岷江冷杉林皆伐后次生群落结构和物种多样性的演替动态

为阐明岷江冷杉林皆伐后次生群落的演替过程,采用空间代替时间的方法,在川西米亚罗林区海拔3100—3600 m的阴坡选择岷江冷杉林皆伐后次生演替10、20、30、40和50a阶段的次生群落作为研究对象,对其群落结构和物种多样性的动态进行了研究。不同演替阶段的树木均呈显著聚集分布。按群落中优势种的重要值将该演替序列划分为3个类型:悬钩子-蔷薇灌丛、白桦阔叶林和桦木-岷江冷杉针阔混交林。随次生演替,乔木和灌木种的物种丰富度趋于增加,而草本种的物种丰富度趋于减少;乔木和灌木种的Shannon-Wiener多样性指数趋于增大,而草本的Shannon-Wiener多样性指数趋于减小;乔木、灌木和草本层的Pielou均匀度指数均趋于增大;乔木层的Simpson优势度指数趋于减小,灌木和草本层的Simpson优势度指数在演替0—40年阶段趋于增大,而在演替50a阶段趋于减小。在该演替序列中,乔木、灌木和草本层的物种组成均呈耐荫种替代非耐荫种的趋势。

Successional dynamics of community structure and species diversity after clear-cutting of faxon fir (Abies faxoniana) forest stands

In the early 1950s, the subalpine forests in western Sichuan province were dominated by old growth Abies faxoniana forests, large scale logging occurred between 1954 and 1965 and clear-cut was used as the predominant harvest method. Up to 1965 timber yield dropped dramatically for a little of harvestable forest stands and timber harvest operation stopped completely in 1998 when the Natural Forest Protection Program began in the region. In order to clarify the recovery processes of the forests region in western Sichuan Province, China, we studied the dynamics of community structure and species diversity over the first 60 year period of secondary successional stages in the Miyaluo forest area. We observed successional changes in the secondary forest community by adopting the concept of space as a substitute for time. We established 34 20 m × 20 m plots at study sites located at altitudes between 3100-3600 m on shady slopes the Miyaluo forest area. Our study showed that the secondary forests were characterized by Betula albo-sinensis, Betula platyphylla, and A. faxonniana. The vascular plants recorded in the plots included 107 species of 79 genera from 38 families (x herb species, y shrub species, and z tree species). Tree density increased over the first 40 years of successional stages, but then declined by the 50 year stage of secondary succession. Size-classes of trees in 20 to 50 year stages of succession, which were mainly small-sized and medium-sized, all showed reverse J-shaped distributions. Tree species, along with shrub and herb species, all showed significantly aggregated distributions at different successional stages. The successional series was classified into three stages according to the importance value of the dominant species: first, the Rubus and Rosa shrub; second, the Betula broad-leaved forest; and third, the Abies and Betula conifer and broadleaf mixed forest. Betula species still were the dominant species in the third stage, but regeneration of A. faxoniana, which is the dominant tree of old growth in the Miyaluo forest area, was increasingly abundant and widespread. As the successional stages shifted from one to three, herb species richness decreased, while tree and shrub species richness increased. Following changes in successional series from 10 years to 50 years at 10 year intervals, the overall species richness in secondary communities was 54, 49, 33, 54, and 59, respectively. The overall species richness decreased over the first three intervals from 10 to 30 year, and then increased over the next two intervals (40 and 50 years). The Shannon-Wiener diversity indices of tree and shrub layer species increased throughout over the intervals from 10 to 50 years, while the indices of herb layer species decreased continuously over the same successional series. The Pielou Evenness indices of all three layers of species increased with the successional time. Simpson Dominance indices of tree layer species decreased over the successional time, while the dominance indices of the shrub and herb layer species increased up through the 40 year interval of the successional stages and then decreased at the 50 year interval. The species composition also varied over the different time intervals of the successional stages. Light-demanding pioneer tree species such as B. albo-sinensis, which regenerated rapidly after logging was being replaced at later successional stages by the effects of increasing canopy closure and competitive advantages of shade tolerant tree species such as A. faxoniana, which was becoming the dominant tree species in an increasingly species diverse plant community as the Miyaluo forest was returning to the old growth forest of its past.