Long‐term impacts of shrub plantations in a desert–oasis ecotone: Accumulation of soil nutrients, salinity, and development of herbaceour layer

Abstract

AbstractThis study used a 40‐year chronosequence of Haloxylon ammodendron plantations to evaluate its impacts on soil and vegetation conditions in a desert–oasis ecotone with extremely low annual precipitation (≈100 mm). We found that the fraction of silt and clay contents significantly increased from 6.4% and 5.1% in Year 0 to 22–23.3% and 15.8–18% in the 40‐year‐old plantation in the soil depths of 0–10 and 10–20 cm, respectively. Soil nutrients (i.e., soil organic matter, total nitrogen, and total phosphorus) were significantly improved after H. ammodendron plantations. However, there was a significant increase in soil salinity, which may negatively affect sustainability of ecosystem restorations in future (drier and warmer) climate. Planted H. ammodendron established and thrived in the first 25 years, but the percent vegetation cover started to decrease afterwards because of reduction in deep soil moisture and less access to groundwater. By comparison, herbaceous plants gradually developed after H. ammodendron plantations and finally dominated the ecosystems with high density (300–400 herbs·m−1), cover (25–30%), and biomass (50–60 × 10−3 kg·m−2) after 30–40 years. These results suggest that although introduced shrubs can act as nurse plants to improve vegetation and soil conditions, their dominance could be a transient state. Thus, evaluation of ecosystem restoration through plantations should use long‐term data, and the stable plant restorations for years or even decades could be a transient state and does not necessarily suggest a successful revegetation effort in the long run. Further, its environmental consequences (i.e., soil salinity) of shrub plantations need to be evaluated in ecosystem restorations especially in a changing and harsh environment.