Effects of mission grass (Pennisetum polystachion (L.) Schult.) invasion on fuel loads and nitrogen availability in a northern Australia tropical savanna

摘要

Pennisetum polystachion (L.) Schult. (mission grass) is an introduced African grass that is now widespread in the tropical savannas of Australia's 'Top End'. To date, the impact of mission grass invasion on the ecosystem function of tropical savannasis unknown. This study presents preliminary results from an investigation into its effects on fire properties and fuel loads. Data from three sites in Litchfield National Park show that mission grass invasion results in fuel loads five times larger thanin uninvaded sites. The grass remains erect during the dry season, resulting in a large fuel load that can carry flames into the canopies of savanna trees. In addition, data show that nitrate availability was 10% lower under mission grass compared with native grasses. This suggests that mission grass may alter the nitrogen cycling in savanna following invasion.