干旱区生态环境知识资源中心

In the present study, we selected a total of 26 Salix sphaeronymphe Gorz shrubs of various sizes on a cutover in the eastern Tibetan Plateau to evaluate the effects of shrub size on richness, cover and biomass of the understorey herbaceous community, grasses and forbs, as well as litter cover and biomass. Results indicated that the richness of herbaceous community, grasses and forbs significantly increased with the increased area of both undershrub canopies and open field. However, the cover and biomass of the herbaceous community beneath the shrub canopies decreased with increasing shrub size. Grasses and forbs, as different functional groups, responded differently to the increasing area of shrubs: the cover and biomass of grasses decreased while those of forbs increased. The cover and biomass of herbaceous community, grasses and forbs in the open field did not obviously vary with area. Under the shrub canopies, the cover and mass of litter positively correlated to area, but this was not the case in the open field. Our results suggest that shrubs have a positive effect on diversity and a negative effect on the cover and productivity of the herbaceous community in forest secondary succession on the alpine cutovers, and that these effects are size-dependent. Moreover, different functional groups of herbaceous plants can respond differently to the presence of shrubs.