黄土高原油松天然纯林结构特征的研究

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

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(TH>10 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。

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 Pi- nus tabulaeformis, and measured stand spatial properties by calculating uniform angle （W）, mingling （M）, and domi- nance （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 al-so 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 hori- zontal 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 diversi- ty 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 m：. Recruitment of P. tabulaeformis was dense and unevenly dispersed, sug- gesting that these populations of mature natural stands were （i） unstable, （ii） tracking a declining trajectory, and （iii） destined for replacement by other species.