ObjectiveA reasonable description of the structure characteristics of forests can provide effective guidance for the forest management. The structural characteristics of Picea asperata-Betula platyphylla mixed forests in Changbai Mountain in northeastern China were studied to provide reference for the optimization and adjustment of the stand structure.

MethodIn order to explore the structure characteristics of Picea asperata-Betula platyphylla mixed forests, two plots of Picea asperata-Betula platyphylla mixed forests were set in Jingouling Forest Farm in Wangqing County of Jilin Province, northeastern China. The spatial structure of the stand and individual levels was analyzed using a trivariate distribution of three commonly used diversity indices, i.e. mingling (M), uniform angle index (W), dominance (U).

ResultThe results indicated that: (1) the trees number distribution of Picea asperata and Betula platyphylla was mainly concentrated in 6, 8 and 10 cm diameter steps. The stand density of two plots was high. (2) With the increase of mingling, the number of trees increased first and then decreased, the vast majority of individual trees were surrounded by two other species among their nearest four neighbors; with the increase of uniform angle index, the number of trees increased first and then decreased. More than half of the trees in the two sample plots were in a random pattern, in which most trees were surrounded by two other species. With the increase of dominance, the number of trees was about the same. The number of dominant trees was slightly higher than the number of disadvantaged trees in two plots. When the structural parameters were combined into moderate mixed, random distribution and sub-dominant state, the number of trees was the largest. (3) In the first sample plot, when the structural parameters were combined into moderate mixed, random distribution and sub-dominant state, the number of spruce was largest. In the second sample plot, when the structural parameters were combined into zero degree mixed, random distribution, and dominant state, the number of spruce was largest. (4) When the structural parameters were combined into moderate mixed, random distribution, dominant and sub-dominant states, the number of birch was the largest in the first sample plot. When the structural parameters were combined into moderate mixed, random distribution, and inferior state, the number of birch was the largest in the second sample plot. (5) The advantage degree of spruce tree species in the stand was higher than birch.

ConclusionThe trivariate distribution of structural parameters can simultaneously express the mingling, uniform angle index, dominance, and contains rich information, which can provide important reference information for structural optimization and adjustment of Picea asperata-Betula platyphylla mixed forests.