Objective The analysis of stand spatial structure at different growth stages is conductive to understanding stand regeneration and stability, which can provide reference for optimizing stand spatial structure and natural vegetation restoration.
Method In the study, the evergreen broadleaved forest in Lushan Mountain, Jiangxi Province of eastern China was taken as the research object. The tree growth was divided into four stages: sapling (1 cm ≤ DBH < 5 cm), small tree (5 cm ≤ DBH < 10 cm), middle tree (10 cm ≤ DBH < 20 cm) and large tree (DBH ≥ 20 cm). The comprehensive index of spatial structure was constructed by four kinds of spatial structure parameters: mingling, neighborhood comparison, crowding degree and uniform angle index. The weight was assigned by entropy weight method.
Result (1) The proportions of sapling, small tree, medium tree and large tree were 72.7%, 16.8%, 6.5% and 4.0%, respectively. The diameter class structure of the stand was generally inverse ‘J’ type. (2) The average mingling of sapling, small tree, middle tree and large tree were 0.609, 0.746, 0.815 and 0.822, respectively. The average neighborhood comparison of them was 0.545, 0.268, 0.132 and 0.089, respectively. The average crowding degree of them was 0.852, 0.895, 0.871 and 0.842, respectively. The average uniform angle index of them was 0.576, 0.563, 0.553 and 0.507, respectively. With the increase of diameter class, the degree of mingling and growth dominance of trees increased, and the density of trees first increased and then decreased. The distribution pattern gradually changed from aggregation distribution to random distribution. (3) The weight of neighborhood comparison of small tree, medium tree and large tree was more than 75.0%. The way of optimizing spatial structure should mainly regulate the degree of forest differentiation. The weight of mingling and neighborhood comparison of sapling were 0.364 and 0.388, respectively. To optimize its spatial structure, the degree of forest mingling and differentiation should be mainly controlled simultaneously. The comprehensive index of spatial structure was large tree (0.054) < middle tree (0.082) < small tree (0.117) < sapling (0.265).
Conclusion The spatial structure of evergreen broadleaved forest in Lushan Mountain was gradually improved with the increase of diameter class. The best spatial structure was the large tree and the worst was the sapling. According to the spatial structure characteristics of trees at different growth stages, different forest management measures can be taken to optimize the spatial structure.
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