青藏高原东北边缘桦木林木本植物种间联结

Interspecific association of birch forests in the subalpine of the northwest border of Qinghai-Xizang plateau

青藏高原东北边缘地区位于我国东部季风区、西北干旱区与青藏高原高寒区的交汇地带,该区既兼具3大自然区的特点,又具有边缘地带气候波动不稳定性和自然生态环境的脆弱性,是全球变化重点监测的地区之一。研究青藏高原东北边缘亚高山桦木林的种间联结,不仅有助于更深刻地认识该地区桦木群落的结构、功能和演替,对于维持该地区群落稳定性以及生态恢复具有重要意义。本文选取青藏高原东北边缘桦木林中20个优势种,采用方差比率法(VR)检验多物种间的联结性,2×2列联表分析共同出现百分率(JI)、点相关系数(Ф)、Dice指数(DI)来表示种间联结程度,用重要值的Pearson相关和Spearman秩相关来检验相伴出现的机率等方法分析其种间关联性。结果表明:群落总体联结VR值为1.094,说明20个种群间表现出净正关联,其统计量W值为10.94说明20个种群之间在总体上的正关联不显著;大多数种对的JI值、DI值在0.4以下,说明种对之间联结程度不显著,Φ值大部分处于[-0.2,+0.2]值域内,说明种对之间的正或负的联结性较弱;而Spearman秩相关所测得的正负关联比要大于Pearson相关所测得的,且Spearman秩相关要优于Pearson相关。从以上结果可以看出,青藏高原东北边缘三种桦树天然次生林处于不稳定的状态,即演替的中期阶段,其逐渐会被地带性植被所取代。

The subalpine of the northeast border of Qinghai-Xizang plateau is an ecotone among the eastern China monsoon region,arid region in west China and alpine and cold region of Qinghai-Xizang plateau. It is the key supervised region of global change with characteristics of each natural region and climate fluctuation and frangibility of natural ecological environment. Interspecific association of birch forests in the subalpine of the northeast border of Qinghai-Xizang Plateau was studied to made for better understanding community structure,function and succession,which was significant for maintaining community stability and ecological restoration. 20 dominant species of birch forests in northeastern border of the Qinghai-Tibet plateau were chosen to analyze interspecific correlations by using overall association（VR）,three association indices,Pearson and Spearman correlation coefficients. The overall association（VR） of communities was 1.094,indicating that the relationship among 20 populations was positive. And its statistical parameter（W） was 10.94,indicating that the total 20 populations had no significant correlation. The percentages of co-occurrence of dominant （JI） and Dice index （DI） among most species were lower than 0.4,showing that the correlations of 20 populations were not significant. The Point correlation coefficients （Φ） among most species were between -0.2 and 0.2,showing that the positive or negative correlations were not significant. The ratio of positive correlation and negative correlation measured by Spearman rank correlation was higher than that measured by Pearson correlation,indicating that Spearman rank correlation was better than Pearson correlation. It is suggested that natural secondary forests of three birch species in northeastern border of the Qinghai-Tibet plateau were in the middle stage of succession,and also they would be gradually substituted by the climax species.