NESTED SPATIAL PATTERNS IN SEED BANK AND VEGETATION OF MEDITERRANEAN OLD-FIELDS

A nested sampling design was used to describe the spatial patterns for the species richness and composition in the seed bank and vegetation of three Mediterranean old-fields (1, 7, and 15 yr after the last ploughing). Three scales were examined hierarchically: sampling units within plots of 0.25 m2 for the vegetation and of 0.05 m2 for the seed bank, 100 m2 plots within fields, and fields of 1000 m2. In spite of the strong spatial variation among sampling units, species richness and composition of both seed bank and vegetation showed hierarchically structured patterns of heterogeneity, while each oldfield was a homogeneous entity. These spatial patterns tended to be partially masked when the data were aggregated at the scale of the plot. Such results stress the use of a nested sampling design for studying variation in species richness and taxonomic composition in both vegetation and seed bank. This design, in combination with CCA, also showed that the vegetation showed a coarser grain than the seed bank, probably in relation to seed clumping.