选择祁连山中部50m×15m的祁连圆柏样方进行树轮生态学取样与分析。分析结果表明,样方内大部分祁连圆柏的树龄小于250年,最近几年有大量幼苗萌生。祁连圆柏的径生长方式各有异同,大部分祁连圆柏在生长过程中出现1次以上生长释放事件,19701980年间出现生长释放的频率最高,占总释放次数的35%,轮宽年表也显示祁连圆柏的轮宽指数自1970s以来持续上升。另外,相关分析结果表明,温度是影响采样点区域祁连圆柏径向生长的主要环境因子,较高的温度有利于树木生长,6、7月份的降水也与树木径向生长呈显著正相关。在全球变暖的背景下,如果能积极开展植树造林,并有效控制人类活动的干扰,该区域祁连圆柏林更新状况将会显著改观。
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.
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