色季拉山急尖长苞冷杉种群不同龄级立木的空间分布格局

Spatial distribution patterns of standing trees at different ages in Abies georgei var.smithii forests in Sejila Mountain

植物种群空间分布格局是种群个体在水平空间的分布、配置状况,是种群对环境适应的生存策略及适应机制的反映。以色季拉山急尖长苞冷杉(Abies georgei var.smithii)原始林为研究对象,在色季拉山东坡设置100 m×100 m固定样地,采用相邻网格法将样地划分为25个20 m×20 m的调查单元,对样地内所有基径≥0.1 cm的急尖长苞冷杉进行调查,记录林木的坐标、胸径、基径、冠幅等信息。依据基径和胸径两个指标将林木划分为12个径级和6个龄级(幼苗、幼树、小树、中树、大树、老树),对种群的径级特征及空间分布格局进行分析。结果显示:(1)急尖长苞冷杉种群在不同径级上的分布成倒"J"型。(2)种群整体、幼苗、幼树随空间尺度的增大依次呈现集群分布、随机分布和均匀分布,小树、中树、大树、老树在所研究尺度内均为随机分布。(3)幼树与幼苗在小尺度上接近或达到负关联,在中、大尺度无显著关联;小树、中树、大树、老树在空间分布上与幼苗、幼树的关联性符合Janzen-Connell假说,但小树、中树、大树、老树之间无显著关联。上述结果表明:色季拉山急尖长苞冷杉种群为稳定增长型种群,小径木以集群方式相互庇护以提高自身适应环境的能力,大径木在小、中尺度抑制林下更新,在大尺度则促进更新。该结果有助于揭示色季拉山急尖长苞冷杉种群的现状与动态规律,可为深入研究该种群维持机制提供理论依据。

The spatial distribution pattern of plant community refers to the individual distribution and configuration in the horizontal space and reflects its survival strategy and adaptation mechanism to the environment.Taking Abies georgei var.smithii forest in Sejila Mountain as the research object,a fixed plot of 100 m×100 m was set on the eastern slope of Sejila,which was divided into 25(20 m×20 m)by the adjacent grid,and the coordinates,breast diameter,base diameter,crown width and other information of the plants with base diameter≥0.1 cm were recorded.The diameter characteristics and spatial distribution patterns in 12 diameter classes and 6 age classes(seedlings,saplings,juvenile trees,adult trees,big trees,and old trees),graded by base diameter and breast diameter,were analyzed.The results show that(1)the distribution of Abies georgei var.smithii at different diameter levels is inverted“J”.(2)The overall population,seedlings,and saplings show the cluster distribution,random distribution,and uniform distribution with the increase of spatial scale,respectively;and juvenile trees,adult trees,big trees,and old trees are randomly distributed within the studied scale.(3)Seedlings are close to or negatively associated with saplings at a smaller scale,and there is no significant correlation at the medium and larger scales.The correlation of juvenile trees,adult trees,big trees,and old trees with seedlings and saplings in spatial distribution is consistent with the Janzen⁃Connell hypothesis,whereas there is no significant correlation between the former size classes.The above results show that the Abies georgei var.smithii in Sejila Mountains tend to be stable growing;trees of small diameter shelter each other in a cluster to improve their adaption to the environment;trees of large diameter inhibit understory regeneration at smaller and medium scales,while promote regeneration at larger scales.The results would contribute to the revealing of the status and dynamics of Abies georgei var.smithii in Sejila Mountain,and thereby provide a theoretical basis for further study on the maintenance mechanism of the population.