Plant functional traits along environmental gradients in seasonally dry and fire-prone ecosystem

Authors


  • Co-ordinating Editor: Martin Zobel

  • Pekin, B.K. (corresponding author, bpekin@purdue.edu), School of Plant Biology, The University of Western Australia
    Current address: Department of Forestry and Natural Resources, Purdue University, 195 Marsteller Street, West Lafayette, IN 47907, USA
    Wittkuhn, R.S. (roy.wittkuhn@dec.wa.gov.au), Science Division, Department of Environment & Conservation, Locked Bag 104, Bentley Delivery Centre 6983, WA, Australia
    Boer, M.M. (matthias.boer@cemagref.fr), School of Plant Biology, The University of Western Australia, 35 Stirling Hwy, Crawley 6009, WA, Australia
    Macfarlane, C. (craig.macfarlane@csiro.au), CSIRO Sustainable Ecosystems, Private Bag No.5, Wembley 6913, WA, Australia
    Grierson, P.F. (pauline.grierson@uwa.edu.au), School of Plant Biology, The University of Western Australia, 35 Stirling Hwy, Crawley 6009, WA, Australia

Abstract

Questions: How does the abundance and richness of plant assemblages with different functional (regeneration and nutrient acquisition) traits vary with fire regime, moisture availability and substrate fertility? What is the role of different functional traits in maintaining plant diversity under changing environmental conditions in seasonally dry and fire-prone environments?

Location: Southwest Western Australia.

Methods: Plant species abundance and soil nutrients were determined at 16 forest sites with variable fire histories across an aridity gradient. All plant species were classified based on their functional traits as (1) perennial or annual, (2) ectomycorrhizal, arbuscular mycorrhizal, ericoid mycorrhizal, orchid mycorrhizal, proteoid or other non-mycorrhizal, (3) resprouters or seeder, and (4) nitrogen fixer or non-fixer. We used a multivariate (fourth-corner) technique to simultaneously test the significance and direction of the relationship between each of these traits and fire frequency, fire interval length, aridity, and soil N, P and C fractions.

Results: The functional response of the vegetation to fire regime was minor and restricted to annual species, which comprised only ∼4% of taxa. Proteoid and ectomycorrhizal species dominated over species with arbuscular and orchid mycorrhizal roots, N-fixers dominated over non-fixers, and seeders dominated over resprouters when N fertility was low but organic labile P was high. Further, proteoid and ectomycorrhizal species richness increased with aridity, while arbuscular mycorrhizal species richness decreased.

Conclusions: While the functional composition of southwest Australian vegetation is largely insensitive to changes in fire regime, nutrient acquisition and, to a lesser extent, regeneration traits provide mechanisms for the vegetation community to adjust to changes in resource availability. Thus, diversity responses to environmental change in seasonally dry and fire-prone ecosystems are likely to be primarily mediated by the composition of nutrient acquisition traits in the vegetation community.

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