The role of seed bank and seed rain in the recolonization of disturbed sites along an aridity gradient

Abstract

The composition of seed bank and seed rain have been studied in different undisturbed vegetation types along an aridity gradient from the Mediterranean to the desert. The recruitment of colonizing species which originated either from the seed bank or the seed rain have been estimated for experimentally created gaps. The species richness of seed bank and seed rain decreases with increasing aridity, while no clear pattern has been observed for the density. The similarity of seed bank and seed rain with the actual vegetation increases with aridity. The seed rain shows overall greater dissimilarity than the seed bank. The seed bank has been found to be the main seed source in recolonization of the gaps in the Mediterranean and in the desert. The relative importance of seed bank compared with seed rain increases towards the desert. The portion of annual species in the vegetation is proposed as the main explanation for the revealed pattern. The special traits and evolutionary strategies of annuals are discussed as likely reasons for the differences in seed bank and seed rain along the gradient.