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

Abstract

This 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.

Responses of four dominant dryland plant species to climate change in the Junggar Basin, northwest China

“…To fix sand dune and combat desertification, H. ammodendron , C. mongolicum , and other shrub species have been widely used in afforestation in the drylands of northwestern China (Yu & Wang, ). Though some considered H. ammodendron a better afforestation species than C. mongolicum due to its stronger drought tolerance (Xu, Ji, Jin, & Zhang, ; Yao, Yan, & Yang, ), our prediction result showed that the suitable habitat of H. ammodendron may contract substantially in the Junggar Basin, while the suitable habitat of C. mongolicum is likely to expand.…”

“…On the one hand, vegetation coverage reduction and degradation driven by climate change and overexploitation of water resources have been observed (Wang, Pan, Wang, Shen, & Lu, ). On the other hand, several drought‐resistant woody plant species have been widely planted since 1970s as large‐scale afforestation efforts to combat desertification in the drylands of northwestern China (Yu & Wang, ). Nevertheless, these efforts are not always successful due to a lack of understanding about the habitat suitability of the planted species and their responses to climatic change.…”

“…Both are dominant species in the southern desert area of the Junggar Basin but with different ecological characteristics (Eziz, ). In addition, they are two of the most widely used plantation species in afforestation and ecological restoration in northwestern China (Yu & Wang, ). A. aphylla is a dominant perennial sub‐shrub species in the Gobi Desert in the northern mountain area of the basin, where the altitude is relatively higher and the climate is colder and wetter than that of the southern desert (Eziz, ).…”

Restoration and rehabilitation of degraded land in arid and semiarid environments: Editorial

“…Their study remarks that the implementation of action plans for land remediation needs to consider social aspects and the implications for long-term sustainability. An increasing number of studies are showing the importance of long-term monitoring in restoration (Shackelford et al, 2018), as vegetation establishment and soil properties can go through transient states over time and may evolve over decades (Yu & Wang, 2018). At landscape scales, geomorphic analysis and remote sensing techniques provide sensitive satellite-derived indices that can offer multiple possibilities for monitoring studies at such large ranges.…”

“…Revegetation efforts generally result in improvement of soil fertility and enhancement of ecosystem services and functions such as carbon sequestration (Gao, Dang, Zhao, Liu, & Liu, 2018), nutrient cycling (Barliza, Peláez, & Campo, 2018;Hu et al, 2018), and soil microbial diversity and activity (Garcia et al, 2018;Liu et al, 2019); nevertheless, it can also lead to adverse effects such as salinity which may affect the success of restoration efforts in the long term (Yu & Wang, 2018) and generally increases plant productivity and carbon sequestration in the medium or long-term, as highlighted by Valdecantos and Fuentes (2018). Also in this issue, Luna, Vignozzi, Miralles, and Solé-Benet (2018) show that woodchip mulch can be effective for trapping runoff and sediment in mine rehabilitation sites, whereas organic amendments formed by composted waste can improve infiltration and reduce water erosion (Figure 2).…”