1. Introduction
Biodiversity patterns and species distributions are increasingly shaped by the combined effects of environmental change and socioeconomic development [
1]. Changes in land use practices, resource demand, and climatic conditions can alter habitat structure, availability, and connectivity, thereby influencing species persistence and spatial dynamics. Since the 1950s, global population growth has accelerated markedly, with annual growth rates exceeding 1.8% at certain periods. As of 15 November 2022, the United Nations announced that the global population had reached 8 billion. Population growth and economic expansion have intensified interactions between human systems and natural ecosystems, leading to widespread landscape transformation [
2]. Recent assessments indicate that land use change, including agricultural expansion, urban development, and transportation infrastructure construction—has become one of the dominant drivers of terrestrial habitat modification worldwide. These processes can influence ecological vulnerability by altering both the quantity and quality of suitable habitats for many species [
3]. Concurrently, climate change is reshaping temperature and precipitation regimes, thereby modifying the environmental conditions under which species persist. In response to changing climates, many species exhibit distributional adjustments along latitudinal and elevational gradients. Chen [
4] reported that a wide range of terrestrial organisms, including trees, insects, and mammals, have shifted their ranges toward higher latitudes and elevations at average rates of approximately 16.9 km and 11.0 m per decade, respectively. Similarly, studies focusing on montane terrestrial animals have documented upward elevational shifts in species distributions [
5]. However, the ability of species to track suitable climatic conditions is constrained by physiological tolerances, dispersal capacity, habitat fragmentation, and biotic interactions. When the pace of environmental change exceeds species’ adaptive or migratory capacity, mismatches between climatic conditions and habitat requirements may arise, potentially increasing the risk of local extinction in certain regions [
6]. Across many parts of the world, rapid economic and social development has been accompanied by profound changes in land use patterns and ecosystem structure. Regions undergoing industrialization, infrastructure expansion, and urban growth often experience increased demands on natural resources, resulting in complex trade-offs between economic development and biodiversity conservation [
7]. China, characterized by pronounced environmental gradients and high biodiversity, provides an informative context for examining these interactions. As the world’s second-largest economy, China has a population of approximately 1.4 billion, and its Human Development Index (HDI) ranked 82nd globally according to the IMF World Economic Outlook (2022;
https://www.imf.org/, accessed on 22 July 2024). During the transition from an agricultural economy to a highly industrialized one, China’s natural environment has undergone substantial changes. For example, between 1950 and 2004, the area of natural forests declined to approximately 30% of total forest cover. By 2021, the total length of highways reached 5.2807 million km, and both highway and high-speed rail networks ranked first globally in total mileage [
8]. Over recent decades, nationwide changes in land use, transportation networks, and forest management practices have continuously reshaped ecological landscapes. Understanding how wildlife responds to these transformations is essential for developing conservation strategies that are both scientifically grounded and compatible with long-term socioeconomic development. Species distribution models (SDMs) are widely used to predict changes in species distribution ranges under various climate change and socioeconomic scenarios [
9,
10]. In particular, a growing volume of species occurrence records and local environmental information has been utilized to develop conservation strategies for species and regions. Examples of such data include population size, GDP, vegetation cover, road construction, and protected area establishment. In recent years, researchers have increasingly employed SDMs to predict shifts in species distributions and the spatial arrangement of suitable versus unsuitable habitats based on data related to human activities and climate change [
11]. However, previous studies exhibit several limitations: (1) They often focus on a limited number of species, typically a single species or a few select species. (2) The study areas are frequently confined to specific regions or individual protected areas. (3) The analysis tends to focus on a narrow set of factors, primarily emphasizing the impact of climate change on species distributions or examining only a few isolated variables. (4) The datasets used for predictions often rely on outdated climate and environmental data [
11,
12,
13,
14]. Consequently, these approaches failed to reflect the dynamics of species distribution shifts in response to diverse climate change and socioeconomic scenarios.
The forest musk deer (
Moschus berezovskii), also known as the musk deer, belongs to the order Artiodactyla, family
Moschidae, and genus
Moschus. It is listed as Endangered (EN) by the International Union for Conservation of Nature (IUCN) and is a Class I nationally protected wildlife species in China. Widely distributed across central and southwestern China [
15], it is also the largest extant species of musk deer in the country. The forest musk deer play an important ecological role and are also of considerable economic significance due to the medicinal value of musk secreted by adult males. Previous studies indicate that more than 70% of global musk and musk-related products originate from China [
16]. Historical records suggest that wild populations experienced substantial declines during the latter half of the 20th century [
17,
18], a pattern associated with habitat modification, hunting pressure, and broader environmental change. Although captive breeding programs and conservation initiatives have contributed to population stabilization or recovery in some regions [
19,
20], the current distribution and long-term habitat suitability of the forest musk deer remain influenced by environmental conditions and patterns of human land use. In this study, we integrate occurrence records of the forest musk deer with updated climatic and anthropogenic variables to model its current and potential future habitat suitability across China. Using a MaxEnt-based species distribution framework and CMIP6 climate scenarios, our objectives are to (1) identify key environmental and socioeconomic factors associated with the species’ distribution, (2) assess potential shifts in suitable habitats under future climate conditions, and (3) provide a quantitative basis for conservation planning and adaptive management. By adopting an objective and integrative perspective, this study aims to contribute to a balanced understanding of how environmental change and human activities jointly shape species distribution patterns.
3. Results
3.1. Suitable Habitat of the Forest Musk Deer
As shown in
Figure 3, the mean AUC value of the model was 0.899 ± 0.001, indicating an excellent performance level. This result demonstrates high predictive accuracy, confirming that the model outputs reliably reflect the habitat distribution of the forest musk deer. In addition to AUC, model robustness was supported by the consistency of prediction outputs across bootstrap replicates, as well as by the response curves and jackknife tests, which together provide complementary information on model stability and the relative importance of predictor variables [
11].
Percent contribution, which reflects the importance of environmental variables to species distribution during MaxEnt model training, indicated that NDVI had the highest contribution (48.8%) in this study, followed by GDP (34.6%) and population density (16.6%). According to
Figure 4, an NDVI value greater than 0.8 correspond to the most suitable survival range (habitat suitability > 0.6) for the forest musk deer, i.e., areas with lush vegetation. As shown in the jackknife plot (
Figure 5), population density had less influence on the distribution of the forest musk deer comparing to two other variables. Additionally, the probability of forest musk deer occurrence increases with decreasing GDP values (habitat suitability > 0.5) and decreasing population density (habitat suitability > 0.55).
This study selected these three anthropogenic factors (PA, GDP, and PD) that significantly influence the distribution of the forest musk deer population. Using each as the sole environmental variable, and without considering the effects of climatic, topographic, and other environmental factors on the species’ distribution, the MaxEnt model was employed to predict the potential distribution area of the forest musk deer (
Figure 6).
Research results indicate that under the influence of NDVI, the highly suitable habitat for forest musk deer covers approximately 901,000 km2, primarily distributed across southern China. These areas include Yunnan, Hunan, Guizhou, and Guangdong Provinces; the Guangxi Zhuang Autonomous Region; Jiangxi, Fujian, and Zhejiang Provinces; the western part of Hubei Province; and the southern part of Anhui Province. The moderately suitable area encompasses approximately 940,800 km2, mainly located in central Sichuan Province, Chongqing Municipality, eastern Hubei Province, southwestern Anhui Province, southern Shaanxi Province, the border region between southern Shaanxi and Gansu Provinces, and the junction between Henan and Hubei Provinces.
With respect to GDP, the highly suitable area is approximately 728,500 km2, concentrated in northern and southern Yunnan Province, northern Guangxi Zhuang Autonomous Region, central and northern Sichuan Province, most of Gansu Province, the border region between Qinghai and Gansu Provinces, and western Shanxi Province. The moderately suitable area spans about 1,727,800 km2, covering central Guangxi Zhuang Autonomous Region, central and northern Yunnan Province, the border between the Tibet Autonomous Region and Sichuan Province, central and western Sichuan Province, Gansu Province, and parts of Shaanxi Province.
Under the influence of population density, the highly suitable area measures approximately 304,300 km2, while the moderately suitable area reaches 3,438,100 km2. These areas are primarily located across Yunnan Province, the Guangxi Zhuang Autonomous Region, northern Guangdong Province, most of Fujian Province, the Tibet Autonomous Region, the border between Qinghai and Sichuan Provinces, central and western Sichuan Province, eastern and southern Guizhou Province, western Hunan Province, most of Jiangxi Province, southern Anhui Province, western Zhejiang Province, western Hubei Province, eastern Chongqing Municipality, most of Gansu Province, southern Shaanxi Province, and the border region of Shaanxi, Shanxi, and Henan Provinces.
3.2. Suitable Habitat Under Current Climate
As shown in
Table 2, among the six natural factors, Annual Precipitation (BIO12), Temperature Seasonality (BIO4), and DEM (Digital Elevation Model) exhibited relatively higher contribution rates, at 43.5%, 32.3%, and 13.3%, respectively.
Figure 7 indicates that the optimal survival range for the forest musk deer corresponds to an Annual Precipitation (BIO12) of approximately 750–1500 mm. The maximum probability of occurrence was observed at DEM values between 1500 and 3000 m. Furthermore, habitat suitability for the forest musk deer is relatively high when Temperature Seasonality (BIO4) reaches 500–600.
As shown in
Figure 8, the unsuitable area for the forest musk deer population is 853.11 × 10
4 km
2. The area of low suitability is 56.07 × 10
4 km
2, accounting for 51.29% of the total suitable area. It is primarily distributed in eastern Tibet, eastern Qinghai, southern Gansu, central–western Sichuan, central Yunnan, southern Guizhou, northwestern Guangxi, western Hunan, northern Guangdong, western Hubei, and southern Shaanxi, among other regions. The area of moderate suitability is 47.70 × 10
4 km
2, accounting for 43.64% of the total suitable area, mainly located in northern Yunnan, central Sichuan, most of Guizhou, northern Guangxi, southern Gansu, and southern Hunan, among other regions. The area of high suitability is 5.54 × 10
4 km
2, accounting for 5.07% of the total suitable area, and is primarily distributed across multiple regions including central–northern Sichuan, northwestern Guangxi, and southern Gansu.
3.3. Suitable Habitat Under Future Climate
Based on the future climate projections generated using the selected high-contribution climatic variables under CMIP6 scenarios, the area of suitable habitat for the forest musk deer is projected to decrease under future climate conditions (
Figure 9). Among the suitability categories, moderately suitable area exhibits the most substantial reduction, declining by 9.09–28.29 × 10
4 km
2, with the greatest loss occurring under the SSP1-2.6-2070s scenario. The low suitability area is projected to decrease by 3.91–17.01 × 10
4 km
2. In contrast, the highly suitable area remains nearly unchanged or shows a slight increase, expanding by 3.68 × 10
4 km
2 under the SSP5-8.5-2070s scenario (
Table 3). The future distribution of the forest musk deer is expected to shift towards the border region of Sichuan, Qinghai, and Tibet. Suitable habitat is projected to predominantly occupy large parts of Sichuan Province and northern Yunnan Province, with persistent and stable distribution also present in areas such as Gansu, Shaanxi, and Hubei. However, habitats in coastal regions are projected to contract significantly. During the 2030s period, the forest musk deer shows extensive distribution across most of Yunnan Province and western Guizhou Province. By the 2050s and 2070s periods, its distribution in Yunnan and Guizhou begins to contract, with notably fewer occurrences within Guizhou Province. It should be noted that local land use changes and anthropogenic disturbances, which were not incorporated into future projections, may further modify habitat availability at finer spatial scales.
As shown in
Figure 10, under all future climate scenarios, the centroid of suitable habitat for the forest musk deer exhibits a pronounced northwestward shift, migrating from the current border region between Sichuan and Yunnan Provinces toward higher-elevation areas in western Sichuan and the adjacent regions of the Tibet Autonomous Region. Among the scenarios examined, the SSP5-8.5-2070s scenario shows the greatest migration distance, reaching 492.49 km, with the centroid shifting from Sichuan Province into the Tibet Autonomous Region. This pattern indicates a consistent tendency for the forest musk deer to track suitable climatic conditions by moving toward higher-elevation regions under ongoing climate change.
4. Discussion
The MaxEnt model is a widely applied predictive approach that infers species distributions based on known occurrence records and environmental variables under a presence-only framework [
34]. In this study, habitat suitability for the forest musk deer was assessed by integrating environmental predictors with occurrence data derived from field surveys, literature records, and authoritative databases such as GBIF and the IUCN. The resulting AUC values (0.899 and 0.940) indicate strong model performance, suggesting that the selected environmental and socioeconomic predictors effectively captured major gradients associated with the species’ distribution. Under current climatic conditions, the predicted distribution encompassed nearly all known occurrence locations while also identifying extensive areas of potential suitable habitat. Collectively, these results suggest that the model provides a reliable representation of the forest musk deer’s distribution across China.
The forest musk deer has been widely reported to be closely associated with forested environments, showing a preference for coniferous forests, broadleaf forests, and mixed conifer–broadleaf forests. Evidence further suggests that habitat use varies seasonally. Previous field-based studies and telemetry observations indicate that mixed conifer–broadleaf forests are preferentially used during spring and autumn, coniferous forests are more frequently occupied in summer, and sun-exposed forest areas are selected in winter. These seasonal shifts likely reflect changes in food availability, microclimatic conditions, and shelter requirements [
35]. In this context, the substantial contribution of NDVI identified in the present study is ecologically consistent with these documented habitat use patterns. As an integrative indicator of vegetation productivity and canopy structure, NDVI is closely related to the availability of forage resources and cover for forest-dwelling herbivores. Similar associations between vegetation indices and habitat suitability have been reported for musk oxen and other cervid species, underscoring the importance of vegetation dynamics in shaping their spatial distributions [
36].
Socioeconomic variables, such as gross domestic product (GDP) and population density, were also associated with patterns of habitat suitability. However, these variables should not be interpreted as indicating direct causal effects; rather, they likely reflect broader gradients of land use intensity and landscape transformation. Areas characterized by higher economic activity and population density are often accompanied by infrastructure expansion, increased accessibility, and alterations in vegetation structure [
37]. Given the pronounced territorial behavior of forest musk deer, with individuals typically occupying exclusive home ranges [
38], such landscape modifications may disrupt habitat continuity and reduce the availability of suitable core habitats. Accordingly, the observed relationships are better understood as spatial associations between land use intensity and habitat suitability, rather than as evidence of negative impacts arising solely from human presence.
Importantly, the ecological effects of human activities are not uniformly negative and can vary substantially depending on hunting intensity, management practices, and spatial context [
9]. In many regions, regulated hunting, habitat restoration initiatives, forest management programs, and captive breeding efforts have contributed positively to the stabilization or recovery of threatened wildlife populations [
11]. In China, long-standing hunting bans, the establishment of nature reserves, and large-scale afforestation programs have, to some extent, reduced direct resource extraction and improved habitat conditions in certain areas.
In addition, agricultural and semi-natural landscapes can serve as supplementary habitats or movement corridors for certain wildlife species, particularly within heterogeneous landscapes. These examples underscore that human–wildlife interactions involve complex trade-offs. Biodiversity outcomes are therefore shaped not simply by the presence of humans, but by the quality of governance, land use planning, and adaptive management strategies [
11].
Climatic variables, such as temperature seasonality (BIO4) and annual precipitation (BIO12), may further influence habitat suitability indirectly by shaping patterns of human land use. Regions characterized by climatic conditions favorable for agriculture or urban development often support higher GDP levels and greater population densities. These socioeconomic patterns can intensify land use conversion and reduce the availability of suitable habitats for forest musk deer. Consequently, the spatial patterns of habitat suitability identified in this study likely reflect the combined effects of intrinsic environmental suitability and the species’ avoidance of heavily modified landscapes. This highlights the interactive and co-determining roles of climatic and anthropogenic drivers in shaping species distributions.
Previous studies have found that elevation significantly influences the distribution of the forest musk deer, with populations showing a preference for habitats at elevations between 1500 and 1900 m [
39]. The present study indicates that elevations of 1500 to 3000 m constitute suitable altitudinal range for the species, encompassing the findings of earlier research. Higher elevations are subject to lower level of anthropogenic disturbance, which may increase the probability of forest musk deer occurrence within these altitudinal zones.
Precipitation and temperature not only directly affect the survival of the forest musk deer but also influence, to some extent, its food and water sources. Studies have shown that food and water availability are determinant factors for habitat selection in wildlife [
40]. The probability of forest musk deer occurrence initially shows an increase followed by a decline with rising annual precipitation (BIO12), with optimal condition occurrences at approximately between 750 and 1500 mm [
17]. Adequate precipitation supports both water and vegetation availability for the forest musk deer, thereby sustain the necessary resources on which forest musk deer depend. Temperatures between 27 °C and 30 °C appear to be the most favorable for the forest musk deer survival and development and promote the growth of herbaceous and shrub plants in mixed coniferous–broadleaf forests. Together, these climatic conditions indirectly shape the spatial distribution of the species by influencing habitat quality and food availability.
Under current climatic conditions, the forest musk deer exhibits a highly fragmented pattern of suitable habitat, with highly suitable areas accounting for only 5.07% of the total suitable habitat. Compared with earlier studies, the present analysis provides a more constrained and refined estimate of suitable habitat extent. Previous research has demonstrated that limited occurrence records can lead to substantial overestimation of potential habitat ranges. By incorporating 1590 occurrence records with high spatial coverage across China, this study improves the robustness and spatial precision of habitat suitability estimates relative to earlier regional or data-limited assessments.
Our findings are broadly consistent with previous studies reporting a stronger negative response of forest musk deer habitats in southeastern China and greater resilience in southwestern mountainous regions. For example, Zhao et al. [
41] identified pronounced habitat contraction in lowland and hilly areas of southeastern China, while Jiang et al. [
42] reported an upward and northward shift in the suitable distribution of musk deer species under climate change. Building upon these studies, our research extends their conclusions by integrating updated occurrence data, anthropogenic disturbance factors, and CMIP6 climate projections at a national scale. This integrated framework allows for a more comprehensive assessment of how climate change and human activities jointly shape both current and future habitat suitability for the forest musk deer.
Notably, this study highlights the relative stability of suitable habitats in high-elevation regions of southwestern China, particularly along the border regions of Sichuan, Qinghai, and Tibet. These areas are characterized by complex topography, extensive forest cover, and comparatively lower levels of human disturbance, which may buffer the impacts of climatic warming. In contrast, suitable habitats in southeastern and coastal regions, dominated by plains and hills, are projected to undergo substantial contraction, likely reflecting greater climatic variability and intensified anthropogenic pressure.
The forest musk deer populations prefer habitats within coniferous forests, broadleaf forests, and mixed coniferous–broadleaf forests. Under future climate scenarios, the stable areas of suitable distribution for the forest musk deer are predominantly forested zones. Accordingly, we recommend continuously advancing forest conservation programs, restoring and protecting woodland areas, and reducing the expansions of human-activity such as construction and agriculture to safeguard the habitat for the forest musk deer. Future research should focus on establishing long-term monitoring frameworks in regions identified as both habitat contraction zones and potential climatic refugia. In particular, systematic population and habitat monitoring along elevational gradients in southwestern China would facilitate early detection of distributional shifts.
From a management perspective, the results emphasize the need for integrative conservation strategies that account for both environmental dynamics and socioeconomic realities. Rather than viewing conservation and development as opposing objectives, spatial planning approaches that incorporate habitat suitability modeling can help identify priority areas for protection, ecological corridors, and zones for sustainable land use.
In regions projected to remain suitable under future climates, particularly high-elevation forest areas, maintaining habitat connectivity and minimizing fragmentation will be critical. In lower-elevation regions, targeted restoration, landscape heterogeneity, and adaptive management may help mitigate habitat loss while supporting human livelihoods. Such evidence-based approaches offer a pathway toward reconciling biodiversity conservation with long-term socioeconomic development.