金沙江干热河谷区车桑子的点格局与负密度依赖研究

Study on the Points Pattern Characteristics and Negative Density Dependence of Dodonaea viscosa of Jinsha River Dry-Hot Valley

  • 摘要: 基于负密度制约假说对植物群落构建规则的解释,研究金沙江流域干热河谷区车桑子的分布格局和负密度依赖(NDD)的作用过程,揭示干热河谷区生态脆弱带优势建群种稳定性机制。采用点格局分析中的成对相关函数O−ring的O(r)以及随机标签模型(RL),分析车桑子种群点格局特征和密度制约效应。结果表明:车桑子种群分布格局聚集频率随着空间尺度呈倒J型(近L型),0~5 m呈较强的聚集分布,5~22 m的尺度上,存在较弱的聚集分布现象,在> 22 m尺度上车桑子种群为随机分布;车桑子和常见木本伴生种在0~9 m尺度上O12(r)> 0.04存在强度关联,12~30 m尺度表现为弱关联,30~72 m主要表现为无关联或较弱的负关联。密度制约的自疏效应在0~40 m尺度上均不明显,但距离制约在小树阶段比在中树阶段明显,同时大树在2 m距离内对同种小树表现出强的庇护效应。车桑子种群从小树、中树到大树的依序生境利用方式没有差异,但小树的额外聚集度明显大于中树,在 0~22 m 尺度上表现出明显的稀疏效应。点格局O−ring函数能更清楚刻画车桑子种群的格局与小尺度的关系,在消除累加效应上,比L函数更有优势。车桑子种群各龄级结构在生境利用上无明显差异。在中小尺度上,密度制约是车桑子为建群种的群落骨架构造的重要因素之一,为物种共存提供空间;在金沙江干热河谷区上缘交错带上,密度制约是车桑子群落构建与生物多样性动态维持稳定性的潜在驱动力之一。

     

    Abstract: Based on the explanation of the community construction rules with the negative density restriction hypothesis, the distribution pattern of mulberry in the dry-hot valley(DHV) of Jinsha River basin, the process of negative density dependent on(NDD) were studied, which provides a reference for revealing the maintenance mechanism of community in the DHV eco-zone. Ripley's o−ring(R), a pairwise correlation function in point pattern analysis, and random-labeling were used to analyze the point pattern characteristics and density-restriction effect of D. viscosa population. The pattern aggregation frequency of D.viscosa population is inverted J type(nearly L type) with spatial scale, and random distribution on medium-large scale. The aggregation distribution of the mulberry population was strong from 0−5 m, and weak from 5−22 m. The aggregation distribution of the mulberry population was random at the > 22 m.O12(r) > 0.04 was strongly correlated with common woody associated species at 0−9 m scale, weakly correlated at 12−30 m scale, and had no correlation or weak negative correlation at 30−72 m scale. The self-thinning effect of density restriction was not obvious at the scale of 0−40 m, but the distance restriction was more obvious at the small tree stage than at the middle tree stage. At the same time, the large trees showed stronger sheltering effect to the same kind of small trees within 1m distance. There was no difference in the order habitat utilization patterns among the subpopulations, but the extra aggregation degree of small trees was significantly higher than that of medium trees, showing obvious sparsity effect at the scale of 0−22 m. The Ripley's O−ring function for point pattern can clearly describe the relationship between pattern and scale of mulberry population, and eliminate the cumulative effect. There is no difference in habitat utilization of different age class structure of D. viscosa population, but there are different degrees of density restriction in different age class structure, and different age class populations can coexist well in medium and large scale. On the medium and small scale, density restriction is another important factor for the community skeleton structure and species coexistence of D. viscosa, which provides space for species coexistence. The density restriction of mulberry population is in the ecotone of the upper edge of the Jinsha River's DHV. Density restriction is one of the potential driving forces for the construction of D. viscosa community and the dynamic maintenance of biodiversity stability.

     

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