Spatiotemporal Evolution of Land Use Structure and Function in Rapid Urbanization: The Case of the Beijing–Tianjin–Hebei Region

Abstract

The rapid increase in urbanization is accompanied by the evolution of land use structure and function. Since its reform and opening up, China has entered a stage of rapid urbanization, which has brought about higher requirements in terms of rational allocation within land use structure and the optimization of land use function. However, most existing studies have evaluated the structure and function of land use separately, resulting in a decoupling of the two, and have not accurately depicted the spatiotemporal characteristics of the evolution of land use. Here, based on statistical data and remote sensing image data, we constructed a dual evaluation index system for land use structure and function which uses the characteristics of land use structure to evaluate the property of land use function directly. We used the entropy weight method to characterize the spatiotemporal evolution of urbanization and land use structure and applied a land use function deviation degree model to discuss the evolution path for land use function. Our results showed that the dominant dimension of urbanization changed from eco-environmental urbanization to economic urbanization in the rapid economic development stage. In terms of quantity within land use structure, urban-agricultural-ecological spaces have developed in a synergistic direction. Regarding the quality of land use structure, its development level exhibited an upward trend in Beijing and Hebei, while Tianjin demonstrated a U-shaped development trajectory. With urbanization development, the dominant function of regional land use has evolved to a higher level of synergy in the Beijing–Tianjin–Hebei region. These results offer inspiration for formulating regional dynamic land use policy and phased planning of urbanization development in rapidly urbanizing regions.

1. Introduction

Land use, the engine of sustainable development, is the link that coordinates the relationship between humans and nature. Existing studies have shown that unreasonable land use will affect the food web [1], cause climate change [2], lead to food crises [3], bring about eco-environmental risks [4], and threaten natural resources and human health [5,6]. Land resources and urbanization are important nodes of the nature–social network in sustainable development [7,8]. Land carries population transfer, social progress, economic development, and spatial agglomeration and expansion in the urbanization process, whilst urbanization promotes the transformation of land use structure and function. The interaction of different urbanization dimensions facilitates changes in land use structure in terms of quality and quantity and the transformation of the dominant function of land use.

Changes in land cover are the outcomes of the long-term interaction between humans and the natural environment, and they are the consequence of numerous factors and conditions [9]. The structure and function of land use bear various dimensions of human production and life; this is the key to solving the contradiction between urbanization and land use [10,11]. With social and economic development and the need for the allocation of land resources, China’s land spatial planning divides land use structure into urban, agricultural, and ecological spaces according to “three zones and three lines (three control lines, namely urban development boundaries, permanent basic farmland, and ecological protection red lines, shall delimit urban space, agricultural space, and ecological space)”, as well as dividing land use function into living, production, and ecological functions, to achieve accurate hierarchical management and multi-departmental cooperation. In this study, according to land space planning in China, urban, agricultural, and ecological spaces are adopted in the land use structure, whilst living, production, and ecological functions are used as the land use functions.

Existing research on the land use index system has involved two aspects. One is exploring land use structure, while the other is analyzing land use functions [12,13]. Such research has mainly used remote sensing technology to study the area transfer between different land types, the related dynamics, and the spatiotemporal evolution of land use structure [14,15]. These studies have analyzed the transformation process between different land types in detail, accurately quantified the area of various land types, and provided a feasible method for scientific land use planning [16,17]. However, this body of research has only evaluated changes in land use structure in terms of quantity, not in terms of quality. In research on urbanization and land use function, land use function is usually explored through landscape identification [18], and it is believed that urbanization has accelerated the tradeoff or synergy between living, production, and ecological functions in land use systems [19]. Some research has realized the importance of the unification of land use structure and function and tried to link them [20]. However, current evaluations of land use structure and function are limited to identifying land use function based on the theoretical relationship between land use structure and function, which fails to establish a direct correlation between land use structure and function in one index evaluation system, leading to a decoupling of theory and practice in land space planning [21,22].

Geographically adjacent regions gradually develop into a community with a common destiny in the process of close resource exchange [23]. Meanwhile, the development goal of a community with a common destiny is to achieve dynamic coordinated development in terms of the optimal allocation of resources. Land use cannot be transferred across administrative boundaries, but land use function can [24]. Consequently, we propose making use of the advantages of cross-regional coordination and multi-dimensional development of a community with a common destiny to promote regional land use with phased characteristics and achieve sustainable development. The Beijing–Tianjin–Hebei (BTH) region is the vital pole of economic growth in China; it has a superior geographical location, advanced high-tech industries, and unique political advantages [25]. Meanwhile, due to the political differences between the two municipalities (Beijing and Tianjin) and one province (Hebei) and limited land resources, it was found that a significant part of the ecological footprint has been transferred from Hebei to Beijing and Tianjin, but no considerable economic benefits have been achieved [26], which has caused regionally unbalanced development and has posed a challenge for coordinated land use development. There are significant differences in the competitiveness of various land types within the BTH region, and the structure of construction land varied between orderly and disorderly from 2006 to 2017, which hindered regional sustainable development [27]. Therefore, we chose the BTH region as the research region to explore the path of the mutual influence between urbanization development and land use.

In the context of advancing ecological civilization and enhancing social welfare in China, several critical questions arise: (1) How can we achieve the mutual transformation and evaluation of structure and function within a land use evaluation index system? (2) What is the pathway for transforming land use function within the context of urban development? Finally, (3) how can we clarify the interaction mechanism between land use function and urbanization development? To address these issues, we propose a dual evaluation index system that encompasses both land use structure and function. This framework elucidates the evolutionary patterns of dominant land use functions throughout the urbanization process in the BTH region, thereby expanding upon existing research on land use index systems. Our findings not only delineate the evolution pathways of dominant land use function through lenses of tradeoff and synergy, but also comprehensively reflect the spatial characteristics related to both quantity and quality within the context of land use structure. Our research offers valuable insights for effective spatial planning in light of ongoing urbanization trends.

2. Study Materials and Study Methods

2.1. Theoretical Framework

Urban development and land use are the relationship between demand and engine, and their relationship and evolution process interact with each other to build a sustainable development system (Figure 1). Since the period of reform and opening up, urbanization in China has entered a phase of rapid advancement [28]. The three primary dimensions driving urbanization are social, economic, and ecological. In the social urbanization dimension, land serves as essential space for both work and residence. Economically, land provides the necessary foundation for production activities. From an eco-environmental perspective, it offers vital areas for vegetation growth and pollution management. Urbanization is pivotal in enhancing human living standards and productivity; however, it relies on limited land resources to sustain its material carrying capacity.

Land use is the engine of urbanization development. According to the definition of territorial space planning in China, the term “urban space” embodies urban economic, social, political, cultural, ecological, and other factors; “agricultural space” describes agricultural production and rural life; and finally, “ecological spaces” mainly provide ecosystem services or ecological products.

In the sustainable development system between urbanization and land use, indicators form the dimensions, various dimensions form the basis of urbanization development and land use subsystems, and the relationship and evolution process of these subsystems result in the creation of a sustainable development system. The theoretical framework of research in this field can be summarized as an “indicators-dimensions-subsystem-relationship and process system”. More importantly, urbanization development has an obvious rule of periodicity, and the evolution of the relationship between urbanization development and land use is further reflected in the change of the dominant land use function under a specific urbanization background, which, in this study, is the key to exploring the relationship and evolution process between urbanization development and land use.

2.2. Study Area, Index System, and Data Source

Beijing (the capital), Tianjin (a municipality), and Hebei (a province) form the BTH region in China (Figure 2). The BTH region has promoted rapid social and economic development, which plays a vital role in China’s urbanization process [29]. The region is located in the North China Plain, accounts for 2.3% of the nation’s land area, and contributed 8.51% of the GDP of China in 2020. The present research aims to provide insights on the land use structure and function in the BTH region and to further understand its unique characteristics.

According to the “indicators-dimensions-subsystems-relationship and process system” in the theoretical framework, the urbanization development subsystem is explained based on social, economic, and eco-environmental urbanization dimensions [30], comprising nine indicators (

Table 1. The urbanization development subsystem.

Subsystems	Dimension	Indicators	Index Meaning
Urbanization development	Social urbanization	Percentage of nonagricultural population (+)	Urban resident population/year-end resident population
		Number of health technicians per 10,000 persons (+)	Health technicians/total population
		Number of students in colleges and universities (+)	Number of students in regular institutions of higher learning
	Economic urbanization	Per capital GDP (+)	GDP/total population
		Percentage of added value of tertiary industry to GDP (+)	Added value of tertiary industry/GDP
		Percentage of total foreign trade imports and exports to GDP (+)	Total foreign trade imports and exports/GDP
	Eco-environmental urbanization	Total wastewater discharge (-)	The sum of industrial wastewater discharge and domestic sewage discharge
		Proportion of days with good air quality (+)	Number of good air quality days/total number of days in the year
		Harmless disposal rate of household garbage (+)	Household garbage treatment/household garbage production

). The land use subsystem realizes the simultaneous evaluation of the structure and function of land use. Meanwhile, the structure considers urban spaces, agricultural spaces and ecological spaces, as well as the input, efficiency, and output of each land space. The function comprises living function, production function, and ecological function (

Table 2. The land use subsystem.

Subsystems	Structure				Function
	Dimension	Indicators		Index Meaning	Living Function	Production Function	Ecological Function
Land use	Urban space	Urban per capita disposable income per unit of land (+)	Input	Urban per capita disposable income/the land area of urban space	f1	f1	0
		Green coverage of built-up areas (+)	Efficiency	Green cover area/the area of urban built-up	f2	0	f2
		Output value of secondary and tertiary industries per unit of land (+)	Output	Output value of secondary and tertiary industries/the land area of urban space	f3	f3	0
	Agricultural space	Total power of agricultural machinery per unit of land (+)	Input	The sum of the rated power of all agricultural machinery power/the land area of agricultural space	0	f4	0
		Total agricultural output value per unit of land (+)	Efficiency	Total agricultural output value/the land area of agricultural space	f5	f5	0
		Grain output per unit of land (+)	Output	Grain output/the land area of agricultural space	f6	f6	f6
	Ecological space	Nature reserve area per unit of land (+)	Input	Nature reserve area/the land area of ecological space	0	0	f7
		Normalized difference vegetation index (NDVI) per land (+)	Efficiency	Mean NDVI from June to September/the land area of ecological space	0	0	f8
		Forest growing stock per land (+)	Output	Forest growing stock/the land area of ecological space	0	0	f9
					F1	F2	F3

Note: f1–f9 are the standardized values of land use structure indicators. F1, F2, and F3 are the original values of land use functions, specifically, F1 = f1 + f2 + f3 + f5 + f6, F2 = f1 + f3 + f4 + f5 + f6, and F3 = f2 + f6 + f7 + f8 + f9.

).

In Table 2, the weights of each indicator are calculated based on the spatial structure of the land use index, highlighting the fact that the structure and function of land use are inherently interconnected. Therefore, we employed a unified index system to simultaneously assess both the structure and function of land use. This approach is predicated on the assumption that if an indicator serves multiple land use functions, it contributes equally to each distinct function.

The research period was 2003–2020. The data were obtained from Statistical Yearbooks of all levels of government, while environmental monitoring data were from the Ministry of Ecology and Environment in China. Based on China’s land use remote sensing monitoring datasets from 2003 to 2020 (i.e., Landsat TM images, generated by manual visual interpretation, with a resolution of 1 km) land use could be classified. The datasets were from the Resource and Environment Science Data Platform (https://www.resdc.cn (accessed on 17 June 2022)). According to the division of “three zones three lines” (the three zones are urban, agricultural, and ecological functional zones, and three lines are urban development boundary, permanent basic farmland, and ecological protection zones) in China’s territorial space planning, land use is divided into urban spaces (construction land, except for rural residential land), agricultural spaces (arable land and rural residential land), and ecological spaces (woodland, grassland, water, and unused land) [31]. Since interannual changes of land use areas were small from 2003 to 2020, when displaying the subsystem of land use structure (production, living, and ecological spaces), we chose 2005, 2010, 2015, and 2020 as the time nodes to divide the research stage. Furthermore, NDVI selected the spatial distribution data of the monthly vegetation index in China from 2003 to 2020, with a resolution of 1 km; data obtained from the National Earth System Science Data Center (https://www.geodata.cn (accessed on 9 November 2022)). This dataset was calculated by the maximum value synthesis method, which represents the data of each pixel when the vegetation growth condition is the best in a month. Based on the growing season in the research area, NDVI values from June to September were selected as the research data.

2.3. Methodology

The entropy weight method and the land use function deviation degree model were used in this study.

2.3.1. Data Pre-Processing

The extremum method is a common method of pre-processing data; it can unify the dimensions of different indicators.

$$f_{ij}=(X_{ij}-min\{X_j\left\}\right)/\left(max\right\{X_j\}-min\{X_j\left\}\right) (+)$$

(1)

$$f_{ij}=\left({\mathit{max}\left\{X_j\right\}-X}_{ij}\right)/\left(max\right\{X_j\}-min\{X_j\left\}\right) (-)$$

(2)

Formulas (1) and (2) apply to the positive indicators and the negative indicators, respectively.

$f_{ij}$ is indicator j in year i.

In addition, $\mathit{max}\left\{X_j\right\}$ is the maximum value and $min\left\{X_j\right\}$ is the minimum value in the research period; when the result value was 0, we used 0.0001 instead of the normalized 0.

2.3.2. The Entropy Weight Method

In this study, the entropy weight method was based on information entropy to objectively determine weights, as is generally used in existing research [32]. The entropy weight method was applied to measure the level of urbanization development, the quality of land use structure, and the calculation of land use functions, as follows:

$$Z_{ij}=f_{ij}/{\sum }_{j=1}^n{f}_{ij}(\mathrm{i}=1,2,3,\dots ,\mathrm{m};\mathrm{j}=1,2,3,\dots ,\mathrm{n})$$

(3)

$$H_j=-k{\sum }_{j=1}^n{Z}_{ij}ln{Z}_{ij}$$

(4)

$$W_j={\displaystyle \frac{1-H_j}{n-\sum _{j=1}^n{H}_j}}$$

(5)

$$\mathrm{k}=1/\mathrm{l}\mathrm{n}\mathrm{m}$$

(6)

$$S_{ij}=W_j{f}_{ij}$$

(7)

$$S_i={\sum }_{j=1}^n{S}_{ij}$$

(8)

Formula (3) shows the proportion of standardized indicators to the sum of standardized indicators.

In Formula (4), $H_j$ is the entropy of the ith indicator, $Z_{ij}$ is the proportion of the jth evaluation object in the ith indicator, and m and n are the number of evaluation indicators and objects, respectively.

In Formula (5), $W_j$ represents the weight of ith indicator, 0 ≤ $W_j$ ≤ 1, $\sum _{j=1}^n{W}_j$ = 1.

In Formula (6), k is the coefficient. In Formulas (7) and (8), $S_{ij}$ is the single indicator value and $S_i$ is the comprehensive development level in year i.

Additionally, in the land use function aspects (Table 2), land use function evaluations were carried out for indicators in the land use structure system. Specifically, if an indicator has a certain function, the standardized indicator value of the structure system assigned to the function was used as the original data in the function. The premise of this assumption was that the contribution of the same structural indicator to different functions would be equal. Then, Formulas (3)–(8) were used to evaluate the land use function.

2.3.3. The Land Use Function Deviation Degree Model

To more intuitively represent the tradeoff and synergy process of the production, living, and ecology functions, a deviation degree model of land use function was built, based on the mechanical equilibrium model [33] (Figure 3). It was assumed that the production function, living function, and ecological function of land use function are three forces. Based on the principle that the mechanical equilibrium model is used to study the dynamic balance process between different forces, the land use function deviation degree model describes the dynamic tradeoff or synergy process among production function, living function, and ecological function. The dynamic tradeoff or synergy process is represented by polar coordinates (F, θ), while F represents the deviation index between the resultant force of land use functions and equilibrium point O; the greater the value, the worse the synergy effect between land use functions. θ is the polar angle, representing the deviation between functions and reflecting the specific synergistic features of land use functions [34]. Moreover, 2π was equally divided by OA, OB, and OC, respectively representing the regions dominated by the three functions; the reverse extension lines of OA, OB, and OC further divided 2π into six parts, with which we could observe the biased function regions in the dominant function regions.

Combined with Figure 3, the specific calculation process was as follows:

$$F1=\sqrt{{OA}^2+{OC}^2+abs(2OA\times OC)\times cos(\mathrm{\angle }XOA-abs\mathrm{\angle }XOC)}$$

(9)

$$\alpha =arcsin{\displaystyle \frac{absOC\times sin(\mathrm{\angle }XOA-abs\mathrm{\angle }XOC)}{F1}}$$

(10)

$$F=\sqrt{{F1}^2+{OB}^2+abs(2F1\times OB)\times cos(\mathrm{\angle }XOA-\alpha -abs\mathrm{\angle }XOB)}$$

(11)

$$\mathrm{\angle }FOB=arcsin{\displaystyle \frac{F1\times sin(\mathrm{\angle }XOA-\alpha -abs\mathrm{\angle }XOB)}{F}}$$

(12)

$$\theta =\mathrm{\angle }XOB-\mathrm{\angle }FOB$$

(13)

In the above formula, $OA$, $OB$, and $OC$ represent living function, production function, and ecological function;

$F1$ is the resultant force of living function and ecological function;

$F$ is the resultant force of living function, production function, and ecological function;

$\alpha$ is the deviation angle of living function and ecological function;

$\theta$ is the deviation degree between land use functions.

3. Results

3.1. Urbanization Development Subsystem

From 2003 to 2020, the overall level of urbanization development in the BTH region demonstrated a consistent upward trajectory. Generally, Beijing, Tianjin, and Hebei exhibited fluctuating upward trends, as illustrated in Figure 4A. Notably, Beijing led Tianjin and Hebei in terms of comprehensive urbanization development. To be specific, during 2003–2020, the comprehensive urbanization development level was from 0.2571 to 0.8484 in Beijing, from 0.2515 to 0.7602 in Tianjin, and from 0.1436 to 0.6925 in Hebei. In Beijing (Figure 4B), the dimensions of social and economic urbanization exhibited an upward trend, ranging from 0.0003 to 0.2131 and from 0.0660 to 0.3963, respectively. In contrast, the eco-environmental urbanization dimension initially displayed a downward trend before shifting to an upward trajectory, with values spanning from 0.1908 to 0.2389. In Tianjin (Figure 4C), the trends on urbanization dimensions were similar to those in Beijing, and social urbanization increased from 0.0221 to 0.2144, while economic urbanization ranged from 0.0317 to 0.3617, and eco-environmental urbanization fluctuated between 0.1977 and 0.1841. In Hebei (Figure 4D), the overall trends in dimension of urbanization exhibited an upward trajectory. The social urbanization was from 0.0003 to 0.2420, while the economic urbanization was between 0.0450 and 0.2638. Additionally, eco-environmental urbanization was observed within the range of 0.0983 to 0.1866. It was found that the strongest development momentum was the economic urbanization dimension in the BTH region, which proved that the economic scale of the BTH region played a crucial role in China [35]. Hebei has progressed simultaneously across three dimensions of urbanization, whereas Beijing and Tianjin experienced an initial decline followed by a subsequent rise in eco-environmental urbanization. This pattern serves as a reminder for economically developed regions to prioritize eco-environmental protection alongside economic development. In addition, the leading dimension changed from eco-environmental urbanization to economic urbanization in Beijing, Tianjin, and Hebei, indicating that economic development occurred at the expense of the environment in the BTH region at the beginning of the research period [36].

3.2. Land Use Subsystem

3.2.1. Spatiotemporal Evolution of Land Use Structure

The quantitative and qualitative aspects of land use structure were analyzed. In terms of quantity (Figure 5), the proportion of urban space showed an increasing trend in the whole BTH region, which illustrated the swift process of urbanization. During the period from 2005 to 2020, the percentages of urban spaces in Beijing, Tianjin, and Hebei were observed to be between 9% and 11%, 12% and 18%, and 2% and 4%, respectively. Agricultural space showed a trend of collective decrease. Specifically, the proportion decreased from 35% to 33% in Beijing, from 66% to 58% in Tianjin, and from 57% to 55% in Hebei. Although permanent basic farmland protection policies had already been formulated, due to urban expansion, most cultivated land was mainly converted into construction land [37,38], resulting in a shrinking of agricultural space in the BTH region. Notably, the proportion of agricultural space decreased the most in Tianjin, while the proportion of urban space increased the most. This was mainly due to the urban expansion caused by the rapid development of Binhai New Area and Tianjin South Railway Station, in which most of the newly developed urban land was converted from arable land and other construction lands [39]. While ecological spaces experienced a process of first downward and then upward trends, in Beijing, the maximum value was 56% in 2005, 2010, and 2020, and the minimum value was 55% in 2015; in Tianjin, the maximum value was 24% in 2020 and the minimum value was 21% in 2010 and 2015; in Hebei, the maximum value was 41% in 2005, 2010, and 2020, and the minimum value was 40% in 2015. This showed that the land layout of Beijing, Tianjin, and Hebei presented the same development trend, which reflected the coordinated development of the land use structure of the BTH region and supported the application of a coordinated regional development strategy [40].

In addition, the entropy weight method was used to comprehensively evaluate the urban space dimension, agricultural space dimension, and ecological space dimension. This approach facilitated an analysis of the quality of land use structure within the BTH region (Figure 6).

The overall quality of the land use structure demonstrated a positive upward trend. Specifically, it was found that Beijing and Hebei had an upward trend, while Tianjin had a U-shaped development trend in the development level of land use structure (Figure 6A). The development level of land use structure in Beijing was from 0.2279 in 2003 to 0.7982 in 2020, in Tianjin from 0.4384 in 2003 to 0.5911 in 2020, and in Hebei from 0.0524 in 2003 to 0.7511 in 2020. During the 2003–2020 period, Beijing moved from 0.0253 to 0.3455 in urban spaces, from 0.1624 to 0.2786 in agricultural spaces, and from 0.0401 to 0.1741 in ecological spaces (Figure 6B). Tianjin moved from 0.0052 to 0.2215 in urban spaces, from 0.0985 to 0.2312 in agricultural spaces, and from 0.3347 to 0.1384 in ecological spaces (Figure 6C). Hebei shifted from 0.0003 to 0.2482 in urban spaces, from 0.0113 to 0.2578 in agricultural spaces, and from 0.0408 to 0.2451 in ecological spaces (Figure 6D). It is worth noting that the development level of ecological space showed a declining trend in Tianjin during the study period; this phenomenon was related to the adjustment of the area of National Nature Reserve of Ancient Coast and Wetland in Tianjin in 2009. Due to the limitations of early technical means, the area of the national reserve was too large when applied to the national reserve, and there were no protected objects in some experimental areas. To realize effective management of nature reserve resources, China issued a statement on the adjustment of five national nature reserves, including the National Nature Reserve of Ancient Coast and Wetland in Tianjin, in September 2009. The range of Tianjin National Nature Reserve of Ancient Coast and Wetland was adjusted from 97,500 hectares to 35,913 hectares, resulting in the reduction of Tianjin’s ecological spatial development level.

3.2.2. Spatiotemporal Evolution of Land Use Function

A novel land use index system was developed to simultaneously evaluate both structure and function. Utilizing the land use function deviation degree model, we derived the land use function deviation index (Figure 7), as well as the polar coordinates of the deviation degree (Figure 8).

From the perspective of the land use function deviation index, during the 2003–2020 period, Beijing moved from 0.0168 to 0.4280, Tianjin from 0.1281 to 0.4748, and Hebei from 0.0040 to 0.4052 (Figure 7). The deviation index of the three regions had a relatively large span, which indicated that the land use function was in the tradeoff stage.

The deviation degree of the land use function is shown in Figure 8. In Beijing, the transformation of the dominant land use function was from production to living function, then to ecological function (Figure 8A). In Tianjin, production turned into living function (Figure 8B). And in Hebei, it was always production function (Figure 8C). From 2003 to 2020, the proportion of production as the dominant function of land use was the largest in the BTH region.

3.3. The Evolution Path of Dominant Land Use Function in the Process of Urbanization

We used Pearson correlation to calculate the correlation coefficient between urbanization development and land use function, thereby investigating the internal relationship between these two subsystems across different time periods (Figure 9). We found that the correlation coefficients were increasing between urbanization and land use functions, except for living function. In particular, during the 2003–2020 period, the correlation between social urbanization and ecological function, economic urbanization and ecological function, comprehensive urbanization and ecological function, economic urbanization and the deviation index, and comprehensive urbanization and the deviation index changed from negative to positive. But the correlation between social urbanization and living function moved from positive to negative, and the correlation between comprehensive urbanization and living function decreased. In summary, with urban development, the production and ecological functions were enhanced; however, the living function diminished. Consequently, in the BTH region, there has been a shift from synergy among living, production, and ecological functions to a trade-off scenario.

Additionally, the relationship between urbanization development and land use function was quantified from a mathematical perspective. Combined with Section 3.2, with the rapid urbanization process, the dominant land use function changed from production to living function, then to ecological function in Beijing; it moved from production to living function in Tianjin; and finally, the dominant land use function was always production in Hebei. Based on the above research results, the quantitative relationship was revealed between urbanization and dominant land use function, where urbanization development was an independent variable, while living, production, and ecological functions were dependent variables (

Table 3. The quantitative relationship of urbanization development and dominant land use function.

Region	Land Use Function	Mathematical Relation Model (Regression Analysis)
Beijing	Living function	Y = 0.5882X − 0.1649, R2 = 0.711
	Production function	Y = 0.7057X − 0.1964, R2 = 0.558
	Ecological function	Y = 0.5328X − 0.1367, R2 = 0.513
Tianjin	Living function	Y = 0.4773X − 0.0550, R2 = 0.839
	Production function	Y = 0.6618X − 0.1131, R2 = 0.896
	Ecological function	Y = 1.957X3 − 0.9634X2 − 0.6015X + 0.3916, R2 = 0.598

).

It was found that, based on the premise that urbanization development had a threshold effect, from 2003 to 2020, when the urbanization development level was 0.2681, the production function turned into the living function; when the urbanization development level was 0.5090, the living function turned into the ecological function in Beijing. In Tianjin, the dominant function changed from production to living function, and the urbanization development level was 0.3149. The dominant function did not change in Hebei, so it was not analyzed. From the production function to the living function, the nodes of urbanization development were different in Beijing and Tianjin, manifesting that the transformation process of the dominant land use function in the same direction had experienced different paths within the BTH region. There were differences in the relationship between urbanization development and land use function, as well as the evolution path of the dominant function within the BTH region (Beijing, Tianjin, and Hebei), which provided new ideas for regional land use planning and social and eco-environmental sustainable development [41].

4. Discussion

4.1. Innovation of the Land Use Index System

The existing research primarily investigated the conversion, structure, and function of land use, thereby providing a comprehensive characterization of land use systems [14,42]. However, the index system of these studies lacked the exploration of the relationship between land use structure and function, resulting in limited effective land use planning and management based on their inherent relationship [43]. This paper expands upon existing research regarding land use index systems by proposing a novel index system in the theory of land use structure and function. Utilizing the BTH region as a case study, it evaluates and analyzes the dynamics of land use structure and function amidst rapid urbanization. We observed that the rapid urbanization and expansion of urban space, alongside the contraction of agricultural space in the BTH region, corroborated the research of Tan et al. [44]. Land use function exhibited a trend of trade-offs, which aligned with the results regarding spatial heterogeneity trade-offs in land use functions identified by Yang et al. through grid-scale analysis [45]. Therein, the index system of land use was based on the theoretical correlation between structure and function. By constructing a dual evaluation index system of land use structure and function, the direct correlation between structure and function was observed, the temporal-spatial changes of land use structure and function were revealed, and the methodology reference was provided for land use research.

4.2. The Characteristics of Urbanization Development and Land Use

During the period from 2003 to 2020, regional urbanization development was generally positive, with Beijing leading the way (rising from 0.2571 to 0.8484 in Beijing, from 0.2515 to 0.7602 in Tianjin, and from 0.1436 to 0.6925 in Hebei). In terms of dimensions, the dominant dimension shifted from eco-environmental urbanization to economic urbanization. This showed that the BTH region was in a stage of rapid economic growth, highlighting Beijing’s significant contributions to eco-environmental construction and confirming that Hebei serves as the primary production base for the BTH region [46,47,48,49]. Furthermore, the regional dominant land use functions were different within the BTH region, which might be connected with the leading economic development pattern, social development level, ecological compensation mechanism, and different concerns of local policies [50,51]. Compared to the inner region of the BTH region, the overall land use structure has exhibited notable changes due to rapid urbanization. Specifically, there was a discernible trend toward an increase in urban space, a decrease in agricultural space, and fluctuations in ecological space. The average annual growth rates for these categories were 2.59%, −0.55%, and 0.06%, respectively. Furthermore, the dominant land use functions fluctuated between the production function and the living function without a clear directional preference (Figure 10). This indicates that land use across the entire BTH region is currently undergoing an adjustment phase, necessitating effective policy guidance for optimal management.

This paper fully expounded the spatial characteristics of land use from the quantity and quality of land use structure and the spatial distribution of urban-agriculture-ecology developed in a synergistic direction in the BTH region. Based on the land use function deviation degree model, we explored the evolution path of land use function under urbanization. At the early stage of the study, production function was dominant in the BTH region, and the land use function deviation index showed an increasing trend, which indicated that the imbalance of land use function, caused by the rapid growth of production, would become more obvious under urbanization development [19]. Generally speaking, the ecological function and living function of a city were more obvious due to the influence of the eco-environment [52]. Rapid urbanization development requires production to provide the driving force, and the expansion of industrial land led to the limited development of ecological function and living function, resulting in a rapid urbanization process in which the demand for the dominant land use function was transformed from living and ecological functions to production function [33,53,54,55]. Based on the evolution trajectory of the dominant land use function in the BTH region from 2003 to 2020, and drawing upon the spiral rise theory of ecological succession, we believe that urbanization development promoted the dominant land use function to evolve to a higher level of synergy. Urbanization development has an obvious rule of periodicity, and the goals of urbanization development are different in various stages [56]. Hence, under rapid urbanization, research on the evolution mechanism of land use structure and function in the BTH region provides a valuable reference for the reasonable development and regulation of land space in the process of urbanization in developing countries.

4.3. Limitations and Policy Suggestion

There are some limitations in this study. It failed to analyze the relationship between the internal dimensions of urbanization development and the structure and function of land use in detail. In the future, we will explore the driving mechanism of land use structure and function in the BTH region under different urbanization development stages, to guide the optimal allocation and governance of land resources.

The BTH region is a vital economic growth pole in China, in which the interaction between urbanization and land use promotes regional sustainable development. Because of the current difficulties in the regional development process, the following policy suggestions are put forward:

(1)

Land use needs to be rationally planned according to the urbanization development stage in the BTH region. The central government should provide classification guidance and planning according to the differences in regional urbanization development, and local governments should carry out in-depth planning to gradually realize the sustainable development of land. It is essential to focus on the coordinated development on a regional scale, adhere to the principles governing inter-regional urbanization processes, and rationally adjust social urbanization, economic urbanization, and eco-environmental urbanization to optimize regional land use.

(2)

Strengthen the utilization efficiency of urban-agricultural-ecological spaces and prevent urban spaces from spreading arbitrarily. In the context of rapid urbanization in the BTH region, the government should control the unreasonable development of urban space by improving the urban land approval procedures and keeping the red lines of arable land and ecological protection.

(3)

Based on the dual evaluation index system of land use structure and function, a direct correlation between land use structure and function was established to realize the connection between theory and practice. The government should strictly implement the urban land classification standards and improve the adjustment mechanism of land use structure and function. We should pay full attention to the internal correlation mechanism between urbanization development and land use, accurately analyze the dominant functional characteristics of land use, formulate development plans, and adopt the dual effect of market and policy drive to coordinate the relationship between humans and land.

5. Conclusions

In a context of rapid urbanization, based on the systematic idea of “indicators-dimensions-subsystem-relationship and process system”, the evolution process of the land use structure and function was revealed. An index system was established to evaluate the land use structure and function simultaneously to explore the transformation process of land use comprehensively. Based on the land use function deviation degree model, the transformation path of land use function was discussed. Based on the Pearson correlation coefficient, the correlation between urbanization and land use function was analyzed, while the mathematical relation was explored between urbanization and land use function through a curve estimation model. This showed that: (i) from 2003 to 2020, the dominant dimension of the urbanization development changed from the eco-environmental urbanization dimension to the economic urbanization dimension, indicating that the BTH region was in the period of rapid economic development; (ii) in terms of the quantity of land use structure, the proportion of urban space showed an increasing trend, the proportion of agricultural space showed a decreasing trend, and the proportion of ecological space experienced a decrease first and then an increase. Additionally, the spatial distribution of urban-agricultural-ecological spaces was developing in a synergic direction. In terms of the quality of land use structure, the development level of land use structure showed an upward trend in Beijing and Hebei, while there was a U-shaped development trend in Tianjin; (iii) the evolution path of the dominant land use function was from production to living function, then to ecological function in Beijing, from production to living function in Tianjin, and it was always in production function in Hebei. With urbanization development, the dominant function of regional land use evolved to a higher synergy level in the BTH region.

The large-scale expansion of built-up areas and the continuous deterioration of the natural environment indicate that rational land use planning is urgently needed. The dual evaluation index system of land use built by establishing the direct correlation between land use structure and function can promote the integration of structure and function, making it possible to evaluate land use resources objectively and effectively and help planners and decision makers to formulate effective land policies. The research results for the BTH region showed that the dual evaluation index system of land use structure and function was an effective evaluation method. Here, we hope to provide a useful template to illustrate the correlation between land use structure and function. Finally, as the study area changes and the data improve, this template can be further improved.