太白山牛皮桦-巴山冷杉混交林空间格局及关联性研究

Spatial Patterns and Associations in a Birch-fir Forest in Mt. Taibai

采用改进的点格局分析法——邻域密度函数(Neighborhood Density Function,NDF)对太白山地区桦林-冷杉林交错区内主要树种的空间分布格局、种间空间关联性及其更新空间关联性进行了分析。结果表明:各树种所有个体整体上都呈随机分布,划分不同层级后,则各林层个体分布格局各异,各树种在较低的林层呈明显聚集分布,随林层增高,中、高层内个体聚集分布的空间尺度降低。两个主要竞争种牛皮桦(Betula albo-sinensisvar.septen-trionalis)和巴山冷杉(Abies fargesii)整体表现出显著空间负相关,巴山冷杉与玉皇柳(Salix yuhuangshanensis)未表现出明显相关性,而牛皮桦与玉皇柳间则有空间负相关的趋势。牛皮桦的更新格局仅依靠自身倒木扰动产生的机会,且被限定在较小尺度上。巴山冷杉在小尺度上会限制自身更新,此外与牛皮桦在小尺度上竞争激烈,可占据利用其空间位置进行更新。从空间格局分析角度认识牛皮桦和巴山冷杉的生态学特性,为进一步研究其共存机制,认识太白山桦林在秦岭植被垂直带中的作用和地位提供参考依据。

An across-scale spatial pattern analysis which is closely related to Ripley＇s K statistic but without cumulate effect was conducted to characterize the spatial characteristics and associations of an old growth birch-fir forest located in Mt. Taibai, China. The study was designed to analyse the spatial distributions of trees in the forests for assessing the different tree species spatial distribution patterns of different trees＇ classes to increase the understanding of the effects of spatial structure, spatial associations, species co-existence and forest form on pattern-process relationships in the forest. The modified spatial point analysis methods ,Univariate and Bivariate NDF （Neighborhood Density Function） were employed to capture spatial distribution pattern and characteristics of the forest. The results of this study showed that all species exhibited random distributions at most spatial scales. When joint forest canopy structure and spatial pattern were conducted, this related changes in vertical layers to changes in spatial pattern. The lower layers tended to be aggregated at most scales for all tree species. But the aggregation degree decreased with canopy height, and the scales decreasing with a layer height increasing. Betula albo-sinensis vat. septentrionalis stems were significantly negatively associated to the Abies fargesii stems in forest at most scales, and there was no significant correlation between Abies fargesii and Salix yuhuangshanensis stems. The sequel of negatively associated was also observed between Betula albo-sinensis var. septentrionalis and Salix yuhuan-gshanensis stems. Betula stems were positively associated with conspeeific dead trees but were limited in small scales （ 〈 5 m） suggesting that seed dispersal and vegetative regeneration influenced the spatial patterning of Betula by itself. Abies influenced recruitment and showed a negatively associated pattern and indicated intense competition with Betula in small scales （ 〈 5 m）. The results elicited from NDF, the modified spatial point analysis suggested that different regeneration strategies among the species play an important role in regulating their spatial distribution patterns, while competition between individuals of Betula and Abies at the all stage also contributes to spatial patterning of these communities. The recruitment limitations of Betula and Abies may affect the persistence of these species and the long-term dynamics of the forest. The mechanism of co-existence of different species in Mt. Taibai should be investigate and discuss in a further research.