不同空间尺度西藏色季拉山急尖长苞冷杉群落谱系结构特征

Phylogenetic structure of Abies georgei var. smithii community at different spatial scales in Sygera Mountains of Tibet, China

基于西藏色季拉山4 hm^2亚高山暗针叶林固定样地调查数据,分析了急尖长苞冷杉群落内6个径级(1~2、2~4、4~7、7~11、11~16、>16 cm)的植物在5个空间尺度(5 m×5 m、10 m×10 m、20 m×20 m、50 m×50 m、100 m×100 m)上的谱系结构。结果表明:不同空间尺度上,该群落的净谱系亲缘关系指数(NRI)和净最近种间亲缘关系指数(NTI)值均大于零,整体上表现为谱系聚集。在小空间尺度(5 m×5 m)上,谱系结构聚集强度最大。在所有空间尺度上,群落内小径级个体表现为谱系聚集,随着径级的增大(DBH>7 cm),逐渐表现为谱系发散,且发散程度随径级增加而增大。小径级个体的谱系聚集强度随空间尺度而增大;而大径级个体(DBH>7 cm)的谱系发散程度随空间尺度增加而增大。小径级群落的生境过滤和大径级群落的竞争排斥作用可能是驱动该区域急尖长苞冷杉群落构建的主要生态学过程。

We analyzed the phylogenetic structure of trees within six diameter classes(1-2, 2-4, 4-7, 7-11, 11-16, >16 cm) in quadrats with different size of 5 m×5 m,10 m×10 m, 20 m×20 m, 50 m×50 m, 100 m×100 m in a Abies georgei var. smithii community in a 4 hm^2 stem-mapping plot located in subalpine dark coniferous forest of Sygera Mountains, southeast Tibet. In various spatial scales, both net relatedness index(NRI) and nearest taxon index(NTI) of the community were larger than zero, indicating a clustered phylogenetic structure with the largest clustering intensity at small spatial scale(5 m×5 m). Community of small-size classes were phylogenetically clustering. In large-size classes(DBH>7 cm) phylogenetic over dispersion became more common, with dispersion increased with increasing tree size under all spatial scales. The intensity of phylogenetic clustering in young trees increased with increasing spatial scales, while the intensity of over dispersion in large trees(DBH>7 cm) increased with spatial scale. Our results suggested that environmental filtering in small-size trees and competitive exclusion in large-size trees might be the main ecological processes driving community assembly in this region.