Early life-history stages drive community reassembly in Australian old-fields

Questions Do native annual forb seedling communities reassemble after agricultural abandonment to an undisturbed condition? Do environmental changes associated with cultivation affect seedling establishment? Is post-abandonment recovery of seedling and vegetation communities more limited by seed availability, seedling establishment or seedling survival? Location Northern Victoria, Australia. Methods Seedling density, species richness and composition were sampled across a 100-yr chronosequence. Standing vegetation, cover of the biological soil crust and soil properties were sampled from the same plots, and the seed bank was sampled from the same sites. Patterns were compared among the seedlings, seed bank and vegetation. Results Native seedling density and species richness did not increase with time-since-abandonment, despite some recovery in species composition. Native density and richness were negatively associated with soil fertility and bare ground and positively associated with biological soil crust cover; exotics showed the opposite pattern. Species composition showed little association with soil resources. Percentage field emergence from the seed bank was unaffected by time-since-abandonment. Compositional similarity between the seedlings and vegetation was higher (81%) than that between the seedlings and seed bank (61%); neither was affected by time-since-abandonment. Conclusions While environmental conditions partially determined patterns of seedling recruitment, seed availability was the main driver of seedling density and composition with time-since-abandonment. Post-establishment mortality was apparently not a major determinant of species composition of the standing vegetation. Thus, seed and microsite limitation interacted to drive community reassembly, but seed availability was relatively more important.