Structure and species diversity of boreal forests in Mt. Baikalu, Huzhong area, Daxing'an Mountains, Northeast China

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Data on the structure and diversity of boreal forest were investigated along 700-1440 m in Mt. Baikalu in Huzhong area, Daxing'an Mountains, Northeast China. A total of 7 species in tree layer, 12 in shrub layer and 115 in herb layer were recorded in 17 plots. Plant communities were clustered using TWINSPAN classification, and the structure characteristics of different communities, plant species richness and α diversity indicated by Shannon-Wiener index in tree layer, shrub layer and herb layer were analyzed. The results were summarized as follows: Four groups of community types characterized by different dominants in tree layer were distinguished: (1) Larix gmelini woodland; (2) mixed Larix gmelini-Betula platyphylla forest; (3) mixed Larix gmelini-Betula platyphylla-Pinus sylvestris var. mongolica forest; (4) pure Larix gmelini forest. These forest types showed no remarkable trend along altitudinal gradient, except that the distribution of Larix gmelini woodland was limited to high altitude. Structural characteristics such as mean tree height, mean tree diameter at breast height (DBH), total basal area, stand density and importance value of Larix gmelini were similar in the same community type. Mean tree height and DBH in the forest types increased with increasing altitude, when those in the Larix gmelini woodland were excluded. The frequency distribution of DBH and height explicitly indicated the horizontal and vertical structure of four forest types. DBH frequency distribution for all four forest types showed a typical reversed J shape, suggesting the forests in Mt. Baikalu were regenerating in a good stage, while majority of height frequency distributions presented a bimodal and approximately symmetric distribution. Species richness and α diversity in tree layer gradually increased from pure Larix gmelini forest to mixed Larix gmelini-Betula platyphylla-Pinus sylvestris var. mongolica and Larix gmelini-Betula platyphylla forest, to Larix gmelini woodland, but no significant trend of diversity occurred in shrub layer and herb layer for different communities. Whether in tree layer, shrub layer or herb layer, species richness and α diversity showed no remarkable trend along altitude, which may be related to the low altitude of this mountain.