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 and and semiarid systems. CCA model suggested that vegetation bands, microslope and vegetation perennial cover were factors shaping the composition of the seed bank. (C) 2003 Elsevier Science Ltd. All rights. reserved.