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Article

Habitat Suitability Evaluation and Ecological Corridor Construction for Asian Elephants: The Case of Jiangcheng, a New Range for Elephants in Southwestern China

by
Lanzhong Zhang
1,†,
Churui Li
1,†,
Cairong Yue
1,*,
Hongbin Luo
1,
Xin Li
1,
Qiongfen Yu
1,
Jia Li
1,
Jian Shen
1,
Song Yang
2 and
Fei Chen
3
1
College of Forestry, Southwest Forestry University, Kunming 650224, China
2
Jiangcheng County Forestry and Grassland Bureau, Pu’er 665900, China
3
Asian Elephants Research Center, State Forestry and Grassland Administration, Kunming 650224, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Forests 2024, 15(7), 1195; https://doi.org/10.3390/f15071195
Submission received: 13 June 2024 / Revised: 1 July 2024 / Accepted: 4 July 2024 / Published: 10 July 2024
(This article belongs to the Special Issue Forest Wildlife Biology and Habitat Conservation)
Browse Figures
Review Reports Versions Notes

Abstract

:
In recent years, the northward migration of elephant herds in China’s Yunnan Province has attracted unprecedented public attention to the conservation of Asian elephants, with habitat fragmentation and human disturbance thought to be key factors. In this study, we used Jiangcheng, a new distribution site for Asian elephants in southwest China, as an example, combined the available remote sensing and monitoring data with the MaxEnt3.4.1 model, to analyze the factors affecting the activities of Asian elephants under the conditions of human disturbance and habitat degradation. The Least Cumulative Resistance model was utilized to construct the potential ecological dispersal corridors, and the key corridors were identified through the gravity model to explore the ecological security pattern of the habitat of Asian elephants in Jiangcheng County. The results show that the habitat of Asian elephants in Jiangcheng County is fragmented, showing a north–south strip distribution, never moving to the northeast. The existing suitable habitat is located in the low-elevation area (<1500 m), which is close to water sources and roads, and there is no nature reserve in this area. The land is mainly occupied by scrub or grassland near mountainous forests, but part of it is also under cultivation, which leads to conflicts between humans and elephants occur frequently. There are 14 ecological source areas, which are mainly distributed in the two regions of Zhengdong and Kangping, and there are 92 ecological corridors, of which 3 are important corridors and 89 are general corridors. This study comprehensively analyzes the current status and connectivity of Asian elephant habitat in Jiangcheng County at the regional scale, which helps to optimize the pattern of suitable habitat, promotes the dispersal of Asian elephants and habitat connectivity, and provides realistic guidance and basic information for the conservation planning of isolated populations of this species and their habitats.

1. Introduction

The Asian elephant, Elephas maximus, is the most representative umbrella species in tropical forest ecosystems and is listed as an endangered (EN) species by the International Union for Conservation of Nature (IUCN) and protected by the law [1]. At the same time, elephant conservation, management, and research are being conducted in response to the 15th United Nations Convention on Biological Diversity, known as the Kunming Declaration. Its habitat range is substantially influenced by topography and vegetation type [2,3]. The most suitable habitat for Asian elephants is low-altitude river valleys, and areas rich in tropical plants are their preferred habitat [4]. Currently, the main threats to the survival of wild Asian elephants are habitat fragmentation and a reduction in suitable habitat, which are all caused by human activities [5,6]. Therefore, in order to better protect elephants, state workers have taken measures such as establishing nature reserves, building wildlife corridors, setting up breeding bases, building food source bases, and so on, with some promising results [7].

Elephants in Yunnan Province

According to the census data, the population of wild elephants in China has increased from just over 100 in the 1980s to over 300 today; that is, their population size more than doubled. They are mainly distributed in areas around Xishuangbanna Dai Autonomous Prefecture, Pu’er City, and Lincang City [8,9]. In recent years, the habitat of these elephants has been somewhat restricted due to urbanization, population growth, and infrastructure development. Simultaneously, with the strengthening of elephant protection measures, the number of wild populations has increased annually, reaching a relatively saturated state. Coupled with food shortages, this has prompted herds to migrate and establish new habitats [10]. In May 2021, a group of elephants migrated northward from their original habitat to areas that had not observed elephants for centuries, finally reaching the Jinning District of Kunming City, Yunnan Province and eventually returning to Pu’er City more than half a year since the beginning of Northward migration of the Asian elephant group. This event attracted the attention of experts and scholars at home and abroad [11]. It is no coincidence that elephant herds have left their original habitats [11]; the “Yunnan north-migrating elephant herd” is a representative event of elephant herds leaving their original habitats, and their increasing number of migrations as well as anthropogenic disturbance and habitat degradation are considered to be important factors. It is essential to study elephant herds that leave their original habitats in order to protect and manage the elephants and their habitats [10]. According to historical documents and investigations, this example of elephant herds leaving their original habitats is not unique or likely to be a random occurrence; since the 1990s, when it was observed that the elephants started to return to Pu’er, the migration of the elephants has shown a long-term continuous trend of moving northward (Figure 1) [11].
As elephant populations continue to grow and the environmental space they require expands, effective protection of elephants and their habitats becomes essential. When existing habitats cannot ensure the survival of wildlife, conflicts between humans and wildlife will intensify, causing substantial economic losses to residents and severe impacts on their lives, production, and personal safety [12]. Therefore, protecting wild elephant resources, preventing human–elephant conflicts, and promoting harmonious coexistence between humans and elephants are major challenges for elephant conservation.
Jiangcheng County, a new distribution area for Asian elephants in southwestern China, is a typical example of a new habitat where elephants and humans coexist near farmland and villages. Using Jiangcheng County as an example, this study combined remote sensing and monitoring data to analyze the factors affecting the activities of Asian elephants under the conditions of human disturbance and habitat degradation by using the MaxEnt model to analyze their habitat suitability. The ecological security pattern of the Asian elephant habitat in Jiangcheng County was explored by using the results of the MaxEnt model simulation as the ecological source, identifying the ecological source loci, constructing potential ecological diffusion corridors by using the Least Cumulative Resistance model, and identifying the critical corridors through the gravity model. This article aims to construct and optimize the understanding of the elephants’ habitat use in Jiangcheng County from the perspective of landscape ecology. The ultimate goal is to improve the habitat suitability for the elephants in Jiangcheng County, maintain ecosystem stability in the study area, and effectively protect elephants and their habitats. Additionally, this study seeks to make full use of wild elephant resources, promote harmonious coexistence between humans and elephants, provide guidance for the sustainable development and planning of the habitat in Jiangcheng County, and propose optimization strategies and suggestions for elephant conservation.

2. Study Area

Jiangcheng Hani and Yi Autonomous County (hereafter referred to as Jiangcheng County) is situated in the southern part of Yunnan Province, between 101°14′ E and 102°19′ E in longitude and between 22°20′ N and 22°56′ N in latitude. Jiangcheng County shares borders with Laos and Vietnam and thus lies at a convergence point of three countries. The county has a total land area of 3544.38 square kilometers, with a forest coverage rate of 76.86%. Since October 2011, 18 wild elephants that previously resided in Jinghong City, Xishuangbanna Prefecture, have migrated to Jiangcheng County, making it a permanent habitat for elephants. As of 2022, the population of elephants in Jiangcheng County has increased to 53, with monitoring data indicating the annual birth of new elephants and continuous growth in their population (Table 1). According to statistics from relevant departments, elephants in Jiangcheng County are primarily distributed across 12 village committees and one community in Zhengdong Town and Kangping Town, encompassing 179 village groups and 13 teams in Zhengdong Farm. The active area covers 1027.77 square kilometers, mainly within the production and residential areas of the local residents [13].
Based on data provided by the Forestry and Grassland Bureau of Jiangcheng County, the habitat of elephants in the region has gradually expanded northwestward from its initial location in Zhengdong Town (specifically, Huashiban Village) to include the jurisdiction of Kangping Town. As shown in Appendix A, the elephants are frequently observed moving between Zhengdong Town, Kangping Town, Yixiang Town in Simao District, and Mengwang Township in Xishuangbanna. Most of the 53 wild elephants in Jiangcheng County are active within the ranges of Kangping Town and Zhengdong Town (Figure 2), moving toward the north and outward, between Mengwang and Simao. However, no natural reserves have been established in the elephants’ active areas in Jiangcheng County; this region has no sizeable contiguous tropical forest area. The elephants often roam at the edge of forests and farmland, primarily relying on crops as their food source. This results in frequent conflicts between humans and elephants and makes farming difficult [14]. Elephants even venture into farmers’ homes at night, causing significant inconvenience, intense psychological distress, and physical danger. Threatened villagers must often shelter at relatives’ or friends’ homes. Nightly visits by elephant herds pose considerable challenges for the protection of wild elephants.

3. Methods

3.1. Data Collection and Acquisition of Environmental Variables

The Land Use and Land Cover (LULC) data represent the spatial distribution of land use types obtained from national remote sensing monitoring (http://www.globallandcover.com, accessed on 19 April 2022). The digital elevation model (DEM) data were derived from elevation data collected by the phased array type L-band synthetic aperture radar (PALSAR) of the Advanced Land Observing Satellite (ALOS) available at https://search.asf.alaska.edu/# (accessed on 24 April 2022). The Normalized Difference Vegetation Index (NDVI) data were obtained from the Resource and Environmental Science Data Publishing System (https://developers.google.com/earth-engine/datasets/catalog/, accessed on 15 May 2022). The hydrology and road data were obtained from OpenStreetMap (OSM) data (https://www.openstreetmap.org/, accessed on 22 June 2022). The vegetation type data were obtained from the Geographic Remote Sensing Ecology Network Scientific Data Publishing System (www.gisrs.cn, accessed on 9 August 2022). The population data were obtained from the National Bureau of Statistics (www.gisrs.cn, accessed on 9 August 2022), and the precipitation and temperature data were provided by the Chengdu Institute of Mountain Hazards and Environment, Chinese Academy of Sciences (https://www.worldclim.org/, accessed on 24 August 2022).
Asian elephant distribution data were obtained from the Jiangcheng County Forestry and Grassland Bureau to monitor the 2021 Asian elephant activity data loci. In order to prevent the model overfitting, 4589 Asian elephant activity sample points were acquired using the buffer zone method of screening and proofreading Asian elephant activity sample point data from Jiangcheng County. As the distribution of Asian elephants in the study area of this paper is mainly concentrated in the two townships of Zhengdong and Kangping, i.e., at a small scale, a buffer zone radius of 500 m was set to retain a distribution point within a range of 1 km, and 386 activity sample points were finally obtained by collation.
To search the literature related to habitat studies on Asian elephants, after selecting the habitat evaluation factors with a high frequency of occurrence, the data of the above 14 environmental variables (Table 2) were subjected to Spearman’s correlation analysis using SPSS.27 software due to the strong correlation between the environmental factors [15]. This was performed to avoid overfitting the model due to multicollinearity among the environmental variables. After removing the vegetation cover factor, the remaining 13 environmental variables were simulated for subsequent optimization (Figure 3) [16]. The data of the 13 environmental factors were transformed into a raster dataset with a resolution of 30 × 30 m using ArcGIS 10.8.1 and converted into the ASCII format for MaxENT modeling operations.

3.2. Habitat Suitability Model

The MaxEnt model is a major research method that can accurately and reliably simulate species distributions by relying only on species’ active sites and environmental data. It has been widely used because it has demonstrated an excellent predictive ability over other models in species distribution studies [20]. The two most critical parameters of MaxEnt are feature combinations and regularization multipliers. Optimizing these parameters can significantly improve the model’s prediction accuracy [21,22,23,24]. In this study, the author utilized the ENMeval package in R to optimize environmental factors. The multiplier level parameter in the model was set to a range of 0.1 to 4, totaling 40 [23,25,26]. There were five feature combination parameters: L for Linear, Q for Quadratic, H for Hinge, P for Product, and T for Threshold, which could produce 29 different combinations [25,26]. In this study, the data package was set from 0.5 to 4, with an increase of 0.5 each time, totaling 12 tuning frequencies and 10 feature combinations, namely, L, QT, H, HP, PT, QH, LQH, LPT, QHP, and LQHPT. The ENMeval package validated these 120 parameter combinations [23,27].
Referring to the optimal feature combination and regularization multiplier configuration determined by the optimal model, the elephant occurrence point data and the selected environmental variable data were imported into the MaxEnt model. The specific model operation parameters were as follows: the model was run 10 times with a maximum of 386 background points. Among them, 75% of the occurrence point data were randomly selected as the training set to establish the model, and the remaining 25% were used for testing. The jackknife test method was used to assess the importance and contribution of each environmental factor to the distribution of elephants. The relationship between the environmental factors and the probability of elephants’ appearance was verified through the response curves of the environmental factors; the results were outputted in the Logistic format [19]. The area under the ROC curve (AUC) was used to evaluate the correlation between the environmental variables and the elephants’ geographical distribution model (the larger the AUC value, the better the correlation and the easier to distinguish habitat suitability). The AUC value evaluation standards were as follows: 0.5–0.6 is unqualified, 0.6–0.7 is poor, 0.7–0.8 is average, 0.8–0.9 is good, and 0.9–1.0 is excellent [28].
The model’s prediction results were converted into the raster format [15]. Based on expert experience and manual grading methods, the habitat suitability for elephants was divided into five levels [29]: unsuitable habitat (0–0.11), marginal habitat (0.11–0.21), low-suitability habitat (0.21–0.34), medium-suitability habitat (0.34–0.50), and high-suitability habitat (0.50–0.93). The resulting map shows the suitable distribution of elephants throughout the entire research area. The ArcGIS10.8.1 software’s spatial statistical function was also used to calculate the area and corresponding proportions of different suitable distribution areas.

3.3. Construction of Ecological Corridors

The construction of wildlife ecological corridors helps to eliminate the impact of habitat fragmentation on biodiversity, which is of great significance in maintaining the structural integrity and functional stability of ecosystems. In this study, the minimum cumulative resistance (MCR) model was used to construct a suitable ecological corridor for Asian elephant dispersal. First, the ecological source, which is the fragmented habitat patches, was determined according to the simulation results based on the MaxEnt model. Second, the minimum resistance (least-cost pathway) was identified between the habitat patches. Finally, the gravity model was used for a comprehensive analysis to screen out the most suitable route as the ecological corridor’s final alternative [28].

3.4. Determination of Ecological Source Areas

Based on the distribution state of Asian elephants generated by the MaxEnt model, the habitat distribution data were screened using the screening tool in ArcGIS. Using the township as a unit, marginal habitats and low-suitability habitats were classified as Level 3 ecological source areas, medium-suitability habitats were classified as Level 2 ecological source areas, and high-suitability habitats were classified as Level 1 ecological source areas. Meanwhile, habitat patches with habitat area <0.5 km2 were excluded, which were used as the basic data for the operation of the minimum cumulative resistance model [30].

3.5. Minimum Cumulative Resistance Surface (MCR Model)

According to the current situation of Asian elephants in Jiangcheng County [5], existing research methods and the importance of each environmental factor simulated by the MaxEnt model and the MCR model were selected to analyze the ecological corridor arrangement in the study area, which was expressed as the number of animals crossing the ecological resistance surface (the resistance faced by different ground cover types). Based on the animal’s instinct to avoid hazards and receive the available benefits, they would naturally choose the path of less resistance [30]. Using this idea, nine environmental factors, namely, elevation, slope, NDVI, land use, distance from the road, distance from the river, distance from the cultivated land, distance from the settlement, and habitat quality, were identified as factors influencing ecological resistance, and the weights and resistance values of the factors were determined (Table 3). ArcGIS software was utilized for the establishment of ecological corridors; the MCR calculation formula is shown in equation [28]:
M C R = f min ⁡ ∑ i = n i = m D i j R i
where Dij is the spatial distance of ecological land from source i to j, Ri is the resistance coefficient of grid i to the spatial expansion of ecological land, ∑ is the cumulative distance and resistance across all cells between grid i and source j, and f is the positive correlation between the minimum cumulative resistance and ecological processes [28].

3.6. Construction of Potential Ecological Corridors

The input element is the center of gravity of each ecological source, i.e., the ecological source point; the sum of the source elements other than this element layer is the target element. The total cumulative resistance baseline was used as the consumption value to generate the ecological cost resistance value that needs to be consumed for the dispersal of Asian elephant populations in this ecological source. Finally, the gravity model was utilized to extract the potential ecological corridors within the scope of the region [30].

4. Results and Analysis

MaxEnt Model

Optimal Feature Combination and Regularization Parameters. According to the analysis of the ENMeval package in R4.4.1, all 120 candidate models were statistically significant, and one recommended model was selected from them (Figure 4). Its deltaAICc value was the smallest (0), indicating that the model had the best mobility from the known distribution area to the prediction area and effectively avoided model overfitting. It represents the optimal model; the corresponding feature combination is P + T, and the regularization multiplier value is 1.5.
Model Prediction Accuracy. Based on the ROC curve evaluation results of the MaxEnt model, the AUC values for the training and validation sets were 0.941 and 0.947, respectively. These results demonstrate that the model’s prediction accuracy is excellent and that the predictions are reliable. Therefore, this model can be used to evaluate the habitat suitability for elephants (Refer to Figure 5).
Environmental factor contribution. The jackknife test model was utilized to analyze the significance of each environmental variable on the distribution of elephants. The results indicated that annual average rainfall, distance to the river, distance to the road, and land use were the primary environmental variables that affected the distribution of elephants, contributing to 50.1%, 17.1%, 12.7%, and 5.9% of the variance, respectively. Together, these variables contributed to 79.9% of the variance in the MaxEnt model. Land use type, altitude, distance to residential points, annual average temperature, and habitat quality were considered secondary factors, contributing to 19.4% of the variance in the model. Vegetation type, distance to farmland, slope, distance to the forest, and normalized vegetation index had the least impact on the MaxEnt model, with a contribution rate of only 0.6%.
Factor analysis of primary and secondary environmental variables. Based on the response curve of the main environmental variables affecting the suitability of the elephants’ habitat (Figure 6), it is evident that the elephants preferred areas with abundant annual rainfall. The most suitable annual precipitation range is between 980 and 1020 mm. They tended to be active in areas closer to water sources, with a probability of appearance of over 50% when the distance to the river (b) was less than 2.5 km. This probability was negatively correlated with the distance to the river, meaning that the farther the location from the river, the lower the probability of the appearance of elephants. Furthermore, when the distance to the road (c) exceeded 1.5 km, the probability of elephants’ appearance gradually decreased. The response curve of the habitat quality factor fluctuated greatly. In the response factor curve (d) of land use, it can be observed that elephants often appeared in other forest lands, paddy fields, and sparse forest lands. The probability of elephants’ appearance in high-coverage grasslands was above 0.5, followed by rivers, reservoir pond pits, and urban lands.
Elephants tended to prefer the medium–low altitude range of 800–1030 m. High altitude restricted their distribution. As the distance to the residential point exceeded 3 km, the frequency of elephants’ appearance gradually decreased. The probability of elephants’ appearance was highest when the temperature was around 20.5 °C. When the habitat quality was around 0.35, 0.75, and 0.98, the probability of elephants’ appearance reached 50%.
Construction of resistance surfaces. Using the raster calculator of ArcGIS 10.8.1, nine environmental factor resistance surfaces, such as elevation, slope, NDVI, land use, etc., were obtained for Asian elephant dispersal, and finally, the integrated minimum resistance surface for Asian elephant dispersal was generated (Figure 7). It can be seen that Jiangcheng County has a relatively high integrated resistance surface resistance value of more than 19 due to the survival and migration of Asian elephants [30].
Construction of ecological corridor. According to the habitat suitability for Asian elephants in Jiangcheng County, a total of 14 ecological source areas with a total area of 437.33 km2 were identified, of which the largest first-level ecological source area, with a total area of 108.167 km2, was mainly concentrated in Kangping Township. Through the corridor analysis, three important Asian elephant ecological corridors and 89 general ecological corridors were obtained; the longest corridor of the important corridors was mainly in Kangping Township and Zhenggang Township, and the remaining 89 general potential corridors were mainly concentrated in the four townships of Kangping, Zhenggang, Baozang, and Jiahe (Figure 8). These migration paths link the townships and, together, constitute the ecological corridors for Asian elephant migration in Jiangcheng County.
Habitat suitability assessment. After reclassification in ArcGIS, the habitat suitability for elephants was divided into five levels (as shown in Figure 9). Figure 9 indicates that the suitable habitat for elephants in the study area is relatively concentrated, mainly in the Zhengdong and Kangping Townships. Only 3.37% of the total area of Jiangcheng County was high-suitability habitat. Medium- and low-suitability habitats accounted for 2.29% and 3.82% of the total area, respectively. Finally, edge habitat accounted for 8.41% of the total county area, while the largest proportion, i.e., 82.11%, was classed as unsuitable habitat. In a word, the proportion of high-suitability and medium-suitability habitats was less than 10% of the total area (Table 4), indicating poor suitability of elephant habitat in this study area. The medium- and high-suitability habitats were connected in a strip distribution, indicating serious fragmentation of the elephants’ habitat in the study area. Urgent protection measures are needed.

5. Discussion

Relevant research results have shown that the cold-season precipitation, altitude, seasonal standard deviation of temperature, warmest seasonal precipitation, slope, and monthly mean diurnal temperature difference are the main factors influencing the distribution of Asian elephants in China [31]. The standard deviation of the seasonal temperature was the most important variable, followed by the monthly mean of the diurnal temperature difference and the mean temperature of the driest quarter. Asian elephants prefer areas at lower elevations and on gentler slopes because travel is physically demanding for the largest land herbivore [32]. Temperature, precipitation, and topography were found to be the primary factors affecting the distribution of Asian elephants in another study [33]. The majority of Asian elephant habitat in the study area is located along the mainstreams of rivers, indicating the significant influence of topography, in agreement with the results of many studies [34,35,36].
This study found that the spatial distribution of Asian elephants has obvious aggregation; the locations with the highest frequency of occurrence are mainly concentrated in Kangping Township and Zhengdong Township, in which there are no nature reserves. The locations where Asian elephant populations appear in Jiangcheng County all conform to three characteristics: (1) Asian elephants, as a migratory behavioral species, have a strong adaptive ability. In recent years, with the strengthening of protection measures, Asian elephants’ fear of people has weakened, the time of their appearance is no longer strictly diurnal or nocturnal as before, and their behavioral habits have changed significantly, with their areas of activity being unrestricted. For example, the frequency of Asian elephants is high in areas with frequent human activities, such as cultivated land and settlements. The areas on both sides of the Manlao River are at a lower altitude (<1500 m) with a gentle terrain; land use types such as cropland and forested land show a mosaic distribution [37], which is conducive to Asian elephants feeding on the farmland as well as to Asian elephants’ rapid entry into the shaded forested areas when they are avoiding risks [28,34,35,36]. (2) Water sources and mud ponds are also crucial for Asian elephants. In locations near rivers, densely populated streams, or reservoirs, Asian elephants appear significantly more often than in other locations, reflecting the Asian elephants’ need for water for survival. In the mud ponds, Asian elephants can obtain mineral elements that are not found in their food sources, which are used to replenish their own metabolic losses and maintain the physiological balance of the body, showing that the Asian elephant’s choice of habitat that includes water sources and mud ponds is crucial [38]. (3) The habitat of Asian elephants in Jiangcheng County is severely fragmented; Asian elephants are mainly distributed to the south of the Manlao River and have never moved to the east of the Manlao River. To the east of Manlao River, the terrain is more undulating [38], the altitude is more than 1500 m, this area is covered mostly by dense forest with more than 60% tree coverage, as a result, there is insufficient sunlight under the forest, making it difficult for elephants to find their favorite food under the forest, such as grass and plantain, and, thus, this area cannot meet the Asian elephants’ food needs [39,40].
The elephants in Jiangcheng County currently migrate and range widely, sometimes even moving northward to Ning’er County. Furthermore, there is no natural reserve or protected area in the range of the elephant herd, significantly increasing the risk of human–elephant conflicts. Research shows that Asian elephants’ activities in other forests, as well as cultivated land and other human activity areas, are more frequent [15,39,40], indicating that the habitat of elephant herds and the area used for human production activities are highly overlapping, thus increasing the probability of human–elephant conflicts, which is also the problem currently affecting the Asian elephant herds in Jiangcheng County. Asian elephants, as large mammals, need to adapt to their environment due to the fragmentation of their habitat, with their natural food plant sources gradually reducing, forcing them toward the cultivated land for food, such as corn, sugar cane, and other crops planted by human beings. They even enter the farmers’ homes to feed on maize and obtain minerals needed by the body (through salt), which has in turn triggered the conflict between humans and elephants. Therefore, more effective protection measures are needed for Asian elephants and their habitat resources to alleviate human–elephant conflicts, which is currently an urgent problem that needs to be resolved [4,41].
Ecological corridors are often used to connect fragmented habitats for wildlife, thus connecting isolated populations of organisms, providing opportunities for genetic exchange between populations, eliminating the effects of habitat fragmentation on biodiversity, and improving ecosystem services. Several experiments have demonstrated that habitats connected by corridors retain more native species than isolated patches, an effect that increases over time. To improve the continuity and wholeness of suitable habitats in potential corridor areas, it is essential to mitigate habitat fragmentation [30], first, by improving the coherence of vegetation and adjusting the planting structure while simultaneously making people aware of the necessity of Asian elephant conservation and management. The three important ecological corridors constructed in this study, two of which are mainly concentrated in Kangping Township and Zhengdong Township, are the core areas where Asian elephants live, while other areas such as Baozang, Jiahe, and Guoqing have extremely obvious habitat fragmentation and intricate ecological corridors. It is recommended that these areas should be used as additional Asian elephant habitats; in the later stage of Asian elephant habitat management activities, the quality and stability of these corridors should be improved as much as possible, and the suitable habitats should be restored and rebuilt to fully achieve their ecological functions [5].

6. Conclusions

This study utilized the maximum entropy model in conjunction with elephant activity point data and various environmental factor data to analyze and evaluate the habitat suitability for the elephants’ activity in Jiangcheng County. This study draws several conclusions.
First, the elephant population in Jiangcheng County is primarily distributed in Kangping and Zhengdong Townships, with a strip-shaped distribution from north to south. The area of the most suitable habitat is relatively small and fragmented, which significantly affects the stable settlement of elephants. Since 2011, 18 elephants have migrated to Jiangcheng, and their population has steadily increased. According to the monitoring personnel, the maximum number of elephants that the area can sustain is 70. However, the elephant herd’s activity area overlaps with human activity spaces, which increases the risk of human–elephant conflicts. Therefore, it is necessary to designate a protected area for elephants as soon as possible to provide a relatively safe habitat for the elephant herd.
Second, the distribution area obtained from the survey conducted by the Forest and Grassland Bureau inspectors and the data provided by the County Forest and Grassland Bureau is consistent with the prediction results of the MaxENT model. This suggests that the MaxENT model applies to the geographical distribution of elephants, providing guidance for further conservation efforts. It should help the Forest and Grassland Bureau and other relevant departments formulate realistic and practical plans to protect elephants.

Author Contributions

C.Y.: methodology and formal analysis. L.Z.: Investigation, data analysis, and writing. C.L.: Investigation and writing. H.L.: Investigation. X.L.: Investigation. Q.Y.: Investigation. J.L.: Investigation. J.S.: Investigation. S.Y.: Investigation. F.C.: Investigation. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China’s “Multi-frequency SAR polarized interferometric data for forest tree height inversion” project (Grant No. 42061072); the Major Science and Technology Special Project of Yunnan Provincial Science and Technology Department’s “Forest Resources Digital Development and Application in Yunnan” project (Grant No. 202002AA100007-015); and Yunnan Province Agricultural Basic Research Joint Special Project, “Estimation of aboveground biomass of Simao pinus forest based on multi-source remote sensing data”, (Grant No. 202401BD070001-117).

Data Availability Statement

Data are contained within the article.

Acknowledgments

I would like to express my gratitude to the Pu’er City Forestry and Grassland Bureau and the Jiangcheng County Forestry and Grassland Bureau for their strong support and assistance in this research.

Conflicts of Interest

The authors declare no conflicts of interest.

Appendix A

The figure below shows iconic photos of elephant herd activity in Jiangcheng County. The detailed activity behavior of these herds was recorded by the staff of the Forestry and Grassland Bureau of Jiangcheng County while using drones to monitor the elephants. Photo credit: Forestry and Grassland Bureau of Jiangcheng County, Pu’er City, and Yunnan Province.
Forests 15 01195 g0a1aForests 15 01195 g0a1bForests 15 01195 g0a1c
Figure A1. Pictures of Asian elephants obtained using drones within the jurisdiction of the whole Zhengdong Township in Jiangcheng County (2021).
Figure A1. Pictures of Asian elephants obtained using drones within the jurisdiction of the whole Zhengdong Township in Jiangcheng County (2021).
Forests 15 01195 g0a1aForests 15 01195 g0a1bForests 15 01195 g0a1c

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Figure 1. Changes in Asian elephant habitats.
Figure 1. Changes in Asian elephant habitats.
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Figure 2. Distribution range of elephants in Jiangcheng County.
Figure 2. Distribution range of elephants in Jiangcheng County.
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Figure 3. Correlation diagram of environmental factors.
Figure 3. Correlation diagram of environmental factors.
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Figure 4. R program model selection results.
Figure 4. R program model selection results.
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Figure 5. Verification of ROC curve of prediction results of the evaluation of the elephants’ habitat by the MaxEnt model.
Figure 5. Verification of ROC curve of prediction results of the evaluation of the elephants’ habitat by the MaxEnt model.
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Figure 6. Relationship between the distribution probability of elephants and environmental factors. Note: (d) In the LULC graph, the horizontal axis 11–12 represents paddy fields and dry land, 21–24 represents forested land, shrubs, sparse forest land, and other forest land, 31–32 represents high-coverage grassland and medium-coverage grassland, 41 represents rivers, 43 represents reservoirs, ponds, and pits, and 51 represents urban land, rural residential areas, and other construction land.
Figure 6. Relationship between the distribution probability of elephants and environmental factors. Note: (d) In the LULC graph, the horizontal axis 11–12 represents paddy fields and dry land, 21–24 represents forested land, shrubs, sparse forest land, and other forest land, 31–32 represents high-coverage grassland and medium-coverage grassland, 41 represents rivers, 43 represents reservoirs, ponds, and pits, and 51 represents urban land, rural residential areas, and other construction land.
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Figure 7. Resistance surface.
Figure 7. Resistance surface.
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Figure 8. Ecological corridors in Asian elephant habitat. Note: Based on the results of the maximum entropy model, the areas with high, medium, and low habitat suitability are categorized into primary, secondary, and tertiary ecological source areas, respectively. The ecological source point represents the central point of each ecological source area.
Figure 8. Ecological corridors in Asian elephant habitat. Note: Based on the results of the maximum entropy model, the areas with high, medium, and low habitat suitability are categorized into primary, secondary, and tertiary ecological source areas, respectively. The ecological source point represents the central point of each ecological source area.
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Figure 9. Prediction of the suitable distribution of elephants in Jiangcheng County based on the MaxEnt model.
Figure 9. Prediction of the suitable distribution of elephants in Jiangcheng County based on the MaxEnt model.
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Table 1. Changes in the population of wild elephants in Pu’er City and Jiangcheng County over the past decade.
Table 1. Changes in the population of wild elephants in Pu’er City and Jiangcheng County over the past decade.
YearPopulation of Wild Asian Elephants
Puer CityJiangcheng County
2011–20125518
20134528
20145943
201510652
201610838
201713738
201813744
201913747
202018147
202112751
202218153
Data Sources: Pu’er City Forestry and Grassland Bureau and Jiangcheng County Forestry and Grassland Bureau.
Table 2. Habitat quality evaluation factors.
Table 2. Habitat quality evaluation factors.
TypeHabitat Quality
Evaluation Factor		Processing MethodReferences
Climate
Factors		Rainfall/mmResampling and unifying the coordinate system[8,15]
Temperature/°C[8,15]
Terrain FactorsAltitude/mResampling and unifying the coordinate system[15,16]
Slope/°Extraction using the Spatial Analysis module of ArcGIS/ArcView3.3[16,17]
Surface Cover FactorsLand UseReclassification of downloaded land use data based on LULC (Land Use/Land Cover)-type standards[10]
Normalized Vegetation IndexResampling and unifying the coordinate system[17]
Land CoverDerived from NDVI (Normalized Difference Vegetation Index) values[15]
Habitat QualityBased on land use data, using the HQ (Habitat Quality) module of the InVEST model. The model was run after inputting the related indicators, combined with the actual conditions of Asian elephants in the study area[18,19]
Vegetation TypeResampling and unifying the coordinate system[15]
Disturbance FactorsDistance to Forest/kmTransformed into a distance layer using the Distance function of the ArcGIS Spatial Analysis module[15]
Distance to River/km[15]
Distance to Residential Points/km[15]
Distance to Road/km[15]
Distance to Farmland/km[15]
Table 3. Resistance factors and classification of ecological source expansion.
Table 3. Resistance factors and classification of ecological source expansion.
Resistance FactorsData BandsResistance ValueWeight
Elevation291–766100.1431
766–102530
1025–124960
1249–150190
1501–2120100
Slope0–1100.105
11–1930
19–2660
26–3390
>33100
Distance to
the river/m		0–500100.162
500–100030
1000–150060
1500–200090
>2000100
Distance to
The settlement/m		0–24631000.0812
2463–412490
4124–607250
6072–859210
8592–14,6070
NDVI0.2—0.121000.042
0.12–0.5170
0.51–0.6430
0.64–0.7410
0.74–0.90
LULCConstruction land1000.1414
Waters30
Grassland60
Forest25
Cultivated land80
Distance to
the road/m		0–11661000.1493
1166–275380
2753–461960
4619–709330
>709310
Distance to
cultivated land/m		0–3511000.0692
351–117280
1172–225760
2257–384040
3840–744510
Habitat quality0–0.41000.1224
0.4–0.6580
0.65–0.7960
0.79–0.9130
>0.9110
Table 4. Prediction of the proportion of suitable areas for elephants in Jiangcheng County under various environmental variable conditions.
Table 4. Prediction of the proportion of suitable areas for elephants in Jiangcheng County under various environmental variable conditions.
Study AreaNon-Suitable AreasMarginal AreasLow-Suitability AreasMedium-Suitability AreasHigh-Suitability Areas
of County Area (%)of County Area (%)of County Area (%)of County Area (%)of County Area (%)
Jiangcheng County82.11%8.41%3.82%2.29%3.37%
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Zhang, L.; Li, C.; Yue, C.; Luo, H.; Li, X.; Yu, Q.; Li, J.; Shen, J.; Yang, S.; Chen, F. Habitat Suitability Evaluation and Ecological Corridor Construction for Asian Elephants: The Case of Jiangcheng, a New Range for Elephants in Southwestern China. Forests 2024, 15, 1195. https://doi.org/10.3390/f15071195

AMA Style

Zhang L, Li C, Yue C, Luo H, Li X, Yu Q, Li J, Shen J, Yang S, Chen F. Habitat Suitability Evaluation and Ecological Corridor Construction for Asian Elephants: The Case of Jiangcheng, a New Range for Elephants in Southwestern China. Forests. 2024; 15(7):1195. https://doi.org/10.3390/f15071195

Chicago/Turabian Style

Zhang, Lanzhong, Churui Li, Cairong Yue, Hongbin Luo, Xin Li, Qiongfen Yu, Jia Li, Jian Shen, Song Yang, and Fei Chen. 2024. "Habitat Suitability Evaluation and Ecological Corridor Construction for Asian Elephants: The Case of Jiangcheng, a New Range for Elephants in Southwestern China" Forests 15, no. 7: 1195. https://doi.org/10.3390/f15071195

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