Abstract: The Xiaolongshan Nature Reserve is one of the Pinus armandii distribution areas in China.Based on large number of field surveys,study was carried out on ecological niches of the eight major populations of the Pinus armandii community,which is located in Xiaolongshan,Gansu Province,using the indexes such as the Levins and Shannon-Wiener′s ecological niche breadth,niche overlap index,and niche proportional similarity.Results show that the ecological niche breadth of the 8 plant populations follow the order of Pinus armandii>Quercus aliena var.acuteserrata>Lonicera lanceolata>Rhus verniciflus>Crataegus kansuensis>Castanea mollissima>Quercus liaotungensis>Tilia paucicostata.The population of Pinus armandii is the highest in Shannon-Wiener niche breadth,being 0.988 8,that of Quercus aliena var.acuteserrata follows,being 0.877 6,and that of Tilia paucicostata the lowest,being 0.352 9 only.The values of niche overlap of the populations in the community are generally low,which demonstrates low competition between most populations,but the niche overlap values of the dominant population of Pinus armandii with the other populations are relatively high,ranging between 0.079 1 and 0.101 3,whereas those of the other populations with that of Pinus armandii are relatively low,being in the range between 0.015 4 and 0.069 0.The overlap value is the highest between Pinus armandii and Castanea mollissima,being 0.101 3 and the lowest between Pinus armandii and Tilia paucicostata,being 0.079 1.There are 4 pairs of populations that have niche proportional similarity higher than 0.5 in value,accounting for 14.28%.They are Pinus armandii and Quercus aliena var.acuteserrata,Pinus armandii and Lonicera lanceolata,Quercus aliena var.acuteserrata and Lonicera lanceolata,and Quercus aliena var.acuteserrata and Rhus verniciflus.And the remaining 24 pairs are lower than 0.5,accounting for 85.72%,which demonstrates that the populations are mostly low in similarity of resource utilization.As one of the most important distribution areas for Pinus armandii in China,Xiaolongshan,the western section of the Qinling Mountains,is characterized by the ecological niche of a warm temperate coniferous forest.

Key words: Pinus armandii community, niche breadth, niche overlap, niche proportional similarity, Xiaolongshan, western Qinling