The Regulation Mechanism On The Stem Diseases Of Poplar Plantation In Northern China By The Stand And Site Management

Stem disease is the main restriction factor for silviculture and development of short-rotation poplar plantations in North China. The disease is host vigor induced that host vigor inherently affects the epidemic. Therefore, control strategy should be made according to site conditions and stand factors including indexes from individual, community and environmental systems. The purpose of this study was to exploit effects of site condition and stand factors on disease epidemics and to provide theoretical guide for ecological management of the disease. This study was carried out in sample plots of poplar plantation in North China. Principle component analysis and correlation analysis was used in this study. The main results were as fallows:1 Seven principle factors were established through principle component analysis on all site factors and stand factors, which included soil water, soil nutrient, stand sanitation, stand biomass, stand crown, stand horizontal distribution and vertical distribution, respectively.2. Close relation between soil water and infection index and morbidity was observed. Underlayer moisture in stand increased when soil water content rate was high, which led serious infections due to higher underlayer coverage and poor atmospheric conditions. High infection index and high morbidity could also be intrigued because of high soil bulk density with poor soil structure, poor ventilation and poor drainage.3. Liner correlation analysis revealed that vertical distribution was significantly and was positively correlated with infectious index and morbidity. Trees in stand with high density, high clear bore height and high ratio of clear bore height to stem height was easier to be infected and therefore the infectious index and morbidity was higher. Infection of the disease could be decreased through lowing stand competition strength by thinning and controlling clear bore height.4. Infectious index was lower in stands with small differentiations among diameter at breast height DBH, in which DBH distribution was concentrated and stand was dominated by dominant trees with little competition for nutrient and large growth room with sufficient illuminations. On the other hand, infectious index was larger in stands with big DBH differentiation. Thinning for control ratios of dominant tree in stand was recommended to decrease DBH differentiation. These measures could improve nutrient uptake, illuminations and decrease competitions between individuals and subsequently control diseases effectively. Trees with the largest canker area in stands had strong infestation abilities. Self-resistance increased along with increment of DBH. Therefore, the control of the disease could be implemented by thinning infected trees with small DBH.5. Infectious index was lower in stands with larger distribution of clear bore height. Morbidity could be decreased through control of clear bore height during young forest.6. A regulation and control model was established based on site condition and stand types. Effects of composition, soil texture, clones, soil bulk density and stand density on infectious index was significant, among which stand composition, soil texture and soil bulk density significantly affected morbidity. Both models matched well for inspections. The application precision for inspection of infectious model was 88.65%, whereas the morbidity model 75.97%, respectively.