The effect of forest woody plant diversity on the resistance to plant diseases and insect pests

This study aimed to investigate the effects of forest woody plant diversity (FWPD) on resisting plant diseases (PD) and insect pests (IP) for verifying forest biodiversity-stability hypothesis. White birch, larch, Mongolian Scots pine and aspen in Amuer Forestry of Da Xing’an Mountains in northern China during 2008-2011 were analysed. Sampled fields were surveyed for PD and IP. The results showed that PD and IP were concentrated on gentle slope of Rhododendron birch forest, hillside Rhododendron larch forest and hillside larch forest. When infection index of disease (IID) of infected field (IIDIF) and canopy density (CD) were fitted, the equation y = -139.32x 2 +116.36x+4.6231 with correlation coefficient (R 2 ) (0.7998) was obtained. When Simpson IIDIF and IID were fitted, the equation y = 0.0022x 2 -0.1422x+2.7906 with R 2 (0.7267) was obtained. When sample’s infection rate of insect pests (IRIP) and Simpson index were fitted, equation y = 0.0007x 2 -0.1174x+5.6639 with R 2 (0.8096) was obtained. These analysis revealed that DI was not increased with increasing CD, but decreased when CD reached certain density. When CD was 0.4176, IID began to fall, while IID and IRIP were decreased with increasing Simpson DI. These results indicate that FWPD differs with different types of forest species compositions. When FWPD is higher, its ability to resist damages of PD and IP is higher.