A Spatiotemporal Analysis of Hainan Island’s 2010–2020 Gross Ecosystem Product Accounting

Abstract

Gross Ecosystem Product (GEP) is a single currency to measure the contribution of an ecosystem to society. It is the sum of the value of products and services provided by the ecosystem to humans. Based on this, GEP characterizes the current situation of the ecological environment in a region and can measure the contribution index provided by ecosystems. Based on land use data, rainfall data, soil data, statistical yearbook, DEM and other data, this paper constructs the accounting framework of Hainan Island’s GEP, quantitatively evaluates Hainan Island’s GEP from 2010 to 2020 and analyzes the research results. The results are as follows: (1) The GEP of Hainan Island’s ecosystem rose from 596.404 billion CNY in 2010 to 1032.096 billion CNY in 2020, an increase of about 42.21% with an average annual growth rate of 6.3%. The overall GEP has shown an upward trend. Among them, the value of regulation service accounts for the largest proportion was up to 73–83%. (2) The overall distribution of GEP in Hainan Island is uneven, decreasing from the central mountainous areas to the eastern coastal areas around to the west. In particular, Danzhou City, Wenchang City and Haikou City have higher values, while Tunchang, Baoting County and Wuzhishan City have lower values, and Wuzhishan City has the lowest values. Hainan Island is rich in natural resources, which contain great value. Through the accounting of GEP, we can clearly determine the value of the ecosystem, which can help the relevant departments estimate the GEP of Hainan Island’s ecosystem. It can provide a reference for Hainan to formulate ecological protection and sustainable development policies, and for the GEP estimation of other islands.

1. Introduction

Ecosystems provide products and services that are the basis for human survival and development. They not only provide people with products necessary for daily life and production, but also provide different services for the ecological environment, including water conservation, climate regulation, carbon fixation and oxygen release [1,2,3]. Therefore, the products and services provided by the ecosystem are the basis for human survival and development [4]. However, rapid urbanization and industrialization have continuously enhanced the ability of humans to intervene in the ecological environment, which has led to an increasingly prominent contradiction between humans and land [5,6,7]. Studies have shown that focusing on the Gross Ecosystem Product (GEP) of urban agglomerations can accelerate human well-being and manage urbanization, but how to quantify the value of ecosystems and convert ecological advantages into economic advantages requires further exploration [8].

Since the last century, some scholars have realized that ecosystem services play an important role in human survival and development, and they have carried out research on ecosystem services. Costanza and Daily proposed the value of ecosystem services, estimating the services that humans directly or indirectly obtain from the ecosystem in the form of currency [9]. This paper not only introduces the concept of ecosystem service function and expounds the service function provided by the ecosystem, but also proposes to evaluate the value of the ecosystem service function, which promotes people’s understanding of the importance of the ecosystem and its service function [1,10]. Ecosystem service function refers to the natural environmental conditions and effects that are formed and maintained by the ecosystem and ecological process. In 2003, The Millennium Ecosystem Assessment (MA) conducted by the United Nations divided the global ES into four categories, namely, supply services, regulation services, support services and cultural services. Recently, IPBES (The Intergovernmental Science–Policy Platform on Biodiversity and Ecosystem Services) has accounted for the economic value of ecosystem services, which is up to hundreds of trillion dollars, and the economic value generated by ecosystems [11]. In 2021, the United Nations launched the Economic Environment Ecosystem Accounting Framework (SEEA-EA), which further reflects that human beings are paying more and more attention to the value generated by the ecosystem, and visualizing and quantifying the value generated, so that we can clearly know the value generated by the ecosystem [12]. With the change of the ecological environment, people gradually realize that the ecological value of a region is not only related to the quality of the local natural environment, but also depends on the degree of understanding of the ecological environment and the degree of damage and control of the regional ecological environment. Therefore, scholars are looking for an indicator that can measure the contribution of ecosystems to human society. In 2013, Ouyang Zhiyun proposed the Gross Ecosystem Product (GEP) [13], which is the total value of products and services provided by ecosystems for human well-being and sustainable economic and social development. The Gross Ecosystem Product is a single currency to measure the contribution of an ecosystem to society to better reflect its value to that society. At present, GEP accounting methods are roughly divided into three categories, including energy-based [14], value transfer method [15] and Biophysical & monetary [16]. One of the important steps in the calculation process of the energy method is parameter localization, which has certain difficulties. The value transfer method has the advantage of requiring simple data, but its accounting results are not high. However, biophysics and monetary law are applied on many scales in China. Since the Gross Ecosystem Product was proposed, corresponding studies have been carried out on many scales. Zhang et al. calculated the gross value of ecosystem production at the national scale, and analyzed the ecological environment status of domestic provinces and cities in 2015 from the perspectives of GEP per unit area and per capita GEP [17]. At the provincial scale, from the perspective of ecological compensation, another study calculated the gross value of ecosystem production in the region, and promoted the establishment of regional ecological compensation standards [18]. At the city scale, according to local characteristics, a “mountain–sea–city” ecosystem gross product accounting system was constructed in another study to make up for the research gap in the study region [19]. At present, the GEP of the ecosystem is calculated from the national, provincial, county, village and single ecosystem scales [17,20,21,22,23,24,25,26].

However, island ecosystems have certain particularities, as they face complex natural and human-made disturbances and are easily damaged and difficult to recover [27,28]. With the rapid development of the economy, human activities have been strengthened, which has seriously affected the island ecological environment. Under the premise of ecological and economic progress, there is a lack of exploration of the total output value of island ecosystems. As an independent natural complex, the island is separated from the mainland, with limited land area, simple geographical composition, relative lack of natural resources, limited environmental capacity and poor stability. This is a typical fragile ecological environment area. Hainan Island, surrounded by the sea, is a tropical coastal island tourist destination. Compared with the mainland, the island’s biological population has a poor ability to self-recover and resist natural disasters, such as frequent typhoons, waves, rainstorms and other external factors [29]. Therefore, the island’s ecosystem is relatively fragile, and once the ecological environment is damaged, it is difficult to recover in a short time.

As one of China’s important ecological function zones and national “ecological civilization” pilot zones, Hainan‘s gross regional output value has risen from 202.053 billion CNY in 2010 to 553.239 billion CNY in 2020, and its per capita GDP has risen from 23,323 CNY to 55,131 CNY, showing an upward trend in GDP. The unique geographical location makes it a sensitive area of climate change and a fragile ecological environment. In the process of accelerating the construction of a free trade port with Chinese characteristics and a national ecological civilization pilot area, the acceleration of urban expansion and the change of land use types have had a profound impact on the ecological environment of the whole island. This study calculates the total ecosystem production value of Hainan Island from 2010 to 2020, quantifies the total ecosystem production value of different regions of Hainan Island in monetary form and compares the changes in the ecosystems of various counties in Hainan Island from the perspective of time and space. Our aim is to help scientifically quantify the services provided by Hainan Island’s ecosystem, recognize the deficiencies of the ecological environment, promote the sustainable development of Hainan Island, strengthen the protection of the ecological environment and provide scientific reference for the construction of a national ecological civilization experimental zone. The main purposes of this study are as follows: (1) To establish the accounting system of Hainan’s ecosystem GDP based on previous methods; (2) From the perspective of time and space, this study analyzes the changes of the gross ecosystem product of all districts and counties in Hainan Province; (3) Based on the previous results, corresponding suggestions are put forward to promote the sustainable development of Hainan Island, strengthen the ecological environment protection and provide scientific reference for the construction of the National Ecological Civilization Experimental Zone.

2. Materials and Methods

2.1. Study Area

Hainan Island is the second largest island in China, located at the southern end of the mainland, with a land area of over 34,400 km² (Figure 1). Hainan Island has a unique geographical advantage. It is warm all year round, with abundant rainfall, rich animal and plant resources, high vegetation coverage and a good ecological environment. As of 2020, Hainan Island had a resident population of 10.1234 million, employment of 5.4097 million and a regional GDP of 553.239 billion CNY, which is increasing year by year. In terms of ecological environmental protection, Hainan Province was the first province to propose ecological construction. In 2019, the state proposed to build the Hainan Provincial National Ecological Civilization Pilot Zone to protect the existing ecological environment and further improve the ecological environment on this basis.

2.2. Data Sources

The data used this study are shown in

Table 1. Data sources.

Type	Resolution	Sources
Land use	30 m	Resource science and satellite center (http://www.resdc.cn/, accessed on 28 September 2022)
DEM	30 m	Geospatial data cloud (http://www.gscloud.cn/, accessed on 28 September 2022)
Precipitation, soil data	1 km	National Earth System Science Data Center (http://soil.geodata.cn/data/dataresource, accessed on 28 September 2022)
Potential evapotranspiration data	1 km	The Qinghai-Tibet Plateau Scientific Data Center (https://data.tpdc.ac.cn/zh-hans/data, accessed on 28 September 2022)
Hainan Statistical Yearbook, Hainan Provincial Water Resources Bulletin, Hainan Environmental Quality Information Bulletin	/	Hainan Provincial People’s Government (https://www.hainan.gov.cn/, accessed on 28 September 2022)
China Environmental Statistical Yearbook	/	National Bureau of Statistics (http://www.stats.gov.cn/, accessed on 28 September 2022)
Price data	/	National Bureau of Statistics (http://www.stats.gov.cn/, accessed on 28 September 2022)
China Forestry Statistical Yearbook	/	National Bureau of Statistics (http://www.stats.gov.cn/, accessed on 28 September 2022)

.The ecosystem type map in this study comes from the Resource Science and Satellite Center (http://www.resdc.cn/, accessed on 28 September 2022), and the rainfall data comes from the National Earth System Science Data Center (http://soil.geodata.cn/data/dataresource, accessed on 28 September 2022); the digital elevation model (DEM) comes from the geospatial data cloud platform (http://www.gscloud.cn, accessed on 28 September 2022) AS-TER GDEM 30 m resolution data; the soil attribute data comes from the National Science and Technology Basic Conditions Platform-National Earth System Science Data Center-Soil Sub-center (http://soil.geodata.cn/data/dataresource, accessed on 28 September 2022); the potential evapotranspiration comes from the Qinghai-Tibet Plateau Scientific Data Center (https://data.tpdc.ac.cn/zh-hans/data, accessed on 28 September 2022); statistical data comes from the “Hainan Statistical Yearbook”, “Hainan Provincial Water Resources Bulletin”, “China Environmental Statistical Yearbook”, “Hainan Environmental Quality Information Bulletin” and the “China Forestry Statistical Yearbook”. The price data is sourced from the China Price Statistics Yearbook and converted according to the price index of that year. The GEP parameters are derived from official data and relevant references.

2.3. Research Methods

Gross Ecosystem Product (GEP) is the sum of the value of products and services provided by ecosystems to society. At present, the content of GEP accounting is calculated from the following three aspects: product value, regulation service and cultural service [13,30]. Gross ecosystem product is the sum of ecosystem product value, regulatory service value and cultural service value:

$$GEP=EPV+ERV+ECV$$

(1)

$$EPV={\sum }_{i=1}^{n}E{P}_i\times P_i$$

(2)

$$ERV={\sum }_{j=1}^{m}E{R}_j\times P_j$$

(3)

$$ECV={\sum }_{k=1}^{l}E{C}_l\times P_k$$

(4)

where GEP is the gross production value of the ecosystem, EPV is the ecosystem product value, ERV is the ecosystem regulation service value and ECV is the ecological cultural service value. $E{P}_i$ is the output of the i-th type of ecosystem product, $P_i$ is the price of the i-th type of ecosystem product, $E{R}_j$ is the amount of the j-th type of ecosystem regulation service function, $P_j$ is the price of the j-th type of ecosystem regulation service function, $E{C}_k$ is the k-th ecosystem cultural service function and $P_k$ is the price of the k-th ecosystem cultural services. The accounting index of this research is detailed in

Table 2. Accounting system of the gross domestic product of ecosystems on Hainan Island.

Service Type	Accounting Indicators
Product service	Agricultural products, forestry products, livestock products, marine aquatic products, water resources, renewable resources
Conditioning service	Water conservation, soil conservation, flood storage and regulation, air purification, water purification, carbon fixation and oxygen release, climate regulation
Cultural services	Natural landscape, tourism revenue

.

2.3.1. Ecosystem Products Provide Value

The value provided by ecosystem products refers to that obtained by human activities from the ecological environment for society. The value provided by the ecosystem products on Hainan Island was evaluated in this study from the amount of value generated by agricultural products, forestry products, animal husbandry products, fishery products and hydropower resources.

(1)

Gross output value of agriculture, forestry, animal husbandry and fishery

Agricultural products of Hainan Island include grain, oilseeds, hemp, tobacco leaves, medicinal materials, vegetables, melons, fruits, etc.; forestry products include wood; fishery products include freshwater aquaculture, marine aquaculture, etc.; animal husbandry products include grazing livestock, raising poultry, etc.

(2)

Hydropower resources value

Electricity resources refer to the total power generation of various types of hydropower stations on Hainan Island throughout the year, and the market value method is used to estimate the value of Hainan Island’s electricity resources. The island’s water resources mainly include agricultural irrigation water, industrial water, and residential water. Statistics of various types of domestic and production water were used in this study to calculate the economic value of water resources at the price of the year.

To sum up, in this paper, the gross production value of agriculture, forestry, fishery and animal husbandry; water resource value; and ecological energy value of Hainan Island are regarded as the value of the products and services provided by the ecosystem of the island to society.

2.3.2. Ecosystem Regulation Service Value

(1)

Water conservation value

The water conservation value is the economic value produced by various substances in the ecosystem to slow down surface runoff and improve water quality [31,32,33,34]. The value of ecosystem water conservation was calculated based on reservoir construction cost:

$$Q_w={\sum }_{i=1}^j\left(P_i-R_i-E{T}_i·A_i\right)$$

(5)

$$V_w=Q_w\cdot P_w$$

(6)

where $Q_w$ is the amount of water conservation (m³/a); $V_w$ is the value of water conservation services (CNY/a); $P_w$ is the engineering cost of the unit storage capacity of the reservoir (CNY/m³) [35]; $P_i$ is the rainfall (mm); $R_i$ is the rainstorm runoff (mm); $E{T}_i$ is the evapotranspiration (mm); $A_i$ is the area of the i-type ecosystem (m²); i is the Type i ecosystem type; and j is the number of ecosystem types.

(2)

Soil conservation value

Soil conservation is the difference between potential soil erosion and actual erosion. The soil conservation value was evaluated from the two aspects of reducing sediment deposition and non-point source pollution by using the substitution cost method, and the sum of the final value is the total value of the soil conservation value function [36,37,38,39]. The value of reducing sediment deposition is:

$$V_{s_1}=\lambda \cdot \frac{A_s}{\rho }\cdot P_s$$

(7)

where $V_{s_1}$ is the value of reducing sediment deposition (CNY/a); $\lambda$ is the sediment deposition coefficient; $A_s$ is the soil retention (t/a); $\rho$ is the soil bulk density (t/m³); and $P_s$ is the cost of the reservoir dredging project (CNY/m³) [40]. The value of reducing non-point source pollution is as follows:

$$V_{s_2}=A_s\cdot C_N\cdot P_N+A_s\cdot C_P\cdot P_P$$

(8)

where $V_{s_2}$ is the value of reducing non-point source pollution (CNY/a); $C_N$ and $P_N$ are the pure contents of nitrogen and phosphorus in the soil (%), respectively; and $P_N$ and $P_P$ are the environmental engineering degradation costs of nitrogen and phosphorus (CNY/t). The soil conservation was assessed by the soil loss equation (USLE) in the ecosystem of Hainan Island, and the soil conservation on Hainan Island was estimated based on previous studies [39,41,41,42,43,44].

(3)

Flood regulation value

The economic value of flood storage and adjustment on Hainan Island is characterized by the economic value of flood storage and adjustment in reservoirs and swamps. The value of flood regulation and storage in ecosystems was calculated based on reservoir construction costs.

Reservoir flood storage and transfer volume were estimated by building a model for reservoir flood control storage capacity and reservoir flood discharge times [45]:

$$C_r=C_t\cdot 0.35$$

(9)

where $C_r$ is the flood storage capacity of the reservoir (10,000 m³/a) and $C_t$ is the total storage capacity of the reservoir (10,000 m³). The amount of flood storage and regulation in swamps was calculated by constructing a model of surface water retention:

$$C_m=0.3\cdot S\cdot {10}^6$$

(10)

where $C_m$ is the swamp flood storage capacity (10,000 m³/a) and S is the total area of the swamp on Hainan Island (km²). The value of flood regulation and storage in the ecosystem of the island was calculated according to the total amount of reservoir and swamp regulation and storage multiplied by the storage capacity cost of the reservoir construction unit:

$$V_t=\left(C_r+C_m\right)\cdot P_w$$

(11)

where $V_t$ is the flood storage value (CNY/a) and $P_w$ is the engineering cost of the unit storage capacity of the reservoir (CNY/m³) [35].

(4)

Air purification value

The air purification value was calculated from the three main aspects of SO₂, nitrogen oxides and dust absorbed by the ecosystem by using the prevention and control cost method [18,21].

(5)

Water purification value

The value of water purification uses the prevention and control cost method to calculate the economic value of water purification by the ecosystem from the absorption of COD and NH3-N in the wetland ecosystem [18,21].

(6)

Carbon fixation and oxygen release value

The carbon sequestration (CO₂) and oxygen release (O₂) were selected as the evaluation indicators of the carbon sequestration and oxygen release capacity of the ecosystem. Carbon sequestration and oxygen release can be calculated by the carbon sequestration rate and net primary productivity (NPP). The carbon sequestration value can be calculated based on NPP and international carbon price, and the oxygen release value was estimated through NPP and medical oxygen production price. Finally, the carbon sequestration and oxygen release value of the ecosystem was obtained as [21,46,47]:

$$V_g=\left(NPP/0.45\right)\times \left(1.62\times CP+1.20\times C\right)$$

(12)

where $V_g$ is the carbon fixation and oxygen release value (CNY/a); $CP$ is the international carbon trading price; and C is the medical oxygen market price.

(7)

Ecosystem climate regulation function

The value of the ecosystem climate regulation function mainly refers to the value generated by endothermic cooling. The endothermic cooling value of the ecosystem includes two aspects: plant transpiration and water surface evaporation. According to the water surface area of Hainan Island and the electricity required to evaporate the same amount of water, the value of water vapor evaporation on the whole island is calculated [48] as shown in the following formula:

$$V_{\delta }=\frac{Q_e\times q\times p\times \epsilon }{\alpha \times 3600}+\beta \times Q_e\times p\times \eta$$

(13)

where $V_{\delta }$ is the value of ecosystem climate regulation; $Q_e$ is the annual evapotranspiration (m³); $q$ is the vaporization heat of water under standard atmospheric pressure (2.26 × 10⁶ J/kg); p is the electricity price; $\alpha$ is the air-conditioning energy efficiency ratio, taking value 3; $\epsilon$ is the operating coefficient of the air conditioner, generally set to 0.130; β is the power consumption per unit volume of water evaporation (125 kWh/m³); and η is the operating coefficient of the humidifier, generally set to 0.123.

2.3.3. Ecosystem Cultural Service Value

The cultural service value of the ecosystem refers to the viewing and entertainment value of the ecosystem obtained by people. This study mainly evaluates the cultural service value of Hainan Island from the total tourism income [17,21].

3. Results

3.1. Ecosystem Product Value

According to the statistical yearbook data of Hainan Province from 2010 to 2020, the total value of the functions provided by ecosystem products on Hainan Island was 72.95 billion CNY in 2010, 134.82 billion CNY in 2015 and 185.81 billion CNY in 2020. The growth rate was 86.05% in the first five years of the period and 37.82% in the last five, with an average annual growth rate of 9.8% for the decade. The total value of agriculture, forestry, fishery and animal husbandry has changed the most, from 70.803 billion CNY in 2010 to 183.900 billion CNY in 2020. Most of the counties and districts with higher values provided by agriculture, forestry, fishery and animal husbandry are located in the eastern part of the island (Figure 2). The use of water resources has been roughly stable at 4.4 billion m³ in the past 10 years, of which industrial water consumption has gradually decreased, and domestic water consumption has gradually increased. In 2020, the economic value of water resources for residents of Hainan Island was 2.116 billion yuan. From 1.154 billion kWh in 2010, the hydropower generation had an economic value of 0.67 billion CNY. By 2020, the total hydropower generation was 1.9 billion kWh, with an economic value of 1.14 billion CNY.

3.2. Ecosystem Products Regulate Service Value

3.2.1. Water Conservation Value

In 2010, the total amount of water conservation on Hainan Island was 33.648 billion m³, the total value of water conservation was 238.948 billion CNY and the unit area value was 7.02 × 10⁶ CNY/km². In 2015, the values were 19.825 billion m³, 160.919 billion yuan and 4.6 × 10⁶ CNY/km², respectively, and by 2020 were 26.424 billion m³, 266.029 billion CNY and 7.6 × 10⁶ CNY/km² (Figure 3), respectively. Among the ecosystem types on Hainan Island, the main contributors to water source and culvert services are forests, shrubs and wetlands. The forest ecosystem had the largest water conservation value in the past ten years, accounting for 68.67% of the total, followed by the shrub ecosystem and wetland ecosystem, accounting for 25.1% and 5%, respectively, and the sum of the three values was 98.14% of the total value of water conservation.

3.2.2. Soil Conservation Value

According to the general soil erosion equation, the average total soil conservation of the Hainan Island ecosystem in 2010, 2015 and 2020 was 8.1 × 10⁸ t. The total value of soil conservation was 31.096 billion CNY, 33.290 billion CNY and 39.688 billion CNY (Figure 4), respectively; the soil bulk density was 1.24 t/m³, and the pure content of nitrogen and phosphorus in the soil was 0.37% and 0.108%, respectively. In terms of the distribution of districts and counties, Qiongzhong City, Baisha City and Wuzhishan City had the highest soil conservation value. Among the ecosystem types on Hainan Island, the soil conservation values of the shrub, forest and grassland ecosystems were relatively large. The shrub ecosystem has the strongest soil conservation ability, which plays a key role in soil and water conservation on the island.

3.2.3. Flood Storage Value

According to the “China Water Resources Statistical Yearbook”, due to the topography of Hainan Island, there are no lakes on the island, so this paper only counts the service value of flood storage and regulation of reservoirs and swamps. In this study, the total value of flood storage and regulation generated by reservoirs and swamps in Hainan Island from 2010 to 2020 has risen from 194.15 billion CNY in 2010 to 429.2 billion CNY in 2020 (Figure 5). According to the evaluation model of lake flood regulation and storage function, it can be determined that in 2010, the water storage capacity of lakes and reservoirs was 3.5 billion m³, and the swamps were 39 billion m³. In 2020, the water storage capacity of reservoirs was 3.92 billion m³, and the swamp was 39 billion m³. After reviewing these statistics, it was found that swampy land plays a great role in regulating the flood storage and regulation of Hainan Island and can provide a large amount of economic value.

3.2.4. Atmospheric Environment Purification Value

The service value of atmospheric environment purification on Hainan Island was calculated from the sulfur dioxide, nitrogen oxides and dust particle emissions. According to the statistical data, it was found that the emissions of these three types of pollutants showed a certain downward trend in 2020, reaching 5900 t, 40,700 t and 9900 t, respectively. According to the price index of the year, the total economic value of atmospheric purification was estimated to be 0.206 billion CNY, of which the purification value of nitrogen oxides was the largest, accounting for 94%. From a spatial point of view, the cities with large emissions of air pollutants on Hainan Island are all located in the northwestern region. Among them, Danzhou City had the largest emissions of pollutants and value from 2010 to 2020 (Figure 6).

3.2.5. Water Purification Value

By analyzing the 2000–2020 Water Resources Bulletin of Hainan Province, and using the prevention and control cost method, the value of water purification services on Hainan Island from 2000 to 2020 was calculated. In 2010, the emission of ammonia nitrogen was 7015.3 t, the chemical oxygen demand was 92,333 t and the economic value was 2.0783 million CNY. In 2015, the emission of ammonia nitrogen was 21,028 t, the chemical oxygen demand was 187,938 t and the economic value was 4.8973 million CNY. In 2020, the emission of ammonia nitrogen was 8100 t, the chemical oxygen demand was 172,800 t and the economic value was 5.4364 million CNY (Figure 7). The value of water purification increased year by year, and chemical oxygen demand provided the largest value for water purification services, accounting for 98% in 2020. In terms of spatial distribution, Danzhou had the largest water purification value in 2010, 2015 and 2020, followed by Haikou and Wenchang.

3.2.6. Carbon Fixation and Oxygen Release Value

In 2010, the total amount of carbon sequestration was 0.14 billion t, and the total amount of oxygen released was 0.1billion t. The total value of carbon sequestration and oxygen release on Hainan Island in that year was 130.0 billion CNY, and the value per unit area was 0.0038 billion CNY/km². In 2015, the total amount of carbon sequestration in Hainan Island’s ecosystem was 0.2 billion t, and the total amount of oxygen released was 0.11 billion t. The total value of carbon sequestration and oxygen released was 148.7 billion CNY, and the value per unit area was 0.0043 billion CNY/km². In 2020, carbon sequestration was 0.15 billion t and oxygen released was 0.1 billion t, with a total value of 227.6 billion CNY and value per unit area of 0.0067 billion CNY/km². From Figure 8, it can be seen that most of the areas with high carbon fixation and oxygen release are located in the central part of the island with high elevation, and the forest coverage rate is as high as 55.38%, which makes the carbon fixation and oxygen release effect of vegetation more obvious.

3.2.7. Climate Regulation Value

Ecosystem climate regulation value refers to the economic value of vegetation and water surface to reduce atmospheric temperature and increase air humidity through transpiration and evaporation processes. The economic value produced by the climate regulation function in the region was obtained. According to the calculation, the total evapotranspiration of the ecosystem on Hainan Island in 2010 was 0.039 billion m³/year, and the economic value was 0.898 billion CNY (Figure 9). In 2015, the evapotranspiration was 0.043 billion m³/year, and the economic value was 1.202 billion CNY (Figure 9). In 2020, the evapotranspiration was 0.043 billion m³/year, and the economic value generated was 1.117 billion CNY (Figure 9). At present, areas with higher climate regulation values are located in the central part of the island, showing a decreasing trend from the central area to the surrounding areas. The value generated by Qiongzhong was the highest in the past three years, and the value generated by Danzhou was the lowest.

3.3. Ecosystem Cultural Service Value

This study selected the tourism income and tourism population of cities and counties on Hainan Island as the evaluation indicators for cultural adjustment services. According to the analysis of the “Hainan Provincial Statistical Yearbook”, the total tourism revenue of Hainan from 2010 to 2020 increased from 25.763 billion CNY in 2010 to 87.268 billion CNY in 2020 (Figure 10). The value of cultural services provided by Sanya and Haikou accounted for 70% of the value of cultural services in the province.

3.4. Change Analysis of GEP

From

Table 3. GEP of Hainan Island counties and cities from 2010 to 2020.

City	GEP(2010)	GEP(2015)	GEP(2020)
Baisha	205.82	274.52	353.56
Baoting	148.91	212.11	218.78
Changjiang	121.52	344.24	295.519
Chengmai	281.16	276.09	489.855
Danzhou	541.98	745.67	1108.81
Ding’an	234.08	277.37	332.85
Dongfang	345.42	697.92	795.20
Haikou	543.20	689.78	907.98
Ledong	358.15	583.96	817.06
Lingao	214.17	302.04	444.98
Lingshui	237.37	223.13	344.53
Qionghai	427.95	393.20	562.64
Qiongzhong	402.67	311.53	504.57
Sanya	403.66	628.93	957.04
Tunchang	191.31	244.88	257.39
Wanning	495.05	450.56	676.34
Wenchang	679.67	709.16	1071.95
Wuzhishan	131.95	117.17	181.90
Sum	5964.04	7428.31	10,320.96

, it can be seen that the GEP values of Wuzhishan City are the highest in each year, while those of Wenchang are the lowest in each year. The GEP values of Hainan Province are in turn Danzhou City, Wenchang City, Oriental City, Haikou City, Sanya City, Ledong County, Wanning City, Qionghai County, Changjiang County, Qiongzhong County, Lingao County, Dingan County, Chengmai County, Baisha County, Tunchang County, Lingshui County, Baoting County and Wuzhishan City in each year. The rankings of Wuzhishan City and Baoting County have not changed in each year, while the rankings of other counties and cities have changed slightly. The change trend of GEP values of each county and city in each year is the same as that of the total GEP values of Hainan Province, and gradually increases from 2010 to 2015.

Table 4. Comparison between GDP per unit area and GEP per unit area.

City	Unit Area GDP (2010)	Unit Area GDP (2015)	Unit Area GDP (2020)	Unit Area GEP (2010)	Unit Area GEP (2015)	Unit Area GEP (2020)
Baisha	0.011	0.019	0.027	0.097	0.138	0.167
Baoting	0.017	0.035	0.049	0.129	0.132	0.190
Changjiang	0.038	0.055	0.077	0.075	0.143	0.182
Chengmai	0.053	0.104	0.168	0.135	0.159	0.236
Danzhou	0.092	0.138	0.188	0.159	0.244	0.326
Ding’an	0.032	0.062	0.088	0.196	0.194	0.278
Dongfang	0.032	0.068	0.082	0.152	0.298	0.350
Haikou	0.270	0.499	0.782	0.237	0.279	0.396
Ledong	0.020	0.038	0.055	0.129	0.235	0.295
Lingao	0.053	0.114	0.152	0.159	0.239	0.331
Lingshui	0.047	0.120	0.176	0.214	0.230	0.311
Qionghai	0.066	0.119	0.171	0.250	0.253	0.329
Qiongzhong	0.009	0.015	0.022	0.149	0.125	0.187
Sanya	0.126	0.214	0.177	0.210	0.342	0.498
Tunchang	0.027	0.048	0.073	0.157	0.154	0.211
Wanning	0.052	0.090	0.125	0.260	0.282	0.356
Wenchang	0.048	0.072	0.107	0.276	0.289	0.436
Wuzhishan	0.012	0.021	0.030	0.115	0.116	0.159

shows that the total amount of GEP in Hainan Island’s ecosystem has not changed much, mainly concentrated in coastal areas. Although the total GEP of the central mountainous area is lower than that of the coastal area, the economic value of some individual indicators, such as carbon fixation and oxygen release value, climate regulation value, water and soil conservation value and water conservation value of the central area, is higher than that of the coastal area. On the contrary, the two accounting items of product provision value and cultural service value are passed. Comparing GEP per unit area with GDP per unit area, except Haikou, GEP in other counties and cities is far greater than GDP. These include, for example, Wenchang, Wanning, Qionghai, Lingshui, Ding’an, Qiongzhong, Tunchang, Dongfang, Baoting, Ledong, Lingao, Wuzhishan, etc.

4. Discussion

The unique geographical location of Hainan Province determines the importance of its ecological location, and the unique island ecosystem has certain vulnerabilities. As one of the national pilot zones for ecological conservation, Hainan’s goal is to achieve a world-leading ecological environment by 2035 and continue to improve the region. The ecosystem of Hainan Island provides many services to local residents, but in the past studies, few have calculated the GEP. In order to have a clearer understanding of the services that ecosystems provide to humans, through GEP accounting, people are encouraged to clearly understand the value that a good ecosystem brings to social and economic development.

(1)

This study calculated the total ecosystem production value of Hainan Island from 2010 to 2020, and the total ecosystem production value shows an upward trend. From the accounting results, the value generated by regulatory services accounts for the largest proportion, which is also consistent with the argument of relevant research. From the perspective of GEP distribution, GEP high value areas are mainly decreasing from northeast to southwest. The areas with a high value of regulation services are mainly located in the central mountainous areas of Hainan Island, and the top three services with the highest value are soil conservation, carbon fixation and oxygen release and water conservation. In 2020, the forest coverage rate in Hainan Province will be as high as 62.1%, which indirectly indicates that the natural ecosystems such as forests, shrubs and grasslands in Hainan Island have extremely important economic value in providing ecosystem regulation services. Therefore, it is necessary to protect and reasonably utilize the local ecological environment while developing resources.

(2)

Hainan Island is located in a tropical region, with extremely rich animal and plant resources. The overall distribution of its ecosystem GDP is mainly decreasing from northeast to southwest. Comparing the GDP per unit area with the GEP per unit area, it is found that the GEP value in economically developed areas is relatively low, while the GEP value in economically underdeveloped areas is relatively high, such as Wuzhishan, Baoting, Baisha, Qionghai, etc. At the same time, by comparing the value of GDP per unit area and GEP per unit area of Hainan Island, only Haikou’s GDP per unit area is greater than GEP per unit area. This is because Haikou’s cultural service industry ranks first in the province and lags far behind other districts and counties. For single accounting indicators, there are three primary indicators in GEP accounting: product providing value, regulating service value and cultural service value. The value of products provided is mainly concentrated in the eastern coastal areas of Hainan Island, and the cultural tourism services are mainly concentrated in Haikou and Sanya, while the other counties and cities are relatively low, presenting an unbalanced situation of cultural service resources. The trend of water conservation, soil conservation, carbon fixation and oxygen release and climate regulation in the value of regulation services is low around and high in the middle. Therefore, it is recommended that relevant departments formulate pertinent ecological measures based on the regional GEP value to convert the generated ecological value into economic value.

(3)

Comparing the three categories of accounting indicators, the value of the product provision and cultural service value is quite different from the value of the adjustment service. From 2010 to 2020, the adjustment service accounted for 73% of GEP. Therefore, the value of the adjustment service occupies a major position in the accounting process, and attention should be paid to the protection of the Hainan ecosystem. At the same time, it is necessary to strengthen the promotion of cultural tourism, hold cultural activities, increase the total tourism income and promote the entrepreneurial development of local residents. In terms of product provision and services, according to the existing ecological environment advantages, it is necessary to rationally plan and utilize natural resources; plant advantageous economic crops; breed advantageous aquatic products; focus on protecting reservoirs, swamps, and other resources; rationally develop hydropower resources; and make further progress for Hainan’s economic contribution.

(4)

From the perspective of social development, Hainan has a good ecological environment and rich natural resources. It is the internal demand to transform the advantages of ecological resources into economic advantages to promote the high-quality development of Hainan. In the GEP accounting process, it was found that each city has its own advantages; for example, Wuzhishan City and Baisha City have high carbon fixation and oxygen release value, high climate regulation value and low product supply value and cultural tourism value. However, the economic development of all districts and counties in Hainan Province is also uneven. Tourism is mainly concentrated in two cities: Haikou and Sanya. The value of urban cultural services in the central region is low. The production of agriculture, forestry, fishery and animal husbandry is mainly concentrated in the eastern coastal region. Therefore, it is suggested that the government should formulate appropriate social and economic development mechanisms according to the characteristics of each district and county’s own GEP value, such as developing eco-tourism, modern biomedicine, healthcare, ecological advantageous agriculture and other industries, and also establish ecological compensation mechanisms and ecological damage compensation mechanisms, make full use of Hainan’s unique ecological resources, and effectively convert ecological values into social and economic values.

(5)

This study has certain limitations and hysteresis, and the results have errors: (1) there are errors in the acquisition and processing of the remote sensing data and climate data used; and (2) due to different sources of reference statistical data, there are also errors in the unit price due to different years and regions.

Although there is a certain amount of error in the results, it should not affect people’s understanding of the value provided by the ecosystem of Hainan Island. The accounting results of this study show that the ecosystem of Hainan Island contains huge ecological benefits, which can reflect the overall ecological environment of Hainan Island and quantify and promote progress towards constructing an ecological civilization.

5. Conclusions

(1)

From the perspective of time, the total value of ecosystem production has increased from 596.404 billion CNY in 2010 to 1032.096 billion CNY in 2020. In the development of this decade, by comparing the accounting results from 2010 to 2020, the average annual growth rates from 2010 to 2015 and 2015 to 2020 were 5.64% and 8.57%, respectively, and sorted as 2020 > 2015 > 2010. The average annual growth rate of the value of products and services was 9.79%, the average annual growth rate of adjustment services was 4.41% and the average annual growth rate of cultural service value was 12.97%. The value of cultural adjustment services rose the fastest, followed by product provision services, and the growth rate of adjustment services was the smallest.

(2)

From a spatial point of view, among the three major indicators of the ecosystem gross product accounting, the district and county with the highest product offering value is Danzhou City, and the lowest is Wuzhishan City. The areas with higher product offering values are mainly distributed in the coastal cities of Hainan Island, and the central area is lower. However, the areas with higher regulatory service value are located in the central mountainous area of the island, and the surrounding coastal areas generate less value. The areas with higher cultural service value are mainly distributed in the eastern coastal area of Hainan Island, and the two cities with higher value are Sanya and Haikou. The distribution of ecosystem GDP of all cities and counties in the island is mainly concentrated in the northeast of the island, with Wenchang, Haikou and Danzhou having a higher ecosystem GDP and Wuzhishan, Baoting and Tunchang having a lower ecosystem GDP. By comparing GEP per unit area with GDP per unit area, only Haikou City has a GDP per unit area greater than GEP per unit area, while other cities have a GDP per unit area smaller than GEP.

(3)

Hainan has special resource advantages, such as South China Sea resources and tropical resources, as well as the largest special economic zone and the only provincial international tourism island in China. Island tourism is a popular tourism project. Under great human disturbance, the island ecosystem is damaged to some extent, leading to the destruction of the island ecosystem. The accounting of Hainan Island’s GEP can provide a reference for subsequent island GEP research, and also provide a reference for relevant government departments to formulate ecological compensation policies. In 2021, Hainan Province released the “Fourteenth Five-Year” Ecological Environment Protection Plan of Hainan Province, in which it clearly proposed that by 2035, the ecological environment quality and resource utilization efficiency should be at the leading level in the world. This study calculated the GEP of Hainan Island in order to provide a reference for Hainan’s ecological planning, ecological governance and ecological compensation. Different ecological planning and ecological governance are carried out for different regions, mainly including: (1) Fully publicize the great ecological value of Hainan and strengthen the participation of the whole people; (2) Establish a suitable ecological protection and development system for each city, customize a diversified ecological compensation mechanism for each city and transform the ecological value and economic value; (3) Create a model for ecological civilization construction and highlight the role of “Hainan Model”.

To sum up, the GEP of Hainan Island’s ecosystem shows a slow rise, and the adjustment service value among the three service values is the largest contributor to the GEP of Hainan Island’s ecosystem. The distribution of GEP of the island ecosystem mainly shows an increasing distribution from the southwest to the northeast. The distribution of ecosystem GDP in Hainan Island is mainly decreasing from northeast to south. Through the analysis of the preceding sequence, the accounting of Hainan Island GEP can not only provide a reference for the GEP accounting of the island, but also provide relevant government departments with corresponding development strategies to coordinate the development of society, economy and ecology.