76 types of CCD types, and select 12 types of CCD from them (
Table 4), which account for more than 10% of the total proportion over the years.
Among these 12 types of coupling, CCD has a relatively high proportion in the high-level coupling stage, accounting for 14.9%, 16.6%, 21.9%, 29.10%, and 24.9% in 2000, 2005, 2010, 2015, and 2020, respectively, showing a trend of first increasing and then decreasing. From the perspective of CCD types at this stage, they are mainly concentrated in HHHL and HHHM. It can be seen that the high CCD is mainly due to the high development level of population, land, and industry. Among the coupling types, the proportion of CCD at the intermediate level coupling stage is relatively low, accounting for 9.8%, 13.2%, 13.5%, 11.6%, and 11.1% in 2000, 2005, 2010, 2015, and 2020, respectively, showing a trend of first increasing and then decreasing. MLLH and HHML are the dominant CCD types in the intermediate level coupling stage, while HMLL and LLLH are also the more abundant types in the intermediate level coupling stage.In the intermediate level coupling stage, there are relatively more administrative villages with high and low development levels in terms of population, NDVI, land, industry. The overall number of administrative villages in the low-level coupling stage among these 12 CCD types in Lingbao City shows a gradually decreasing trend, accounting for 24.8%, 19.4%, 16.5%, 9.2%, and 8.7% in 2000, 2005, 2010, 2015, and 2020, respectively.LLLH and LLLM are the main reasons for the low-level coupling in Lingbao City. In addition, LMLL and MLLH have a larger number of administrative villages in the high-level coupling stage. It can be seen that in the low-level coupling stage, administrative villages with low development levels in population, land, and industry dominate, which is the main reason for Lingbao City’s low-level coupling stage.
3.5. Influencing Factors of County URT and NDVI Coupling Coordination Degree
As can be seen from
Table 5, the influence of all factors on the CCD of URT and NDVI over the years has reached a significant level (P < 0.05). Among all the driving factors, AS and TCC have the most significant impact on CCD,and their average effect on CCD is more than 11%. The second is TDC and DEM, both of which have an average influence of more than 10%, indicating that they have a more important influence in the coupling coordination degree. In addition, DYR has less effect on CCD. From the perspective of influencing factors, the order of the average impact on each administrative village over the years was AS> TCC> TDC > DEM > DYR.