| Dalbergia odorifera is one of the national key protection of rare and endangered plants, Phyllachora dalbergiicola is the main disease.The annual incidence rate can reach 80% or more. Plant leaves and branches on the infection after the formation of a large number of moles,tar spot of Dalbergia odorifera caused by Phyllachora dalbergiicola is a common occurrence in plants of Dalbergia odorifera, and it seriously affected the rate of photosynthesis, caused host leaf shedding in advance.Forest environment, forest stand spatial distribution pattern of resource allocation has direct effect to disease spread,outbreak and infection.Good stand habitat can promote individual tree growth, and enhance the ability to resist disease, so according to the classification standard of landscape vertical structure, tree layer selection in canopy structure index, forest layer index and open degree as the stand spatial index in shrub and herb species diversity index selection, explore the relationship between forest vertical structure the indexes and the Phyllachora dalbergiicola in Dalbergia odorifera in.The results are as follows:(1) The relationship between stand structure and Phyllachora dalbergiicola in Dalbergia odorifera. According to the degree of influence on the growth of trees, from the canopy structure index selected first grade branch diameter (Dtb), first order branch angle (Atb), branch under high (Hub), crown length ratio (PLCH), leaf area index (LAI),canopy density (CLD), crown shape ratio (CSR), crown surface area (CSA), crown width(W) a total of ten indicators, as the canopy structure index to search correlation between Phyllachora daleergiicola in Dalbergia odorifer and the canopy structure. Comprehensive analysis, the importance of PLCH, LAI, hub. W. TLA,CSA are large to Phyllachora dalbergiicola in Dalbergia odorifera,these could be main index for search. Leaf area index (LAI) and branch under height (Hub) were significantly positive correlation, crown length with height (PLCH), crown width (W), crown surface area (CSA), leaf area per plant number (TLA) showed a very significant negative correlation.Using ArcGIS software in the Voronoi diagram to determine value of the wood structure unit and center adjacent to the adjacent wood n, calculate degree of kinds of trees layer index and open degree.After the investigation.the average forest layer index of various structural units in 0.10-0.50. and most of them were concentrated in the 0.1-0.3 range, indicating that the differentiation degree of the stand was weak. Most open degree greater than 0.3 structure cell proportion was more than 50%, the largest proportion of 89%, but all kind of open land is greater than 0.5 unit space ratio shall not exceed 20%, the basic maintenance in 10% the left, average open degree index were between 0.1-0.6, the variation is small that tree growth space. Forest layer index, open degree are very significantly negative correlation with Phyllachora dalbergiicola in Dalbergia odorifera. When forest layer index and open degree increased, the disease index decreased gradually.(2) The relationship between shrubshrub and herbage species diversity and Phyllachora dalbergiicola in Dalbergia odorifera. Species richness index (S), Shannon diversity index (H) and Simpson diversity index (D) as shrub species diversity index were selected.The forest investigation shows, Dalbergia odorifera plantations shrub and herbage plants mainly in the Leguminosae and Gramineae plants. Others in Compositae, Euphorbiaceae, Oleaceae, Malvaceae, Labiatae, Apocynaceae, marantaceae, Cyperaceae, Rubiaceae, etc. Species richness index, Shannon diversity index showed significant negative correlation with Phyllachora dalbergiicola in Dalbergia odorifera, Simpson diversity index showed significant positive correlation. With the gradual increase in species diversity, the disease index decreased rapidly, but increased to a certain value, the disease index decreased gradually. When the species richness index beyond 10, the Shannon diversity index beyond 2.0, Simpson diversity index beyond 0.3, the disease index decreased slowly.(3) The regression models about landscape vertical stratification structure and Phyllachora dalbergiicola in Dalbergia odorifera plantations. Through screening index, crown length with height PLCH, leaf area index (LAI), branch under height (Hub), crown width (W).leaf area per plant number (TLA), crown surface area (CSA). forest layer index.open degree, species richness index(S), Shannon index (H), Simpson diversity index(D) as independent variables, disease index as dependent variable, establish regression models about landscape vertical stratification structure and Phyllachora dalbergiicola in Dalbergia odorifera plantations. There is a serious multicollinearity among variables, so establish a linear regression model. Model test results show that the fitting effect of each model better, the accuracy of the index of the model respectively: under branch height is 78.31%, crown length ratio is 85.15%, leaf area index is 72.54%, crown width is 85.96%, total leaf area is 85.70%, crown surface area is 87.96%, forest layer index is 87.70%, open degree is 85.28%, species richness index is 89.47%, Shannon diversity index is 76.20%, Simpson diversity index is 82.95%. The results indicated that 11 regression prediction model with high precision and certain reference value in disease control. |
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