Seed Banks and Vegetation of Three Contrasting Sites in an Urban Eucalypt Forest Reserve

Abstract

Grass species, sedges and dicotyledons in the vegetation and the buried germinable seed of a natural subtropical eucalypt forest, a mown and a road bank site were identified in four consecutive seasons and the data pooled to give a more precise assessment of taxa present each year. Differences in the relative proportions of taxa, differences in species density, origin and life history of grass species in the seed bank and vegetation, as well as differences in biomass and rate of germination of buried germinable grass seed, in the three sites were investigated. In all three sites, grasses were the dominant taxa of the ground stratum of the vegetation with each site having its own group of mainly perennial grasses. The seed banks were dominated by grasses in the forest site, sedges in the mown site and dicotyledons in the road bank site.

There were significant differences in species density of grasses in both the vegetation and buried germinable seed between sites, with the forest site having a significantly lower species density in its seed bank than the mown and road bank sites, and the vegetation of the forest and mown sites having a lower species density than the road bank site. However, there was a high correlation between the grass species of the vegetation and the buried germinable seed in each of the three sites - the species which dominated the vegetation also dominated the biomass of buried germinable seed in each site. The mown and road bank sites had larger numbers and biomass of buried germinable grass seed than the natural forest site. There were no differences in the number of days to first germination and the number of days to 50% germination of the buried germinable seed between any of the sites. Exotic grass species were present in the seed banks of the forest, mown and road bank sites. Exotics were prevalent in the vegetation of the mown and road bank sites but not evident in the vegetation of the forest site. Exotic species with higher buried germinable seed numbers and similar germination rates to the native species are likely to have a competitive advantage over the native species. It appears that the mown and road bank sites, may act as reservoirs for the more competitive exotic grass species, enabling them to invade the seed banks of the forest areas.