Ecological Security Pattern Construction in Rural Settlements Based on Importance and Vulnerability of Ecosystem Services: A Case Study of the Southeast Region of Chongqing, China

Abstract

With the development of urbanization, a large number of village settlements have disappeared. As important carriers of ethnic and cultural heritage, village settlements are important for the continuation of folk culture and farming spirit. Building a regional ecological security pattern helps to protect the integrity of village settlements and promote the sustainable development of the Chinese nation. In this work, the importance of ecosystem services was first obtained by using the Integrated Valuation of Ecosystem Services and Tradeoffs model (In-VEST) and the revised universal soil loss equation model (RUSLE) to evaluate the regional ecosystem services in the southeastern region of Chongqing (SRC). Then, the ecological importance evaluation results were combined with the sensory evaluation results to derive ecological conservation importance areas and identify ecological source points in their high-value areas. Finally, the ecological corridors were obtained by the minimum cumulative resistance model (MCR). The regional ecological security pattern was constructed, i.e., the triangular protection area strategy of “one screen, one belt, and three cores”. The results show the following: the total area of ecological source sites larger than 20 km² in SRC is 436.02 km², accounting for 2.28% of the area of SRC. The largest ecological patch is 69.93 km², accounting for 16.04% of the total area of ecological source sites. Thirteen ecological source sites were identified as follows: four in Youyang County, three in Shizhu County, three in Wulong County, and one in Pengshui County. There are 78 ecological corridors with a total length of 4832.82 km, including 32 important ecological corridors with a length of about 1544.53 km and 46 potential ecological corridors with a length of about 3288.29 km. Based on the minimum cumulative model constructed by eight resistance factors, the spatial variation of the ecological resistance surface was analyzed, showing a trend of being high in the west and central part and low in the surrounding area. There are one high-value area of the resistance surface of Wulong County Nature Reserve and one high-value area of ecological sensitivity that overlap to the extreme, and which should be given sufficient protection attention. The core protected areas consist of three mountains including the Qiyao Mountain Range, the Wuling Mountain Range, and the Wulong County Nature Reserve. The ecological security pattern in SRC based on the mode of “source–ecological corridor–ecological node” can identify important ecological function areas, providing scientific guidance for sustainable development and ecological security protection in the ethnic village settlements in China.

1. Introduction

Rural settlements are important spatial carriers of production and life for rural residents [1]. With the continuous development of urbanization, the rural settlements around towns and cities have suffered large-scale destruction. In addition, disorderly expansion, illegal alterations, and encroachment on farmland have further damaged the integrity of the landscape, customs, and spatial structure of rural areas. Rural settlements carry on the wisdom of the Chinese farming civilization, and the trend of their mass annihilation has alerted us to the urgency of conservation. In the context of rural revitalization in the new era, we focus on the conservation of rural settlements. The current hot topics of this research include spatial pattern evolution of rural settlements [2], tourism resilience assessment [3], landscape pattern optimization [4], style inheritance [5], influence factors, etc. [6]. Jian Yuqing et al. [7] used the landscape expansion index method to explore 35 years of land use changes in rural settlements in Guangdong Province, and the results showed that land use was dominated by edge-like expansion, with socio-economic factors being the main driving factors of land use evolution in rural settlements. Hu Hangxiao et al. [8] analyzed the suitability of rural construction in mountainous areas of Fujian Province by taking the coupling of soil and water resources and rural settlements as an entry point. They hold the view that rural settlements showed a trend of concentrated aggregation throughout the day, and the spatial distribution was highlighted by arable land. Yang Xingzhu et al. [9] analyzed the functional transformation and spatial reconfiguration of rural settlements using Geographic Information System(GIS) spatial analysis tools and rural assessment methods, indicating that an emphasis on tourism market demand and multiple subject dynamics were the main controlling factors promoting the transformation and reconfiguration of settlements. In addition, foreign scholars such as Behnaz Aminzadeh [10] have proposed methods and recommendations for interventions in rural settlements in Tehran to improve the structure and function of the regional landscape, which is an important guide to sustainable land use planning patterns in rural areas.

Ecological security patterns originated from the theory of landscape ecological planning [11], which is an important element of sustainable development strategy. The multi-level spatial landscape ecological patterns were constructed by analyzing the structural functions of ecological elements in the region comprehensively based on the dominant ecological nodes, corridors, and habitat patches. The preservation of environmental integrity and the reduction in domestic land use disputes are of enormous practical importance. Early studies on ecological security patterns mainly focused on land health research [12] and ecosystem value assessment [13]. With the increasingly close connection between economic development and ecological construction, the system coupling analysis of natural ecology and social economy [14] has become a hot research subject. The basic path of “source identification-resistance surface construction-corridor identification” [15,16] was usually carried out in the construction of ecological security patterns in China. In terms of source identification, Li Hui et al. [17] chose a nature reserve as a source without considering regional environmental factors. The most serious disadvantage of this method is that it lacked a certain degree of objectivity. Zhu Lingxi et al. [18] derived ecological source sites from the evaluation of ecological patches by the single selection of impact factors in the importance of ecological services. The defect of this strategy is the vulnerability of the ecosystem was not accounted for itself. In the construction of resistance surfaces, Lin Yilin et al. [19] used the land vegetation allocation method to construct resistance surfaces. The major drawback of this method is that it is difficult to describe differences that impede species migration under similar vegetation belts. With the expansion of the study, several methods further modified the construction of resistance surfaces such as the nocturnal light index [20] and habitat quality [21]. To identify the corridor, the minimum cumulative resistance (MCR) model is widely used at present.

The SRC is mostly mountainous and hilly, with abundant forests and water sources and a high value of ecosystem services, but some areas are characterized by stone desertification and fragile ecological substrate conditions [22]. With the pressure of urbanization, the environmental quality of the region has declined significantly. There is an urgent need to reconcile ecological construction and economic development. According to a related study [23], 70.91% of the national traditional villages in Chongqing selected by the Ministry of Housing and Construction as of 2019 are distributed in the SRC. In this work, we construct ecological safety for SRC by using the evaluation elements of ecological service importance and ecological service sensitivity to provide an important theoretical basis for the protection of the style of SRC rural settlements and regional ecological safety.

2. Study Area and Data Sources

2.1. Study Area Overview

SRC is located in southwestern China (28°11′–30°31′ N,107°21′–109°12′ E) and consists of six districts and counties in Chongqing (Figure 1). The region has a temperate subtropical monsoon climate, dominated by mountainous and hilly terrain, with the Qiyao Mountains and the Wuling Mountains situated there. The vegetation is dominated by warm coniferous forests and subtropical evergreen broad-leaved forests with abundant forest resources. Due to the staggered water systems such as the Yangtze River and Wujiang River, the combination of sufficient rainfall and the suitable temperature has formed an excellent ecosystem that feeds the precious and long-established plant and animal species on the land with important ecosystem service values. As an important ecological corridor and ecological barrier zone in southwest China, the SRC is deep inland and climate change has triggered the expansion of rock desertification in southwest China [24], resulting in its relatively fragile ecological base. On the other hand, negative human production activities have further exacerbated the conflict between land use and ecological conservation.

2.2. Data Source

Land use information, a digital elevation model (DEM), the normalized vegetation index (NDVI), evapotranspiration information, precipitation information, and soil information are used in this study. The NDVI data were generated by the MOD13Q1 v6.1 product. The DEM data with a spatial resolution of 30 m were both obtained from the geospatial data cloud website (http://www.gscloud.cn/ (accessed on 6 October 2022)). The land use data in SRC were obtained from the 2020 Landsat 8 remote sensing image interpretation. The meteorological data include weather station data such as precipitation, temperature, sunshine hours, and raster data of evapotranspiration from the website of China Meteorological Data (https://data.cma.cn/ (accessed on 12 October 2022)), which are mainly used to calculate water content function and net primary productivity of vegetation. Soil data are obtained from the World Soil Database (HWSD). Transportation data for calculating resistance values include the 2018 highway network, national highway network, railroad road network, etc., much of which were collected from local natural resource management departments.

3. Research Methodology

This work focuses on the prominent problem of urbanization expansion on the conflicting land use of SRC rural settlements, using In-VEST v3.12, RUSLE v2.0 and ArcGIS v10.7 to build a regional ecological assessment model. Firstly, the importance of ecosystem services was assessed such as soil and water conservation, carbon fixation and oxygen release, and habitat quality. Additionally, the important ecological protection areas were identified by quantitative analysis. Secondly, the ecological sensitivity of the area was evaluated by natural factors and human subjective factors, using vegetation cover, elevation, slope, slope direction, and land use data. Then, the ecological source sites were identified by superimposing the results of the dual evaluation. The relevant resistance factors were assigned with the land use types to construct the ecological resistance surface. Finally, the ecological corridors were extracted by the MCR model to construct the ecological security pattern of SRC (as shown in Figure 2).

3.1. Ecological Source Identification

Ecological source sites are the source points for the continuation of biological species and ecosystem dispersal, which play a role in hindering ecosystem degradation, and provide important guarantees for the maintenance of regional ecological security. In this study, the importance of ecosystem services and the sensitivity of ecosystems were evaluated based on the important impact factors in the natural and human categories. Then, the results of the “dual evaluation” were superimposed and analyzed to obtain the results of the ecological conservation importance assessment. Finally, the areas with relatively high conservation importance and areas with high conservation importance are considered ecological source sites to achieve precise identification of ecological source sites.

3.1.1. Ecosystem Service Importance Assessment

According to the ecosystem characteristics and related research results of Chongqing [25,26], four types of key ecosystem service factors were selected for importance evaluation. The four single factors were analyzed in a model, as detailed in

Table 1. Methodology for assessing the importance of ecosystem services.

Ecosystem Services	Assessment Methods	Fundamentals
Soil Conservation	RUSLE Model	A = R × K × LS × (1 – C × P); A is the average annual soil conservation amount per unit area (t/(hm2·a)); R is the rainfall erosion force factor; K is the soil erodibility factor; LS is the slope length factor; C is the cover management factor; P is the soil and water conservation measure factor.
Water Conservation	In-VEST Model Water Yield Module	${\mathrm{Y}}_{\mathrm{x}\mathrm{j}}=($$1-{\mathrm{A}\mathrm{E}\mathrm{T}}_{\mathrm{x}\mathrm{j}}$$/{\mathrm{P}}_{\mathrm{x}}$$)\times {\mathrm{P}}_{\mathrm{x}}$$; {\mathrm{Y}}_{\mathrm{x}\mathrm{j}}$ is the water yield of raster x of the jth land use type (mm), ${\mathrm{A}\mathrm{E}\mathrm{T}}_{\mathrm{x}\mathrm{j}}$ is the actual evapotranspiration of raster x of the jth land use type (mm); ${\mathrm{P}}_{\mathrm{x}}$ is the annual precipitation at x (mm). ${\mathrm{A}\mathrm{E}\mathrm{T}}_{\mathrm{x}}$$/{\mathrm{P}}_{\mathrm{x}}=($$1+{\mathrm{W}}_{\mathrm{x}}$$\times {\mathrm{R}}_{\mathrm{x}\mathrm{j}}$$)/(1+{\mathrm{W}}_{\mathrm{x}}$$\times {\mathrm{R}}_{\mathrm{x}\mathrm{j}}$$+1/{\mathrm{R}}_{\mathrm{x}\mathrm{j}}$$); {\mathrm{R}}_{\mathrm{x}\mathrm{j}}$ is the dryness index under land cover type j at node x; ${\mathrm{W}}_{\mathrm{x}}$ is the available moisture content of vegetation.
Carbon sequestration and oxygen release	In-VEST Model Carbon Storage Module	Ctotal = Cabove + Cbelow + Csoil + Cdead; Ctotal is the total carbon stock (t/km2); Cabove is the aboveground carbon pool stock; Cbelow is the underground carbon pool stock; Csoil is the soil pool carbon stock; Cdead is the dead organic matter pool stock.
Habitat quality	In-VEST Model Habitat Quality Module	The habitat quality of different patches was evaluated by combining land use/cover type, threat source type, threat intensity, and the sensitivity of different cover types to threat factors.

. The five levels of the natural breakpoint approach were used to split the evaluation results such as high, relatively high, general, relatively low, and low. The evaluation results of the four single factors were superimposed with equal weights and divided into five levels to obtain the evaluation results of ecosystem service importance.

3.1.2. Ecosystem Sensitivity Assessment

Ecosystems are becoming increasingly vulnerable and unstable due to factors such as natural disasters and negative human activities [27]. In this study, five assessment parameters were selected and classified into five sensitivity classes (

Table 2. Eco-sensitivity evaluation factors.

Evaluation Factor	Low	Relatively Low	Sensitivity Levels General	Relatively High	High	Weight
Vegetation cover	<16	16–57	57–147	147–172	>172	0.19
Elevation	<570	570–818	818–1073	1073–1370	>1370	0.18
Slope	5	5–10	10–15	15–20	>20	0.25
Slope orientation	Flatland (1) Southern	South (2) Southwest	East (3) Western	North (4) Northwest	North (5)	0.15
Land Usage	Artificial	Arable land	Forest/Grassland	Scrub/Wetlands	Waters	0.23

) based on the research results of relevant ecological safety model construction [28,29] and using the natural breakpoint technique [30]. These evaluation factors were normalized and superimposed to obtain the ecosystem sensitivity of SRC.

3.2. Resistance Surface

The resistance surface reflects the strength of the impediment to the spatial circulation of ecological species. The greater the resistance value, the more ecological service value is lost, reducing the migration and dispersal of organisms. The undulating mountain ranges in SRC impede the flow of species between ecological sources to a certain extent. According to relevant research results [31,32], resistance factors such as land use type, elevation, slope, vegetation cover, rivers, and roads were selected, and the weights of each factor were determined using hierarchical analysis to generate a resistance surface by superposition. The ecological resistance weights and coefficients are shown in

Table 3. Resistance surface impact factor.

Evaluation Factor	Classification Criteria	Resistance Value	Weight	Evaluation Factor	Classification Criteria	Resistance Value	Weight
Land Usage	Woodland	10	0.18	Distance from river	<1	10	0.09
	Grassland	30			1–3	30
	Water bodies	50			3–5	50
	Arable land Artificial	70			5–10	70
	land	90			>10	90
Elevation	<300	10	0.12	Distance from railroad	>10	10	0.07
	300–500	30			5–10	30
	500–1000	50			2–5	50
	1000–1500	70			1–2	70
	>1500	90			<1	90
Slope	<8	10	0.21	Distance from highway	>10	10	0.07
	8–15	30			5–10	30
	15–25	50			2–5	50
	25–35	70			1–2	70
	>35	90			<1	90
Vegetation cover	90–100	10	0.17	Distance from national highway	>5	10	0.09
	80–90	30			2–5	30
	70–80	50			1–2	50
	60–70	70			0.5–1	70
	0–60	90			<0.5	90

.

3.3. Corridor Extraction and Ecological Security Pattern

Based on the least resistance model, the path with the lowest cost between each ecological source point, i.e., ecological corridor, is calculated. Its role is to guarantee the effective connectivity of ecological factors between source sites and the integrity of ecosystem functions. By using the minimum cumulative resistance model to measure the path with the minimum cumulative resistance value between ecological source sites, the ecological corridor can be extracted. Its calculation formula is as follows:

$$\mathrm{MCR}={\sum }_{\mathrm{i}=\mathrm{n}}^{\mathrm{m}}{\mathrm{D}}_{\mathrm{i}\mathrm{j}}\times {\mathrm{R}}_{\mathrm{i}}$$

(1)

In the equation, MCR stands for minimum cumulative resistance; D_ij represents the species’ spatial separation from the source grid j to the landscape cell i; R_i is the coefficient of ecological resistance for landscape cell i; and f is the function of the minimal cumulative resistance and ecological process. The serial numbers of the source grid and the target grid are m and n, respectively.

4. Results

4.1. Ecosystem Services Importance

The four different types of ecosystem service functions in the SRC have different spatial distribution characteristics (Figure 3). Soil conservation is influenced by factors such as slope, slope length, vegetation cover, and soil erosion, and the occupancy rate of both high-value and low-value areas is low, and most areas have an average level of soil and water conservation capacity. The single most striking observation to emerge from the data comparison was that—although there is no obvious polarization phenomenon—the overall soil conservation capacity is relatively low. The high-importance area of water source connotation is gathered and distributed in the central and northeastern part of Youyang County, as well as the southeastern part of Pengshui County and Qianjiang District. There is some evidence that abundant precipitation and high vegetation cover may affect water source connotation. The high-importance area of carbon sequestration and oxygen release is large and mainly distributed in the northeastern part of Qianjiang District and the central and southeastern part of Shizhu County, with a zonal distribution from northeast to southwest along the Qiyao Mountain Range and the Wuling Mountain Range. The main distribution areas of high habitat quality are along the Qiyao Mountains and the Wuling Mountains, with the southwestern part of Wulong County, the northeastern part of Qianjiang District, and the southwestern part of Xiushan County as secondary distribution areas.

Using the GIS software functional analysis tool, the results of the four types of ecosystem service assessment in the SRC were subjected to functional overlay analysis and combined with the natural breakpoint method to obtain the results of the five levels of ecosystem service importance assessment (Figure 4). One interesting finding is the areas of high and relatively high importance areas for ecosystem services are 2378.9 km² and 7140.72 km², with a sum of 49.77%, mainly in the southeastern part of Shizhu County, the northeastern part of Qianjiang District, the southwestern part of Wulong County, and the Wuling Mountains in Youyang County. This area is a high-density area of woodland, which has important functions of water connotation and soil conservation. The area of general important area is 5080 km², accounting for 26.56% of the total area, scattered in six counties and districts. The area of lower important area is 3708.2 km², accounting for 19.39%. The area of low importance zone is 818.68 km², accounting for 4.28%, mainly distributed in the northwestern part of Shizhu County, the central part of Wulong County, the southeastern part of Qianjiang District, and the downtown area of Xiushan County, with low vegetation coverage.

4.2. Ecosystem Sensitivity Assessment Results

The ecological sensitivity evaluation results were obtained by spatial superposition analysis of natural factors and human factors, and the evaluation results were divided into five levels using the natural breakpoint method (Figure 5). The obvious finding to emerge from the analysis is that the overall ecosystem sensitivity of the SRC gradually increases from south to north, with general sensitivity dominating, with an area of 5397.88 km², accounting for 28.22% of the total area; this is followed by relatively low sensitive areas, with an area of 4827.43 km², accounting for 25.24%. Both are mainly agricultural land, with relatively stable ecological comprehension. In addition, their relatively highly sensitive area and highly sensitive area have an area of 3873.79 km² and 1821.44 km² respectively, accounting for 20.25% and 9.52% of the total area, and they are primarily found in the region of the Qiyao Mountain Range, the Wuling Mountain Range area and the surrounding areas of Wulong County, and the central part of Pengshui County. The high altitude and steep slope of these areas, the occurrence of natural disasters such as landslides and mudslides in the rainy season, and the poor natural environmental conditions are important factors leading to the sensitivity of their ecological zones. The low-sensitive areas cover an area of 3206 km², accounting for 16.77%, mainly in the southeastern part of Youyang County, Xiushan County, and the northeastern part of Qianjiang District. These regions have primarily forested terrain, with high vegetation cover and strong water connotation, as well as soil conservation capacity, which is conducive to the survival and continuation of plants and animals.

4.3. Eco-Source Identification Based on the Importance of Ecological Conservation

The spatial distribution pattern of ecological protection importance in SRC was obtained by applying spatially weighted superposition to the results of ecosystem service importance evaluation and ecosystem sensitivity evaluation (Figure 6). The results show that the area with high and relatively high ecological protection importance are 1960.26 km² and 4749.83 km², accounting for 10.25% and 24.83% of the total area, respectively, and are mainly located in the Qiyao Mountain Range, the Wuling Mountain Range, and the southwestern part of Wulong County. These areas have a large number of nature reserves and forest nature parks with high ecological service values. The areas of general, relatively low, and low-value ecological protection zones are 5836.5 km², 4723.49 km², and 1856.42 km², respectively, accounting for 30.52%, 24.7%, and 9.7%. They are mainly distributed in the railway network, expressway network, national road network, the cultivated land region in the southeast of Youyang County, the cultivated land region in the southeast of Xiushan County, and the central area of each county and town.

The patches with high and relatively high ecological protection importance ratings were taken as ecological source sites, and the area of ecological source sites was identified as 6710.09 km², accounting for 35.08% of the land area in the SRC, with the general trend of spatial distribution increasing from south to north, showing a contiguous strip distribution in nature reserves such as the Qiyao Mountains, the Wulong Mountains, and the Wuling Mountains. However, due to the constraints of inconvenient management and the small size of the source site to achieve effective ecological value radiation, after repeated simulations and reference to the research results of Sun et al. [33], this study decided to designate the patches with an area larger than 20 km² as the final ecological source sites (Figure 7). A total of 13 ecological patches were larger than 20 km², and the area of ecological source sites was 436.02 km², accounting for 2.28% of the SRC.

In terms of regional characteristics, the largest ecological source site has an area of 69.93 km², accounting for 16.04% of the total ecological source site area, spanning two counties, southwestern Shizhu County and northeastern Pengshui. The patches larger than 20 km² were converted into elements to identify 13 ecological source sites, and Wulong County had 5 ecological source sites, ranking first in number, with many natural forest parks and high ecological service value in the area. The number of ecological source points in Shizhu County is 4, ranking 2nd, and the rich natural resources of the Qiyao Mountains maintain the ecosystem health of the district. Youyang County and Qianjiang District have 3 and 1 ecological source points, respectively. The Wuling Mountains and the Wujiang River system provide excellent soil conservation and water containment service functions for these two counties and districts.

4.4. Eco-Resistance Surface Analysis

The eight resistance factors were analyzed by reclassifying the resistance assignment (Figure 8), the expansion resistance surface of ecological nodes in the SRC was obtained after weighted superposition (Figure 9), and the weighting of the resistance surface was taken as shown in Table 3. When the resistance value is smaller, the ecological service value loss caused by species circulation is smaller. From the overall spatial perspective, the resistance surface shows a trend of high in the west and central part and lower in the surrounding area. The high values of the resistance surface were mainly distributed in the southeastern part of Shizhu County, central Wulong County, central Qianjiang District, central Pengshui County, central Youyang County, and northwestern Xiushan County, which were highly influenced by human activities and reached the maximum value in the central city of each district and county, and gradually decreased from the central city to the surrounding area. One interesting finding is the high value of resistance surface in Wulong County is also the high value of ecological sensitivity in spatial distribution, where animal migration activities are more affected by obstruction. On the other hand, the areas with lower values of resistance surface are distributed in the northeast, southwest, and southeast areas of SRC, and the areas with lower values of resistance are far away from towns and important rivers. These areas are relatively backward in economic development and less influenced by human activities.

4.5. Ecological Corridor Extraction and Ecological Security Pattern Construction

Ecological corridors play a role in facilitating the flow of ecological processes and protecting biodiversity [34]. In this study, 13 ecological source points were derived by identifying the source centers, followed by combining the minimum cumulative resistance surface with ecological source points and using the MCR model for cost path analysis. The minimum depletion paths were derived as important ecological corridors and the secondary minimum cost depletion path corridors as potential ecological corridors. The SRC ecological corridors are made up of both significant ecological corridors and potential ecological corridors (Figure 10). The findings indicate that there are 78 ecological corridors with a total length of 4832.82 km, including 46 prospective ecological corridors with a length of about 3288.29 km and 32 major ecological corridors with a length of approximately 1544.53 km each. The ecological corridors in the SRC are mainly along woodlands, water systems, and mountains, arranged spatially in a spiderweb pattern. The most interesting finding was that the ecological corridors pass through most nature reserves and forest parks, providing an important guarantee for the integrity and connectivity of the ecological pattern of SRC.

The ecological source sites in the SRC are mainly distributed in the Qiyao Mountain Range area, the Wuling Mountain Range area, and the high-value areas of habitat quality in each district and county. The extracted ecological corridors are radially distributed in a spiderweb style to guarantee the integrity of the ecological pattern. In this work, we construct the ecological security pattern of the SRC based on the spatial distribution characteristics of the natural ecological base, ecological source land, and ecological corridors. Through the integrated planning of various elements of the source areas, the optimized ecological security pattern of “one screen, one belt, and three cores” is proposed (Figure 11). It is worth noting that the triangle reserve has a stable ecological service system, and intends to provide a reference for the ecological construction work in SRC.

“One screen” refers to the base on the northwest to the southeast trend of the Qiyao Mountain Range, building up a natural protective barrier in the northern part of the SRC. The importance of ecosystem services in the Qiyao Mountain Range is high, the distribution of ecological sources is concentrated, ecological corridors are staggered, and the rich forest resources have the functions of regulating ecological climate and degrading pollution, which provide an important guarantee for soil conservation, carbon fixation and oxygen release, and species habitat.

The “one belt” refers to the ecological protection belt built according to the trend of the Wuling Mountains and several corridors connecting ecological sources, insisting on the combination of protection and treatment and based on the current situation of economic development and overall scientific planning. While promoting the restoration of arable land and forest land, it will protect the industrial development of the SRC and build it into an ecological civilization demonstration belt.

In Figure 11, the three blue circles represent the “three cores” section. The “three cores” refer to the Qiyao Mountain Nature Reserve, the Wulong Mountain Forest Park Reserve, and the Wuling Mountain Nature Reserve, respectively. These core reserves are linked by ecological corridors to form a stable triangle of an ecological network in SRC. Radiation from the core areas to the periphery will enhance ecological values and build a solid ecological security pattern.

5. Conclusions

The research results of this paper show the following:

(1)

The ecological source area is 436.02 km² or 2.28% of the area of SRC, and there are 13 ecological patches greater than 20 km². The largest ecological patch is 69.93 km² or 16.04% of the overall ecological source area. It is primarily found in the regions of the Qiyao Mountain Range, Wuling Mountain Range, and Wulong Mountain Range.

(2)

A total of 4 in Youyang County, 3 in Shizhu County, 3 in Wulong County, and 1 in Pengshui were among the 13 ecological source sites that were found to be concentrated in wooded resource-rich locations. In the SRC, 78 ecological corridors totaling 4832.82 km in length were found, comprising 46 prospective ecological corridors totaling about 3288.29 km and 32 essential ecological corridors measuring about 1544.53 km.

(3)

The spatial variation of the ecological resistance surface is evident based on the minimal cumulative model built by eight resistance elements, and the resistance surface exhibits a pattern of being high in the west and central part and low in the surrounding area. According to spatial distribution, Wulong County’s high-value area of resistance surface is also a high-value region of ecological sensitivity and should receive adequate protection.

(4)

The Qiyao Mountains area, the Wuling Mountains area and the Wulong County Nature Reserve are all rich in natural resources and are key conservation areas for the construction of the ecological security pattern in SRC.

6. Discussion

6.1. Spatial Heterogeneity of Ecosystem Services

The natural environment and human activities work together on ecosystem service functions, and different ecosystem services in the SRC are spatially heterogeneous, as shown in Figure 3. With the expansion of urbanization, regional land use changes, and the increase in urban land will certainly have an impact on surface runoff, which leads to a decrease in soil and water conservation capacity. In addition, the increase in residential construction land will also affect the ecosystem [35], and the resistance to linkage between large ecological patches increases and habitat quality decreases. On the other hand, the higher value of vegetation cover areas have relatively stronger carbon sequestration and oxygen release capacity, and better ecosystem stability [36]. The forest resources in the SRC are focused on the Qiyao Mountains, the Wuling Mountains, and the Wulong Mountains, and the vegetation acts as a natural ecological barrier that can effectively prevent the diffusion of air pollutants and water pollutants. In summary, the value of ecosystem services in the SRC is positively correlated with positive ecology and negatively correlated with negative human activities on the environment.

6.2. Spatial Heterogeneity of Ecological Corridors

Promoting the co-development of economic construction and ecological protection is an important element of the urbanization process [37]. Ecological corridors, which are a component of the biological landscape, are crucial for connecting ecological patches and stabilizing regional ecological security. The distribution of ecological corridors, according to the current study, reveals regional space heterogeneity. When impacted by both natural and artificial influences, the resistance surface of species migration and energy flow increases, the ecological service cycle value is low, and the length of ecological corridors is shorter. On the contrary, when the species flow is less influenced by the resistance surface, the ecological corridor is longer. However, there is still no unified method on how to set the optimal ecological corridor width value.

6.3. Optimization and Suggestions

Species dispersal, biogenetic migration, and habitat expansion are ecological processes of natural systems. Promoting the stable development of ecological processes is conducive to the optimal construction of ecological security patterns. This work proposes the following optimization suggestions: First, enhance ecological patch protection and improve regional ecosystem stability. The important ecological patches identified in the SRC based on model calculations have good integrity, and their ecological service functions should be maintained and habitat quality improved. For ecological patches within the urban construction area, they should be combined with the construction of urban parks, forests, green areas, and other ecological landscapes to avoid disorderly and chaotic expansion of urban areas. Secondly, the width of ecological corridors should be reasonably set to optimize the connectivity of important ecological corridors. Since the Chongqing municipal government has not issued guidelines related to ecological corridors, we refer to the relevant regulations in the urban design guidelines for territorial spatial planning [38]. When the width of ecological corridors is 100–200 m, species migration is stable, the value of regional ecological services is better, and there is a positive impact on ecological processes. Third, reasonable planning of land construction and targeted restoration of damaged patches should be undertaken. Water restoration areas, reinforcing soil protection, avoiding soil erosion, and building ecological riverbank landscape, are important In the woodland restoration area, broken ecological patches should be repaired to maintain ecological diversity and avoid degradation caused by ecology. Adhere to the principle of combining reasonable planning and targeted restoration to achieve low-cost and high-level ecological protection.

6.4. Advantages and Outlook

The traditional identification of ecological source sites is based on the top 10 forestland or nature reserves in terms of area size [39,40], which inevitably causes bias in the identification of important ecological source sites. In order to ensure the precise identification of significant ecological source sites and ecological corridors, which is conducive to maintaining the integrity of regional ecological structure and function, this study combines the findings of the importance evaluation of ecosystem services and ecological sensitivity evaluation with multivariate factor analysis. In addition, scholars such as Ahmed Eladawy [41] proposed a relatively homogeneous overall spatial pattern for Yoshkar-Ola’s scheme of constructing an ecological security pattern, with weak dispersion of ecological sources to the surrounding natural environment and relatively fragmented radiation of ecological values between regions. This work proposes an ecological network restoration plan for the triangle protection belt that optimizes the ecological security pattern. By increasing the mutual radially between the ecological functions of the three core areas, a stable triangular ecological protection zone is formed to improve the feasibility of the research results on the ground.

On the other hand, there are shortcomings in this study. First, different ecological services in the region are in a symbiotic relationship with each other, and this work extracts ecological patches by superimposing ecosystem services, which may have caused the problem of duplication of ecological function structures. Subsequent studies can explore the differences of different ecological services and further improve the content of ecological security pattern construction. Second, when we constructed the ecological corridor, we reduced it to a linear element, which is inconsistent with the actual construction. Ecological landscapes are heterogeneous, which can affect the shape and width of ecological corridors. The next research work can summarize the width and shape of ecological corridors under different ecological landscape conditions. Third, the scientific construction of the resistance surface of the ecological safety pattern is a difficult point of the research content, and scholars have conducted a lot of model calibration and project landing studies on the resistance surface [42,43,44], but failed to form a unified guiding scheme. This paper assigns resistance surfaces to natural and human factors to enhance ecological circulation. However, insufficient consideration has been given to the correction effects of each index and the characteristics of the resistance surface differences within different landscapes. A comparative study of the accuracy of the different index corrections can be carried out later to further define the advantages and disadvantages of the correction indices under different conditions.