| On the occurrence of the moso bamboo dieback(Ceratosphaeria phyllostachydis)in seven main producing counties,in Jiangxi Province,this research analyzed the relationships between moso bamboo dieback and stand factors,site factors,the influence of spatial competition potential structure and individual trees spatial structure on the moso bamboo dieback,and discussed relationships between those factors and the moso bamboo dieback,the research would provide the basis for prevention of dieback and forest healthy management.The main results were as follows.(1)These relationships between moso bamboo dieback and five stand factors were analyzed,including age,density,evenness,diameter of breast height(DBH)and canopy density.The results showed that density had extremely significant positive correlation with disease index(DI)and disease incidence rate(DIR),stand age and evenness were extremely significant negative correlation with DI and DIR,DBH was significant negative correlation with DI and DIR,DI and DIR were not correlated with canopy density.Those findings indicated that with the increase of stand age and DBH,DI and DIR would gradually decrease,the evenness and density would be adjusted to make the stand more uniform and bamboo density less,DI and DIR would reduce.(2)The relationships between dieback of moso bamboo and five site factors were analyzed,including slope,position,direction,altitude and soil layer thickness.The results showed that the soil layer thickness were extremely significant negative correlation with DI and DIR,altitude were extremely significant positive correlation with DI and DIR,slope was extremely significant positive correlation with DI and significant positive correlation with DIR;slope direction was significant positive correlation with DI,and not correlation with DIR;slope position had not correlation with DI and DIR.Therefore,when the moso bamboo would be planted on the sunny slope with thin soil layer,higher altitude and steep slope,they would be more susceptible to infect dieback.(3)The relationships between plant diversity indices of three community levels and dieback of moso bamboo were studied in three kinds of different type stand.The results showed that DI and DIR in the pure bamboo stand were much lower than in the two kinds of mixed bamboo stand(bamboo mixed stand with conifer and the bamboo mixed stand with hardwood),the average DI were not very different in the bamboo mixed stands,so were DIR.The correlation between plant diversity indices and DI,DIR was further analyzed.The plant diversity indices of tree layer in two bamboo mixed stands were closely related to DI and DIR,showing significant or extremely significant negative correlation,they had weak correlation or no correlation in the shrub layer and herb layer.In the pure bamboo stand,those correlations were significant positive in the shrub layer and herb layer.So increasing the mixed proportion of pure bamboo stand and the plant diversity of tree layer would be the key to control dieback,while clearing the miscellaneous irrigation of shrub layer and herb layer would effectively prevent the invasion and transmission of dieback.(4)Regression analysis was used to establish two prediction models of the DI and DIR,which reached extremely significant level(R~2=0.715,p<0.01;R~2=0.694,p<0.01).The two models screened out the dominant factors from 11 factors,including age,density,evenness,DBH,canopy density,slope,slope position,slope direction,altitude,soil layer thickness and stand type.The results showed that the two prediction models of DI and DIR simultaneously screened out the six dominant factors,which were evenness,age,density,altitude,soil thickness and stand type.The density and altitude were positively correlated with DI and DIR,the age,evenness,stand type and soil layer thickness were negatively correlated with DI and DIR.(5)The correlation between spatial competition potential structure and DI were studied in the different type stand,the different density stand and the different evenness stand.In different type stand,the negative correlation between competitive potential indices and DI of pure bamboo stand were significantly higher than that of two mixed stands.In different density stand,there were significant or extremely significant negative correlation between competitive potential indices and DI in high density stands,the correlation was weakened with the decrease of stand density,there was no correlation between competition potential indices and DI in low density stands.In different evenness stands,there were significant or extremely significant negative correlation between the competitive potential indices and DI in the cluster distribution stands,the correlation between competitive potential indices and DI weakened with the increase of evenness,in the uniform distribution stands,the competition potential indices and DI had no correlation.(6)At the individual scale,according to the different type stand,different density stand and different evenness stand,this paper analyzed the relationship between neighborhood comparison(NC)of DBH,crown,tree height and DI.In the pure bamboo stand,these were extremely significant negative correlation between NC of DBH,crown,tree height and DI,there were significant difference among the dominance.In the mixed stand,the correlation between DI and NC of DBH,crown,tree height became weak.In different density stand,these relationships were extremely significant negative correlation at high density,with the decrease of density,these correlation were gradually weakened.In low density stand,there was no correlation.In different evenness stand,when the stand was clustered distribution,there were extremely significant negative correlation between NC of DBH,crown,tree height and DI When the stand was evenly distributed,NC of DBH,crown,tree height had no correlation with DI.This indicated that in the low density stand,mixed stand and even distribution stand,the dominance of single moso bamboo was higher,and the disease was not easy to occur. |
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