Landscape Ecological Analysis Of Pine Wilt Disease In The Three Gorges Reservoir Region

Pine wilt disease(the pothegen is pine wood nematode,Bursaphelenchus xylpohilus,PWN)is the most devastating pine tree disaster in China,even in the world.It took a irreversible damage to the global forest ecological system and enviroment.Since 1980s,the disease spreaded into China and heavily damaged our pinewood resources and quality,landscape pattern and environment.It became one of the most dangerous quarantine pest.The proverious studies showed that the hosts of PWN are mainly different pines and extended widely.Pinus massoniana is the main host of PWN in china.After several decades studies,there still didn't have an effective method to control it.The Three Gorges Reservoir Area is the main water resources and hydropower engineering in China,which has an important ecological status.However,the pine trees have suffered pine wilt disease for a long time,and the pine resource and quality seriously declined,and give a great threat to ecological security.In the recent years,invasion species are becoming a hotspot in the large scale.Landscape ecology is a interdiscipline in theoretical and practical significance.Its research scale is above individual,population,community and ecosystem,and covers a wide range and scale,and provide a theory support for studying pine wilt disease which has a multiple and complex infestation cycle.In this research,we took the cities Yi Chang and Chong Qing in Three Gorges Reservoir Area as object,utilized the landscape ecological methods and tools,and linked the pine wilt disease with landscape pattern,aiming at the land planning and regional development.According to the biological characteristics of Monochamus alternatus and B.xylpohilus,we reclassified the land use types,and analysized from three space scales.At district space scale,we searched the relationship between different landscape patterns and pine wilt disease,and assessed the ecological risk.At city space scale,we searched the relationship between pine wilt disease and host and anthropogenic patch,and analyzed the situation based on the main factors.At region scale,we searched the relationship between pine wilt disease and human activities,and forecasted the risk based on main factors.At last,we proposed preventive and control strategy.The results were showed as follows.1.Takes Yi Ling district for research and analysis.The largest area and area?mn of landscape type was forestry landscape,and among them,the coniferous type was the largest one.The most complicated degree of fragmentation(Ci)was water landscape.The most larggest separation(S_i)was traffic landscape.The highest dominance(Di)was other forest landscape,and coniferous forest area was followed.Based on the biological characteristics and flying ability of vector insect M.Alternatus and landscape ecological safety standard,we analyzed the differences of heterogeneous patches to pine wilt disease.As traffic roads is the main factor of road network density,and the results shows it has a significant positive correlation in chapter 4,the ecological resistant to impede M.alternatus flying ability from large to small were water landscape,anthropogenic landscape,other forsts landscape and agriculture landscapeand traffic road landscape.The risk assessment in Yi Ling showed that the midland had a high risk,and the tendency became low in the edge which might be correlated with forest and coniferous coverage.The area along the Yangtze River had a higher risk,the reason of which was the frequent human activity close to Yangtze River and its branches.Particularly in the area of Three Gorges Dam,the risk level was highest.The results showed the distance between the neighboring investigation sites was more than 50 km,and the risk had no correlation with the distance,and had a linear correlation within 50 km,which meant the high risk.2.Using the classical landscape ecological indice,we analyzed four districts which were Yi Chang Municipal district,Yi Du,Yi Ling and total area.we searched out the relationship of host patch and anthropogenic patch landscape pattern with pine wilt disease.The results showed that the situation of pine wilt disease has a positive correlation with host patch landscape shape index.The anthropogenic patches had no significant correlation with pine wilt disease.From the total and two districts analysis,host patch(pine tree)was the vital reason affecting pine wilt disease,and the distribution area and complexity has a positive correlation with pine wilt disease.Human activities was deemed to a important factor affecting the disease,but this disease had no correlation with anthropogenic patch which might be caused by the absense of considering human activity intensity and need a further study.3.In order to study the effect of human activitiy intensity to pine wilt disease,at the region space scale,we studied the relathionship between spreading of pine wilt disease and the density of human activities.From recent ten yesrs economical and epidemic data,the result showed the situation of pine wilt disease is still grim in The Three Gorges Reservoir Area.The results of the human activities factors in Yi Chang showed GDP,total freight turnover,the density of road network and total population had been growing.Among them,the GDP and total freight turnover increased significantly.In the decade,total population was on an even keel.The data of Chongqing had the same results.GDP,total freight turnover,the density of road network and total population had a more obvious growing trend.During this period,pine wilt disease had a clear expansion.According to factor analysis,the density of road network and total population could represented the pine wilt disease.Based on the results,we forecasted the disease in the next decade,the research results showed the disease would enlarge in Yi Chang with the urbanization,the growing of density of road network and total population.In Chong Qing,the forecasted disease was more serious than Yi Chang.4.Corridor is an essential structure part in a landscape.In the different time and space scale,corridor is indispensable landscape component,which can affect the change of biological population in the landscape.It can perform multiple action connection,spreading energy and biology flow,and can also hinder the flighting of M.alternatus and spreading of pine wilt disease.We analyzed the landscape pattern transition from 2006 to 2015 in the Three Gorges Reservoir area.We quantitied transitions by landscape index,and analyzed their correlation with the disease situation,the main corridors in the Three Gorges reservior include water,human,agricultural,forest and grassland corridors.The result showed the water corridor ecological effect is outstanding.From the transformation of water corridor,total area and total edge had a opposite trends in epidemic and non-epidemic area.From the total edge of agriculture corridor,epidemic area increased,and non-epidemic area declined.The trend of grassland and human landscape corridor index had no inconsistency.Therefore,grassland and human landscape corridor index could not be used as a factor to measure the occurrence,epidemic spread and corridor effect,but human activity intensity transition was direct factor to pine wilt disease in human landscape.5.Based on the above results,we concluded some comprehensive strategies and ideas.To the P.massoniana patches that suffered pine wilt disease,we should follow operational principles,decline the shape index,improve the resistant ability.To the other natural patches,such as agricultural patch,we should follow operational principles too,reduce the landscape shape index.Based on the effect of density of road network with pine wilt disease,we should take advantage of water corridor and other types in terms of human landscape to reduce the possibility of pine wilt disease.It is recommended to set checkpoint at cross-regional area and key roads,and stop circulation of epidemic wood and product to prevent the spread of pine wilt disease.