Abstract:

Objective: This paper aims to quantitatively evaluated the effects of site factors on the occurrence degree of Japanese red pine (JRP) needle blight disease in pure pine forests, by constructing the disease based index (DBI) evaluation system of the pine disease. Method: Based on the main principles of forest disease occurrence, the result affecting the occurrence of JRP needle blight were attributed to the comprehensive effect of stand factors and site factors. Temporary sample plots were set up in the pure forest ecosystem of Japanese red pine with relatively consistent forest age (34±2 a) to screen the key stand factors affecting the occurrence of pine needle blight, establish the functional relationship between the key stand factors and the disease severity index of pine needle blight was established, and the optimal model was selected as the guide curve. The DBI curve group of pine needle blight was obtained by stretching the guide curve in an equal proportion, which in turn showed different disease based indexes from the bottom to the top, that is, the action level of the site on the occurrence degree of pine needle blight. Result: 1) Based on the mainprinciple of forest disease occurrence, the concept of disease based index (DBI) was proposed. 2) The quantitative method of disease based index of JRP needle blight was determined, which contained contains 9 steps:set the plots, investigate the disease severity index of stands, investigate the stand factors, screen the key stand factors, determine the datum of stand factors, establish alternative guide curve model, determinate and evaluate guide curve model, draw the guide curve as well as establish the curve groups. 3) Stepwise regression analysis showed that stand density was the key stand factor affecting the occurrence of JRP needle blight. The guide curve equation was established according to the proposed quantitative method:Q=65.61/(1+e^{-0.0015x+2.32}), and the determination coefficient R²=0.519 8, indicating that the fitting equation was reliable. When this model was used to estimate the disease severity index of JRP needle blight, the average estimation error is 5.35%.4) A quantitative evaluation system was established by stretching the main curves of the disease base index of red spot blight in equal proportions to form a curve group. The 5 curves of the system from bottom to top were:Ⅰ-light disease occurs, Ⅱ-mild disease occurs, Ⅲ-moderate disease occurs, Ⅳ-severe disease occurs, Ⅴ-especially severe disease occurs. Conclusion: The guide curve model and curve group diagram of the disease based index of Japanese red pine needle blight can quantitatively evaluate the effect of site factors on the potential occurrence degree of pine needle blight, which can provide a theoretical basis for rational and effective management of pure Japanese red pine forest, and will become an important part of the ecological control method of forest pests.

Key words: JRP pure forest, pine needle blight, disease based index, Kunyushan Mountains