Hidden effects of forest management practices: responses of a soil stored seed bank to logging and repeated prescribed fire

Forest management practices have the potential to impact upon native vegetation. Most studies focus on the effects of management on the above-ground vegetation communities, with little attention given to the soil stored seed bank. Here we examine the soil stored seed bank of a long-term experimental site in south-eastern Australia, which has experienced timber harvesting and repeated prescribed burning over a 20-year period. At each of 213 long-term vegetation measurement plots, 3.5 kg of soil was collected and germinated in a glasshouse over a period of 2 years. Comparisons were made between the experimental treatments considering differences in species richness, abundance and community composition of the understorey seed bank. Logged sites had a higher diversity and abundance of seedlings compared with unlogged sites, which is consistent with observed changes in standing vegetation within 10 years following logging. Prescribed burning resulted in a lower diversity and abundance of seedlings, which contrasts with the increase in species diversity observed in response to frequent fire in standing vegetation. Individual taxa that declined in the seed bank in response to frequent fire were all taxa for which germination is enhanced by exposure to smoke. Contrary to expectations, these did not exhibit a corresponding decline as standing plants. While management actions above ground are having minor impacts, greater effects were seen in the soil stored seed bank.