Dynamic Analysis Of Coniferous Forest And Potential Distribution Of Bursaphelenchus Xylophilus Based On Landsat Images

Forest resources closely affect the change of the ecological environment. As the important component of urban forest of Nanjing, coniferous forest dynamic changes are crucial to the change of urban ecological environment. Bursaphelenchus Xylophilus is a kind of deadly disease, which mostly occurs in the coniferous forest and spreads rapidly in the short term. Bursaphelenchus Xylophilus has created serious harm on pine forest. So, it is greatly important to study the potential regions of this disease so that the relevant departments can take effective measures in advance to prevent the disease. The effective precaution of Bursaphelenchus Xylophilus play a crucial role in maintaining the forest health and its sustainable development.In this study, the study area is located in the scenic forest region in Purple Mountain and the Landsat images including 5 yeasof 2000, 2002, 2006, 2008 and 2011 were chosen and pretreated. On the basis of the data collection and pretreatment, the classification method, random forest, was firstly used to discriminate the coniferous forest from other objects and then, dynamic changes of coniferous forest during ten years were analyzed. The third, the different occurrence trends of Bursaphelenchus Xylophilus disease among ten years were analyzed according to the changing characters of coniferous forests of the primary factors which determined the onset of Bursaphelenchus Xylophilus were confirmed as topographic factors and meteorological factors. Finally, fuzzy comprehensive evaluation method was used to calculate suitable values of Bursaphelenchus Xylophilus disease occurrence and the potential distribution regions in Purple Mountain were simulated.The results showed that:(1) The classification method, random forest, was used to extract coniferous forest information and the arrcury achieved about 80%. Through the analysis of coniferous forest information, it could be found that the area of coniferous forest was on the decline. And changes of coniferous forest were affected by many factors, according to meteorological datas over ten years and the fact that Bursaphelenchus Xylophilus disease is managed strictly, it could be drawn that pests and diseases was the primary factor of the changing characters of conifer forests. According to the survey, Bursaphelenchus Xylophilus disease is one of the six most harmful pests and diaeases which mainly occurs on coniferous forest as only one. So, it could be considered that Bursaphelenchus Xylophilus disease was the primary factor of the changing characters of conifer forests, and then the change regions of the coniferous forest were similar to high-risk regions of Bursaphelenchus Xylophilus disease.(2) Compared with 2004-2011 year census data of Bursaphelenchus Xylophilus disease in the scenic forest region in Purple Mountain, the area of possible regions of Bursaphelenchus Xylophilus disease changed the biggest from 2006 to 2008 year, which trended coincide with the maximun number of dead wood from 2006 to 2008 year. It explained that it was credible that the change regions of coniferous forest were similarly as possible regions of Bursaphelenchus Xylophilus disease. And the correctness of extraction of coniferous forest information was tested and verified.(3) In distribution area of coniferous forest, suitable value of sample points of possible regions and impossible regions of Bursaphelenchus Xylophilus disease was almost same and both more than 0.9. Potential distribution regions of Bursaphelenchus Xylophilus disease in the scenic forest region in Purple Mountain was simulated, which showed that Bursaphelenchus Xylophilus disease was suitable for surviving in the whole distribution regions of coniferous forest. In fact, the scenic forest region in Purple Mountain is actually high-risk areas of Bursaphelenchus Xylophilus disease. The result of the study is consistent with the reality.