Soil fertile islands of shrub canopy and impacts on vegetation in chronosequence of Caragana microphylla

In order to understand the soil fertile islands of shrubs and the effect of shrub canopy on herbaceous vegetation in the chronosequence of Caragana microphylla in Horqin Sandy Land,the soil nutrient status and vegetation distribution patterns under shrub canopy and between shrubs were studied.The results show that the N,P,K and organic matter in soil increase with the time increase of shrub establishment,and the soil nutrient in plantation shrub community are significantly lower than that in natural community;in natural community and shrubs established in 1987,total N and organic matter in surface soil under shrub canopy are significantly higher than that between shrubs.However,there is no significant difference for shrubs established in 2000 and 1995;herbaceous vegetation coverage,number of species,plant density and height,and biomass increase with the time increase of shrub establishment while herbaceous vegetation coverage and plant density of shrubs established in 1987 are 1/2 less than that of natural community;plant density and biomass under shrub canopy are higher than that between shrubs for all Caragana microphylla communities,which means that shrubs is more favorite for promoting herbaceous growth than forming soil fertile islands.