| Poplar canker caused by Cytospora chrysosperma is a trunk disease,which occurs seriously in the "Three Northern" areas of China and a large number of poplar trees have been killed by it.Prevention stands at the core of poplar canker control,and to figure out the law of the epidemic disease forms the prerequisite and foundation for prevention.On the basis of collecting and analyzing the occurrence data of poplar canker at the county level from 2002 to 2015 in Northeast China for 14 years,this paper compared and analyzed the epidemic trend of poplar canker according to different latitudes,elevations,forest management divisions,functional zones and other classification methods.With the help of space-time scanning statistics(Sa TScan)technology,it also analyzed the spatial and temporal pattern of poplar canker in Northeast China for 14 years by using the county(district,city)administrative unit as the sample statistical unit and retrospective space-time scanning method,which revealed the space-time distribution and epidemic characteristics of poplar canker in Northeast China.Meanwhile,Max Ent model and Arc GIS technology were used to reveal the potential distribution and suitability of poplar canker,to evaluate the contribution rate of various environmental variables to the disease occurrence,and to predict the potential distribution under different climate change over the next 30 and 50 years.The risk of poplar canker in Northeast China was analyzed by multi-index comprehensive evaluation method,which aims to provide scientific basis for the prevention and control of poplar canker in Northeast China.The main results are as follows:1.The correlation between the occurrence trend of poplar canker and latitude interval is not significant in Northeast China,but the incidence rate in high altitude area is significantly lower than that in low altitude area in the same latitude interval.Among the different forest management zones,the occurrence of canker varies largely in degree.Thefarmland protection forest area of Songliao Plain has a relatively single forest species,which constitutes a relatively concentrated geographical distribution area of poplar canker.The disease occurs with low and medium degree in the water conservation forest area along the Changbai Mountains and in the South of timber forest of the Greater Khingan,while it basically does not occur in the timber forest in the North of the Greater Khingan and that in the Lesser Khingan Mountains.In different functional areas,the incidence rate of poplar canker in urban landscaping areas is higher than that in farmland protection areas,and the higher the overall incidence rate,the more significant the gap is.2.The average incidence of poplar canker in Northeast China showed a fluctuating upward trend on the whole with 27.62% average annual rate of rise.A total of 149 counties have suffered 901 times in the past 14 years,but the disease varied greatly in incidence in different areas.The spatial and temporal distribution of disease is characterized by "outbreak-aggregation-spread-stability".The spatial aggregation effect of disease is obvious.In 2002-2015,the cumulative incidence area scan showed one space-time aggregation region of class I and more than 4 of class II;the annual spatial scanning statistics revealed 14 aggregation regions of class I and 37 of class II,which showed the three-stage variation law of "expansion-concentration-expansion ".The aggregation region of class I were mainly concentrated in Liaoning province(LLR=86469.86,p <0.001).Diseases also showed significant spatiotemporal aggregation effect.The spatiotemporal scanning results of continuous time dimension from 2002 to 2015 showed that there were 1 class I aggregation area and 6 class II aggregation area.A class of clustering areas were concentrated in Liaoning province from 2009 to 2015(LLR =64182.00,P < 0.001).In view of the results of this study,the outbreak of poplar canker in local areas will probably be more frequent and severe in the future.3.The suitable distribution area of poplar canker covers most areas of Heilongjiang,Jilin and Liaoning province.Among the 19 environmental variables,the three environmental variables that have the greatest influence on the occurrence of canker are the variation coefficient of precipitation,the standard deviation of precipitation in the warmest season and the seasonal variation of temperature,whose effects on disease occurrence took up 28%,25.3% and 24.8% of the model contribution rate respectively,while the sum of contribution rates of the other 16 environmental variables was only21.9%.In the next 30 and 50 years,the potential distribution and suitability of poplar canker in different climate change scenarios will expand and aggravate.The mostfavorable distribution showed the trend of the disease aggravation in the most ares of Liaoning,Jilin and Heilongjiang provinces and the Northeast of Inner Mongolia Autonomous Region.The suitable areas for each grade are expanding outward in the North and West of Inner Mongolia,and the appropriate levels will rise.4.The results of risk analysis show that the host of poplar canker was widely distributed in Northeast China,and the occurrence of the disease has caused serious economic and ecological,environmental and social hazards to the local area.Meanwhile,the disease has latent infection characteristics,and it is difficult to identify and quarantine during transportation,and once colonized,it is very difficult to control and eradicate,and the comprehensive risk evaluation value R=1.87 is obtained.It is a moderately dangerous forest pest in Northeast China,and in order to monitor and prevent such disease,the main focus should be placed on prevention and control and quarantine inspection.The spreading trend of poplar canker in Northeast China will be further intensified in the future. |
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