Abstract
Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air‐filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in stabilized sand dune plantations.
Highlights
Pioneer species play an important ecological role in the stabilization of mobile sand dunes and the diversity of desert species
Restoration studies indicate that populations of native sand pioneer shrub species decrease gradually, such as the annual Agriophyllum squarrosum and perennial Artemisia halodendron (Zuo et al, 2008), while herbaceous species that depend on increased soil nutrient levels gradually establish (Fan, Zhang, Ma, Li, & Zhao, 2016; Li, He, Duan, Xiao, & Jia, 2007; Wang, Li, Xiao, & Pan, 2006) and under natural regeneration, pioneer shrub species eventually disappear (Tobe, Zhang, & Omasa, 2005; Zhu, Dong, & Huang, 2009)
Our results showed that the density of soil seed bank in the moving sand dunes is higher than that of fixed dunes due to a significantly larger percentage of dead shoots, which pointed to a potential loss of fruit in stabilized sand dunes than in mobile sand dunes
Summary
Pioneer species play an important ecological role in the stabilization of mobile sand dunes and the diversity of desert species. There is a considerable amount of literature on plant–environment relationships (Comstock & Ehleringer, 1992; Cook & Irwin, 1992; Monier & Wafaa, 2003; Parker, 1991; Yair & Danin, 1980; Zuo et al, 2008), but few discuss the mechanisms and/or occurrence of reduced natural regeneration of native species in post-sand dune stabilization. To fill this knowledge gap it is necessary to determine the biological and environmental limiting factors
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