1. Introduction
Ecosystem services (ESs) are defined as the environmental conditions and processes provided by ecosystems to support and sustain human survival and development [
1]. ESs are diverse and primarily revolve around supporting human life by providing essential resources like food and water [
2]. These services also play a role in regulating climate and hydrology [
3]. Additionally, ESs provide cultural services such as recreation and cultural amenities to people, while also contributing to soil erosion prevention [
4]. Ecosystem service flows facilitate the transmission of ESs from ecosystems to human society. This is the dynamic process by which certain ESs move within different spatial regions over time, such as water flow, wind flow, and sand flow [
5,
6,
7].
ESs have been extensively studied in recent decades [
8,
9]. Research on the dynamics of ecosystem services is no longer limited to static quantitative measures and necessitates a more profound exploration. For example, spatial indicators are used to evaluate ESs [
10] and the trade-offs and synergistic relationships between ESs [
11]. Furthermore, research has also examined the evaluation of ESs on various spatial scales [
12,
13].
In the late 20th century, the prominence of ESs rose and became a crucial consideration for socioeconomic development and human well-being. The evaluation of ESs has gradually gained recognition in forming ecological security patterns [
14,
15,
16]. In 2014, the United Nations introduced an experimental framework for ecosystem accounting to integrate the benefits and costs provided by ecosystems to humans into socioeconomic systems, highlighting the significance of ecosystems in promoting social development [
17,
18]. There is a diverse classification of ESs, as well as various evaluation methods and indicators [
12,
19]. However, there is currently no unified and standardized evaluation system in place. ES evaluation models include the InVEST model [
20], ARIES model [
21], SolVES model [
22], and Enviro Atlas, EPM model. Among these models, the InVEST model is considered the most mature and advantageous [
20]. InVEST is a GIS-based model that has been specifically developed to evaluate various ESs within landscapes across different land use scenarios [
23]. Researchers have suggested that clarifying and evaluating ESs and integrating them into individual, corporate, and government decision-making processes can lead to the formulation of environmentally beneficial plans, ultimately achieving long-term harmonious development between humans and nature [
24,
25].
National parks have a vital role in China as protected natural areas, holding significant value in the ecosystem. These parks feature unique landscapes, cultural and natural heritage, and a variety of biological species [
26]. The goal of establishing a national park system is to safeguard the authenticity and integrity of natural ecology and cultural heritage, protect biodiversity, and create a security barrier for the environment. It is a key element in constructing China’s ecological civilization system [
27]. Ruoergai National Park is situated in the transitional zone of the three natural regions of the country. It serves as a crucial water conservation and ecological functional area in the upper Yellow River basin. Known as the largest “plateau solid reservoir” globally, it also provides habitats for a diverse range of rare bird species. The park’s diverse species play a crucial role in maintaining ecological balance, regulating climate, and conserving soil and water [
28,
29]. Therefore, assessing Ruoergai National Park’s ecosystem services can help protect and utilize its rich natural resources, enhancing the region’s overall ecological benefits.
This paper focuses on Ruoergai National Park as the research area and examines the land use change characteristics based on the area’s basic data in different periods. The study utilizes the InVEST model to evaluate the ESs of the study area and identifies important areas for protection and utilization. These findings can assist decision-makers in developing plans for the protection of the area and provide a theoretical and scientific basis for park operation and management, ecological protection and restoration, and achieving the sustainable development of ecological and economic benefits. Additionally, the research contributes to the understanding of ecological service functions in alpine grassland meadow areas and provides a theoretical basis for further studies.
2. Study Area
The geographical coordinates of Ruoergai National Park (Sichuan area) range from 101°37′53.650″ E to 103°13′37.304″ E and 32°45′27.811″ N to 33°59′59.063″ N. Situated in the rift basin on the eastern edge of the Qinghai–Tibet Plateau, it is the confluence of the Qinling Mountains, Dieshan Mountains, and Minshan Mountains. The park is located in the northwest region of the Aba Tibetan and Qiang Autonomous Prefecture in Sichuan Province, at the junction between Sichuan, Gansu, and Qinghai Provinces. The study area is in the upper reaches of the Yellow River, administratively affiliated with Ruoergai County, Hongyuan County, and Aba County in Sichuan Province (
Figure 1). The total area of the park is 13,829 km
2, with the Sichuan area covering 8336 km
2. It encompasses six natural reserves of various types, including four nature reserves and two national wetland parks. The park is particularly abundant in wetland resources, accounting for 91% of the swamp wetlands in the Ruoergai area. The landform of the study area consists of denuded hilly plateaus and high plains. The plateau landform is characterized by shallow hills and swamps, with intermittent hills and crisscrossing, winding ravines. These features result in extensive swamps and numerous oxbow lakes. The park is rich in river resources, being part of the Yellow River system, which includes the 174 km main stream of the Sichuan section of the Yellow River and three tributaries: Heihe, Baihe, and Jiaqu.
5. Discussion
5.1. Drivers Affecting Ecosystem Services in Ruoergai National Park
Ecological systems are crucial for human survival and have a significant impact on regional sustainable development. Ruoergai National Park, as a key ecological functional area, plays a vital role in protecting ecosystem health, promoting ecological restoration, and maintaining functional stability. This study examines the changing trends, influencing factors, and important functional divisions of ESs in the area. The findings indicate that from 2010 to 2020, Ruoergai National Park witnessed an upward trend in soil conservation, water conservation capacity, and habitat quality, but a downward trend in carbon storage capacity. Recent years have seen increased rainfall, low temperatures, and a cold and humid climate in the Ruoergai area, which has positively contributed to improved water conservation capabilities. The study area has a significant amount of unused land, including wetlands and glaciers in the northern and central parts, as well as extensive grassland and woodland. The vegetation conditions overall are favorable, contributing to improved soil retention capacity and habitat quality. However, human activities have led to an increase in construction land and a decrease in grassland, thereby hindering the improvement in carbon storage capacity. Since the establishment of the Ruoergai Wetland National Nature Reserve in 1998, measures such as wetland ecological restoration, land desertification control, and water ecological protection and restoration have effectively mitigated ecological degradation. Changes in climate conditions and human activities are the driving forces behind the spatial distribution changes in ESs in Ruoergai National Park.
5.2. Strategies to Restoration Grasslands in the Future
Continued efforts should be made to strengthen the implementation of grassland ecological restoration projects. Firstly, prioritizing the preservation of native wild grass species resources and establishing a technical system for the domestication, selection, breeding, and expansion of these species is crucial. Secondly, it is important to adopt appropriate engineering restoration measures that are tailored to local conditions. Lastly, establishing pilot projects for the restoration of degraded grasslands and developing specific and targeted protection plans is necessary, such as grassland fencing [
49]. Simultaneously, raising awareness about ecological protection is essential. Regional and departmental management agencies should focus on improving the institutional system of grassland education, organizing various publicity and public activities to promote people’s understanding of and commitment to grassland protection. In the future, the restoration of degraded grasslands should integrate new technologies and materials from the field of ecological restoration, fostering innovation and forming a diverse and integrated technical system. This approach will enable the refined management of ecological restoration in degraded grasslands.
5.3. Limitations and Future Perspectives
In order to analyze the reasons for the changes in the spatial and temporal distribution of ESs, this article conducted a detailed analysis of each element of the evaluation process. The spatial distribution of ES is primarily influenced by climate conditions, land use changes, and human activities. Additionally, ecological sensitivity is also an important factor that affects ecosystem evaluation. It primarily represents the sensitivity of the ecosystem to natural and human activities in the evaluation area, which can be observed through indicators such as soil erosion and rocky desertification [
50]. By combining ecological sensitivity and ecological function importance in the spatial evaluation results, a more scientifically formulated ecological protection and restoration system for Ruoergai National Park can be developed.
However, this study has some limitations as it only focused on four typical ESs. The parameter setting of the model was based on relevant research and continuous debugging, which may have introduced subjective factors. To enhance the protection and utilization of Ruoergai National Park, it would be beneficial to include more comprehensive ESs, such as biodiversity assessment and water quality purification, in future research. Additionally, the time range of this study was limited to 2010–2020, which may not have captured longer-term changes in land use and ESs. In future research, we can delve into the trade-offs and synergies between ESs. By proposing more targeted and accurate ecological protection policies, we can provide a scientific basis for coordinating ESs and promoting a balanced development of ecology and the social economy.
6. Conclusions
This article utilizes the InVEST model to analyze the changing trends, spatiotemporal distribution, and influencing factors of soil conservation, carbon storage, water supply, and habitat index in Ruoergai National Park from 2010 to 2020. The results reveal the following:
From 2010 to 2020, the overall land use types in Ruoergai National Park ranked in the following order from largest to smallest: grassland > unused land > forest > water body > construction land. The transitions between land types have remained relatively stable with no significant changes. The areas of grassland and water have decreased, while forest land and unused land have been the main recipients of these transitions. Conversely, the areas of construction land and unused land have increased, with grassland and water being the primary sources. The grassland area experienced an upward trend from 2010 to 2015, followed by a downward trend from 2015 to 2020, resulting in a total decrease of 5.83 km2 in the grassland area.
Climatic conditions, land use changes, and human activities are the primary factors influencing changes in ESs. Between 2010 and 2020, the total soil conservation capacity of Ruoergai National Park initially decreased, then increased, and finally showed an overall increase of 1.81 × 105 t. The soil conservation capacity improved, particularly in forested areas. The distribution of soil conservation exhibits a spatial pattern of being “high in the west and low in the east”. During the same period, the total carbon storage in Ruoergai National Park initially increased, then decreased, and ultimately exhibited a decreasing trend, with a total decrease of 1.53 × 105 t. The carbon storage declined, despite the presence of diverse forestland vegetation types with the highest carbon storage. The overall carbon storage in the study area follows a spatial distribution pattern of being “high in the west and low in the east, low in the north and high in the south”. From 2010 to 2020, the total water conservation amount in Ruoergai National Park initially decreased, then increased, and finally showed an increasing trend, with an increase of 7.9 × 105 mm. The water conservation amount improved. Unused land exhibited high water production, while forest land and grassland had moderate levels, and water areas and construction sites showed low water production. The overall water supply in the study area demonstrates a spatial distribution pattern of being “high in the east, moderate in the west, high in the north, and moderate in the south”. Between 2010 and 2020, the habitat quality of Ruoergai National Park remained relatively stable. Most areas have relatively high habitat quality, although the northern, central, and some eastern parts experienced relatively high levels of habitat degradation. The overall habitat quality in the study area exhibits a spatial distribution pattern of being “high in the west and low in the east, low in the north, and high in the south”.
From 2010 to 2020, the importance of ESs in the study area exhibited a pattern of “four increases and one decrease”. This means that the area of moderately important, highly important, and extremely important areas increased, while the area of generally important areas decreased. The order of the proportion of ESs in the study area is as follows: moderately important > highly important > extremely important > generally important. By 2020, the total distribution area of highly important areas and extremely important areas for ESs in Ruoergai National Park amounted to 4592.73 km2, which accounted for half of the total area of the study area. The predominant land use types in this area are woodland and grassland, which have optimal ecological system service functions. The total area of moderately important areas with ESs in the study area is 3323.89 km2, accounting for approximately 40% of the total area. The land use type in this area is mainly unused land. Therefore, in the next planning and policy formulation process, greater attention should be given to the protection and utilization of land types such as forest land, grassland, and unused land.