Old-field Succession Sequence in Loess Area in Northern Shaanxi of China

Hierarchical clustering method was applied for division of stages of old-field succession of loess area of Northern Shaanxi, and the similarity among different communities in abandoned field of different abandoned year and site condition can be learnt quantitatively, and stages or sequence of old-filed succession can be determined. The result revealed that the stages of old-field succession are: polydominant association of annual weed artemisia scoparia and other perennial herbage→Lespedeza davurica and perennial herbage association→artemisia vestita and perennial herbage association→tuft grass bothriochloa ischaemum and perennial herbage association→undershrub Buddleja alternifolia association. Among them, the appearance of shrub association (undershrub Buddleja alternifolia) contrasts results in former studies that it was impossible to form shrub association in loess area of Northern Shaanxi. Thus, this study is not only a complement of former studies, but also a new discovery and innovation.