# Economic Loss of Pine Wood Nematode Disease in Mainland China from 1998 to 2017
## 3 Results  
### Trends in Areas Infected by Pine Wood Nematode Disease in Mainland China from 1998 to 2017  
According to the fluctuation trend of the disease occurrence area, the pine wood nematode disease situation is divided into three stages in China. The first stage was from 1998 to 2001, when the pine wood nematode disease area showed a slowly rising trend. The second stage was from 2001 to 2013, during which the area of pine wood nematode disease showed a downward trend. The third stage was from 2013 to 2017, when the area of pine wood nematode disease increased rapidly (Figure 1). The area of pine wood nematode disease showed two extremes in 2001 and 2013. During the period from 1998 to 2001, the incidence area of pine wood nematode disease increased significantly, with an average annual increase of 5%, and reached to a maximum value of 84,688 hectares in 2001. During the period from 2001 to 2013, the incidence area of pine wood nematode disease showed a downward trend, and reached a minimum of 38,356 hectares in 2013. However, since then, the epidemic has expanded again, showing a more rapid growth trend than before, with an average annual increase of 22%, and the diseased area in 2017 reached 85,024 hectares (Table A1). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Service Type** & **Service Function** & **Equivalent Factor** \\ \hline \multirow{4}{*}{Regulating service} & Gas regulation & 1.70 \\  & Climate regulation & 5.07 \\  & Purifying the environment & 1.49 \\  & Hydrological regulation & 3.34 \\ \hline \multirow{4}{*}{Support service} & Soil retention & 2.06 \\  & Maintain nutrient cycling & 0.16 \\  & Biodiversity & 1.88 \\ \hline Cultural service & Aesthetic landscape & 0.82 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Equivalent service value of forest ecosystem per unit area of coniferous forest. At the provincial level, in the past two decades, pine wood nematode disease has broken out in a total of 18 provinces in China, and the severity of pine wood nematode disease has varied among regions (Figure 2). Jiangsu, Zhejiang, Anhui, Shandong and Guangdong Province have experienced pine wood nematode disease for 20 consecutive years. Henan, Guangxi, Sichuan, and Yunnan provinces got infected again after the epidemic area was successfully removed. Among them, the cumulative disease in Henan and Yunnan Provinces occurred for less than 10 years, and in Guangxi and Sichuan Provinces it occurred for more than 10 years. The pine wood nematode disease was discovered between 2000 and 2002 in Shanghai, and the epidemic area was successfully removed afterwards; Liaoning Province was the new epidemic area in 2016. From the spatial perspective, the scale infected declined from the east to the west in general. The province with the most severe pine wood nematode disease is Zhejiang Province, with an average annual diseased area of 22,667 hectares, followed by Guangdong Province, with an average annual diseased area of 15,333 hectares, and Jiangsu Province, with average annual diseased area of 12,667 hectares. The other provinces all had diseased areas of less than 6667 hectares. The average annual area infected in Guangxi, Guizhou and Yunnan Province was less than 667 hectares, and the average annual area infected in Shanghai was only 16 hectares. Overall, Zhejiang, Guangdong, Jiangsu, and Anhui provinces were the provinces most severely infected by pine wood nematode disease for 20 consecutive years, and the cumulative diseased area was greater than 66,667 hectares. Liaoning Province had an average annual area of 1594 hectares, and the disease spread rapidly. At the same time, due to the northeast forest farm and the high geographical latitude, Liaoning Province is the front line for the northward spread of pine wood nematode disease. Pine wood nematode disease has occurred in the southern region for 20 consecutive years, and the disease area has been increasing, and spreading rapidly to the north (Table A2).