# Economic Loss of Pine Wood Nematode Disease in Mainland China from 1998 to 2017
## 2 Materials and Methods
### Economic Loss Evaluation
#### 2.2.1 Direct Economic Loss Evaluation  
Economic loss evaluation methods mainly include the market price method, opportunity expenditure method, contingent value method, and the benefit transfer method [39], while there is also the multiple method, which comprises the biomass estimation method and curve evaluation method [40; 41]. The market price method is simple and can quickly calculate and obtain the evaluation results, while the opportunity expenditure method, the contingent value method and the benefit transfer method can better reflect people's willingness to pay and have dynamic characteristics. The multiple method is mainly based on the results of China's forest resource value accounting, and the evaluation results reflect the national average. In the actual assessment at the province level, there will be big differences between regions. The biomass estimation method can be applied for different regions, forest stands and forest ages, but the calculation is burdensome; the curve method requires a large number of forest stands covering tree species, thus in practice, it is difficult to collect data on the growth law of forest age and the annual growth loss rate of forest trees caused by diseases. Therefore, we chose the market value method to assess direct economic losses, which is highly practical. \begin{table}
\begin{tabular}{c c c} \hline
**Evaluation Method** & **Secondary Indicator** & **Tertiary Indicator** \\ \hline \multirow{8}{*}{Direct Economic Loss} & Loss of forest material resources & Loss of forest volume \\  & Loss of forest by-products \\ \cline{2-3}  & Loss of prevention and & Loss of prevention and control expenditure \\  & control expenditure & \\ \cline{2-3}  & Ineffective forestry expenditure & Ineffective afforestation expenditure \\  & Ineffective trending expenditure & Ineffective management and \\  & & maintenance expenditure \\ \hline \multirow{8}{*}{Indirect Economic Loss} & Loss of gas conditioning service & Loss of climate regulation service \\  & Adjustment service value loss & Loss of purification of environmental service \\  & & Loss of hydrological regulation service \\ \cline{1-1} \cline{2-3}  & Support service value loss & Loss of soil conservation services \\ \cline{1-1} \cline{2-3}  & & Loss of nutrient recycling service \\ \cline{1-1} \cline{2-3}  & & Loss of biodiversity service \\ \cline{1-1} \cline{2-3}  & Cultural service value loss & Loss of aesthetic landscape service \\ \hline \end{tabular}
\end{table} 
Table 1: Evaluation index system for economic loss of pine wood nematode disease. Loss of forest volume: The loss of standing wood volume growth or stand cumulative growth volume caused by pine wood nematode disease. The results calculated using the formula of growing wood volume loss (Equation (1)) are shown [30]. \[La=S\times Ad\times Ta \tag{1}\]  
where \(La\) is the loss of forest volume; \(S\) is the annual loss area of pine wood nematode disease; \(Ad\) is the annual growth loss per unit area; and \(Ta\) is the forest price per unit stock. Loss of forest by-products: The loss of forest by-products (pine resin) caused by pine wood nematode disease is calculated using Equation (2). \[Lo=Y\times S\times P \tag{2}\]  
where \(Lo\) is the loss of forest by-products; \(Y\) is the annual average yield per unit area of healthy forests; \(S\) is the annual loss area of pine wood nematode disease; and \(P\) is the average price of pine resin in its origin. Loss of prevention and control expenditure: The expenditure on investigating and monitoring the epidemic situation in epidemic areas, the removal and treatment of epidemic wood, the prevention and control of epidemic areas and the prevention of non-epidemic areas [42]--this is called ineffective expenditure when the forest is infected by the pine wood nematode disease. Equation (3) is used for calculation.