Post-fire vegetation dynamics in nutrient-enriched and non-enriched sclerophyll woodland

Exotic plant invasions are a significant problem in urban bushland in Sydney, Australia. In low-nutrient Hawkesbury Sandstone communities, invasive plants are often associated with urban run-off and subsequent increases in soil nutrients, particularly phosphorus. Fire is an important aspect of community dynamics in Sydney vegetation, and is sometimes used in bush regeneration projects as a tool for weed control. This study addressed the question: 'Are there differences in post-fire resprouting and germination of native and exotic species in nutrient-enriched communities, compared with communities not disturbed by nutrient enrichment?' We found that in non-enriched areas, few exotic species emerged, and those that did were unable to achieve the rapid growth that was seen in exotic plants in the nutrient-enriched areas. Therefore, fire did not promote the invasion of exotic plants into areas that were not nutrient-enriched. In nutrient-enriched areas after fire, the diversity of native species was lower than in the non-enriched areas. Some native species were able to survive and compete with the exotic species in terms of abundance, per cent cover and plant height. However, these successful species were a different suite of natives to those commonly found in the non-enriched areas. We suggest that although fire can be a useful tool for short-term removal of exotic plant biomass from nutrient-enriched areas, it does not promote establishment of native species that were not already present.