Study On The Canker Disease Occurrence Mechanism Of S Hort-Rotation Poplar Plantations Under The Different Spatial Scales

Host-based disease, mainly including poplar canker and rotten skin disease, is the mainconstraints of plantation and development of poplar. In this study, aiming to short-rotationpoplar plantation forest in the northern China, it analyzed relations between diseaseoccurrences and various factors at different layers of region—stand—individual. By usingprinciples and methods of landscape pathology, researches on the characteristics of diseasehappened to poplar stem at the regional scale, and relations between disease occurrence andhost itself as well as community characteristics were analyzed. At the stand level, relative index(average ratio of individual and community), crown shape, spatial utilization of nutrition wereselected to discuss the impact on occurrence of poplar canker due to above indicators. At theindividual level, the neighborhood comparison among diameter at breast height, tree height andthe size of tree crown was used to describe the spatial relations among single trees and impactson disease occurrence due to the spatial structure, which has important significance on forestmanagement measurement oriented eco-control of tree disease.At the regional level (100km~2), the impacts of density and canopy cover on averagedisease occurrence of poplar is significant. The disease occurrence of stand has positivecorrelation with plantation age (1-12years)(R=0.72, p<0.01), as well as stand density(R~2=0.3638, p=0.0037). It indicates that the disease occurrence of stand increased with theincreasing of plantation age and stand density. Meanwhile, with the increasing of stand canopycover, the average disease occurrence of stand increased too.Both plantation type and stand type have significant impacts on disease occurrence. Thedisease occurrence of stand in isolated patches is lower than in the pure forest, mixed forestand other type of stands. And the disease occurrence among in the pure forest, mixed forest andother type of stands has no significant difference, but higher than which of corpes. The diseaseoccurrence rate of trees located in different geographic situation is significantly different(F=3.30,p=0.021). The disease occurrence of poplars near the village is higher than of which located in other places. The disease occurrence rate and DSI of fine managed stand issignificantly lower than stand with extensive management.DSI among different types of poplar is extremely different. Of which the average DSI ofpoplar107is the lowest (DSI%<4%); and the DSI of triploid Chinese white poplar is thehighest, up to10.48%, higher than other kinds. Overall, the difference of DSI amongP.euramricana (Dode) Guineir cv.'zhonglin-46', poplar Langfang, Chinese white poplar,P.deltoid bartr. CI. Lux I-69/55and poplar108are slight,but significantly lower than triploidChinese white poplar.The correlation between relative diameter,relative height,relative crown,branchstretching,crown round degree,crown projection ratio and canker occurrence index of poplar107and108would significantly decline with the decrease of stand density. The impact ofbranch stretching on disease occurrence is more significant than other indicators. Thecorrelation between crown volume and growth space competition index and canker occurrencehas the trend of decreasing with the decrease of stand density. The canker occurrence of DN113poplar has no correlation with those indicators.From the result of multiple regression equation, except relative crown and crown rounddegree, other indicators have significant correlation with disease occurrence, with integrationreaction. Of which, the impact of stand density,relative diameter,relative height,branchstretching, crown volume,growth space index and growth space competition index on diseaseoccurrence is significant. The stand density,relative height,relative crown,branch stretchingand growth space index has significant negative correlation with disease occurrence, whichmeans the disease occurrence rate decreases with the increase of those indicators. The equationfitted very well (R~2=0.615, P＜0.001).The correlation between canker occurrence of poplar plantation and neighborhoodcomparison of diameter at breast height, tree height and the size of tree crown was analyzed.The result shows that poplar107,108and DN113in the same density, the occurrence of cankerhas significant negative correlation with neighborhood comparison of diameter at breast height,tree height and the size of tree crown. And the correlation decreased with the declining of the density. When the planting space reaches to3m×4m, the occurrence of canker would not beimpact by individual dominance.There is significant difference of canker occurrence of poplar107,108and DN113underdifferent indicator. The disease occurrence of three kinds of poplar in dominant tree (1) andco-dominant tree (0.75) and absolutely suppressed tree (0) is significantly different. Theoccurrence of suppressed tree (0.25) is obviously higher than dominant tree (1); it indicates thatthe trees under dominant situation would be less impacted by disease than suppressed trees; theoccurrence of suppressed tree is generally higher than intermediate trees. There exist a certaindifference of disease occurrence between suppressed trees and absolutely suppressed trees, butno significant difference for poplar107. Considering the variable of height and crown, thedisease occurrence of poplar108and DN113among dominant, co-dominant and intermediatetrees have no significant difference.