Objective To analyze the univariate and bivariate distribution characteristics of DBH and tree height of Larix gmelini natural forest in Huzhong forest zone of Greater Khingan Mountains Region, and to reveal the size distribution of forest fragile zones of forest communities.
Method Three sample plots of L. gmelini forest with different species composition (herbage-Larix, Rhododendron-Larix, and Ledum-Larix) were set up in Huzhong Forest Farm, the relationship between the DBH and the tree height was studied by the whole and layered method.
Result (1) The DBH distribution of herbage-Larix forest followed a single peak distribution and the other two plots followed a bimodal distribution. The DBH distribution of the three plots was left-biased. The tree height distribution of Rhododendron-Larix forest was multimodal, and the other two plots were unimodal. (2) The DBH distribution of the upper and lower layers of the three plots were all unimodal. The DBH distribution of the upper layer on all the three plots was left-biased, the lower layer of the herbage-Larix forest was right-biased, the Rhododendron-Larix forest was left-biased, and the Ledum-Larix forest was approximately normal. The height distribution of Rhododendron-Larix forest in the upper and lower layers was bimodal, and the other two plots followed single distribution. The height distribution of the upper layers of these plots was the left-biased, while the height distribution of the lower layers of the three plots was right-biased. (3) The percentage of small diameter trees in herbage-Larix forest and Rhododendron-Larix forest was significantly higher than that in the large diameter forest. The ratio of tree height to DBH in small diameter forests was significantly higher than that in large diameter forest. The ratio of small diameter trees in the upper layer of herbage-Larix forest and Rhododendron-Larix forest was larger than that of the large diameter forest, the ratio of large DBH trees in the lower layer of Ledum-Larix forest and Rhododendron-Larix forest was higher than that of small diameter forest. However, no significant difference was found in the ratio of height and DBH between the upper and lower layers of the three plots.
Conclusion The average height of the high-density Rhododendron-Larix forest is higher than that of the low-density Ledum-Larix forest and herbage-Larix forest, and the average DBH has no significant difference in different density and different typed forests. The ratio of tree height to DBH in small diameter forest is significantly higher than that in large DBH forest, but the difference is not obvious in upper and lower standings.
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