Lin WANG*, Li WANG2, Jinxiang WANG

1. College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China; 2. Center of Energy and Environment Technology, Harbin Institute of Technology, Harbin 150001, China

Abstract In this paper, remote sensing accounting model was used to assess the ecological capital of Baita Town, Weifang. Based on the present situation of the town, NPP statistical model was constructed on the GIS platform based on the relationships between NPP, LAI and NDVI. After loading the ground statistics, the ecological capital in the town was accounted. In 2015, the ecological capital of Baita Town was 175 245 600 yuan, and the gross domestic product (GDP) of the town was 308 380 000 yuan, that is, the ecological capital was 0.57 times the amount of GDP.

Key words Ecological capital, Small town, Assessment model, Remote sensing accounting model

1 Introduction

R. Costanzaetal.[1-2]proposed the concept of natural capital in 1997. In 1999, Huang Xingwen defined ecological asset as "an ecological landscape entity for which the owner implements ecological ownership and from which the owner can obtain economic benefits"[3]. Wang Jianminetal.[4-5]believe that ecological assets are state-owned ecological economic resources that can be measured in monetary terms and that can bring direct, indirect or potential benefits. In the 1970s, Holdern[6], Westman[7]and other scholars began research on global ecosystem services, and the concept of ecological asset value assessment also emerged. The more mature assessment methods used abroad include InVEST model[8], ESR model, ARIES model, SoLVES model[9]and so on. The more mature assessment methods used in China mainly include estimating ecological assets based on the unit area value and conducting remote sensing estimation for ecological assets through establishing measurement models[10]. Based on the value system of Costanza[1], Xie Gaodietal.[11]established a value standard system for domestic ecological asset assessment. Freeman[12]publishedEnvironmentandResourceValueAssessment:TheoryandMethodologyin 1993, in which the framework of the ecological capital value assessment method system was constructed. Zhu Wenquanetal.[13]used remote sensing technology to dynamically assess China’s terrestrial ecological assets. However, the estimation on ecological assets in most current studies is below the total value of the ecological assets, and they only calculated the value of ecological services[10]. For the estimation of total amount of ecological assets, many scholars such as Carraro, Siniscalco, Rubio and Goetz integrated ecological capital into the ecological growth model to establish an endogenous economic growth model with environmental resources[14]. In terms of research scope, indicator system and accounting method, corresponding management strategies and recommendations based on social development and ecological assets are still not in place[10]. At present, the scale of research at home and abroad is mostly city. There are few studies on ecological capital accounting for towns. Limited by town’s scale and materials, existing methods are often difficult to achieve the desired results.

2 Overview of the study area

Baita Town (118°42′58″-118°48′22″ E, 36°16′55″-36°23′52″ N) of Changle County, Weifang City is located in the middle of Shandong Province, covering an area of 57.6 km2. It is located at the junction of Changle, Linqu and Anqiu counties. In Baita Town, there are 17 administrative villages, 39 natural villages, 6 549 households, 22 898 people and 1 736 ha of cultivated land. The cultivated land per capita in Baita Town is only 0.075 ha, and even worse, more than 90% of that is barren mountains.

The Gaoya Reservoir in the jurisdiction is a first-class water source in Shandong Province and a national important drinking water source. It is the most important water source in Changle County and even Weifang City. The total storage capacity and usable storage capacity of the reservoir are 150 million and 57.88 million m3, respectively, which is a national second-class reservoir.

3 Accounting methods for ecological assets

Ecological capital accounting methods can be roughly divided into two categories: one is the commonly used accounting methods, and the other is the model accounting methods. The commonly used accounting methods include direct market value method, alternative market value method, hypothetical market assessment method and energy analysis approach. The ecological capital model accounting methods mainly include InVEST model[8], ESR model, ARIES model, SoLVES model[9]and so on. The commonly used accounting methods do not fully consider the types of ecosystems in the study area and the differences between different regions, and they are difficult to accurately reflect the true value of the ecosystems. The remote sensing accounting models can avoid errors caused by interpolation using ground observations. What’s more, they can precisely invert some ecological and non-ecological parameters. Building a remote sensing accounting model on the GIS platform and loading ground statistics will help to realize the automated assessment of regional ecological capital. This study selected the removing sensing accounting model method.

(i) Calculation of ecological capital. Ecological capital is the sum of all service functions and natural resource values provided by ecosystems in the region[15]. Its calculation formula is as follows:

(1)

whereVis the total value of ecological capital;C=1, 2, …,nrepresents the type of ecosystem;Vcrepresents the ecological value of the ecosystem of typeC. The calculation formula ofVcis as follows:

(2)

whereirepresents thei-th ecological service function of the ecosystem of typeC;Vcirepresents the unit area value of thei-th ecological service function of the ecosystem of typeC;jrepresents the number of patches in whichVciis spatially distributed in a certain area;Sijrepresents the area of plaque;Rijrepresents the ecological parameter ofVciin different plaques, depending on the quality of the ecosystem, usually characterized by vegetation coverage (f) and net primary productivity (NPP)[15]. The calculation formula ofRijis as follows:

Rij=(NPPj/NPPmean+fj/fmean)/2

(3)

where NPPmeanis the mean value of net primary productivity;fmeanis the mean value of vegetation coverage; NPPjis the net primary productivity of vegetation in thej-th plaque; andfjis the coverage of vegetation in thej-th plaque.

(ii) Calculation of NPP. NPP refers to the amount of organic matter accumulated in vegetation per unit time and unit area[16]. It is a common method to conduct relevant research using MODIS NPP data[17-18]. However, the resolution of MODIS NPP data is 1-10 km. It is difficult to meet the needs of quantitative research at small town scale. Climate-related models use fewer parameters, and their calculation is simple, such as the Miam model[19]and the Thornthwaite model[20]. The Miam model believes that the main factors affecting NPP are annual average temperature and annual rainfall, so it is a statistical model of annual average temperature, annual rainfall and NPP. The Thornthwaite model takes into account the effects of factors such as the soil, topography and biological characteristics of plants, and it is a statistical model of evapotranspiration and NPP. These two models are widely used in large-scale NPP estimation[21-22]. At a larger scale, the spatial distribution map of meteorological data is obtained by interpolation of meteorological data, and then the spatial distribution map and spatial distribution characteristics of NPP are obtained through further calculation. The scale of town is small. It is impossible to interpolate meteorological data to obtain a surface layer, that is, NPP spatial distribution map could not be available using climate-related models.

The net primary productivity of vegetation is significantly correlated with the leaf area index (LAI). The normalized vegetation index (NDVI) can sensitively reflect changes in LAI[23]. Based on the relationships between NPP, LAI and NDVI, Zheng Yuanrun proposed the NPP statistical model[24]:

NPP=-0.639 4-67.064×ln(1-NDVI)

(4)

(iii) Calculation of vegetation coveragef. Vegetation coveragefis calculated by the normalized vegetation index (NDVI)[25], which is the best indicator to reflect plant growth and spatial density[26].

(5)

NDVI is obtained through combining two bands of the spectrum, based on the differences in absorption characteristics of plants and land types between red and near-infrared bands. The calculation formula is as follows[27]:

(6)

whereρNIRand ρredare the near-infrared reflectance and the red-band reflectance, respectively.

4 Accounting and analysis of ecological assets

4.1 Service value of ecosystemCostanzaetal.[1-3]made the principles and methods of ecosystem service value accounting clear in a scientific sense, and estimated the service value of various ecosystems item by item. However, his accounting standards have large errors in the application of certain ecosystems. Referring to the research results of Costanza, Xie Gaodi[28]assumed that the strength of ecological service function is linear with biomass, and developed a table of equivalent factors for the ecological service value of China’s cultivated land (Table 1). The equivalent factors for ecological service value in each province are given. The biomass factor of Shandong Province is 1.38[29].

Table 1 Equivalent factors of cultivated land ecosystem

EcosystemserviceEquivalentfactorGrainproduction1.00Materialsupply0.10Waterconservation0.60Landscapeentertainment0.01Soilformationandconservation1.46Wastetreatment1.64Biodiversitymaintaining0.71Gasregulation0.50Climateregulation0.89

Xie Gaodi proposed that the economic value of an ecological service value equivalent factor is equal to 1/7 of the national average grain yield market value[28]. According to the national average grain price in 2015, the service value of cultivated land ecosystem in China and Shandong Province was calculated. The results are shown in Table 2.

Table 2 Value of services of cultivated land ecosystemyuan/(ha·year)

EcosystemserviceValueofChinaValueofShandongProvinceGrainproduction1786.972466.02Materialsupply178.70246.60Waterconservation1072.181479.61Landscapeentertainment17.8724.66Soilformationandconservation2608.973600.38Wastetreatment2930.634044.27Biodiversitymaintaining1268.751750.87Gasregulation893.481233.01Climateregulation1590.402194.75Total12347.9517040.17

Referring to the ecological service value equivalent table of ecosystems in China, combined with the composition of land use in the town, the ecological service value equivalent table of the ecosystems in the town was formulated. The results are shown in Table 3.

According to the relationships between equivalent factors for forest land, grassland, water body, garden land, bare land, construction land and cultivated land, the value of the ecosystem services of the six land use types was calculated, and the results are shown in Table 4.

4.2 Net primary productivity of vegetationUsing the pre-processed remote sensing image, NDVI was calculated (Fig.1). The value of NDVI was substituted into Formula (4) to calculate the net primary productivity of vegetation. The results are shown in Fig.2.

Table 3 Equivalent table of service value of ecosystems in Baita Town

EcosytemserviceForestlandGrasslandWaterbodyGardenlandBarelandConstructionlandGrainproduction0.100.300.100.2000.010Materialsupply2.600.050.011.32500Waterconservation3.200.8020.382.0000.030Landscapeentertainment1.280.044.340.6600.010Soilformationandconservation3.901.950.012.9250.020Wastetreatment1.311.3118.181.3100.010Biodiversitymaintaining3.261.092.492.1750.340Gasregulation3.500.8002.15000Climateregulation2.700.900.461.80000

Table 4 Value of ecological services of ecosystems in Baita Townyuan/(ha·year)

EcosytemserviceForestlandGrasslandWaterbodyGardenlandBarelandConstructionlandGrainproduction246.60739.81246.60493.2024.660Materialsupply6411.65123.3024.663267.480.000Waterconservation7891.261972.8250257.494932.0473.980Landscapeentertainment3156.5198.6410702.531627.5724.660Soilformationandconservation9617.484808.7424.667213.1149.320Wastetreatment3230.493230.4944832.243230.4924.660Biodiversitymaintaining8039.232687.966140.395363.59838.450Gasregulation8631.071972.8205301.9400Climateregulation6658.252219.421134.374438.8400Total53882.5417853.98113362.9435868.261035.730

Fig.1 NDVI of Baita Town

Fig.2 NPP of Baita Town

4.3 Vegetation coverageVegetation coverage refers to the ratio of the vertical projection area of vegetation to the area of the entire study area. The calculation results of NDVI were analyzed. According to Formula (5), vegetation coverage (f) was calculated. The results are shown in Fig.3.

Fig.3 Vegetation coverage in Baita Town

4.4 Total amount of ecological capitalUsing ArcGIS and ENVI software, the value of each parameter was substituted into the calculation formula of ecological capital to calculate the ecological capital of the town in 2015. The calculation results about the ecological capital of Baita Town are outputted, as shown Fig.4. Water showed the biggest ecological capital per unit area, reaching 9 142 800 yuan/km2. After analysis, it was found that this was mainly because that the water conservation, landscape entertainment and self-purification capacity of water body were much higher than those of other land use types. The ecological capital per unit area of forest land ranked second, which was 5 494 900 yuan/km2. Forest land shows an obvious role in water conservation, soil formulation and conservation, biodiversity maintaining and gas regulation. The ecological capital per unit area of garden land ranked third, 3 763 700 yuan/km2. The ecological capital per unit area of grassland (1 812 700 yuan/km2) and cultivated land (1 734 300 yuan/km2) was close to each other.

According to statistics, the ecological capital of Baita Town in 2015 was 175 245 600 yuan. In 2015, the GDP of the town was 308 380 000 yuan. The ecological capital was 0.57 times as big as GDP. The ecological capital per unit area was 3 154 700 yuan/km2. This value is much higher than the ecological capital per unit area of grassland and cultivated land, is close to the ecological capital per unit area of garden land, and is close to the average ecological capital of Chongqing in 2000 and lower than its ecological capital in 2010[30]. The town’s ecological capital was mainly composed of water, cultivated land and forest land, of which the ecological capital accounted for 51.65%, 33.13% and 13.11%, respectively of the town’s ecological capital. The results are shown in Table 5.

Fig.4 Ecological capital of Baita Town in 2015

Table 5 Total ecological capital of Baita Town

ForestlandGrasslandCultivatedlandGardenlandWaterbodyBarelandConstructionlandTotalEcologicalcapital∥104yuan2296.87208.465802.85161.849051.413.13017524.56Proportion∥%13.111.1933.110.9251.650.020100

5 Conclusions

According to the characteristics of land use in Baita Town and the ecological service functions of each land use type, the land use types in the town were merged into forest land, garden land, grassland, cultivated land, water body, bare land and construction land.

The ecosystem services of Baita Town were divided into supply service, support service and regulation service. The examples of supply service mainly include taro, grain planting, fishing, wood, crop straw and water source conservation forest. The examples of support services mainly include reservoir landscape belt, vegetation to prevent surface soil erosion and self-purification of water to provide habitats. The examples of regulation service mainly include absorption of CO2, release of O2, adjustment of temperature and alleviation of greenhouse effect.

NPP is an important parameter for the calculation of ecological capital. According to the existing conditions of the town, the NPP statistical model constructed based on the relationships between NPP, LAI and NDVI was selected for ecological capital accounting. The calculation results show that in 2015, Baita Town’s ecological capital was 175 245 600 yuan, and the gross domestic product (GDP) was 308 380 000 yuan,i.e., the ecological capital was 0.57 times the amount of GDP. The ecological capital per unit area was 3 154 700 yuan/km2, which was much higher than the ecological capital per unit area of grassland and cultivated land and close to the ecological capital per unit area of garden land. The composition of ecological capital is dominated by water, cultivated land and woodland, of which the ecological capital accounted for 51.65%, 33.13% and 13.11%, respectively of the town’s ecological capital.