Spatial niches of bark beetle population in Picea crassifolia natural forests

Investigation of bark beetles in Picea crassifolia natural forests was carried out at four stands of different damaging degree in Maixiu National Park,Qinghai Province,from May to September in both 2005 and 2006.Six main species of bark beetles were found in the forests.The spatial resources of bark beetle population were divided into three cells and the niche breadth and competition indices among species in height cell,width cell and different states of P.crassifolia were calculated based on the niche theory.Conclusions are obtained as the followings:Dendroctonus micans,as the initial bark beetle,harms spruce stand first,and always the base part.Ips n.sp.,I.nitidus and Pseudips orientais having wide niche breadths in both height and width cells are the second most important species.Though the bark beetles have wide niche breadth and the ratios are similar,all of them can turn to harm the healthy trees directly when population densities are big enough.Polygraphus poligraphus and Tomicus sp.are following bark beetles and also have differences in selecting host trees.P.poligraphus prefers the moist and weak trees.It is revealed that bark beetles are living stably and coexistently in these spatial cells through various selections and utilization in spatial resources of host trees.