Soil seedbanks in natural and restored boxironbark forests at Stawell Gold Mine, Victoria

Abstract

Natural communities have the capacity to regenerate themselves, and this functional ecosystem attribute must be regarded as a key indicator of success for revegetation programmes. The accumulation of species (and individuals) as dormant propagules in a soil seedbank, representing potential future states for the vegetation, is one possible index of revegetation success. Here, we investigate the soil seedbanks for five natural vegetation (Box-Ironbark forest) remnants, a topsoil stockpile and three revegetated mine-site areas associated with gold mining at Stawell (Victoria, Australia). The revegetation efforts largely date from 1987 and, in terms of their composition and structure, are relatively similar to natural vegetation remnants. Soil samples were treated with heat or smoke (plus control) and were monitored for seedling emergence, species composition and density in the glasshouse for 150 days. Seedling densities in treated seedbank samples were high (2 200 to 17 500 seedlings m-2) while species richness was low, ranging from 10 to 20 species per sample. Exotic species made up 22?61 % of emergents and 33?50% of species observed. Correlation of seedbank composition and density with chemical attributes of soils, and with above ground (extant) vegetation at sites showed few significant relationships. Total species richness and the proportion of exotic species varied significantly between natural bushland remnants and revegetation areas. Richness was highest, and the proportion of exotic species was lowest in natural bushland samples. Total emergent numbers and the density of exotic emergents did not vary significantly between remnant bushland and revegetation areas. Declining vigour of some woody species in revegetation sites that are well represented in the seedbank, including Acacia pycnantha and A. genistifolia, indicates that the reintroduction of fire might be an appropriate management practice to facilitate long-term recovery of a functional community on these revegetated surfaces, but the potential for the establishment of weed species from the seed-bank following fire may pose a challenge to management.