The Coordinative Evaluation of Suburban Construction Land from Spatial, Socio-Economic, and Ecological Dimensions: A Case Study of Suburban Wuhan, Central China

Abstract

As a zone lying adjacent to urban areas, construction land development in suburbs includes urban expansion caused by urbanization and rural construction land increments caused by rural development. Given the necessity of satisfying urban and rural development demands while protecting the ecological environment, goals of land use efficiency, socio-economic coordination, and ecological benefit need to be ensured simultaneously, which indicates that the coordinative development of suburban construction land is of great significance, thereby raising the need for a reasonable evaluation for the coordinative level from multiple dimensions. However, the evaluation of suburban construction land coordination considering spatial, socio-economic, and ecological factors is insufficiently studied. To fill the research gap, this study comprehensively evaluates the coordination of suburban construction land at the town level. Specifically, four indicators from spatial, socio-economic, and ecological dimensions, including landscape pattern, accessibility, socio-economic symbiosis, and ecological functional suitability, are selected. By utilizing coupling coordination degree estimation, the coordination among the four selected indicators is evaluated. By adopting a case study of suburban Wuhan, different coordinative levels regarding suburban construction land development are identified and respondent suggestions to promote the coordination of suburban construction land under current China’s land use policies are provided. This study contributes to understanding the coordinative development of suburban construction land and proposing a method to estimate the coordination.

1. Introduction

Urban expansion and its associated impacts, especially on suburbs, have been the subject of intense discussion. In developed countries and cities, such as the United States and Europe, urban sprawl has been a persistent phenomenon. Between the 1990s and 2000s, despite a population growth of only 6%, urban areas in developed regions of Europe expanded by 20% [1]. The causes of this expansion have included factors such as a lack of effective planning, deregulation, transportation development, and property tax policies [2,3]. This expansion has also raised concerns about its environmental and socio-economic impacts, including the loss of agricultural land, the degradation of soil functions, increased traffic due to urban decentralization, and associated social and economic side effects [4,5]. Meanwhile, in developing countries such as China, social and economic development has experienced unprecedented progress since the Reform and Opening-up, which refers to the policy initiated in 1978 to transition China to a market economy and promote urbanization. China’s urbanization rate increased from 17.92% in 1978 to 67.00% in 2024 [6], and it is projected to reach approximately 80% in 2050 [7,8,9]. With urbanization, population aggregation, industry development, and urban construction raise considerable land demands. Rural land, especially cultivated land, has been proven to be the greatest source of urban land expansion. Being adjacent to urban areas, suburbs are thought to be the most affected areas by urban expansion and face the conflict between limited land resources and huge land use demands for development. The economic benefit of land use has been focused on for a long time, which brings the outcome of rapid land transition from non-construction land to construction land in suburbs [10,11,12]. As a result, negative effects such as low land use efficiency, urban–rural development imbalances, landscape fragmentation, habitat islands, and loss of biodiversity have emerged [13]. Therefore, urban expansion and suburban land use management have become common challenges faced globally.

For developing countries like China, the intense human–land relationship has been a bottleneck for sustainable development [14,15]. Improving land use efficiency, utilizing stock construction land, promoting co-development between urban and rural areas, and protecting the natural ecological environment have been the goals of city land use planning [16,17,18]. The coordination of construction land development has been proposed, which encourages a balance between social, economic, and spatial benefits during land optimization [19,20], and therefore, a comprehensive estimation of coordination is needed.

During the process of suburban land transition, land use structure, landscapes, and functions experience tremendous change [21,22,23]. Four challenges can be summarized during suburban construction land development. The first challenge is landscape change, which is mainly caused by urbanization. To protect the primary cropland and the ecological environment, the Chinese government encourages intensive land use to improve land use efficiency. Spatially, the development of construction land is encouraged to be aggregated and regularized. The second task is to increase the accessibility between suburban and urban areas, which not only enables residents to gain urban services but also increases the functional integration of urban and suburban areas based on people and material flows [24]. Hamidi and Ewing (2014) pointed out that poor accessibility is one of the main reasons for urban sprawl [25]. In addition, in some cities, the public infrastructure network is not constructed following construction land development, which results in so-called spatial inequality [26,27]. To improve land use efficiency and residents’ convenience in life, spatial accessibility needs to be considered when optimizing suburban construction land. The third goal is to promote the co-development of urban and suburban areas. For a long time, the urban-centered development mode widened the development gap between urban and non-urban areas; therefore, the optimization of resources and industries has been conducted to implement coordination between urban and suburban areas. Such coordination can be estimated from socio-economic statistical data [28]. Fourth, ecological coordination is an inevitable indicator. At the macro-scale, ecological civilization construction is the most important goal in China’s current policies regarding land use and regional planning to implement sustainable development [29]; at the individual scale, ecological environment has great effects on residents’ objective and subjective well-being. The development of suburban construction land is a complicated process. To estimate the coordinative development of suburban construction land, multiple dimensions regarding spatial, socio-economic, and ecological effects should be considered.

Existing studies on evaluating suburban construction land coordination are often conducted from a single dimension and most are from land use or socio-economic dimensions. Such single-dimension estimations usually neglect the coordination of spatial, socio-economic, and ecological outcomes by suburban construction land development. In the application of suburban town planning, it is necessary to identify the main factor that leads to the construction land imbalance; further, strategies can be proposed to improve comprehensive coordination.

To fill the research gap, this study chooses four indicators, including landscape pattern, accessibility, socio-economic symbiosis, and ecological functional suitability, to estimate suburban construction land development from spatial, socio-economic, and ecological aspects. Then, a coupling coordination degree method is applied to estimate the coordinative level of construction land at the town scale. For each town that is identified as uncoordinated, the main reason that leads to the imbalance is analyzed. Based on the results, respondent solutions are provided. The graphical abstract of this study is shown in Figure 1.

2. Literature Review

2.1. Suburbs and Suburban Construction Land

The definition of a suburb has been debated for decades, with no consensus on a common standard. Through a review of studies on suburban identification, Forsyth (2012) summarized the characteristics of suburbs based on location, function, and social features [30]. Generally, suburbs are located on the outskirts of a town or city but within commuting distance. The Oxford English Dictionary describes a suburb as land existing immediately outside a town or city. In the practice of identifying suburbs, low population and settlement density are mostly considered [23,31]. For example, Gianotti et al. (2016) developed a decision tree model incorporating population density to identify urban, suburban, and rural areas in central and eastern Massachusetts [32]. Peng et al. (2020) proposed a three-dimensional approach that integrates land development size, pattern, and density using Landsat TM and DMSP/OLS data with Self-Organizing Feature Map (SOFM) clustering to identify the urban–rural fringe of Beijing [33]. Wang et al. (2024) proposed a multi-source data approach integrating population, nighttime light, land use, and point-of-interest (POI) data to delineate urban–rural boundaries in Guizhou Province [34]. Administrative boundaries and zoning based on the city planning of suburbs are also referred to in some studies [35,36], which are determined by local land use management offices according to the development level and population density. In this study, the up-to-date administrative boundaries published by the government are utilized to identify the suburbs.

Urban land growth patterns can be classified into infilling, edge expansion, and frog-leap [37,38]. In fast-urbanization areas, urban land expands rapidly and therefore causes land transition in suburbs. Infilling and edge expansion are the dominant patterns of urban construction land development in suburbs. In addition, there are a large number of rural settlements in suburbs [39]. According to remote sensing image monitoring, the increment in rural residential land in China is also at a fast pace [40]. The ongoing out-migration of rural people to urban areas and increment in rural construction land indicate inefficient land utilization, and the fast development of construction land raises people’s concerns about issues like urban–suburban integration, social-economic coordination, and ecological protection. Since suburbs are the most affected areas facing urban expansion and they are confronted with pressures from both urban and rural construction, the coordinative development of construction land in suburbs is important. In summary, suburbs, in this study, are residential municipalities close to a city, and suburban construction land refers to both urban and rural construction land.

2.2. Construction Land Coordination Analysis

Policies and strategies related to suburban construction land coordination can be found both in developed and developing countries, and the perspectives and focuses are varied in countries with different urbanization stages.

In developed countries with an urbanization rate around 80%, the focus of suburban construction land management is on controlling urban sprawl to protect the rural landscape and natural environment. For example, the “Green Belt Policy” in the UK was implemented to limit urban sprawl, protect farmland, and maintain countryside areas that are close to urban centers [41,42]. The “smart growth” policy in the United States encourages the utilization of stock construction land, development of mixed and public transit, and promotion of high-density communities [43,44] to solve urban sprawl and satisfy the demands for economic and community development and environmental protection [45]. The United States also implements the Transfer of Development Rights (TDR) mechanism to transfer development rights from conservation areas to development zones through market-based transactions, aiming to control urban sprawl while achieving a balance between ecological protection and urban growth [46]. In Italy, recent regional regulations have set thresholds for land conversion to promote the goal of zero land consumption by 2050 [47].

In developing countries, however, there is large land demand for urbanization. Therefore, policies and strategies regarding urban–rural coordination in developing countries focus not only on controlling the urban sprawl but also ensuring needed resources for both urban and rural areas. For example, the average urbanization rate in Africa in 2018 was 43%, which was lower than the worldwide average rate (55%) [8]. The early stage of urbanization in Africa determines that African countries have to ensure enough land resources for urban development, to solve problems like poverty and inequality. As Turok (2015) pointed out in his study, the primary task of African countries is to enable urban growth [48]. At the same time, these countries are also faced with challenges like environmental damage, water scarcity, and food insecurity caused by haphazard urban expansion. It is crucial to maintain a balance between urban development and environmental protection.

For developing countries with a higher urbanization rate like China (67%), the national development goal is shifting from economic to ecological civilization construction, which seeks social, economic, and ecological benefits simultaneously. Policies such as “Urban–Rural Integration and Regional Coordination” put forward requirements for optimizing resource allocation between urban and rural areas and promoting high-quality development. For the development of the countryside, “New Urbanization” and “Rural Revitalization” encourage the intensive and economical use of land resources to improve rural life quality and protect the natural environment [49]. To promote efficient land use, the “Linking the Increase and Decrease of Urban and Rural Construction Land” policy (Zeng Jian Gua Gou, ZJGG) controls the total amount of construction land by offsetting increases in urban construction land with reductions in rural construction land. This policy is conceptually similar to the United States’ TDR, where development rights are shifted to balance growth and protection. However, ZJGG is implemented through administrative regulation, while TDR operates through market-based transactions. Moreover, ZJGG emphasizes food security and urban–rural integration, whereas TDR focuses on cultural heritage and ecological preservation.

From the aforementioned review of policies and strategies related to land use coordination, differences can be summarized in countries in different urbanization stages. Countries with a high urbanization rate focus on controlling urban sprawl to protect the rural landscape and natural environment, countries in the middle stage like China have to address the challenge of balancing urban expansion and limited land resources, and countries in the early urbanization stage like African countries emphasize urban growth. Even though the key issues are varied, the importance of the coordinative development of construction land in suburbs is implied in these policies.

Existing applications of construction land coordination usually focus on a single dimension. For example, Long and Li (2012) applied TM data to analyze the relationship between rural construction land transition and farmland [50]. By adopting a correlation analysis, they demonstrated the significant negative relationship between rural construction land and farmland, which denoted the uncoordinated development of rural construction land. Martinuzzi et al. (2015) estimated future land use change in protected areas in the U.S. by using an econometric-based method [51]. By setting different land use policies and crop prices, they demonstrated the coordinative relationship between urban expansion and land use in protected areas. As conclusions, they proved that urban expansion generates much pressure on natural vegetation in protected areas; however, land use policies like discouraging urbanization and increments in crop prices have positive effects on natural land cover preservation in protected areas. In addition, the coordinative relationship between construction land and the ecological environment is also of concern in many studies. For example, Liu et al. (2018) applied a coupling coordination degree model to estimate the coordination between urbanization and the eco-environment of 30 provinces in China [52]. Based on their analysis, they demonstrated spatial heterogeneity in such coordinative relationships in different provinces.

In summary, relationship quantification methods like correlation analysis, scenario simulation, and coupling coordination degree methods are usually utilized to estimate the coordinative development of construction land. However, two research gaps can be determined. First, in most studies, suburbs are not distinguished. Second, existing studies usually estimate construction land coordination from a single dimension. In fact, the effects of suburban construction land development are complicated, which not only affect its own scale, pattern, and function but also impact the social, economic, and ecological environments that it is embedded in. From a comprehensive perspective, this study estimates the coordinative level of the suburban construction land from multiple dimensions based on indicators of landscape pattern, accessibility, socio-economic interaction, and ecological suitability.

2.3. Coordination from a Symbiotic Perspective

For decades, the city-centered development mode in China escalated the development imbalance between urban and rural areas [53,54]. Strategies like “urban–rural integration” were then proposed as solutions, which encourage a co-existent and co-developed relationship between urban and rural areas [55]. Comprehensive evaluation based on a series of indicators is the most common method to estimate the coordination [56]. However, this method usually neglects the effects of the interaction between urban and suburban areas, which is one of the key characteristics of suburbs. Symbiotic theory, originally introduced in biology to examine the co-existence of dissimilar organisms, emphasizes the degree to which symbiotic units derive benefits from their interrelationship. By treating geographical entities as biological organisms, symbiotic analysis was adopted widely in urban studies and regional planning [57,58,59]. With the ability to quantify the benefit that the units gain from the relationship, symbiotic theory is employed in this study to estimate the socio-economic coordination between urban and suburban areas. The goal of promoting urban–suburban coordinative development is to promote the co-development of urban and suburban areas, narrow the development gap between them, rationalize the allocation of resources, and implement regional sustainable development. From this point, symbiosis, especially mutualism, which denotes that both participants gain balanced benefits from interactions, is an ideal “multi-win” development status. Differently from social network analysis which focuses on analyzing the node position and network structure, symbiotic theory pays more attention to the “interaction” of the relationship between the participant units and the extent of the benefit that this relationship brings to the units. For example, Victor and Hope (2011) applied symbiotic theory in studying urban–rural integration and respondent effects on rural development [60]. Wang et al. (2016) analyzed the symbiotic patterns of rural residential land, based on which they developed a rural settlement restructuring model [61]. Tian and Wang (2019) analyzed socio-economic symbiosis among prefecture-level cities and the effects of such symbiosis [59]. The participant units of these three studies were urban–rural areas, rural settlements, and prefecture-level cities, respectively.

By decoupling the symbiotic system into symbiotic units, the interface, environment, and pattern, symbiotic theory enables the quantification of interactions and their contribution to units’ development [62,63]. In the context of urban studies, symbiotic benefit can be interpreted as economic growth and social improvement. In summary, symbiotic theory is capable of estimating urban–suburban coordination based on quantifying the areas’ socio-economic interdependence. Hence, this study adopts a symbiotic analysis method to quantify socio-economic coordination as one of the indicators to estimate the comprehensive coordinative level of suburban construction land development.

3. Study Area and Data Source

In 2020, Wuhan’s gross domestic product (GDP) reached USD 226.41 billion and ranked 9th nationwide, while its total land area of 8569.15 km² ranked 10th. Wuhan is characterized by its flat terrain and well-developed transportation network, establishing it as a representative mega-city in China. Additionally, Wuhan has an officially set boundary for its main urban and suburban areas. The city comprises 13 sub-regions, including 7 main urban districts and 6 suburban districts, with suburban Wuhan consisting of 80 towns. The officially set boundaries of urban and suburban areas make the statistical yearbook data of suburbs available. Given the representativeness of Wuhan and the feasibility of data collection and analysis, suburban Wuhan was selected as the study area. From 2010 to 2020, Wuhan’s population urbanization rate increased from 64.69% to 74.70%. During the same period, the city’s construction land area expanded from 874.75 km² to 1496.12 km², as shown in Figure 2.

In this study, land use data were extracted from Wuhan’s official land use database, provided by the Wuhan Municipal Bureau of Natural Resources and Urban Rural Development. The landscape pattern, spatial accessibility, and ecological functional suitability of Wuhan in 2020 were estimated. To evaluate the socio-economic symbiosis, statistical data from Wuhan Statistics Bureau Yearbook and Hubei Statistical Yearbook (2015–2020) were collected, and the socio-economic symbiosis between urban and suburban areas in 2020 was finally estimated.

4. Methodologies and Data Collection

4.1. Single-Dimension Estimation

4.1.1. Landscape Pattern from Land Use Dimension

To address the conflict between construction land demand and limited land resources, the ZJGG land use policy was proposed, which rules that any increase in urban construction land is equal to the same amount of decrease in rural construction land, thereby ensuring that the total construction land area remains controlled. Under this background, the development goals for construction land can be summarized as total area control, spatial distribution aggregation, and landscape regularization.

Therefore, a comprehensive landscape pattern index is proposed in this study to assess the coordination of suburban construction land. Specifically, four representative indicators are selected from the perspectives of land use scale, dominance, spatial concentration, and fragmentation: the TA (total area), LPI (largest patch index), AI (aggregation index), and FD (fragmentation degree). These indicators are described as follows.

TA—the total area of construction land, reflecting the extent of human activity and the intensity of land development.

LPI—the largest patch index, describing the proportion of the largest patch of construction land within a total area. Higher LPI values for towns indicate that their construction land exhibits stronger spatial dominance.

AI—the aggregation index, evaluating the degree to which suburban construction land patches are spatially clustered. A higher AI value indicates a greater degree of spatial agglomeration, suggesting that the construction land is more concentrated and compact. “Utilize urban and rural stock land” is one of the basic guiding rules of the current Chinese spatial planning system. It is necessary to optimize and re-develop existing construction land to implement intensive land use. Therefore, the aggregation level of rural construction land is an important indicator to estimate suburban construction land coordination.

FD—the fragmentation degree.

$$FD={\displaystyle \raisebox{1ex}{$NP$}\!\left/ \!\raisebox{-1ex}{$TA$}\right.}$$

(1)

where NP is the number of construction land patches and TA is its total area. FD reflects the extent of the fragmentation of construction land. A higher FD indicates that construction land is highly fragmented, with limited spatial cohesion. From the perspective of agricultural development and ecological protection, the FD is an important indicator for estimating suburban construction land coordination.

All the indicators needed to be standardized to ensure comparability. For the negative indicator FD, the following formula was applied to convert it into a positive indicator.

$$x_{ij}^{\text{'}}=max\left\{x_{ij}\right\}-x_{ij}$$

(2)

Finally, the comprehensive landscape pattern index was calculated as the weighted sum of the standardized indicators. The weights of each indicator were determined using the Delphi method, with values of 0.14, 0.21, 0.35, and 0.30, respectively. A higher index value indicated an ideal suburban construction land distribution at the town level under the framework of suburban coordination. The results were classified into five coordination levels of landscape pattern using the Natural Breaks method: low, medium–low, medium, medium–high, and high.

4.1.2. Accessibility from Spatial Dimension

The different functions of cities and the countryside drive suburban people to visit urban areas and conduct certain activities, which vary from daily routines, such as work, to non-daily activities, such as purchasing items in large markets [64]. With the land use expansion of urban areas, public infrastructure such as public roads is also developed, which enables varied flows to move between urban and suburban areas. Therefore, accessibility was selected as an indicator to describe the spatial coordination of urban and rural construction land. High accessibility not only reflects the convenience of suburban people having access to urban services but also indicates the degree of integration between urban and suburban areas through the flows of people, goods, and information. Suburban accessibility to urban services corresponds to the serving ability of urban areas. Therefore, the serving area of an urban area is developed based on time-cost accessibility, which is assessed by considering the land use type and general time cost. The time cost of the suburbs in this study was developed based on a questionnaire investigation about the characteristics of residents’ daily life. In summary, motorcycle was the main transportation type. Detailed information about the investigation and respondents’ characteristics can be obtained in our other studies [64,65]. The time-cost table is shown in

Table 1. Time cost of different land use types.

	Farmland	Garden Land	Forest Land	Grassland	Urban Areas	Rural Settlements	City Road	Rural Road	Water	Other Lands
Speed (km/h)	2	1	1	3	8	4	60	30	/	3
Time cost (meters per second)	0.55	0.27	0.27	1.11	1.67	0.83	16.67	8.33	/	0.83

. Due to the spatial proximity of suburbs to the urban area, only city and rural roads were considered the main transportation, and other types like airplanes, ferries, and trains were excluded. The speed of humans traveling through different land use types was determined based on existing studies and adjusting to local residents’ transportation preferences [64].

The accessibility analysis process included the following steps. First, urban areas were defined as the source for the analysis. The time-cost raster was generated by overlaying multiple time-cost layers, including the unit time costs associated with different land use types and road types (as shown in Table 1). Then, the accessibility surface was produced using the Cost Distance tool in ArcGIS 10.3, where each raster cell value represented the cumulative time cost required to reach the urban area. This accessibility surface was subsequently classified into five categories based on time thresholds (0.5 h, 1 h, 1.5 h, and 2 h), and the proportion of land area within each threshold was calculated for each town. Finally, the accessibility index of each town was computed as a weighted sum of these proportions, with weights assigned as 0.45, 0.25, 0.15, 0.10, and 0.05, respectively. The results were classified into five accessibility levels using the Natural Breaks method: low, medium–low, medium, medium–high, and high.

4.1.3. Socio-Economic Symbiosis from Socio-Economic Dimension

Symbiotic theory highlights that symbiotic units derive mutual benefits from their interactions [66,67]. Benefits were assessed through a system evaluating the comprehensive development level of urban and rural areas in Wuhan. To estimate regional comprehensive development, four main indices were selected: GDP, population, and the proportion of secondary and tertiary industry production [68,69]. Other indicators included urban population, annual income per capita, the proportion of individuals with compulsory education, the proportion of people with non-farming work, medical care staff per capita, the proportion of individuals with basic insurance, the urbanization rate, and construction land per capita. Data for both urban area and suburban towns were collected from the period 2010 to 2020. To mitigate multicollinearity among the indicators, principal component analysis (PCA) was adopted to obtain comprehensive estimation. Finally, the socio-economic development level of both urban and suburban areas in Wuhan were assessed.

Under the framework of symbiotic theory, “Mutual benefit” does not imply that the symbiotic units gain equalized socio-economic benefits; it underscores their interdependence. For instance, in an urban–suburban symbiotic system, suburbs often provide agricultural and industrial resources to support urban development. However, cities typically do not reciprocate these benefits to suburbs at an equivalent level, resulting in an asymmetrical symbiotic relationship. In this study, the interdependence of the socio-economic development between symbiotic units was quantified and used as a reference to assess symbiosis. Before calculating the symbiosis between urban Wuhan and suburban towns, a correlation analysis needed to be conducted. Pearson’s correlation coefficient, r, was employed to measure the correlation, which was calculated as follows:

$$\mathrm{r}={\displaystyle \frac{{{\displaystyle \sum }}_{i=1}^n\left(x_i-\overline{x}\right)\left(y_i-\overline{y}\right)}{\sqrt{{{\displaystyle \sum }}_{i=1}^n{\left(x_i-\overline{x}\right)}^2}\sqrt{{{\displaystyle \sum }}_{i=1}^n{\left(y_i-\overline{y}\right)}^2}}}$$

(3)

where n represents the number of years, and $x_i$ and $y_i$ denote the socio-economic development levels of urban Wuhan and suburban towns, respectively. $\overline{x}$ and $\overline{y}$ represent the mean values.

The symbiotic index (SI) was calculated by first defining $\Delta Z_{ij}$ to quantify the relative extent of socio-economic development between urban and suburban areas:

$$Z_{ij}={\displaystyle \frac{d{Z}_i/Z_i}{d{Z}_j/Z_j}}={\displaystyle \frac{Z_{j}d{Z}_i}{Z_{i}d{Z}_j}}$$

(4)

$$Z_{ji}={\displaystyle \frac{d{Z}_j/Z_j}{d{Z}_i/Z_i}}={\displaystyle \frac{Z_{i}d{Z}_j}{Z_{j}d{Z}_i}}$$

(5)

where $Z_i$ represents the comprehensive assessment of the socio-economic development in areas i and j, $d{Z}_i$ denotes the change in $Z_i$ over a given period, and $\Delta Z_{ij}$ quantifies the impact of changes in $Z_j$ on $Z_i$.

The SI was then calculated as follows:

$$S{I}_{ij}={\displaystyle \frac{\left|Z_{ij}\right|}{\left|Z_{ij}\right|+\left|Z_{ji}\right|}}$$

(6)

$$S{I}_{ji}={\displaystyle \frac{\left|Z_{ji}\right|}{\left|Z_{ij}\right|+\left|Z_{ji}\right|}}$$

(7)

where $S{I}_{ij}$ + $S{I}_{ji}$ = 1. A high $S{I}_{ij}$ value indicated stronger socio-economic symbiosis, benefiting suburban towns.

4.1.4. Ecological Functional Suitability

Ecological function suitability refers to the natural conditions and processes within an ecological system that sustain key ecosystem functions, such as human survival, climate regulation, and water regulation. The ecological functional suitability value was obtained by applying a comprehensive evaluation method. The evaluation system, as shown in

Table 2. The evaluation system for ecological functional suitability.

Criterion Layer and Weights	Factors	Sub-Factors	Values
Ecological protection bottom line ($F_1-0.41)$	Natural preservation areas, water source conservation areas, wetland reserves, and natural scenic areas	Protection area	5
		Non-protection area	0
Ecological service value ($F_2-0.27)$	Ecological service value	Waterbody	5
		Garden/forest land	4
		Grassland	3
		Cropland land	2
		Rural construction land	1
		Urban construction land	0
Ecological functional suitability ($F_3-0.32$)	Sensitive areas of rivers and lakes (0.11)	<250 m	5
		250–500 m	4
		500–1000 m	3
		1000–1500 m	2
		1500–2000 m	1
		>2000m	0
	Sensitive areas of water sources (0.21)	<250 m	5
		250–500 m	4
		500–1000 m	3
		1000–1500 m	2
		1500–2000 m	1
		>2000 m	0

, was built, referring to the study of Wu et al. (2019) [70]. The weights of each factor were determined by the Delphi method.

The bottom line for ecological protection was defined using related city planning and mapped using ArcGIS 10.3. The ecological service value was classified based on the value of ecological services per unit area of different terrestrial ecosystems in China [71]. An ecologically sensitive area was developed by buffer analysis. In this study, sensitive areas such as water sources, rivers, and lakes were primarily considered.

4.2. A Comprehensive Coupling Coordination Estimation

Coupling coordination estimation is a widely used method for evaluating the degree of coordination between systems. Specifically, coupling refers to the phenomenon in which two or more systems influence each other through various interactions, while coordination represents a benign and harmonious relationship among multiple systems. Together, the coupling coordination degree quantifies the extent to which these systems are compatible [59,72]. The coupling coordination degree is quantified as follows.

$$C=n\sqrt[n]{{\displaystyle \frac{{{\displaystyle \prod }}_{m=1}^n{Y}_m}{{\left({{\displaystyle \sum }}_{m=1}^n{Y}_m\right)}^n}}}$$

(8)

where $C$ represents the coupling degree of n indicators, and $Y_m$ denotes the evaluation value of each indicator.

$$T={{\displaystyle \sum }}_{m=1}^n{\beta }_m{Y}_m$$

(9)

where $T$ indicates the coordinative level, and ${\beta }_m$ represents the contribution of each indicator. Considering the equal significance of spatial, socio-economic, and ecological systems, ${\beta }_m$ in this study was set to 1/n.

$$D=\sqrt{C\times T}$$

(10)

where $D$ represents the coupling coordination estimation level.

Based on previous studies, the coupling coordination degree can be classified into five levels: the low level (severe imbalance, $D\in \left(0, 0.2\right]$), medium–low level (mild imbalance, $D\in \left(0.2, 0.4\right]$), medium level (moderate coordination, $D\in \left(0.4, 0.5\right]$, medium–high level (good coordination, $D\in \left(0.5, 0.8\right]$, and high level (optimal coordination, $D\in \left(0.8, 1\right]$.

5. Results and Analysis

Indicators from four aspects were considered and each factor was estimated at the town level to comprehensively estimate the coordinative level of suburban construction land development. The final evaluation results are shown in Figure 3.

(1)

Landscape pattern of suburban Wuhan

Under the framework of urban–rural construction land coordination, the development goal of suburban construction land can be summarized as scale control, distribution aggregation, and landscape regularization. Therefore, a comprehensive index was derived through the weighted calculation of four landscape indices to estimate the landscape pattern of suburban construction land in Wuhan, which reflected the level of land use coordination, as shown in Figure 3a. The results show that the number of suburban towns with low, medium–low, medium, medium–high, and high land use coordination is 14 (17.5%), 22 (27.5%), 20 (25%), 13 (16.25%), and 11 (13.75%), respectively, indicating that suburban towns in Wuhan are mainly characterized by medium-level land use coordination. Towns with high land use coordination are mainly distributed in northern Huangpi, southern Jiangxia, and western Xinzhou. In contrast, towns with low coordination are primarily located in western Hannan, eastern Dongxihu, and southern Caidian. These areas are generally closer to main urban areas, where construction land tends to be more fragmented and less aggregated. This reflects clear spatial heterogeneity in suburban construction land coordination.

(2)

Accessibility of suburban to urban areas

In the process of rural spatial restructuring, conducting rural settlement relocation and building public infrastructure intensively is more efficient and economical as compared with building public infrastructure in every rural settlement, especially those located in remote rural areas [64]. Therefore, along with urbanization and construction land aggregation, the accessibility of suburban to urban areas is supposed to increase, which not only reflects the integration of urban and suburban interactions but also indicates the convenience for suburban people to gain access to urban services.

Based on the accessibility analysis, the capacity of suburban construction land where local people live and work was estimated at the town level, as shown in Figure 3b. The results show that the number of suburban towns with low, medium–low, medium, medium–high, and high urban–suburban accessibility is 18 (22.5%), 22 (27.5%), 21 (26.25%), 13 (16.25%), and 6 (7.5%), respectively. This indicates a generally medium-to-low level of accessibility in suburban Wuhan. Towns with the highest accessibility to urban areas are mostly located near the urban area, such as those in southern Xinzhou and Huangpi, and western Jiangxia. In contrast, towns with low accessibility are primarily found in southeastern Jiangxia, which is far from the urban area. Additionally, several towns in eastern Dongxihu District also show low accessibility despite being spatially close to the urban area. The abundant rivers and lakes inside this district lead to its low accessibility to the main city.

(3)

Socio-economic symbiosis

The comprehensive socio-economic development levels of urban and suburban areas were evaluated to assess the urban–suburban symbiosis. First, a correlation analysis was conducted to examine the correlation between urban and suburban socio-economic development levels. The correlation analysis confirmed that the socio-economic development of suburban towns is strongly associated with that of the main city, with all significance levels (p-values) below 0.02 and Pearson’s correlation coefficients greater than 0.900. Then, the symbiosis between the main city and suburban town was calculated. The 80 towns were classified into five categories by adopting the Natural Break method according to the values of symbiosis, including low (51.25%), medium–low (16.25%), medium (18.75%), medium–high (11.25%), and high (2.5%), as shown in Figure 3c. The evaluation results indicate that most towns of suburban Wuhan have not developed a mutual and beneficial relationship with the main city in terms of socio-economic development. Spatially, socio-economic symbiosis generally increases with proximity to the main city. For instance, two towns located in southern Huangpi and Xinzhou exhibit the highest symbiotic values. The spatial proximity and well-connected public infrastructure support symbiotic interactions between the main city and its suburban areas.

(4)

Ecological functional suitability

Ecological protection plays an important role in estimating suburban construction land coordination. Given that construction land areas are expanding, the land use transition of non-construction land into construction land will inevitably change the land use type, landscape, and function and lead to ecological risks. Therefore, the ecological functional service of suburban Wuhan was estimated at the town level based on considering the ecological protection bottom line, land use ecological service value, and ecological sensitivity. The evaluation results show that the number of towns with low, medium–low, medium, medium–high, and high ecological coordination is 32 (40%), 19 (23.75%), 19 (23.75%), 6 (7.5%), and 4 (5%), respectively, as shown in Figure 3d. This indicates that the overall ecological coordination level in suburban Wuhan is below medium. The ecological coordination generally presents a spatial pattern of low values in the central area and high values in the peripheral areas. This suggests that urban expansion has significantly affected the ecological environment of the inner suburbs, leading to low levels of ecological functional services. For example, ecological imbalance is observed in most towns in Dongxihu, northern Jiangxia, and parts of Caidian District.

(5)

A comprehensive evaluation of construction land coordination

Considering that the coordinative development of suburban construction land implements co-benefits for spatial, socio-economic, and ecological environments, the coupling coordination degree was estimated, as shown in Figure 3e.

In general, the number of towns with a severe imbalance, mild imbalance, moderate coordination, good coordination, and optimal coordination level is 19 (23.75%), 20 (25%), 10 (12.5%), 18 (22.5%), and 13 (16.25%), respectively. The 19 towns that are with severe imbalance in the coupling coordination degree belong to six districts; in detail, 7 out of 12 in Dongxihu, 5 out of 17 in Xinzhou, 3 out of 14 in Caidian, 2 out of 18 in Jiangxia, 1 out of 3 in Hannan, and 1 out of 16 in Huangpi are estimated to have severely imbalanced construction land development. All the six suburban districts are diagnosed as having imbalanced construction land distribution; however, there is a difference in the area proportions of towns with poorly coordinated construction land. Dongxihu holds the highest proportion (58.3%); Hannan (33.3%), Xinzhou (29.4%), and Caidian (21.4%) have a medium proportion; and Jiangxia (11.1%) and Huangpi (6.3%) have the lowest proportion. To develop a targeted strategy to solve this imbalance, the main reason for the lack of coordination was analyzed at the town level (Figure 4).

According to the coupling coordination degree estimation, the importance of spatial, socio-economic, and ecological dimensions were considered equally important, and the weights of landscape pattern, accessibility, socio-economic symbiosis, and ecological functional suitability were set as the same. Hence, the reason for imbalance was determined based on the indicator with the lowest evaluation level.

The results offer suggestions for solving the suburban construction land imbalance. Two towns in Dongxihu and three towns in Xinzhou are identified as having landscape-orientated construction land imbalance. According to the field investigation conducted in 2020, types of suburban construction land landscape imbalance can be classified into disorganized spaces, dense distributions, abandoned settlements, and unused construction land areas, as shown in Figure 5. To solve the problem, the abandoned settlements and unused construction land can be consolidated to build settlements for relocation, which aligns with China’s “New Countryside construction” strategy. People that are willing to resettle and accept compensation can move to the newly built community and the original areas can be restructured. Therefore, the general landscape of suburban construction land can be aggregated and organized. Additionally, measures such as road widening, house yard arrangement, and illegal annex dismantling can be adopted to regularize the construction land landscape.

Accessibility-orientated imbalance includes two towns which are located in the marginal area of Jiangxia District and one town in the remote area of Huangpi District. The long distance from the main urban area, combined with weak transportation infrastructure, results in accessibility imbalance. Motorbikes and public buses are two important transportation methods of suburban Wuhan, which rely on public roads. Public road expansion, missing link supplementation, and road network building are feasible methods to enable urban–suburban interactions and to increase accessibility.

One town in Dongxihu and another two towns in Caidian are identified as areas with the socio-economic incoordination of construction land. The low level of estimated socio-economic symbiosis indicates that the benefit that the towns gain from the urban–suburban interactions are limited.

Table 3. Annual growth rate of construction land area and GDP.

	The Annual Growth Rate of Construction Land Area	The Annual Growth Rate of GDP
Huangpi	4.45%	12.19%
Dongxihu	6.04%	16.85%
Caidian	4.07%	0.00%
Hannan	6.77%	8.00%
Jiangxia	4.03%	7.11%
Xinzhou	3.19%	9.64%

shows the annual growth rate of the construction land area and GDP of each suburban town from 2015 to 2020. From the results, it is seen that Dongxihu and Caidian have considerable annual growth rates of construction land area; however, their GDP growth rates are at a low level, which indicates the low efficiency of land use from the input–output perspective. The GDP growth rate of Hannan is notably high compared with other suburban districts. Even though the total area of Hannan is small, the socio-economic symbiosis between Hannan and the main urban area is at the highest level, which also demonstrates the importance of socio-economic symbiosis.

Eight towns are identified as showing ecological functional suitability imbalance, and most of them are located in Hannan, Caidian, and Dongxihu Districts. Table 3 shows that the growth rates of the construction land of these three districts are at a high level, which indicates that their development is with the sacrifice of the ecological environment. Along with the expansion of construction land, respondent land use change brings ecological risks, which have negative effects on ecological landscapes and function and also increase ecological sensitivity. The estimation results provide an early warning for local ecological protection. Spatial regulation such as ecological bottom-line zoning, construction land aggregation, and non-construction land consolidation are needed.

6. Discussion

6.1. Importance of Construction Land Coordinative Evaluation

In developing countries like China, urbanization is an important impetus of regional social and economic development and is accompanied by the aggregation of people and urban land expansion. Such countries face the dilemma that urbanization requires much land while they have limited resources. Therefore, the process of urbanization has a particularly profound impact on the transformation of rural land, resulting in phenomena such as rural areas near cities being fully embedded into dense urban areas or suburban land becoming increasingly fragmented due to polycentric development and infrastructure expansion [73]. In this case, the coordinative development of construction land is necessary. On one hand, suburbs are the first places faced with urban expansion, which largely changes their land use types and landscapes and further causes a tense relationship between suburban development and the ecological environment. On the other hand, parts of suburbs remain rural, and the dominant primary and secondary industries in suburbs determine an unbalanced resource flow between urban and suburban areas; therefore, urban–suburban co-development is needed to avoid the development gap.

The differences in land use change pattern, development level, and ecological environmental risk in different suburban towns are supposed to result in heterogeneity in the coordinative level of construction land. Similar coordination challenges at the urban–rural interface are also widely observed in developed countries such as the United States. As Laband et al. (2020) point out in their study, land use changes resulting from urban expansion tend to be concentrated at the urban–rural interface, where intense resource competition, functional mixing, and ecological pressures often converge [13]. The coordinated development of these areas relies on the integration of multidimensional factors, which further confirms the necessity of developing a coordinative evaluation framework for suburban construction land in this study.

In this study, 80 towns that belong to six suburban districts of Wuhan were analyzed. Single-dimension and comprehensive coordination were evaluated at the town scale. The results show that construction land in northern suburban Wuhan is evaluated as coordinated in landscape pattern, accessibility, and ecological functional suitability; however, the socio-economic imbalance reveals that this area fails to gain equivalent benefit compared with what it offers to urban development. Given the situation of town planning, the multiple-dimensional imbalance evaluation of suburban construction land is helpful to find out the main problem that these towns are facing. For the northern part of suburban Wuhan, Huangpi needs to raise the efficiency of utilizing urban–suburban flows to improve the current situation of unbalanced socio-economic development. The results also show that 19 out of 80 towns are estimated as the most uncoordinated, and ecological imbalance is identified as the biggest problem. This result is consistent with the finding in other studies that urbanization sacrifices the rural ecological environment by land transition [74,75]. Guided by the strategies of rural revitalization and new urbanization construction, and in applications for improving suburban ecological environment quality, these towns can be further investigated through methods like field and questionnaire investigations. In addition, land use pattern-based, accessibility-based, and socio-economic relationship-based imbalance in suburban construction land in towns are also identified.

Due to limited land resources and the necessity of implementing regional sustainable development, the intensive and efficient utilization of land use is encouraged. In the scope of suburbs, it is important to monitor land transition and also estimate the coordination of suburban construction land to seek social, economic, and ecological benefits. The performance of the proposed method demonstrates the existence of heterogeneity in suburban construction land coordination, which is helpful for feasible and applicable town planning.

6.2. Implications on Suburban Planning from Multi-Dimensions

Spatial regulation is the key concept of China’s current national spatial planning system [76]. The zoning of the “three lines” serves as the primary way for implementing spatial regulation. The “three lines” refers to the urban development boundary, the arable land and permanent basic farmland boundary, and the ecological conservation boundary. The urban development boundary, which originates from an urban growth boundary, restricts disorderly urban expansion and offers a reasonable direction for urban development [77]. The arable land and permanent basic farmland boundary refers to the minimum amount of farmland under regular cultivation, which is a guarantee of food security [78]. The ecological conservation boundary is the bottom line for ecological environmental safety, which is usually estimated based on ecological services, sensitivity, and biodiversity [79]. The “three-lines” strategy highlights the significance of coordinated construction land development in balancing land demands for urbanization with land use controls for cropland preservation and ecological protection. In this study, the coordination of suburban construction land is an organic integration of landscape pattern, spatial accessibility, socio-economic interactions, and ecological sustainability. Regarding the findings of this study, some implications and suggestions are offered as follows.

(1)

Landscape regulation

Given the continued rapid urbanization in China, the scale of construction land in suburban areas exhibits a trend of expansion. Suburban construction land includes both urban and rural construction land. Despite the ongoing rural–urban migration of people, rural construction land in China is still expanding; in addition, the distribution of rural construction land was originally sparse [80]. There is a drastic conflict between land demand for urbanization and land waste in rural construction land distribution. Controlling urban growth and consolidating rural construction land, therefore, has been an inevitable way, as a response to land demand and resource optimization. Spatially, the regulation of suburban construction landscape is needed. In this study, the western part of suburban Wuhan is identified as an uncoordinated construction land area, including Caidian, Dongxihu, and Hannan, which implies that the construction land development in these areas shows an inefficient and unaggregated trend. Construction land suitability based on land use efficiency, socio-economic benefit, and ecological suitability can be assessed to guide spatial, social, and economic suburban construction land restructuring.

(2)

Accessibility improvement

Improving the accessibility of rural construction land has been a primary objective in optimizing rural spatial development [81,82]. Similarly, enhancing suburban accessibility to main urban areas is essential for promoting urban–suburban integration. As the back-land of urban areas, suburbs link urban and rural areas. The improvement of accessibility brings benefits to suburban development and strengthens the interaction among urban, suburban, and rural areas. Accessibility has also been shown to have a positive effect on the subjective well-being of rural residents [83]. To enhance suburban accessibility, several measures can be implemented, including expanding public road networks, developing interurban railway systems, and increasing public bus services.

(3)

Socio-economic symbiosis enhancement

In China, the urban–rural dual structure has long been thought to be the reason for the unbalanced urban–rural development situation [84]. Specifically, the structure drives the flow of human capital and other resources into cities, further widening the development gap between urban and rural areas. To address this disparity, urban–rural integration has been proposed and implemented nationally to promote urbanization equality and revitalize rural development. From a social-economic perspective, symbiosis characterizes the interaction between urban and suburban areas [85]. A high level of socio-economic symbiosis denotes mutual benefits for both urban and suburban areas, fostering a multi-win development situation.

In an urban–suburban symbiotic system, symbiotic units are composed of urban and suburban areas; the symbiotic environment consists of natural, social, political, and economic factors, providing resources and capital for regional development; the symbiotic interface is formed by the public infrastructure network, facilitating the connection between urban and suburban areas; and the symbiotic relationship is defined by urban–suburban interactions, the embedded environment, and their dynamic interdependencies. From the analysis results of this study, towns that are identified to have uncoordinated relationships with urban areas in socio-economic aspects are mostly located in the marginal place of the suburban areas. Under the framework of symbiotic theory, solutions can be proposed like industry restructuring to strengthen the development level of towns (symbiotic unit development), the implementation of urban–suburban integration policies (symbiotic environment enhancement), and public road construction, especially increasing road network connectivity (symbiotic interface improvement).

(4)

Ecological functional suitability increment

Ecological protection is an important task in advancing ecological civilization and the Beautiful China initiative. Top–down strategies, such as “Comprehensively Promoting the Construction of a Beautiful China”, introduced in January 2024, emphasize strengthening ecological protection through comprehensive, nationwide approaches covering all stages. Land use transitions and landscape changes are inevitable as suburban construction land expands. Typically, the primary source of newly developed construction land is arable land [86]. Moreover, urban expansion threatens ecological security and leads to a decline in biodiversity [87,88]. To ensure that the natural environment continues to sustain human production and habitation while also protecting biodiversity, ecological coordination must be prioritized in construction land development. Two key measures can be adopted to enhance ecological coordination. The first is spatial governance, where the ecological conservation boundary should be rationally delineated and strictly enforced. The second is arable land consolidation and aggregation, a widely implemented approach in Western countries to improve land use efficiency and promote environmental protection [89,90,91].

In summary, landscape pattern, accessibility, socio-economic symbiosis, and ecological functional suitability are four indicators that reflect the effects of suburban construction land development from different dimensions. The evaluation of suburban construction land coordination is an evaluation of the relationship between the four aspects, which develops the basic structure of the evaluation model for suburban construction land coordination in this study.

6.3. Reliability of the Provided Framework and the Limitations

Against the background of rapid urbanization, land transition is occurring at a fast pace, especially the expansion of construction land in suburbs. Suburban construction land development influences spatial, socio-economic, and ecological environments simultaneously. The ultimate goal of the coordinative development of suburban construction land is to promote regional sustainable development, which is defined as utilizing resources to meet human needs, being in harmony with nature, and implementing intergenerational equity [92,93]. Therefore, the provided framework of estimating the coordinative level of suburban construction land was conducted with spatial, socio-economic, and ecological dimensions. First, landscape change is the most direct outcome of construction land expansion. Intensive land utilization is encouraged to improve the land use efficiency. Second, the spatial accessibility of suburban residents reflects urban–suburban interactions and the ability of local people to use services in cities. Verma and Raghubanshi (2018) pointed out that sustainable development should address human needs and improve quality of life while achieving development [94]. Spatial accessibility is considered since it is an important indicator of quality of life [83]. Third, urban–suburban socio-economic symbiosis actually reflects balanced development between urban and suburban areas. For a long time, the city-based development mode neglected development demands in non-urban areas and widened the development gap between urban and non-urban areas. The application of symbiotic analysis considers both urban and suburban socio-economic development and estimates the coordination between the two areas by analyzing their interdependence. Finally, the ecological outcome should also be considered to reflect the relationship between construction land and the ecological environment. In this study, ecological functional suitability was utilized. The coordination of suburban construction land could be comprehensively evaluated by combining the four indicators together. The ideal coordinative development of suburban construction land is able to optimize the benefits of spatial, socio-economic, and ecological benefits and, therefore, to implement the goal of regional sustainable development.

However, there are several limitations to this study. First, this study does not distinguish between urban and rural construction land, and they were analyzed simultaneously as suburban construction land; however, their development process and the socio-economic and ecological effects differ. The contribution of urban and rural construction land can be differentiated and analyzed in following studies. Second, this paper chose suburban Wuhan as the study area, which was identified according to existing city planning; however, debates on the identification of suburbs remain. Since this study focused on estimating the coordinative level of suburban construction land, this study did not endeavor much in identifying the exact boundaries of suburbs. Population and settlement density can be referred to in future studies to elaborate on the identification of suburbs. Third, spatial, socio-economic, and ecological aspects were used to estimate the suburban construction land coordination by considering the national policy background and local reality, and there are also other types of imbalance like cultural conflicts. Field investigation and face-to-face questionnaires can be conducted to integrate cultural factors. Currently, this framework is primarily applied in ex-post assessments, that is, to evaluate the existing level of coordination in construction land use. This is mainly because socio-economic symbiosis analysis depends on statistical data. However, with the support of reliable predictive data in future research, the framework could also be adapted for ex-ante assessments based on scenario modeling.

7. Conclusions

This study builds a comprehensive evaluation system by considering spatial, socio-economic, and ecological aspects to evaluate the coordinative level of suburban construction land. Specifically, four factors, including landscape pattern, accessibility, socio-economic symbiosis, and ecological functional suitability are integrated to evaluate the coordinative level of suburban construction land at the town level. Choosing suburban Wuhan as the study area, the proposed method estimates the coordinative level of construction land in Wuhan’s suburban town from both a single dimension and multiple dimensions. In addition, the most uncoordinated construction land areas of towns are identified with an analysis of the main reason for them. In summary, 19 towns belonging to six districts in total are estimated as the areas with the most uncoordinated construction land. Based on the reasons that lead to the incoordination, landscape pattern regulation-based, spatial accessibility-based, socio-economic symbiosis-based, and ecological function suitability-based implications and suggestions are given, which will help the decision-making process of spatial regulation, urban–suburban integration, and ecological protection.

This study has two contributions. On one hand, the coordination of suburban construction land is assessed through four key dimensions including land use, spatial, socio-economic, and ecological aspects, based on which a comprehensive evaluation system is developed. On the other hand, by adopting a case study method, this study shows the application of the evaluation model to regional coordinative construction. This study provides a systematic perspective of understanding the coordinative development of suburban construction land.