1. Introduction
Since the 20th century, global climate has undergone significant changes, with the United Nations Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report confirming that climate warming is an undeniable fact [
1]. This global warming, alongside shifting precipitation patterns, has led to an increase in extreme weather events [
2], impacting not only plant growth and geographic distribution [
3,
4] but also causing the disappearance of specific phytoclimate zones [
5], posing major challenges to ecosystem structure and biodiversity. Changes in temperature and precipitation due to climate change will affect species’ environmental tolerance. When these changes surpass a species tolerance threshold, they must either adapt or shift their distribution to find suitable habitats [
6]. For species with limited ranges, habitat loss due to future climate change presents a serious threat, heightening their risk of extinction [
7]. Understanding the change in species distribution under global climate change is therefore crucial for their conservation.
Prunus mira Koehn is a plant species of the Rosaceae family, native to the Qinghai–Xizang Plateau and also found in the provinces of Sichuan and Yunnan [
8]. Compared to other peach varieties,
P. mira is distinguished by its smooth pit [
9]. As one of the most ancient and widely distributed endemic tree species on the Xizangan plateau,
P. mira demonstrates remarkable resilience to cold, drought, barren conditions, and diseases, with a potential lifespan spanning thousands of years [
9,
10]. It is called the “Living Fossil Group” of peach resources in the world [
11].
Prunus mira is of great value for ornamental, culinary, and medicinal purposes [
11,
12,
13]. In recent years, the natural habitat of
P. mira has been shrinking due to environmental changes, human activities, and socio-economic development. In traditional Xizangan culture, the fruit is commonly used as livestock feed, making it difficult to preserve for propagation, which has led to the aging of the species [
12,
13,
14]. The rapid decline in species populations has made the protection of
P. mira increasingly urgent. Current research on
P. mira has primarily emphasized the physiological and genetic aspects [
14,
15], leaving the suitable distribution area and environmental driving variables under the context of climate change largely unexplored. Understanding the impact of climate change on the suitable habitats of
P. mira is crucial for unraveling the mechanisms behind its distribution and for providing a foundation for its sustainable development, utilization, and conservation.
Species Distribution Modeling (SDM) predicts potential species distribution based on the relationship between the ecological environment and climate factors [
16]. At present, the most commonly used models for predicting species distributions include the Maximum Entropy Model (MaxEnt) [
17], Ecological Niche Factor Analysis Model (ENFA) [
18], Genetic Algorithmic Model (GARP) [
19], Bioclimate Analysis and Prediction System (BIOCLIM) [
20], and Domain Models (DOMAIN) [
21]. Among these, the MaxEnt model is widely used due to it is ease of operation and reliable predictions with limited sample data [
22,
23]. In recent years, the MaxEnt model has been widely used in studies of invasive species, conservation of flora and fauna, disease transmission, and species response to climate change [
24,
25,
26,
27,
28].
We used the MaxENT model to predict the suitable habitable area of P. mira in Nyingchi in different time periods. The main objectives of our study are as follows: (1) to assess the current spatial distribution pattern of P. mira and identify the key environmental variables that shape its distribution; (2) to forecast the future distribution of P. mira and its response to environmental factors like temperature and elevation under different climate scenarios; and (3) to analyze the expansion patterns of P. mira under the background of climate change. This study aims to provide a scientific reference value for the development, utilization, and protection of P. mira under future climate change.
4. Discussion
The MaxENT model has been widely utilized in species distribution modeling due to its unique advantages. However, the model is sensitive to sampling bias, and its default parameter settings can lead to overfitting, negatively impacting the final predictions [
38,
39]. By employing the ENMeval data package to optimize the combination of various parameters, the prediction accuracy of the model can be significantly enhanced, allowing for a more accurate reflection of the environmental factors influencing species distribution [
35]. To address the issue of multicollinearity among environmental variables, correlation analysis combined with the jackknife method is employed to eliminate factors with minimal influence. Additionally, to mitigate overfitting, the model regularization frequency and characteristic parameters are optimized. Following these adjustments, the correlations among environmental factors are low, and the average AUC value of the final model across all periods exceeds 0.99, demonstrating high accuracy and precision in predicting habitat suitability. This study effectively predicts the suitable habitat for
P. mira across different time periods.
The current distribution area of
P. mira is mainly concentrated in the central and northern parts of Nyingchi, along the Yarlung Zangbo River and Niyang River basins. This result is consistent with previous investigations of
P. mira [
27,
40]. Through the application of the jackknife method and the regularization training gain, it was determined that the main influencing factors are temperature seasonality (bio4), mean temperature of coldest quarter (bio11), isothermality (bio3), and elevation (ele). The first three variables are all related to temperature, indicating that temperature significantly impacts the distribution of
P. mira, particularly temperature seasonality (bio4), which has a contribution rate of 30.1%. During the growth period,
P. mira is not well-suited to areas with excessively large seasonal temperature fluctuations. The optimal range for temperature seasonality (bio4) is between 134 and 576, suggesting that seasonal temperature changes should remain moderate for optimal growth. Additionally, when the mean temperature of the coldest quarter (bio11) is between −2.6 °C and 2.7 °C, isothermality (bio3) ranges from 43 to 57, and elevation is between 2783 and 4089 m, these conditions are also suitable for the growth of
P. mira. Based on the growth characteristics of
P. mira [
22], the suitable altitude and climate of Nyingchi provide unique growth conditions that favor its growth [
29,
30,
31]. Thus, it can be concluded that the Nyingch area is conducive to the growth of
P. mira under the current climate conditions.
Over the past 60 years, the issue of warming in the Qinghai–Xizang Plateau has become increasingly prominent, with temperatures showing a continuous upward trend [
41]. In this case, the frequency of extreme weather has increased, climate instability has intensified, and the species composition and community structure of the plateau have changed; this can have an impact on the reorganization and replacement of vegetation communities, but the diversity of regional vegetation does not necessarily decrease [
42]. Previous studies have shown that global warming may actually lead to an increased species diversity [
43]. In this study, it was found that the suitable area for
P. mira will expand under four future climate scenarios compared to the current suitable area. Specifically, under the 2021–2040 SSP370 climate pathway, the suitable habitat area of
P. mira is projected to its maximum, accounting for 49.70% of the total area. On the whole, moderate warming is most conducive to the growth of
P. mira, while high warming conditions are unsuitable for its growth. Increased seasonal temperature differences due to climate warming in the future may further limit its growth and development.
Compared with the current situation, the suitable growth area for
P. mira is expected to expand under future climate warming scenarios, with the area of expansion exceeding that of contraction. Thus, the distribution of
P. mira will be significantly influenced by climate change. Under low levels of climate warming, the expansion of
P. mira continues to decline, whereas moderate warming conditions are most favorable for its expansion. From a spatial perspective, the primary areas of expansion are the high-altitude regions in the north and south of Nyingchi, which aligns with the observed trend of temperate tree species migrating to higher altitudes in response to climate warming [
44]. The Nyingchi region is influenced by the Indian Ocean monsoon and experiences moisture that advances northward along the Yarlung Zangbo River Gorge, resulting in abundant precipitation. Moreover, the region’s numerous rivers and substantial meltwater from snow and ice provide ample water for plant growth. Therefore, water is not a limiting factor for the growth of
P. mira in Nyingchi.
In this study, the contribution rate of soil factors reached 10.4%, but their impact on regularization training was not substantial. This may be attributed to the complex terrain and diverse soil types in the Nyingchi area, which likely means that soil requirements for P. mira growth are not as critical. Nonetheless, the relationship between soil factors and their distribution warrants further investigation. Additionally, while this study considered climate, topography, soil, river, and vegetation factors, it did not account for certain factors such as human activities. The operation of the MaxENT model is limited by the data on species existence, and the acquisition of some data in the Nyingchi area is limited due to its unique regional characteristics. In future studies, we should aim to gather more comprehensive and timely data, incorporating more factors and geographical distribution data into model prediction to more accurately forecast the suitable areas for P. mira. Furthermore, integrating considerations of species dispersal ability, land use change, interspecies competition, and human impacts, along with expanding the spatial coverage of data and employing more advanced modeling techniques, will enhance predictive reliability. This approach will help deepen our understanding of the effects of climate change on species distribution and provide new insights for the scientific protection and rational utilization of P. mira.
To protect P. mira in the future, it is essential to proactively survey and safeguard suitable high-altitude habitats based on the predicted expansion trends. Restoration efforts should focus on these areas to facilitate migration under climate warming. Additionally, core habitats, particularly in the Yarlung Zangbo and Niyang River basins in Nyingchi, must be protected from human development and land use changes. Further research on the impacts of climate change, including soil and human activities, is necessary to improve predictive accuracy and enhance the effectiveness of conservation measures. These strategies will ensure the long-term survival and expansion of P. mira under future climate conditions.