Analysis of spatial structure characteristics based on diameter class of trees in primeval Quercus aliena var. acuteserrata community in the forest area of Xiaolong Mountain, Gansu Province.

Using the software of single tree sampling in a fixed plot and stand structure analysis,we explored the distribution pattern, isolation and size differentiation for different sizes of dominant tree species in Quercus aliena var. acuteserrata virgin forest community in the forest area of Xiaolong Mountain in Gansu Province, western China.There were more medium and small sized individuals in Q.aliena var. acuteserrata virgin forest community, stand diameter class distribution was of inverted “J” type, and the diameter class for constructive species Q.aliena var. acuteserrata population followed a normal distribution. The stand mean uniform angle index was 0.542. The individual distribution for constructive species of Q.aliena var. acuteserrata population was slightly aggregated, for seedlings and saplings it was moderate aggregation, for medium diameter trees it was a random distribution and for large trees it was a slightly aggregated distribution. The seedling and sapling individuals of Meliosma cuneifolia var.glabriuscula and Carpinus turczaninowii var.stipulata population showed the transition state from aggregated distribution to random distribution, and their medium diameter trees aggregated distribution. Individuals of Carpinus henryana, Acer mono, Tilia oliveri and Sorbus alnifolia population in different diameter classes showed different degrees of aggregation distribution. The seedling and sapling and medium-diameter individuals of Carpinus turczaninowii population showed aggregated distribution and its large individuals showed uniform distribution. The average mingling of stand was 0.700, belonging to transient state from the moderate to strong mixture. The mingling of C.henryana and Q.aliena var. acuteserrata population decreased with the increase of DBH, and the mingling of Acer mono, C.turczaninowii, and T.oliveri population decreased first and then increased with the increase of DBH. The mingling of S.alnifolia, M.cuneifolia and C.turczaninowii var. stipulata population increased with the increase of DBH. The mean value of neighborhood comparison of Q.aliena var. acuteserrata was 0.166 and in the dominant position in stand. The seedlings and saplings of M.cuneifolia var. glabriuscula were more competitive than other species. The order of dominance of dominant tree species from high to low was Q.aliena var. acuteserrata, C.turczaninowii, A.mono, T. oliveri, C.henryana, S.alnifolia and M.cuneifolia var. glabriuscula. The community characteristics of this plot can be used as the direction and guidance for the management of Q.aliena var. acuteserrata secondary forest in Xiaolong Mountain.