PLOS ONE2014-01-13 1:22 AM

The Importance of Large-Diameter Trees to Forest Structural Heterogeneity 大径树木对森林结构异质性的重要性

Abstract
Large-diameter trees dominate the structure, dynamics and function of many temperate and tropical forests. However, their attendant contributions to forest heterogeneity are rarely addressed. We established the Wind River Forest Dynamics Plot, a 25.6 ha permanent plot within which we tagged and mapped all 30,973 woody stems ≥1 cm dbh, all 1,966 snags ≥10 cm dbh, and all shrub patches ≥2 m2. Basal area of the 26 woody species was 62.18 m2/ha, of which 61.60 m2/ha was trees and 0.58 m2/ha was tall shrubs. Large-diameter trees (≥100 cm dbh) comprised 1.5% of stems, 31.8% of basal area, and 17.6% of the heterogeneity of basal area, with basal area dominated by Tsuga heterophylla and Pseudotsuga menziesii. Small-diameter subpopulations of Pseudotsuga menziesii, Tsuga heterophylla and Thuja plicata, as well as all tree species combined, exhibited significant aggregation relative to the null model of complete spatial randomness (CSR) up to 9 m (P≤0.001). Patterns of large-diameter trees were either not different from CSR (Tsuga heterophylla), or exhibited slight aggregation (Pseudotsuga menziesii and Thuja plicata). Significant spatial repulsion between large-diameter and small-diameter Tsuga heterophylla suggests that large-diameter Tsuga heterophylla function as organizers of tree demography over decadal timescales through competitive interactions. Comparison among two forest dynamics plots suggests that forest structural diversity responds to intermediate-scale environmental heterogeneity and disturbances, similar to hypotheses about patterns of species richness, and richness- ecosystem function. Large mapped plots with detailed within-plot environmental spatial covariates will be required to test these hypotheses.
论文摘要 大径树木决定了许多温带和热带森林具有的结构,动力学和功能。然而,他们附带对森林异质性的贡献却很少被提及。我们建立了25.6公顷(ha)永久地的风河森林动态图,在该永久地中我们标注和绘制了所有30,973棵不小于1厘米胸径(dbh)的木质树干,所有1,966棵不小于10厘米胸径(dbh)的断枝,和所有不小于2平方米的灌丛。26类树种的底面积为62.18 平方米/公顷(ha),其中树木占61.60 平方米/公顷,高大灌木占0.58平方米/公顷。大径树木(胸径不小于1米)由占1.5%的树干,占31.8%的底面积和占17.6%的异质性底面积组成,其中底面积中占主体的为美国铁杉和北美黄杉。北美黄衫,美国铁杉以及所有混合树种中的小径亚群体,相对于完整空间随机性(CSR)空值模型表现出高达9米的显著聚集(P≤0.001)。大径树木的模式或者和完整空间随机性(CSR)相似(美国铁杉),或者表现出轻微聚集(北美黄杉和西部红松)。大径和小径北美铁杉之间显著的空间斥力表明,以十年为时间尺度,大径北美铁杉通过竞争相互作用对树量起管理作用。对两个森林动态图的比较表明,森林结构多样性能对中等规模的环境异质性和紊乱作出反应,这与有关物种丰富性模式和丰富的生态系统功能的假设类似。我们要求带有详尽内图环境空间协变量的大型绘制图来检验这些假设。

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