黄土高原油松天然纯林结构特征的研究

结构是森林群落的基本特征,决定着群落的功能和发展方向。该研究采用结构参数角尺度(W)、混交度(M)、大小比数(U)以及样地纵剖面图分析了两块长宽均为60 m×60 m的油松天然林的空间结构特征,同时采用胸径(DBH)、树高(TH)和冠幅面积(CA)分布的直方图以及Shannon-Wiener多样性指数分析了它的非空间结构特征。结果表明:油松天然林种间隔离程度很低(=0.019),几乎为油松纯林,个体大小分化均匀(=0.478),整体呈随机分布(=0.485)。小树(TH≤5 m)个体相对较少,而大树(TH10 m)占多数且其树高分布集中。平均树高多样性THD=2.35,胸径集中分布在14~34 cm,58.4%~62.8%的树冠面积分布在20~40 m~2。林下油松幼苗更新丰富,但分布不均。这些特征表明成熟的油松天然林群落结构不稳定,可能趋向衰退并将逐渐被其他阔叶树种代替。

Structural properties of natural Loess Plateau forest stands dominated by Pinus tabulaeformis

The structure of vegetation strongly regulates community function and the future direction of successional processes.In this study, we deployed two sampling plots measuring 60 m × 60 m in natural vegetation dominated by Pinus tabulaeformis, and measured stand spatial properties by calculating uniform angle (W), mingling (M), and dominance (U) indices and by constructing elevation plots.Concurrently, we explored non-spatial attributes of the stands using frequency distribution plots of diameter at breast height (DBH), tree height (TH), and crown area (CA);we also calculated Shannon-Wiener tree height diversity indices.Both vegetation plots were dominated by P.tabulaeformis, which accounted for > 98% of trees in the area.Trees of different dimensions were spatially differentiated in a regular manner (U=0.478) with low species segregation (M=0.019).Tree dispersions in both plots were random in the horizontal plane (W=0.485).We found few small trees (TH ≤5 m) in the plots.Large trees (TH >10 m) made up the greatest proportion of the population (66.9%-84.1%), and their height distribution was clumped.The mean TH diversity index (THD) was 2.35.Most DBH values fell within the 14-34 cm range, and most (58.4%-62.8%) dimensionless CA indices were within the range of 20-40 m2.Recruitment of P.tabulaeformis was dense and unevenly dispersed, suggesting that these populations of mature natural stands were (i) unstable, (ii) tracking a declining trajectory, and (iii) destined for replacement by other species.