Seed bank structure along a semi-arid gypsum gradient in Central Spain

The aim of this paper is to evaluate seed bank density and composition along a semi-arid gypsum gradient in Central Spain. Seed bank density was relatively high (16,214 seed/m 2) with a very clumped spatial distribution. Landform and microslope were the best predictors for seed density, indicating that density can be at least partly interpreted as a result of the physical processes regulating secondary dispersal. A high number of species appeared in the seed bank (68) being most of them annual gypsophytes. A relevant feature is that three widely distributed perennial gypsophytes occurred among the 10 more abundant species ( Helianthemum squamatum, Lepidium subulatum and Sedum gypsicola). Presence of perennial among the most frequent species of the seed bank is not a shared characteristic with other arid and semi-arid systems. CCA model suggested that vegetation bands, microslope and vegetation perennial cover were factors shaping the composition of the seed bank.