Changes in soil properties and plant community following twelve years of fencing in a typical oasis–desert ecotone

Livestock grazing is the main cause of vegetation degradation and soil erosion in arid oasis–desert ecotones. Fencing has become the most important measure to promote the recovery of species diversity and plant community stabilization. In this study, we analyzed the changes in soil physical–chemical properties and plant diversity, niche width and overlap, inter-species associations, and community stability in a typical desert oasis ecotone of the Hexi Corridor in Northwest China following 12 years of continuous fencing. Available nutrients, particularly available nitrogen, increased significantly over the fencing period. However, no significant changes were observed in soil organic matter or total nitrogen. In the shrub layer, the dominant species shifted from Nitraria sphaerocarpa to a combination of Nitraria sphaerocarpa and Reaumuria songarica and then Reaumuria songarica. This shift was likely driven by greater nitrogen availability. In the herbaceous layer, the dominant species changed from Zygophyllum mucronatum and Suaeda glauca in the early stage (2–4 years) to Artemisia scoparia in the middle stage (5–8 years), and to Eragrostis minor in the late stage (9–10 years). The community diversity showed an increasing and then decreasing trend with 12 years of fencing. The niche overlap value for Reaumuria songarica was significantly higher than Nitraria sphaerocarpa from the sixth year. Reaumuria songarica became the keystone species after 12 years of fencing, and the recovery of Reaumuria songarica increased negative interspecific associations. These findings suggest that after 12 years of fencing, the soil and vegetation remain in a transitional phase, indicating that desert ecosystems require extended periods for full recovery.