中文摘要：

以陕西省丹汉江流域退耕地南坡和北坡不同退耕年限的自然恢复植物群落为研究对象,开展群落物种组成调查,并进行物种多样性特征分析和群落极点排序,对该区退耕地恢复过程中的植被演替规律进行研究.结果表明：研究区退耕地植被演替的阶段依次为：一年生草本群落→多年生草本群落→灌草群落→乔灌草群落.形成多年生草本群落需2～5a,形成灌草群落需7～10a,形成乔灌草群落需30a以上.南坡和北坡不同类型退耕地的植被演替阶段相同,物种多样性指数略有差异.随着退耕年限的增加,南坡物种多样性指数总体呈先降后升的趋势;而北坡物种多样性指数呈先波动上升,而后在退耕30a时略有下降.

英文摘要：

Taking naturally recovering plant communities on the croplands having been retired for different years and distributed on the southern and northern slopes in the Dan-Han River watershed of Shaanxi Province as test objects,an investigation was conducted on their community species composition,diversity characteristics,and community polar ordination.In the study area,the vegetation succession process on the retired croplands followed the stages of annual herb community→perennial herb community→shrub-herb community→arbor-shrub-herb community.The formation period for perennial herb community,shrub-herb community,and arbor-shrub-herb community was about 2-5 a,7-10 a,and more than 30 a,respectively.On the southern and northern slopes,different types of retired croplands had the same vegetation succession stages,and had small discrepancies in species diversity indices.With increasing retired years,the species diversity indices on the southern slope increased after an initial decrease,while those on the northern slope had a fluctuated increase first,and slightly decreased by the end of the 30 a.