| At present the biggest threat to the mangrove forests in China is the harm of Sphaeroma.Sphaeroma has caused more serious destruction in Dongzhaigang ever since large areas of mangroves'death was first found in Dongzhaigang in 2012.At the same time,people found Sphaeroma distribute in Guangxi Beihai and other places.Domestic and foreign scholars learn about the classification and life habits of Sphaeroma,but little they know about the influence of Sphaeroma to mangrove community,the the outbreak process of Sphaeroma,the distribution characteristics of Sphaeroma and so on.Based on interpretation of remote sensing image,field investigation and monitoring,the research analyzes the distribution characteristics of Sphaeroma in Dongzhaigang mangrove forest,and discusses the main factors of influencing the distribution of Sphaeroma.Specific content as follows:1.The classification and distribution of Sphaeroma harm extentCombined with different periods of remote sensing image and field verification,the Sphaeroma harm extent of mangrove in Dongzhaigang is divided into four grades,and generate hazard rating distribution of Sphaeroma.The area of the four levels of harm extent:severe injury zone,covers an area of 8.24 hm~2,moderate injury zone,covers an area of 183.52hm~2,mild injury zone,covers an area of 152.41 hm~2,and the normal forest area undisturbed by Sphaeroma,covers an area of 1207.46 hm~2.2.The extent of Sphaeroma harm in different mangrove communitiesSuperpose Sphaeroma hazard map of mangrove in Dongzhaigang group with plant community distribution,we can get 4 grades of Sphaeroma hazard area of 59 different communities,and then according to the comprehensive evaluation method,calculate the preference coefficient(M)of Sphaeroma in different mangrove plant communities,the results show that Sphaeroma tends to choose Bruguiera Sexangula-Bruguiera Sexangula community(M=5.50),and other communities respectively are Bruguiera Sexangula-Bruguiera gymnorrhiza community(M=5.45),Sonneratia caseolaris-Sonneratia apetala community(M=4.23),Avicennia marina community(M=4.14)and Rhizophora stylosa-Avicennia marina community(M=3.91).And semi-mangrove community(M=0.01),Lumnitzera racemosa communities(M=0.01),Excoecariaagallochacommunity(M=0.01),Ceriops tagal-Bruguiera Sexangula community(M=0.01)and so on will not be choosed by Sphaeroma ordinarily.3.The spatial factors of influencing the distribution of Sphaeroma harm1)Comprehensive evaluation of Sphaeroma harm in different regions of DongzhaigangAccording to Sphaeroma hazard area of each grade in four areas of of Dongzhaigang protected areas(Tashi district,Daoxue district,Sanjiang district and Luodou district),calculate evaluation of Sphaeroma harm in different regions(P)based on comprehensive evaluation method.We found that:the most serious region of Sphaeroma harm is Daoxue District(P=1.230),other regions followed by respectively are Luodou district(P=0.615),Tashi district(P=0.574)and Sanjiang district(P=0.101).2)The relationship between Sphaeroma harm level and tidal creek positionInterprete all tidal creek on the remote sensing image(width>1m),and set the buffers to0-10m,10-20m,20-30m,30-40m,and 40-50m in ArcGIS environment.Then statistic the quantity of plaques of different Sphaeroma harm level in buffers.Results show that the amount of plaque of the severe disasters will reduce with increase of distance;Moderate and mild plaque number are the highest in hazard in 10-20m,second to 0-10 m,and then gradually reduce with the increase of distance;The number of patches in normal community change unregularly.For the number of patches of each different buffer Sphaeroma hazard rating with comprehensive evaluation method,Sphaeroma harm coefficient(N)are obtained in each buffer.Results show that 10-20 m are most severely affected by the mass of specialised to harm(N=250),the second respectively 0-10 m buffer(N=235),20-30 m buffer(N=129),30-40 m buffer(N=88),40-50m buffer(N=36).Based on field monitoring,we verify that the submerge time and Sphaeroma harm extent has a certain relevance,especially in community types of the high tide,and there is a significantly positive correlation between thelevel of Sphaeroma outbreak and submerge time.3)The relationship between level of Sphaeroma harm and residential positionSetting up 2000m buffer besides coastline anddividing the buffer into average area,analysis the number of residential patches,group risk index of residential,Sphaeroma harm plaque quantity data and the number of Sphaeroma different level paches correlation,we found significant correlations between Sphaeroma harm and the number of patches in residential areas(a=0.804,P=0.029),residential coefficient D(b=0.788,P=0.035).4)The relationship between level of Sphaeroma harm and aquaculture ponds positionOn the base of the buffer beside coastline,analysis the number of aquaculture ponds patches,group risk index of aquaculture ponds,Sphaeroma harm plaque quantity data and the number of Sphaeroma different level paches correlation,we found significant correlations between Sphaeroma harm and the number of patches in aquaculture ponds(c=0.777,P=0.040).5)The influence of pacth structure on level of Sphaeroma harmBy using fragstates software,calculate with the main landscape index of the plant community in the patch scale,and conduct the correlation analysis combined with harm extent of each patch plants.We can get to know that there is a significant negative correlation between the level of Sphaeroma outbreak and plaque area(Area),plaque perimeter(Perim),and plaque adjacent index(PROXIM),and there is a significantly positive correlation between the level of Sphaeroma outbreak and perimeter area ratio(PARA);Results show that more severe the Sphaeroma harm of mangrove plant community group,the smaller the plaque area;the longer the patch perimeter of plant community,the more gently the Sphaeroma harm extent;the closer the distance between each plant plate,the heavier the Sphaeroma harm extent;the greater the perimeter area ratio,namely the more complex the shape of patches,the heavier the Sphaeroma harm extent.At last,according to the analysis results above,the mechanism of Sphaeroma outbreak has been discussed preliminary. |
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