# Economic Loss of Pine Wood Nematode Disease in Mainland China from 1998 to 2017
## 2 Materials and Methods
### Economic Loss Evaluation
#### 2.2.2 Indirect Economic Loss Evaluation Method  
The indirect economic loss caused by forest diseases and insect pests mainly comes from the loss of non-market economic value [44], including the loss to the social and ecological environment. Although the indirect economic loss of forest pests and diseases and the loss of the value of forest ecosystem services are two different concepts, they are consistent in the evaluation content [30]. The method for evaluating the value of forest ecosystem services was firstly created by [PERSON] et al. in _Nature_[45]. The evaluation was based on the economic theory that the total economic value of resources is the sum of the surplus of producers and consumers. Since then, domestic scholars have evaluated the service value of China's terrestrial ecosystems on the basis of this, and they all used parameters provided by [PERSON] in their evaluation process [46; 47; 48]. Through a questionnaire survey, [PERSON] et al. obtained an equivalent scale of ecological service value per unit area of the ecosystem, and constructed a method for valuing ecosystem services [49]. Later, using model calculations and geographic information spatial analysis methods, a dynamic evaluation method for the service value of China's terrestrial ecosystem was proposed and the service value of China's terrestrial ecosystem in 2010 was evaluated [50]. Among these methods above, the ecological service value equivalent per unit area of the ecosystem proposed by [PERSON]'s method is more consistent with China's national conditions and has the characteristics of dynamic evaluation. Therefore, [PERSON]'s dynamic equivalent factor method is used for economic losses caused by wood nematode disease in this study. The Value of One Standard Unit Ecosystem Service Value Equivalent Factor  
A standard unit ecosystem service value equivalent factor (hereinafter referred to as the standard equivalent) refers to the economic value of the annual natural grain output of farmland with an average national output of 1 \(\mathrm{hm}^{2}\)[51]. In order to eliminate the interference of human factors and accurately measure the economic value of the grain output by the farmland ecosystem under natural conditions, this study determined that the economic value of an ecological service value equivalent factor is equal to the national average grain yield market value [52]. In practice, the market value of the three main grain crop yields can be selected instead of the national average grain yield market value [49]. In addition, considering people's willingness to pay for the value of forest ecosystem services, this study uses the development stage coefficients that characterize the relative level of willingness to pay to modify the theoretical value of forest ecological service values to obtain the realistic value [53]. Basic Equivalent Scale of Ecosystem Service Function Value Per Unit Area  
This is achieved by referring to [PERSON]'s [50] research and using its coniferous forest ecosystem basic equivalent table (Table 3). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Description** & **Value/Unit** \\ \hline _Ta_ & Forest price per unit stock & 341.18 (CNY/m\({}^{3}\)) \\ _Ad_ & Annual growth loss per unit area & 3.55 (m\({}^{3}\)/hm\({}^{2}\)) \\ \(Y\) & Annual average yield per unit area of healthy forests & 1350 (kg/hm\({}^{2}\)) \\ \(P\) & The average price of pine resin in its origin & 15.25 (CNY/kg) \\ _Cp_ & Prevention and control expenditure per unit area & 1783.50 (CNY/hm\({}^{2}\)) \\ _Cc_ & Afforestation expenditure per unit area & 14,293.15 (CNY/hm\({}^{2}\)) \\ _Ct_ & Tending expenditure per unit area & 1748.22 (CNY/hm\({}^{2}\)) \\ _Cm_ & Management and maintenance expenditure per unit area. & 1260.74 (CNY/hm\({}^{2}\)) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameter description table. Construction of Dynamic Equivalent Scale of Ecological Service Value Per Unit Area  
Water supply and hydrological regulation are related to changes in precipitation.