Similarity between seed bank and vegetation in Mediterranean grassland: a predictive model

The similarity in species composition between seed bank and vegetation was analysed in Mediterranean grasslands in relation to altitude, topography an d grazing. Soil samples were collected in permanent plots in autumn at the end of the summer drought period and in spring, before the new seed fall an d after the natural winter seed stratification. The seed bank composition w as determined by greenhouse germination over a nine-month period. Presence/ absence of species in the standing vegetation throughout the complete annua l cycle, and the percentage area of bare ground in October, were recorded i n the same plots. The species composition of the standing vegetation is cle arly determined by altitude, topography and grazing, while the floristic co mposition of the seed banks is only related to altitude and topography in t he case of autumn seed bank and with any of the three factors in the spring seed bank. Relative abundances of grasses, legumes and forbs also show dif ferent patterns in vegetation and seed bank data. Sorensen similarity betwe en the autumn seed bank and the vegetation declines as altitude rises, but there are no significant differences for topography and grazing. This simil arity decreases in the case of the spring seed bank and does not show any s ignificant relationship with any of the factors. The perennial/annual ratio and the proportion of bare soil in October are proposed as explanatory var iables in a predictive model of similarity between the seed composition of the seed bank and vegetation.