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

关键词:  油松, 天然林, 空间结构, 非空间结构, 角尺度, 混交度, 大小比数

Key words:  Pinus tabulaeformis, natural forest, spatial strucutre, non-spatial structure, uniform angle index, mingling, dominance

摘要:

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(M^-=0.019),几乎为油松纯林,个体大小分化均匀(U^-=0.478),整体呈随机分布(W^-=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 m²。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。

Abstract:

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.