元宝山南方红豆杉克隆种群分布格局的分形特征

FRACTAL PROPERTIES OF DISTRIBUTION PATTERNS OF TAXUS CHINENSIS VAR.MAIREI CLONAL POPULATIONS IN THE YUANBAOSHAN MOUNTAIN,CHINA

南方红豆杉（Taxus chinensis var.mairei）是提取抗癌药物紫杉醇的珍贵资源植物。分布于广西元宝山自然保护区的南方红豆杉,自然状态下以克隆繁殖方式进行种群更新,研究其种群克隆生长的空间分布格局,可揭示种群克隆繁殖特性和生态适应机制,对南方红豆杉这一珍稀濒危物种的保护和管理具有重要意义。利用分形理论中的计盒维数和信息维数,对元宝山的南方红豆杉克隆种群空间分布格局的分形特征进行了分析,结果表明：种群空间分布格局存在分形特征,其计盒维数介于0.9931-1.3531之间,信息维数介于1.3508-1.6521。南方红豆杉克隆种群格局的计盒维数远离最大理论维数值2,种群总体对空间的占据能力较弱。克隆构型指数与种群计盒维数密切相关。分析结果显示,克隆构型趋于“密集型”的种群具有较强的空间占据能力,而克隆构型趋于“游击型”的种群其空间占据能力较弱。信息维数与种群的集聚强度密切相关,其差异反映了种群格局强度的变化,较大的信息维数反映种群个体的集聚强度较高,而较小的信息维数则反映出种群个体间的集聚强度较弱,其维数值大小与分株种群数量、分株种群斑块的空间配置密切相关。

Aims Taxus chinensis var. mairei is the material from which taxol, an effective low-toxicity cancer-resistancemedicine, is distilled. This species reproduces asexually, especially through sprouting from stems, which enables Taxus to expand its spatial occupation and maintain its population. Therefore, study on clonal properties of Taxus populations may provide a scientific basis for protecting and regenerating populations. This study addresses the following questions： 1 ） what are the fractal properties of population distribution patterns, 2） are clonal architecture and fractal properties correlated and 3） are fractal properties and aggregation correlated？ Methods Based on a survey of Taxus, we established four 40 m×15 m plots in its central distribution area in Yuanbaoshan Nature Reserve. For each plot, we determined the spatial coordinates of each Taxus individual. For Taxus 〉 3 m tall, we measured height, crown size, height to branches and diameter at breast height; for shorter Taxus seedlings and saplings, only height was measured. We also estimated or measured cover and height of shrubs and herbs. Fractal properties of population patterns were analyzed by using the box-counting dimension and the information dimension. Important findings The box-counting dimension ranged from 0. 993 1 to 1. 353 1, which was far from the theoretical value 2, indicating low degree of spatial occupation. Significant correlation between the clonal architecture index and the box-counting dimension indicates that degree of spatial occupation was closely related to clonal architecture, i.e., populations tending to have phalanx clonal architecture had a stronger degree of spatial occupation than those tending to have guerrilla clonal architecture. The information dimension varied from 1. 350 8 to 1. 652 1 with community type. The Pearson correlation between information dimension and pattern index is significant, suggesting that differences of information dimension could reflect variation of the aggregation intensity. Information dimension was closely related to number and spatial distribution patterns of tamers.