Is the soil seed bank a reliable source for passive restoration of intensive grazed habitats in river riparian areas of western Iran?

Abstract

Soil seed banks serve as reservoirs of seeds for subsequent regeneration of plants particularly in areas prone to disturbance, such as intensive grazed areas along rivers. The potential of soil seed bank (SSB) for vegetation restoration was assessed in overgrazed riparian areas in Gamasyab river, Iran. Therefore, SSB composition, density and diversity and, its relationship with aboveground vegetation (AGV) were investigated along the river. Fifteen transects were set perpendicular to the river and along each transect, 6 plots (1 m × 1 m) were established, in total 90 plots. In each plot, soil was collected for SSB experiments and AGV was sampled during the growing season. The similarity between SSB and AGV was estimated by the Jaccard similarity index and non-metric dimensional scaling (NMDS). Spatial beta diversity was calculated by the mean Bray-Curtis index for the SSB and vegetation compositions, separately. A total of 136, 108 and 134 species were identified in the upper (0–5 cm) and lower (5–10 cm) soil layers and, AGV, respectively. Annual and perennial grasses were dominant in SSB composition at 0–5 cm depth while the frequency of perennial grasses was highest in SSB at deeper depth and vegetation composition. The beta diversity of AGV was significantly higher than for SSB. Similarity between SSB and vegetation was low (7.92%–22.40%), nevertheless, most species in AGV were found frequently in the SSB. So, we argued that restoration of degraded vegetation in our riparian could rely on SSB. It is expected that after grazing exclosure, vegetation would restore mostly with perennial grasses through SSB and vegetative growth.