Abstract: [Objective] The purpose of this paper was to analyze and evaluate the effect of forest factors on the occurrence of pine needle blight (DI and DSI) quantitatively, thus to provide theoretical guidance for the forest management and prevention of the pine needle blight in pure forests of Kunyushan Mountains.[Method] Pinus densiflora pure forests with relatively consistent forest age (about 34 a) were targeted as the research object in Kunyushan Mountains. Six forest indexes, including forest density, canopy cover, tree height, height under branch, diameter at breast height (DBH) and crown cover, as well as the disease incidence (DI) and disease severity index (DSI) of the pine needle blight were investigated. Variance analysis, correlation analysis and multiple comparisons were used to analyze the relationship between forest factors and pine needle blight. The key factors affecting the occurrence of needle blight were obtained by redundancy analysis.[Result] Pine needle blight was prevalent in P. densiflora forests, with 96.3% of the sample plots being infected. Overall, the DI and DSI in high density forests (2 956~4 089 tree·hm^-2) were significantly higher than low density forests (688~1 822 tree·hm^-2) and middle density forests (1 823~2 955 tree·hm^-2). DI and DSI in low canopy cover forests (< 30%) were significantly lower than that of middle canopy cover forests (30%-70%) and high canopy cover forests (> 70%). In different groups of tree height, height under branch, crown cover and DBH, the DI and DSI decreased with the increase of group values. Results from regression analysis and multiple comparisons showed that forest density affected disease incidence (DI) and disease severity index (DSI) positively and significantly (r=0.761, P< 0.01; r=0.748, P < 0.01). The disease incidence and disease severity index were affected by canopy cover significantly and positively (r=0.509, P < 0.01; r=0.442,P < 0.01). Tree height had significant influence on the disease incidence and disease severity index (r =-0.443, P<0.01; r =-0.362, P <0.01). The disease incidence and disease severity index decreased with the increase of the height under branch significantly (r =-0.460,P <0.01;r =-0.419,P <0.01). They also were negatively correlated with diameter at breast height, and the correlation was extremely significant (r=-0.425, P<0.01; r=-0.373, P<0.01). The disease incidence and disease severity index decreased significantly with the increase of crown cover (r=-0.345, P<0.01; r=-0.381, P<0.01). Redundancy analysis proved that forest density and height under branches contributed the most to occurrence of pine needle blight.[Conclusion] The occurrence of pine needle blight is relatively common but not serious in Kunyushan Mountains region. The disease incidence and disease severity index are different in different forest factors groups, and they are highly significantly influenced by the forest factors. RDA analysis shows that forest density and height under branch have the most significant impact on pine needle blight. It is suggested that the control of needle blight in pure Pinus densiflora forests in Kunyushan Mountains should be controlled mainly by important factors by conducting reasonable pruning and thinning.

Key words: Kunyushan Mountains, Pinus densiftora pure forests, pine needle blight, disease incidence, disease severity index, stand factors