The effect of shrub community on understory soil seed bank with and without livestock grazing

Shrub communities often modify understory soil and vegetation characteristics. However, the effect of individual shrubs on the soil seed bank (y6SSB) could be variable in grasslands depending on the presence of grazing. We examined how grazing influences patch-level effects of shrubs on local soil seed bank (SSB) density, species richness, and composition. Twenty individuals of Crataegus pseudomelanocarpa(dominant woody species in the study area) were randomly selected in the degraded ecotone between forest and grassland in northern Iran, 10 in grazed and 10 in ungrazed areas. Soil samples were collected under shrubs and the space between shrubs and then transported to the greenhouse. The seedling emergence method was used to estimate SSB density and composition in the greenhouse. In total, 61 species germinated from the soil samples with 47 species in the grazed sites (43 species in shrub, 34 species in open) and 54 species in the ungrazed sites (43 species in shrub, 46 species in open). SSB density and richness were significantly lower under shrubs compared with outside in the ungrazed areas while the converse results were found in the grazed areas. Although grazing decreased SSB density and species richness, this decrease was less pronounced under the shrubs, indicating the nursing roles of shrubs against grazing on seed production by herbaceous plants.