Factors affecting species diversity of plant communities and the restoration process in the loess area of China

The Loess Plateau of China is a special region that has suffered from soil erosion and water loss for a long time. Ecological restoration is an urgent task for this region. This study aims to characterize the variation in the vegetation restoration process on the abandoned croplands in the loess area. A series of quadrats were set up in different restoration stages in the Yancun watershed, Shanxi Province, an area of typical loess hills and gullies. Species and environmental data were recorded in each quadrat. Multivariate analysis and indices for species richness, diversity and evenness were used in the analysis. A series of plant community stages with different composition, structure and environments were identified by clustering analysis (UPGMA). These communities included three main restoration stages, grassland stage, scrubland stage and forest stage, and nine sub-stages, i.e. nine associations. Canonical correspondence analysis (CCA) showed that time since abandonment was the key factor for the restoration process, and the first CCA axis was effectively a time gradient. Elevation, soil type, slope and aspect were also important in the restoration process in the loess area. Species richness and diversity increased, and evenness decreased in the restoration process. The variation of species richness and diversity significantly correlated with time since abandonment, elevation and soil type. Time since abandonment is most important to the restoration process and species diversity is the main indicator of community changes in restoration in the Loess Plateau. For effective management, abandoned lands should be kept from disturbance.