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Article

Sustainable Agricultural Development Models of the Ecologically Vulnerable Karst Areas in Southeast Yunnan from the Perspective of Human–Earth Areal System

by
Xiaoqing Zhao
1,*,
Yifei Xu
1,
Qian Wang
1,
Junwei Pu
2,
Xiaoqian Shi
1,
Pei Huang
2 and
Zexian Gu
2,3
1
School of Earth Sciences, Yunnan University, Kunming 650500, China
2
Institute of International Rivers and Eco-Security, Yunnan University, Kunming 650500, China
3
Nujiang Forestry and Grassland Administration, Lushui 673100, China
*
Author to whom correspondence should be addressed.
Land 2022, 11(7), 1075; https://doi.org/10.3390/land11071075
Submission received: 24 May 2022 / Revised: 9 July 2022 / Accepted: 13 July 2022 / Published: 14 July 2022
(This article belongs to the Section Land Socio-Economic and Political Issues)
Browse Figures
Versions Notes

Abstract

:
Rocky desertification in ecologically-fragile karst areas limit regional socio-economic development in the face of significant human–earth conflict. Coordination of ecological restoration and agricultural development is critical for sustainable development in karst areas. From the perspective of the human–earth areal system, the framework of sustainable agricultural development was proposed in typically karst areas. We integrated principles of ecological vulnerability, resource and environmental carrying capacity, agricultural foundation, suitability of agricultural land, and the farmers’ willingness. In this study, we found the ecological vulnerability of Guangnan County was slight, but the proportion of moderate and severe vulnerability areas was high, with significant differences between the two sides of the line “Zhe (Zhetu)-Lian (Liancheng)-Yang (Yang Liu-jing)-Ban (Banbang)”. Then, we divided Guangnan County into three ecologically vulnerable zones. Following that, we proposed sustainable agricultural models for various zones. In slightly to mildly vulnerable zones, we propose constructing economic–ecological agricultural models, including woody oil, plateau characteristic fruiting forest, ecological tea plantations, suburban agriculture, and cultural–ecological tourism. In moderately to severely vulnerable zones, we recommend developing a stereoscopic agriculture model that combines planting and breeding, vegetation restoration, and herbivorous animal husbandry. In extremely vulnerable zones, we suggest constructing an ecologically natural restoration model and an agricultural ecological–tourism model. Our research provides references for ecological restoration, agricultural development, poverty alleviation consolidation, and rural revitalization in ecologically vulnerable karst areas of southeast Yunnan and similar regions.

1. Introduction

With rapid industrialization and urbanization, the human impact on the human–earth areal system becomes non-negligible [1,2,3]. When the human disturbance is significant, the vulnerability of the geographic environment is intensified, and the difficulty of ecological governance is increased. The human–earth areal system is a complex dynamic system formed by the interaction of humans and their activities with the geographic environment in a specific region [4,5,6]. Coordinating a sustainable human–earth relationship has become an important issue to solve [7,8].
Currently, studies on the human–earth relationship have mainly focused on the single-factor carrying capacity of the system and its interaction with human activities [9]. Studies also addressed coupled development of the human–earth system, together with vulnerability evaluation and coordination of supply and demand [10,11]. Along with loess, desert, and cold deserts, karst is one of China’s four ecologically vulnerable areas. The natural recovery of karst ecosystems is slow and challenging due to their fragility and substantial human interference [12,13,14]. The fragile characteristics, such as soil erosion, rocky desertification, declining ecosystem service functions, and difficulties in people’s lives, are apparent. Additionally, farmers are compelled to continue agricultural production due to the lack of alternate livelihood opportunities [12,15]. It seriously threatens the regional ecological environment and food security while generating limited economic benefits. Therefore, karst ecosystems are prone to the vicious circle of “fragile ecology-economic backwardness-ecological damage-further ecological deterioration”, resulting in “ecological poverty” [16,17,18]. Agricultural and corresponding industrial development models should be optimized for sustainable rural development to realize rural revitalization in the karst areas [5,19,20].
Researchers proposed different agricultural development models to coordinate the human–earth areal system in the ecologically vulnerable karst areas and realize sustainable development up to a point. They argued that the primary task in karst areas is to restore regional surface vegetation while addressing ecological poverty caused by the fragile ecological environment [21,22,23]. Focusing on the farmers’ livelihood, policymakers have combined ecological engineering projects to form five development models with rocky desertification management as the core in Guizhou and Guangxi provinces. Firstly, based on the regional vegetation succession and land production conditions in karst areas, the grass-livestock management model of rocky desertification was proposed to increase farmers’ income and reduce disturbances on the ground surface [24]. Secondly, based on the dual pattern of overground and underground runoff systems in karst areas, forest and grassland restoration, as well as soil and water conservation models along with integrated watershed management, are recommended for dealing with rocky desertification and impoverishment [25]. Thirdly, farmers should change the farming location to reduce soil erosion and adopt a stereoscopic agricultural development model where large surface cuts and slope-farming aggravate ecological degradation [26]. Fourthly, the ecological agriculture model comprises of characteristic agriculture that addresses ecological problems and promotes the benign development of the karst ecosystem [25,27]. Fifthly, the ecological sightseeing agriculture model is gradually emerging through the combination of the karst landscape and agricultural landscape, fully exploring the ornamental aesthetic value of karst areas [25]. Additionally, the ecological migration model was proposed to consider ecosystem carrying capacity, resource utilization, and farmers’ livelihoods [28]. In summary, the existing studies mainly focused on regional vegetation restoration, economic development, sustainable livelihoods, and zoning treatment for different levels of rocky desertification. However, few studies have proposed sustainable agricultural development models in different ecologically vulnerable areas, integrating ecological restoration, farmers’ willingness, economic benefits, and resources and environment carrying capacity.
Guangnan County is located in the rocky desertification-prone area contiguous to Yunnan, Guangxi, and Guizhou, as an example of a typical karst region in southeastern Yunnan. It is a national county for rocky desertification key management. Despite the gradual implementation of ecological projects since 2002, the rocky desertification area has been reduced by 288.98 km2. Again, Guangnan County is socio-economically backward and was once listed as a key poverty alleviation county in China. The relative poverty is still severe despite Guangnan County being delisted in November 2020. It is still a typical region with prominent ecological environment destruction and lagging social-economic development. Exploring a set of sustainable agricultural development models to solve ecological and rural economic backwardness problems is therefore crucial.
Based on the theory of the human–earth areal system, this study proposed the framework of sustainable agricultural development in the typical karst region. Following that, we classified the types of ecologically vulnerable zones and proposed sustainable agricultural models for various zones. The findings would be useful for ecological restoration, agricultural development, poverty alleviation consolidation, and rural revitalization in ecologically vulnerable karst areas of southeast Yunnan and similar regions.

2. The Framework of Sustainable Agricultural Development in Karst Areas

2.1. The Human–Earth Interaction

There are dual problems of ecological fragility and socio-economic backwardness in karst areas of southwest China [12,18]. The solid regional karstification and low efficiency of surface water accumulation have been affecting the surface cover system, and causing severe soil erosion and rocky desertification. Meanwhile, socio-economic development was rather lacking due to the constraints of traditional cultivation habits, backward technology, poor information access, and a unique mountain culture. It has formed an ecologically fragile and socio-economically backward human–earth areal system, limiting its sustainable and coordinated development [13,29]. When the degraded natural environmental system and poor human social system interact, they are prone to ecological damage; and economic poverty exacerbates the ecological vulnerability (Figure 1). It has distinctly affected the carrying capacity of ecosystems and related economic activities. Therefore, the combination of ecological restoration and agricultural development are the keys to solving the ecological and socio-economic problems in the karst areas [30].

2.2. Ecological Restoration

A stable natural environment is a basis for regional sustainable development [31,32]. Ecological problems are prominent under the interaction of water, atmosphere, soil, land, creature, and people in karst areas [18,23,33,34]. The unique geological conditions generate a low rate of soil formation, resulting in a shallow soil layer and a lack of arable land resources, which is not conducive to agricultural farming [13,35]. The hot and humid climate promotes karst landform’s development, forming a runoff system of overground and underground dual patterns, resulting in a shortage of surface water [21,34,35]. Significant surface fluctuation provides potential conditions for soil erosion and other geological disasters. Furthermore, the natural environmental conditions only meet the requirements of calciphilous and xerophytic vegetation, and most vegetation cannot grow here, so the biodiversity is relatively low. The difficulty of ecological restoration continues to intensify with unreasonable human interference and increased rocky desertification further [12,36]. Therefore, issues such as regional resource utilization contradiction and ecological problems such as rocky desertification should be resolved in a coordinative manner.

2.3. Agricultural Development

The economic development of karst areas in China heavily relies on traditional agriculture based on corn and rice cultivation [15]. It is not advisable to introduce an advanced agricultural development model blindly. Adversely, the original agricultural foundation is of great significance for local farmers to develop suitable agriculture, which could enhance the overall productivity as well as ecological and cultural values [5,7,20,37,38]. Meanwhile, traditional crop cultivation should realize “Grain for Green” projects in slope croplands. It should thoroughly combine the regional differences in the topography and landscape of karst areas to develop stereoscopic agriculture. Depending on the characteristic landscape of karst areas and ethnic minority culture, it should create a landscape with idyllic tourism features and promote the development of agricultural eco-tourism [38,39,40]. In addition, the government should introduce advanced agricultural technologies to improve crop production [22,41], and social capital, such as companies and enterprises, to sell agricultural products [42].

2.4. Five Principles of Sustainable Agricultural Development

Sustainable development of the human–earth areal system in karst areas should prioritize the efficient coordination of ecological restoration and agricultural development. Agricultural development is built on ecological restoration, while ecological restoration is supported financially and technically by agricultural development (Figure 1). First and foremost, the karst ecosystem is fragile and even irreversible to some extent. The local ecological vulnerability must be taken into account, which refers to the sensitive response and resilience of an ecosystem or landscape to external disturbances at a specific spatial–temporal scale [43,44,45]. Furthermore, its socio-economic activities are constrained by resource and environmental carrying capacity, a critical factor that severely limits development intensity and is the basis for agricultural production activities. Moreover, agricultural development should consider the agricultural foundation, the suitability of agricultural land, and the willingness of local farmers to ensure better implementation by locals. These are critical in developing distinct agricultural development models that incorporate specific industries tailored to local conditions [42,46,47,48].
In brief, reasonable and sustainable agricultural development models are conducive to ecological protection and agricultural production synergistic development. In this study, we built the framework of sustainable agricultural development models in the southeastern Yunnan’s karst areas (Figure 1). We also integrated ecological vulnerability, resource and environmental carrying capacity, agricultural foundation, suitability of agricultural land, and farmers’ willingness as principles. It aims to maximize sustainability while minimizing contradictions in the karst human–earth areal system, and realize the delicately coordinated operation of the karst’s human–earth areal system.

3. Materials and Methods

3.1. Study Area

Guangnan County (23°29′~24°28′ N, 104°31′~105°39′ E) is located in southeastern Yunnan Province, southwestern China, at the junction of Yunnan, Guizhou, and Guangxi provinces, with a total area of 7730.09 km2 (Figure 2). The mountainous and semi-mountainous areas account for 94.7% of the county, prone to geological disasters, such as landslides and mudslides. The terrain is high in the southwest and low in the northeast, with an average elevation of 1280 masl. Guangnan County belongs to the central subtropical plateau monsoon climate zone, with an average annual temperature of 16.7 °C and average annual precipitation of 1056.5 mm. The hot and humid climate has been promoting karstification, making it a typical area of karst landform.
The karst landscape (monadnock, peak cluster, and needle karst) with prominent ecological fragility characteristics is widespread, accounting for 3/5th of Guangnan County. A total of 27.42% of the karst area was dominated by rocky desertification due to the particular geological conditions and unreasonable human interference [13,29,49]. A total of 65.42% of the permanent, poor, and ethnic population (771,900 as of the end of 2020) of Guangnan County was an agricultural population involved in traditional farming and animal husbandry.

3.2. Data Sources and Processing

The 2020 Landsat8 OLI winter image data (10 m spatial resolution) and DEM data (30 m spatial resolution) were obtained from Geospatial Data Cloud (http://www.gscloud.cn/ (accessed on 12 November 2020)). We classified the land use (i.e., land use types, such as paddy field, dry land, garden land, forest land, grassland, construction land, rural settlement, water area, and unutilized land) through man–computer interactive interpretation according to the spectral and texture characteristics of remote-sensing images. Rocky desertification grades were classified based on the rock exposure rate, vegetation, and soil cover. The land use and rocky desertification interpretation accuracy were 87.32% and 81.63% through field verification, accurately meeting the research needs. Other non-remote-sensing data are shown in Table 1.
Combined with the characteristics of high topographic fragmentation and significant land differentiation in mountainous karst areas, we conducted sensitivity experiments on four spatial raster scales of 300 m × 300 m, 100 m × 100 m, 50 m × 50 m, and 30 m × 30 m, followed by choice of 100 m × 100 m as appropriate raster size. All spatial data were uniformly converted into the WGS84-UTM48N projection system to ensure spatial consistency.

3.3. Evaluation of Ecological Vulnerability

3.3.1. Evaluation Index System

Ecological vulnerability is the joint result of the natural properties of ecosystems and human activities [33,45]. In this study, natural impacts reflect the natural environmental background of karst areas, including water bodies, climate, topography, geology, vegetation, and soils. Anthropogenic impacts reflect the intensity of human activity disturbance from social, economic, and landscape perspectives [7,44,50], including GDP density, agricultural population share, road level, and landscape fragmentation (Table 2).

3.3.2. Model of Ecological Vulnerability Evaluation

We chose the Spatial Principal Comment Analysis (SPCA) model to evaluate ecological vulnerability [44,45,51]. Some integrated variables were substituted for all the variables by rotating the spatial axes of the characteristic spectra. The subjectivity introduced by artificially determined weights can be reduced accordingly. It represents the vast majority of information when the contribution exceeds 85%. Meanwhile, the results can be implemented on a spatial raster. The model is as follows:
E V I = ∑ i = 1 n r 1 P C 1 + r 2 P C 2 + ⋯ + r n P C n
where EVI is the ecological vulnerability index; ri is the score of the i-th principal component; PCi is the contribution of the i-th principal component.
According to the result, we selected the six principal components with the highest contribution and cumulative contribution exceeding 85% (Table 3) to build the inverse model of ecological vulnerability:
E V I 2020 = 0.40 P C 1 + 0.20 P C 2 + 0.09 P C 3 + 0.06 P C 4 + 0.061 P C 5 + 0.05 P C 6

3.3.3. Ecological Vulnerability Classification

We standardized the result using the extreme value method based on the ecological vulnerability evaluation and karst areas’ ecological characteristics. Moreover, the natural breaks method was used to divide ecological vulnerability into five grades [44,50,52]: slight vulnerability (0 < EVI ≤ 0.2), mild vulnerability (0.2 < EVI ≤ 0.35), moderate vulnerability (0.35 < EVI ≤ 0.45), severe vulnerability (0.45 < EVI ≤ 0.6), and extreme vulnerability (EVI > 0.6).

3.4. Collection of Farmers’ Willingness

There are 18 townships and 167 villages in Guangnan County. Based on the level of ecological vulnerability and industrial diversification in each township, we selected 38 villages from 6 townships to conduct the questionnaire survey (Figure 2). Considering the farmers’ finite education level and cognitive ability, we refined the questionnaire and respondents based on the pre-survey (Tables S1 and S2). In each village, we surveyed 2 village cadres and 8~10 farmers with fields, with a total sample size of 400 questionnaires. Among them, village cadres are the leaders of village self-governance, familiar with the overall development of the village, and villagers are likely influenced by their ideas. A total of 387 questionnaires were retrieved, and the effective rate was 96.75%, including 307 questionnaires from farmers and 80 from village cadres.
The farmers’ questionnaire consisted of three parts: personal and family situation, agricultural cooperative organization situation, and willingness to industrial development. In the samples, the proportion of men (70%) outnumbered that of women (30%). Most farmers were middle-aged and elderly (76.5%), with an average age of 50.2. Most farmers (93.9%) had only junior high school education or below, and only a few farmers had higher education. Additionally, only 23.5% of farmers were satisfied with their current income.

4. Results Analysis

4.1. Ecologically Vulnerable Zones

4.1.1. Result of Ecological Vulnerability Evaluation

In 2020, the ecological vulnerability grade of Guangnan County was dominated by the areas of slight vulnerability that accounted for about 30.56% of the total area. In contrast, moderate, severe, mild, and extreme vulnerability areas accounted for about 20.06%, 19.28%, 16.59%, and 13.21% of the total area, respectively. Here, moderate and severe vulnerability areas cumulatively accounted for 39.34% of the total area (Figure 3a).
In terms of spatial distribution, vulnerable areas showed distinct differences between north and south along the line of “Zhe (Zhetu)-Lian (Liancheng)-Yang (Yang Liujing)-Ban (Banbang)”. The ecological vulnerability of the region south of the line was found to be high, with moderate, severe, and extreme vulnerability areas that accounted for about 52.85% of the total area. This area was developed by having carbonate rocks, which promoted the growth of calcareous vegetation, while biodiversity and ecosystem service functions were relatively low. Damage to surface cover usually promotes soil erosion having shallow and poor soil formation conditions. Additionally, an increase in population and production activities based on traditional agriculture has caused significant disturbance to the ecological environment. The region north of the line was majorly dominated by slight and mild vulnerability areas, which cumulatively accounted for about 47.15% of the total area. The restoration projects, such as “Grain for Green”, and the implementation of ecological afforestation projects have helped to increase regional vegetation cover that also reduced deleterious phenomena, such as soil erosion.

4.1.2. Division of Ecologically Vulnerable Zones

According to the quantitative structure and spatial distribution of each ecological vulnerability grades, we divided Guangnan County into three ecologically vulnerable zones that included: (1) slightly to mildly vulnerable zone; (2) moderately to severely vulnerable zone; and (3) extremely vulnerable zone (Figure 3b). This formed a spatial basis for the construction of agricultural development models.
In the slightly to mildly vulnerable zone, It has relatively a low ecological vulnerability grade and was mainly located in the region north of the line “Zhe-Lian-Yang-Ban”, which comprised about 47.15% of the total area. In the moderately to severely vulnerable zone, the area with a relatively high ecological vulnerability grade was mainly located in the region south of the line “Zhe-Lian-Yang-Ban”, which accounted for 39.64% of the total area. In the slightly to mildly vulnerable zone, the area with the highest ecological vulnerability grade was mainly found located in the region south of the line “Zhe-Lian-Yang-Ban”, which comprised 13.21% of the total area.

4.2. Sustainable Agricultural Development Models in Different Zones

4.2.1. Analysis of the Principles of Sustainable Agricultural Development Models

Ecological Vulnerability

The results of ecological vulnerability analyses show that the area of moderately to severely vulnerable areas in Guangnan County is relatively large. Furthermore, we contend that the regional ecological vulnerability would be further aggravated without timely restoration and optimization of traditional agricultural development models.

Resource and Environmental Carrying Capacity

Our present research reveals that resource and environmental carrying capacity had distinct spatial differences in Guangnan County [13,53]. Results indicate that northeastern and southeastern regions had a higher carrying capacity and were more suitable for production activities. In contrast, south, southwestern, and northwestern had a lower carrying capacity that needed focused ecological restoration and protection.

Agricultural Foundation

The hot and humid climate in Guangnan County is conducive to the growth of various crops, such as corn, rice, cereals, tubers, and soybeans, and economic crops such as oilseeds, sugarcane, vegetables, tobaccos, peppers, and gingers. By the end of 2020, the ratio of three industries to GDP in Guangnan County was 29.39:28.07:42.53, having domination of the primary industry. Among them, agriculture and animal husbandry were the leading industries, with the ratio of agriculture, forestry, animal husbandry, and fishery being 47.84%:6.32%:44.78%:1.07%.

Suitability of Agricultural Land

Our previous research showed that suitable agricultural regions are mainly distributed in the northeast and southeast of Guangnan County, accounting for 49.8% of the total area [13,53]. The northwest is a critical area for ecological protection, whereas the southwest is not suitable for agricultural development due to severe rocky desertification. Moreover, in recent years, Guangnan County has formed a woody oil industry with good ecological and economic benefits, such as Camellia oleifera, Malania oleifera, and walnuts, along with characteristic agricultural industries such as tea, babao rice, flue-cured tobaccos, and sugarcane. Our study indicates that it should become the main cultivation direction of agricultural development.

Farmers’ Willingness

(1) Willingness to plant. A majority (95.8%) of the farmers were willing to continue planting traditional food crops such as corn and rice. This is mainly because of the habit of planting in previous years, the inertia of earning income, and the inability to find suitable crops to change due to technical and financial constraints, according to our survey.Besides, mostly elderly people were left behind with an increasing number of migrant workers. They could only grow traditional crops such as corn to achieve basic subsistence living because of their limited energy and physical strength to change crops. Further, when we asked what else they were willing to plant, 53.1% of the farmers showed no willingness to plant others, whereas 31.3% preferred to grow other crops with higher economic benefits (Figure 4a). Results further indicate that approximately 8.8% of the farmers were willing to plant Chinese herbs (Rhizoma paridis, Bletilla striata, Polygonatum sibiricum, honeysuckle, lily, etc.), whereas 4.2% were willing to plant fruit trees (citrus, plum, pear, peach, etc.). In contrast, a small number (2.6%) of farmers expressed their willingness to carry out land transfer when they do not have enough resources to continue planting. Moreover, when we asked whether the choice of crops takes into account economic income or environmental protection, 65.5% of the farmers considered economic income, whereas 23.8% took into account both. In contrast, 1.0% of the farmers only considered environmental protection, and 9.8% said they did not think of either. Additionally, 86.0% of the farmers expressed a willingness to plant crops with economic and ecological benefits when conditions permit, while 14% said they would not consider it.
(2) Willingness to breed. Our survey indicates that 47.9% of the farmers were willing to breed humped cattle, followed by no longer breeding (41.7%). Only 10.4% tended to breed other livestock (pigs, goats, chickens, ducks) (Figure 4b).
(3) Willingness to develop rural tourism. In our survey, most farmers (71.7%) expressed their willingness to cooperate with the guidance and planning of rural tourism. In contrast, 28.3% of the farmers held the opposite view because they were worried that their interests in tourism development could not be effectively guaranteed (Figure 4c).

4.2.2. The Construction of Sustainable Agricultural Development Models in Different Zones

Models in Slightly to Mildly Vulnerable Zone

In this zone, vegetation coverage and biodiversity were relatively high. The resource and environmental carrying capacity was the highest, with high ecological stability. It was located in a suitable agricultural area, with a conducive hydrothermal condition, thicker soil layer, and good agricultural foundation. It was dominated by traditional crops, providing essential agricultural and ecological products for the whole region.
In a sample of 54 farmers, only 22.3% of farmers are satisfied with their current income. A total of 33.3% of farmers were willing to plant other crops. Among them, the proportion of medicinal materials, fruit trees, and other economic crops was 7.4%, 5.6%, and 20.4%, respectively. A total of 24.1% were willing to raise livestock products, and 13.0% were willing to breed humped cattle. Additionally, 72.2% of the farmers considered economic income when choosing crops, whereas 18.5% considered both economic income and environmental protection, and 9.3% did not think of either. A total of 88.9% also expressed willingness to plant crops with economic and ecological benefits. In addition, most farmers (77.8%) were willing to cooperate with rural tourism development. Therefore, the development models should be constructed with the economic and ecological type as the main direction.
In addition, only 48.2% of agricultural product distribution channels of farmers are through cooperatives or companies, followed by vendors (29.6%), and self-marketeers (20.4%). The specialization of marketing channels is low, so only 37.0% of farmers were satisfied. Consequently, the government should continuously introduce social capital and projects to promote product sales. In addition, introducing advanced technology is necessary to extend the industrial chain, enhance added value, and achieve brand effect.
(1) Woody oil development model. Farmers should rely on ecological projects such as “Grain for Green” and plant woody oil crops on slope cropland. The majority of the zone is suitable for planting woody oil species (e.g., Camellia oleifera and walnut) and developing the woody oil industry (Camellia oleifera + walnut). Planting woody oil trees occupy less arable land, and it is a high-quality species for vegetation restoration in karst areas. Furthermore, based on the actuality of the labor force and original planting, Chinese herbs such as Rhizoma polygonati, Rhizoma Curcumae, Curcuma zedoary, and Sarcandra glabra could be interplanted in the forest undergrowth.
(2) Plateau characteristic forests development model. Farmers should implement the “economic forests and economic crops” model in the slope cropland and dry land. This would build a win–win economic and ecological benefit by creating water-conserving and ecological forests. The characteristic economic forests could be based on species, such as Alnus nepalensis, Cunninghamia Lanceolata, Camellia oleifera, citrus, and chestnut. It should make Alnus nepalensis as the main afforestation species that are known to improve soil fertility. Cunninghamia Lanceolata has a characteristic of rapid growth, which is an essential species for karst greening. Moreover, the climate and soil conditions are also suitable for citrus cultivation Additionally, Guangnan County has a long chestnut cultivation history with high-quality commodities. Economic crops, such as sugarcanes, Panax pseudoginseng, tobaccos, and rapes should be planted to realize multi-industry synergistic development.
(3) Ecological tea plantations development model. The model underlines that local farmers should take Diwei County as the center and develop ecological tea plantations around Zhetai, Zhetu, Babei, and Liancheng. They should establish stereoscopic models of “tea and anise” and “tea and rice” around the tea plantations to promote Guangnan’s “ecological tea” strategy. Guangnan County has a long history of tea cultivation with a wide variety of tea. In addition to wage income, tea sales can become tea farmers’ primary income. Nevertheless, there are still severe constraints on the tea industry, such as a shortage of labor, discarded tea plantations, backdated processing technology, and the lower sale price of raw tea. Therefore, ecological tea plantations should strictly be controlled from raw material to the quality of tea products. It should achieve a “unified management and unified acquisition”.
(4) Suburban agriculture development model. This model suggests that with the county as the center, local farmers should integrate the suburban agricultural development model of “vegetable bases and poultry breeding and agricultural leisure experience”, which benefited from a better agricultural foundation and a relatively broad market. It aims to carry out the functions of product supply, ecology, and leisure while forming a green barrier. Local farmers could rent out their land-by-land transfer to build vegetable bases and integrate modern sprinkler irrigation technologies to grow vegetables on a large scale. Local farmers could also develop poultry breeding to provide urban residents with meat, eggs, and milk products (Figure 5). In addition, traditional agricultural practices, such as picking, fishing, feeding, catering, accommodation, and planting could be built to provide urban residents with places for leisure and entertainment.
(5) Cultural–ecological tourism. Guangnan County has various ethnic minorities and cultural resources with an outstanding ecological environment. Therefore, local farmers could construct a cultural–ecological tourism model of “landscape and idyllic scenery, and minority culture” (Figure 6). It is possible to build a museum showing the folk customs of ethnic minorities as well as a destination tourism, integrating sightseeing, leisure, experience, well-being, and vacation functions. Moreover, farmers could broaden their income channels while transforming traditional agricultural production into ecologically, economically, and culturally diversified services.

Models in Moderately to Severely Vulnerable Zone

The zone had a moderate resource and environmental carrying capacity having relatively intensive human production activities. It was the main area for socio-economic activities with a better agricultural base, but with a small arable land.
In a sample of 54 farmers, only 23.8% of farmers are satisfied with their current income. A total of 53.4% of farmers refused to grow other crops, followed by other economic crops (29.0%), medicinal materials (10.4%), and fruit trees (4.1%). Only 3.1% of farmers showed their wiliness to land transfer. Additionally, 61.7% of the farmers only considered economic income, whereas 25.9% considered economic income and environmental protection, and 11.4% did not think of either. A total of 84.5% also expressed willingness to plant crops with economic and ecological benefits. In addition, most farmers (52.8%) tended to breed humped cattle, and only 29.5% of the farmers were not willing to develop rural tourism. Therefore, the development models should take ecological and economic type as the main direction. The coordinated development of ecological protection and social development should be achieved based on ecological restoration and securing natural resources needed.
(1) Stereoscopic agriculture model combining the planting and breeding. Traditional crops, such as corn, are more prone to soil erosion and, produce low economic benefits. It should be combined with locational characteristics such as topography to build a stereoscopic agriculture model by combining planting and breeding. Natural restoration could be implemented in steep lands because of less human interference. The areas of gentle slopes should be planted with a combination of trees and grasses. The model of “fruit forests and economic crops”, “fruit forests and Chinese herbs”, and “fruit forests and pasture” should be implemented to solve the problem of single undergrowth species of fruit forests. Low-lying land is the central area for paddy and dry farming, which is vulnerable to flooding and other disasters. It could be integrated with the construction of water conservation projects to implement the “rice and fish” development model. Further, dry farming should be transformed into pluralistic cash crops, fruits, and Chinese herbs from single food crops. The farmers could also implement the interplanting of “corn and sweet potatoes” and “corn and beans”. Moreover, the intercropping of “corn and rape” and “peanut and rape” should be carried out to achieve the transformation of “one season into two seasons”. The farmers could also plant cash crops such as tobacco, Panax pseudoginseng, ginger, and pepper by cultivating suitable varieties to develop efficient food and cash crops. In addition, the farmers could develop breeding industries to achieve comprehensive development based on food crop cultivation and the pasture grasses industry.
(2) Vegetation restoration model. It should construct a vegetation restoration model of “forests and Chinese herbs” and “forests and pasture grasses”. The main forestry crops are Malania oleifera, Camellia oleifera, peppers, and zenia insignis. Meanwhile, the leading Chinese herbs are Rhizoma paridis, Bletilla striata, and Polygonatum sibiricum. Pennisetum purpereum is the main pasture grass. Moreover, Malania oleiferas, Camellia oleifera, peppers, and zenia insignis have a strong adaptability to drought tolerance in the exposed limestone mountains. These are also suitable species for karst mountain restoration. In addition, the woody oil industry should be developed with Camellia oleifera and walnut crops to appropriately extend the industrial chain, developing it as a characteristic and advantageous industry.
(3) Herbivorous animal husbandry model. Guangnan County has a long history of animal husbandry. Farmers mostly raised local yellow cattle, humped cattle, and black goats. The humped cattle have a large population in Yunnan, having delicious meat, and adaptive features, such as heat and cold resistance, low disease, and a low death rate. Guangnan County has abundant grasses to be planted to meet the demand for livestock development. The cultivation of pasture grasses have benefits for soil and water conservation, and for ecological restoration. Currently, humped cattle breeding in Guangnan County is mainly captive breeding (Figure 7), which has less impact on surface vegetation with low labor costs. We found that annual net profit from cattle could be 2000~3000 CNY and even 4000 to 5000 CNY, when managed properly.

Models in Extremely Vulnerable Zone

The zone had a high rock exposure and rocky desertification, which made ecological management and restoration extremely difficult. The regional resource and environmental carrying capacity was found to be the lowest, and the land was mainly not suitable for agriculture, with fewer agricultural activities.
In a sample of 54 farmers, only 23.4% of farmers are satisfied with their current income. Most (66.7%) farmers refused to grow other crops. However, they had a stronger willingness to raise humped cattle (63.3%). Additionally, about 70% of the farmers were willing to cooperate with rural tourism development. Therefore, it should take ecological type as the main direction. The primary task here is to implement vegetation restoration and relieve ecological pressure. Appropriate socio-economic activities should also be limited to areas with good conditions.
(1) Ecologically restoration model. Grasses are the first choice for karst vegetation restoration as they have a faster growth rate [22,36]. The farmers should choose plants that are cold-resistant, calciphilous, and have a wide range of applications to promote the positive vegetation succession of a “grass–shrub–tree”. It should also be supplemented by artificial intervention measures to maintain ecological stability by integrating water infrastructures, the inefficient transformation of Camellia oleifera forests, and ecological projects.
(2) Agricultural eco-tourism model. The zone is rich in caves, peak clusters, and low-lying lands with high aesthetic, educational, and ornamental cultural values (Figure 8). The agricultural eco-tourism model of “rice culture and karst landscape” should be built. With a long history of rice culture, Guangnan County has developed mature rice technologies and precious wild rice seeds (such as Babao rice). In addition, water infrastructures should be integrated with the depression catchment area to vigorously develop the Babao rice industry and form a karst idyll landscape. The farmers should also take advantage of traditional rice cultivation technologies and rely on Zhuang culture, which would integrate rice cultivation with leisure, parent–child entertainment, and characteristic catering.

5. Discussion

5.1. The Evaluation and Division of Ecological Vulnerability

The karst ecosystem is a multi-level, multi-factor complex system. Our developed index construction is key to ecological vulnerability evaluation from the perspective of the natural environment and social and human environment. Compared to similar studies [7,44,50]. We highlighted the characteristics and importance of lithology and geological disasters in the karst areas. Different lithologies often lead to varying incidences of rocky desertification, which could effectively reflect geological conditions. The occurrence of geological disasters could further exacerbate their ecological vulnerability. In addition, based on the mechanism of rocky desertification in karst areas and combined with the land use data, we selected landscape fragmentation indicators that could better reflect the characteristics of the human environment.
In the classification of karst ecological vulnerability and ecologically vulnerable zones, workers have classified the vulnerability classes by equating the difference of indicators, histogram and standard deviation [54], triangle methodology [7], and natural breaks method [44,50,52]. The natural breaks method is typical for classifying ecological vulnerability classes, which can make the similarity of each class the biggest, but the difference between classes the biggest. Accordingly, the natural breaks method was used in our classification.

5.2. The Constructional Ideas of Sustainable Agricultural Development Models

The coordination of ecological and socio-economic development is crucial in the karst mountainous areas. The effective control of rocky desertification is the core goal of constructing a sustainable agricultural development model as an important ecological problem in restricting karst areas’ development. According to the rocky desertification problems and farmers’ livelihoods, researchers have forwarded comprehensive models for rocky desertification in response to the ecological carrying capacity of different areas. It followed the principles of local conditions, market demand, ecological and economic benefits, zoning management, operability, and gradual progress: for instance, the Huajiang model of controlling severe rocky desertification in Guizhou province for restoration and maintenance of the ecosystem [27]; the Guohua model of governing moderate rocky desertification in Guangxi by considering three-dimensional characteristics of mountainous areas and hydrothermal conditions [55]; the Bijie model of governing mild rocky desertification in Guizhou considers soil erosion and restoration of vegetation productivity [56]. These models of ecological, animal husbandry, vegetation restoration, soil and water conservation, stereoscopic agriculture, ecological economy, ecological tourism, and ecological migration have gradually formed with the continuous improvement of rocky desertification management models. These models are significant for restoration and coordinate ecological and economic benefits in karst areas to a certain extent. Even so, they did not fully consider ecological vulnerability, ecosystem carrying capacity, resource utilization, industrial development, or, particularly, farmers’ willingness.
As the main implementer of the model, farmers’ willingness should be fully considered to mobilize their enthusiasm for ecological governance and agricultural production activities [46,47,48,57]. This study shows that farmers tend to increase their income and focus on economic benefits without ecological protection, which is not conducive to the sustainable development of karst ecosystems. In addition, farmers’ willingness varies depending on their education level, marketing channels for agricultural products, transportation conditions, production facilities, and household income. Taking the willingness to grow medicinal materials as an example, we conducted a multinomial logistic regression model on potential influencing factors by setting the reference category to none. It was found that transportation conditions and the number of laborers affected farmers’ willingness. The improvement in transportation conditions makes farmers more willing to plant medicinal materials. However, 38.5% of the farmers are still not satisfied with it at present. Therefore, farmers’ satisfaction with infrastructure such as transportation should be concerned. The mechanism of these factors’ impact on the industry’s industrial development willingness should be deeply explored, providing references for local governments.
Regional human–earth areal system coordination can start from such elements as resource, environment, human, economy [58]. Among them, the latter two are the most active and changing, and are considered the main force to promote the evolution [59]. Meanwhile, internal elements and their interaction with the external environment continue to strengthen the dissipative structure of the whole system and provide a driving force for regional development, providing an impetus for regional development [10,58]. Therefore, the ultimate goal of regional development is to build a system structure and function suitable for productivity development [5,8,60]. In the karst areas, the harsh and closed geographical conditions contribute to the “vicious circle” of ecological degradation and poverty in the karst areas [13,29]. To break this cycle, the locals should not start from the natural environment system or human social system alone. It could not promote the endogenous force of the system and even aggravate the internal imbalance in the long run. Optimization of the subsystems should not be implemented independently and mechanically. It should focus on the synergy and dynamic development of both concerning different elements, characteristics, stages, and trends of the system. In addition, the construction of a sustainable human–earth areal system should notice the spatial differences within the region that carry out refined and differentiated regulation.
This study proposed agricultural development models for three types of ecologically vulnerable zones so that human activities and geographical environments could be spatially matched and coordinated in the subdomain, realizing a win–win for ecological and economic benefits. In the slightly to mildly vulnerable zone, economic and ecological type-oriented development models prevents ecological degradation while maximizing the potential for economic growth. For example, compound management in the woody oil forest could effectively improve soil organic matter, nitrogen, phosphorus, and potassium content. In the moderately to severely vulnerable zone, ecological and economic type-oriented development models prioritize ecological benefits while diversifying the mode of production sources of income by combining with the particular geographical environment. For example, forest and grass vegetation restoration is the primary project in the mountainous karst areas [12,34,61], which could be integrated with traditional Chinese medicine planting to generate multiple incomes. In the extremely vulnerable zone, ecological type-oriented development models restrict the natural environment from large-scale human disturbance and firmly safeguard the ecological benefits. For example, tourism could drive local employment and bring more income than agriculture and animal husbandry [38,40]. Under the conditions of proper strategy formulation, the tourism resources planted by Babao rice can be fully exploited.
However, the proposed models are, to some extent, more theoretical. In the future, they should be put into practice to promote the sustainable development of the human–earth areal system in ecologically vulnerable karst areas.

6. Conclusions

With an emphasis on ecological and rural development issues from the perspective of the human–earth areal system, this study proposed the framework of sustainable agricultural development, and integrated principles of ecological vulnerability, resource and environmental carrying capacity, agricultural foundation, suitability of agricultural land, and the farmers’ willingness. The ecological vulnerability of Guangnan County was slight, but the proportion of moderate and severe vulnerability areas was high, with significant differences between the two sides of the line “Zhe (Zhetu)-Lian (Liancheng)-Yang (Yang Liu-jing)-Ban (Banbang)”. Then, we divided Guangnan County into three ecologically vulnerable zones. Following that, we proposed sustainable agricultural development models appropriate for various zones. In the slightly to mildly vulnerable zone, we recommend constructing economic–ecological agricultural models, including woody oil, plateau characteristic forests, ecological tea plantations, suburban agriculture, and cultural–ecological tourism. In the moderately to severely vulnerable zone, we underline the construction of ecological–economic agricultural models that combine stereoscopic agriculture with planting and breeding, vegetation restoration, and herbivorous animal husbandry. In the extremely vulnerable zone, we highlight the construction of ecologically agricultural models, including natural restoration and agricultural eco-tourism.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/land11071075/s1, Table S1: Questionnaire for village cadres; Table S2: Questionnaire for farmers.

Author Contributions

Conceptualization, X.Z. and Y.X.; Data curation, X.Z. and J.P.; Formal analysis, Y.X. and Q.W.; Funding acquisition, X.Z.; Investigation, X.Z., Q.W., J.P., X.S. and Z.G.; Methodology, X.Z.; Validation, X.S., P.H. and Z.G.; Visualization, Y.X. and P.H.; Writing—original draft, X.Z., Y.X., Q.W. and J.P.; Writing—review & editing, X.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China [42061052]; Construction Project of Graduate Tutor Team in Yunnan Province (C176230200); Joint Fund of Yunnan Provincial Science and Technology Department and Yunnan University [2018FY001-017]; Postgraduate Innovative Research Project of Yunnan University [2021T008].

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Framework for sustainable development of the karst human–earth areal system.
Figure 1. Framework for sustainable development of the karst human–earth areal system.
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Figure 2. Location of the study area.
Figure 2. Location of the study area.
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Figure 3. Spatial distribution of ecological vulnerability areas and ecologically vulnerable zones in Guangnan County. (a) Spatial distribution of ecological vulnerability areas; (b) Spatial distribution of ecologically vulnerable zones.
Figure 3. Spatial distribution of ecological vulnerability areas and ecologically vulnerable zones in Guangnan County. (a) Spatial distribution of ecological vulnerability areas; (b) Spatial distribution of ecologically vulnerable zones.
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Figure 4. Farmers’ willingness structure. (a) Willingness to plant; (b) Willingness to breed; (c) Willingness to rural tourism development.
Figure 4. Farmers’ willingness structure. (a) Willingness to plant; (b) Willingness to breed; (c) Willingness to rural tourism development.
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Figure 5. Examples of suburban agricultural development model. (a) Leek industry; (b) Poultry breeding).
Figure 5. Examples of suburban agricultural development model. (a) Leek industry; (b) Poultry breeding).
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Figure 6. Examples of cultural–ecological tourism. (a) Cultural landscape; (b) Landscape scenery).
Figure 6. Examples of cultural–ecological tourism. (a) Cultural landscape; (b) Landscape scenery).
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Figure 7. Example of herbivorous animal husbandry model (humped cattle basement).
Figure 7. Example of herbivorous animal husbandry model (humped cattle basement).
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Figure 8. Example of agricultural eco-tourism model (karst landscape).
Figure 8. Example of agricultural eco-tourism model (karst landscape).
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Table
Table 1. Main data and sources.
Table 1. Main data and sources.
DataSource
Water bodiesGuangnan Water Bureau
MeteorologyGuangnan Meteorology Bureau
GeologyGuangnan Natural Resources Bureau, Guangnan Ecological Environment Bureau
Socio-economic statusGuangnan Statistics Bureau
SoilGuangnan Agriculture and Technology Bureau
Tourist attractionsGuangnan Tourism Bureau
Rocky desertification governs statisticsGuangnan Forestry Bureau
Farmers’ willingnessA questionnaire survey investigated by the research group
Table
Table 2. Index system of ecological vulnerability.
Table 2. Index system of ecological vulnerability.
ObjectiveCategoryIndexDescription
Natural impactWater bodiesWater network density indexReflect the abundance of water resources
ClimateAnnual average temperatureThe better the combination of water and heat, the more favorable the regional vegetation growth and soil and water conservation
Annual rainfall
TopographySlopeTopography and geology are the substrate conditions that cause ecological vulnerability, of which lithology is the basis for the problem of rocky desertification
Surface cutting degree
GeologyGeological disaster-prone area
Lithology
VegetationVegetation coverageReflect the vegetation cover conditions within the karst areas
Habitat Quality IndexHabitat support is the basis for the proper functioning of the ecological environment in karst areas
SoilsSoil erosion amountSoil degradation and rock exposure reduce productivity and ecological problems, such as soil erosion and rocky desertification.
The proportion of Rocky Desertification
Anthropogenic impactSocial economyGDP densityIncreased population aggravates the carrying pressure on ecosystems; increased development intensifies ecological vulnerability
Agricultural population density
Road level
LandscapeLandscape fragmentationHuman activities create different types of land use in the surface system. The higher the surface fragmentation, the higher the intensity of disturbance to the surface
Table
Table 3. The result of Spatial Principal Component Analysis.
Table 3. The result of Spatial Principal Component Analysis.
Principal Component FactorPC1PC2PC3PC4PC5PC6
Eigenvalue0.150.070.040.020.020.02
Contribution (%)39.8819.609.176.405.624.46
Cumulative contribution (%)39.8859.4868.6575.0580.6685.12
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Zhao, X.; Xu, Y.; Wang, Q.; Pu, J.; Shi, X.; Huang, P.; Gu, Z. Sustainable Agricultural Development Models of the Ecologically Vulnerable Karst Areas in Southeast Yunnan from the Perspective of Human–Earth Areal System. Land 2022, 11, 1075. https://doi.org/10.3390/land11071075

AMA Style

Zhao X, Xu Y, Wang Q, Pu J, Shi X, Huang P, Gu Z. Sustainable Agricultural Development Models of the Ecologically Vulnerable Karst Areas in Southeast Yunnan from the Perspective of Human–Earth Areal System. Land. 2022; 11(7):1075. https://doi.org/10.3390/land11071075

Chicago/Turabian Style

Zhao, Xiaoqing, Yifei Xu, Qian Wang, Junwei Pu, Xiaoqian Shi, Pei Huang, and Zexian Gu. 2022. "Sustainable Agricultural Development Models of the Ecologically Vulnerable Karst Areas in Southeast Yunnan from the Perspective of Human–Earth Areal System" Land 11, no. 7: 1075. https://doi.org/10.3390/land11071075

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