Soil properties and plant species in an age sequence of Caragana microphylla plantations in the Horqin Sandy Land, north China

In the semi-arid Horqin Sandy Land of north China, Caragana microphylla, a leguminous shrub, is the dominant plant species and is widely used in vegetation reestablishment programs to stabilize shifting sand. We collected soil samples and investigated the invaded plant species in an age sequence of 0-, 5-, 13-, 21-, and 28-year-old C microphylla plantations to assess the effects of the shrub on soil physicochemical properties and development of herbaceous species diversity. Soil samples were taken from two depths (0-5 and 5-20 cm) under the shrub canopy and in the mid-row location between shrubs. Results showed that shrub establishment and development improved soil water holding capacity (WHC), enhanced organic C and total N accumulation, and decreased pH and bulk density. Carbon and nitrogen concentrations increased significantly with increasing plantation age and had increased by 15.3-20.5-fold and 11.1-13.6-fold at 0-5 cm depth at 28 years of plantation compared with non-vegetated dune, although incremental rates were faster in the early establishment stage (0-13 year) than late successional stage (13-28 year). It was found that C. microphylla contributed significant enrichment effects with higher C and N contents under their canopies as compared with alleys. With increased plantation age, the 'islands of fertility' expanded and enrichment ratios decreased. At the same time, C microphylla facilitated the colonization and development of herbaceous species by ameliorating stressful environmental conditions. Species diversity increased with increasing plantation age. The simple, artificial vegetation system developed toward a complicated, artificial and natural ecosystem capable of reversing desertification. (C) 2003 Elsevier B.V. All rights reserved.