藏东南急尖长苞冷杉群落空间点格局分析及其时空动态

为探究藏东南色季拉山急尖长苞冷杉（Abies georgei var.smithii）群落的空间分布格局及其时空动态,在急尖长苞冷杉纯林中设置1个1 hm²的固定样地,记录样地内所有高度>2 m的急尖长苞冷杉的年龄、胸径、冠幅和坐标等指标。根据径级分布分析种群的径级结构,采用点格局分析方法对种群的空间格局进行分析。结果显示：（1）急尖长苞冷杉的径级分布为倒"J"型,结构稳定,自然更新良好。（2）成树在各个时期和不同尺度上都呈随机分布;幼树在1891年之后的各个时期在小尺度（2 m）上呈聚集分布,1981-2012年在1-41 m尺度上陆续出现聚集分布;幼苗在1861-1920年在小尺度（1-2 m）上呈聚集分布,1951-1980年出现聚集分布的尺度范围最大（1-35 m、41 m和48 m）。（3）在不同时期中,不同年龄组树木之间几乎都呈正关联或无关联;成树和幼树随时间推移从无关联到在各个尺度上陆续出现正关联的变化;成树和幼苗随时间呈无关联、中大尺度（32-35 m、44 m和49 m）正关联和无关联的变化;幼苗和幼树呈现从无关联转变为小尺度（8 m）正关联和小、中尺度（1-30 m）正关联的变化。研究结果表明：成树在小尺度上对幼龄树存在一定的抑制,但在较大尺度是促进的。1951-1980年样地中的幼苗数量大量增加,随后30年幼树的数量因幼苗长大也有增加,这在一定程度上增大了竞争。但总体来看急尖长苞冷杉群落在演替过程中具有种内促进作用。

Spatial point pattern analysis and spatio-temporal dynamics of Abies georgei var. smithii forests in southeast Tibet

In order to investigate the spatial pattern and spatiotemporal dynamics of Abies georgei var. smithii community in Sygera Mountains, the southeastern Tibet, China. A permanent plot of 1 hm² was set up in Abies georgei var. smithii stand. All the fir individuals were mapped in the plot and age, diameter at breast high (DBH), crown width and coordinates for each smith fir tree > 2 m were recorded. The diameter class structure was analyzed according to its distribution, and the spatial pattern of the population was analyzed by point pattern analysis. The results showed that (1) the diameter class distribution of A. georgei var. smithii was inverted "J" shape, indicating that the community had a stable structure and good natural regeneration. (2) The adult trees were almost randomly distributed in different periods and scales. The juveniles were aggregated at a small scale (2 m) in each period after 1891. Seedlings were aggregated at 1-41 m scale from 1981 to 2012 and at small scales (1-2 m) from 1861 to 1920. The largest scale range (1-35 m, 41 m, and 48 m) of seedlings aggregation was observed in 1951-1980. (3) In all the five periods, there was almost no or positive association between trees at different age groups. The association between adult and juveniles shifted from no association to positive association at all scales. Adults and seedlings showed no correlation at medium and large scales (32-35 m, 44 m, and 49 m), but the positive and or uncorrelated changes over time. Seedlings and juveniles showed a change from no association to positive association at small scale (8 m) and then positive association at small and medium scale (1-30m). The number of seedlings in the plot increased greatly in 1951-1980, and the number of saplings in the following 30 years also increased as the seedlings grew up, which in part increased competition in the fir stand. In general, Abies georgei var. smithii community had an intraspecific promoting effect during its succession.