[Vegetation succession on retired croplands during their recovery processes in Dan-Han River Watershed of Shaanxi Province, Northwest China].

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, dif ferent 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.