Tree-ring records of Qilian Juniper''s growth and regeneration patterns in the central Qilian Mountains
祁连山中部祁连圆柏生长与更新方式的树轮记录

In Qilian Mountains,Sabina przewalskii is one of the most important intolerant trees on south-facing mountain slopes.In this study,a plot of 50m×15m of the Qilian Juniper community in the central Qilian Mountains was used for stand structure and dendroecological sampling.Within the plot,all trees(>5.0cm DBH) were cored and diameter at breast height was measured.Besides,the amount of all trees and saplings was recorded respectively with their spatial distribution patterns being mapped.A total of 23 trees and 64 saplings were cored and recorded respectively in this plot. The community of Qilian Juniper was very sparse and its compositions could be simply divided into two layers,i.e.the arborous layer and the herbaceous layer.The arborous layer was entirely occupied by Qilian Juniper.The diameters of trees in the plot ranged from 9cm to 33cm,with 78.3% of all individuals falling into the diameter range between 10cm and 25cm.The age structure indicated that most of the trees in this region were less than 250 years old,and there were not any trees with an age of less than 60 years being found in this stand.It was notable that there were large numbers of saplings in the plot now.The radial growth rates of Qilian Juniper of this plot varied between 0.02mm per year and 1.84mm per year,with the mean radial growth rate being 0.62mm per year.Release events in radial growth,indicative of different disturbances,occurred once or more in most of the trees during the last 200 years,with the highest frequency of releases occurred in the 1970s.The result of correlation function analysis indicates that temperature is the main environmental factor influencing tree ring growth of Qilian Juniper in this region,and high temperature could accelerate the radial growth.Besides,precipitation in June and July of the growth season is significantly and positively correlated with the radial growth of Qilian Juniper.The tree-ring chronology displayed a persistent growth increase from the 1970s to now,suggesting a positive growth response to the global warming.Under recent climate warming,it can be concluded that the forest would have regrown rapidly in this region once the anthropic disturbances are well controlled.More extensive samplings and corresponding physiological research will greatly improve our knowledge of Qilian Juniper's growth and regeneration patterns in different environmental gradients.