Ecosystems

, Volume 11, Issue 1, pp 77–88

Andropogon gayanus (Gamba Grass) Invasion Increases Fire-mediated Nitrogen Losses in the Tropical Savannas of Northern Australia

  • N. A. Rossiter-Rachor
  • S. A. Setterfield
  • M. M. Douglas
  • L. B. Hutley
  • G. D. Cook
Article

DOI: 10.1007/s10021-007-9108-x

Cite this article as:
Rossiter-Rachor, N.A., Setterfield, S.A., Douglas, M.M. et al. Ecosystems (2008) 11: 77. doi:10.1007/s10021-007-9108-x

Abstract

Invasive alien grasses can substantially alter fuel loads and fire regimes which could have significant consequences for fire-mediated nutrient losses. The effects of the alien grass Andropogon gayanus Kunth. (Gamba grass) on fire-mediated nutrient losses was evaluated in Australia’s tropical savannas. Losses of macronutrients during fire were determined by comparing the nutrient pools contained in the fine fuel before fire and in the ash after fire. Pre-fire grass nutrient pools were significantly higher in A. gayanus plots than in native grass plots for all nutrients measured (N, P, K, S, Ca, and Mg). Nutrient losses were substantially higher in A. gayanus plots, with 113% higher losses for N, 80% for P, 56% for K, 63 for S, 355% for Ca, and 345% for Mg. However, only losses of N and Mg varied significantly between grass types. A simplified savanna ecosystem nutrient budget estimated that A. gayanus fires led to the net N loss of 20 kg ha−1 y−1. This is a conservative estimate because total fuel loads were relatively low (7.85 t ha−1) for A. gayanus invaded plots leading to a relatively moderate intensity fire (6,408 kW m−1). Higher A. gayanus fuel loads and fire intensities could potentially lead to losses of up to 61.5 kg N ha−1 from the grass fuel. Over the long term, this is likely to lead to depletion of soil nutrients, particularly N, in the already low-fertility tropical savanna soils.

Keywords

biological invasionsexotic grassesfire intensityfine-fuel consumptioninvasive alien speciesnitrogennutrient losses

Copyright information

© Springer 2007

Authors and Affiliations

  • N. A. Rossiter-Rachor
    • 1
    • 2
    • 3
  • S. A. Setterfield
    • 1
    • 3
  • M. M. Douglas
    • 1
    • 3
    • 4
  • L. B. Hutley
    • 1
    • 3
  • G. D. Cook
    • 2
    • 3
  1. 1.School of Science and Primary IndustriesCharles Darwin UniversityDarwinAustralia
  2. 2.CSIRO Tropical Ecosystems Research Centre, PMB 44WinnellieAustralia
  3. 3.Tropical Savannas Management Cooperative Research CentreCharles Darwin UniversityDarwinAustralia
  4. 4.School for Environmental Research, Tropical Rivers and Coastal Knowledge (TRACK) Research HubCharles Darwin UniversityDarwinAustralia