青藏高原东缘林线杜鹃-岷江冷杉原始林的空间格局

为深入理解高山林线原始林中优势树种的空间结构特征和种间关系,以青藏高原东缘林线杜鹃-岷江冷杉原始林1 hm²样地调查数据为基础,采用成对相关函数g(r)函数,分析了优势种岷江冷杉(Abies faxoniana)和凝毛杜鹃(Rhododendron agglutinatum)各径级的空间分布格局和各径级间的空间关联性。结果表明:岷江冷杉和凝毛杜鹃径级分布连续,呈倒"J"型,均为进展种群。小尺度上,对于岷江冷杉活立木(小树+中树+大树)、小树、中树为显著聚集分布,大树为均匀分布,死树则为随机分布;凝毛杜鹃活立木(小树+中树+大树)、小树、中树、大树、死树均为显著聚集分布。小尺度上随径级增大岷江冷杉的分布格局从聚集分布趋于均匀分布。岷江冷杉大树与其小树的空间关联验证了Janzen-Connell假说中的距离制约效应。通过验证接受了随机死亡假说,发现种内的密度制约效应不明显。两个树种的枯立木对凝毛杜鹃小树均表现为排斥关系,而对岷江冷杉小树表现为相互独立的关系。两个优势种总体表现为相互独立,但种间不同径级间的空间关联性各异。

Spatial pattern analysis of a Rhododendron-Abies virginal forest near timberline on the eastern edge of Qinghai-Tibetan Plateau, China

Although biological characteristics of different populations in timberline area are widely studied, the spatial relationships of main tree species are still poorly understood due to a lack of studies. In order to improve the understanding on the spatial structure and relationships of rhododendron species and canopy trees in virginal forests near timberline with less anthropogenic influence, we studied the role of spatial patterns and associations of Abies faxoniana and Rhododendron agglutinatum on the eastern edge of Qinghai-Tibetan plateau, China. Based on the investigation in a 1 hm² Rhododendron-Abies virginal forest plot near timberline on the eastern edge of Qinghai-Tibetan plateau, China, the pair correlation function g(r) was used to analyze the spatial patterns of two dominant species, A. faxoniana and R. agglutinatum, with different size classes and the spatial associations of intra- and inter-species between different size classes. Both species showed continual distribution of DBH size classes and a reverse J-shaped pattern, suggesting an increasing population. For A. faxoniana, alive trees (small + middle + big), small trees and middle trees showed significantly aggregated distribution, and big trees showed regular distribution, while dead trees showed random distribution at small scales. For R. agglutinatum, alive trees (small + middle + big), small trees, middle trees, big trees and dead trees all showed significantly aggregated distribution at small scales. A. faxoniana tended to be from aggregated distribution to regular distribution with increasing size classes at small scales. A. faxoniana big trees showed significant repulsion pattern with its small trees at 0 6 m, while showed significant attraction pattern at 8 13 m, and showed independent pattern at other scales, and those patterns validated the distance dependence effects of Janzen-Connell hypothesis. Random mortality hypothesis was accepted through random labeling test, and there was no clear evidence of density dependence effect of both intra-species. Standing dead trees of both species showed repulsion pattern with small trees of R. agglutinatum at small scales, suggesting that it was not favorable for the settlement of small trees of R. agglutinatum around standing dead trees, while standing dead trees showed independence pattern with small trees of A. faxoniana at small scales. There was no significant spatial association between trees alive of the two species, while different classifications of size classes of the two species showed different spatial associations. Particularly, A. faxoniana big trees showed repulsion pattern with small and middle trees of R. agglutinatum at small scales. A. faxoniana big trees showed significant repulsion pattern with big trees of R. agglutinatum at 0 4 m, while showed attraction significant pattern at 4 11 m, suggesting that there were spatial segregation between those two species. Intra-specific spatial associations were highly positive for individuals of both species in adjacent size classes, while big trees and small trees exhibited significantly negative association. Spatial patterns and associations of A. faxoniana and R. agglutinatum of different size classes reflected differentiation of spatial niche in Rhododendron-Abies virginal forests. It was inferred that adaptation of the two species to the habitat of alpine timberline and spatial segregation of patches between the two species contribute to the coexistence of A. faxoniana and R. agglutinatum.