Abstract: The niche of age group of plant population is one important aspect of the resource utilization which changed with the time. According to the height of plant’s individuals, the population was divided into three age gradients-tree group, sapling group and seedling group. The niche characteristics of different age groups of Castanopsis fargesii and Elaeocarpus japonicus were studied, which are the dominant plants in evergreen broad-leaved forest in Jinyunshan Nature Reserve, Chongqing. The results indicate: (1)The realized niche breadths of C. fargesii and E. japonicus at three age groups are rather wide while their resource utilization capacities are not strong. It is obviously that the niche breadths and resource capacities of the two species became wider or stronger when they grew up to the canopy. (2)The degree of niche speciation of C. fargesii and E. japonicus at seedling group are very high, while niche generation of the two species at tree group and sapling group are not high. (3)The niche breadths and resource utilization capacities of E. japonicus are larger than C. fargesii at tree group and sapling group except that of at seedling group. (4)The niche overlaps of C. fargesii and E. japonicus are large, which indicated that the resource competition of the two species was violent. The trend of niche overlap of the two species with age group likes V character. It means that the overlap is lowest at sapling group which would be involved in the deficiency of the middle age group of C. fargesii, which was resulted from the violent competition at seedling group.

Key words: age group, niche breadth, niche overlap, resource utilization capacity, Castanopsis fargesii, Elaeocarpus japonicus