Does low-intensity surface fire increase water- and nutrient-availability to overstorey Eucalyptus gomphocephala?
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The objective of this study was to investigate how the management practices of prescribed fire and understorey vegetation removal affect water and nutrient relations of old, yet prematurely declining Eucalyptus gomphocephala. Long unburnt sites were established in Yalgorup National Park, Western Australia, adjacent to frequently burnt state forest sites. Trees were allocated to vegetation clearing, prescribed fire or no prescribed fire treatments. Prescribed fire was achieved in only one long unburnt national park site so that the results were pseudoreplicated but analysed accordingly. Soil chemistry, plant nutrient availability and tree foliar carbon and nitrogen isotope ratio and nutrient concentration were investigated. No effects of vegetation clearing were found. Prescribed fire sites were associated with sky exposure and bare ground whereas no prescribed fire sites were associated with shrub and litter cover and litter depth. Foliar carbon isotope ratios were significantly more negative in prescribed fire, relative to no prescribed fire, treatments on long unburnt sites. Soil exchangeable Zn and Mn and plant available (estimated by charged resin beads) Mg were higher on prescribed fire, relative to no prescribed fire, long unburnt sites. Seedling bioassays indicated elevated P and Cu availability on prescribed fire, relative to no prescribed fire, treatments. In overstorey E. gomphocephala, foliar N levels were elevated (but not to excessive levels), and there was a trend toward elevated foliar Mn, in prescribed fire relative to no prescribed fire treatments on long unburnt sites. In the context of our large-scale pseudoreplicated case study, prescribed fire provided a pulse of water and N, (with some indications towards provision of elevated Mn, Cu and Mg) availability to E. gomphocephala in decline on sites with a history of a long absence of fire that may in part underpin observations of elevated tree health on sites that have a history of relatively frequent fire.
KeywordsEcophysiology Eucalyptus Prescribed fire Restoration
We gratefully acknowledge funding support from the Bushfire Cooperative Research Centre and The Forest Fire Management Group (Department of Environment and Conservation—Western Australia, Department of Environment and Heritage—South Australia, Department of Sustainability and Environment—Victoria, Forestry Tasmania and Forests New South Wales). Darren Harvey managed the vegetation clearing operations, site preparation and prescribed fires. The fire management authority reference group: Rick Sneeuwjagt, Drew Haswell, Tony Blanks, Dr Tim Wardlaw, Craige Brown, Vic Jurskis, and Dr Paul Barber provided advice. We thank Dr Robert Archibald for technical assistance and Daan Lock (Arbor Oxygen) for foliar sampling. Soil and leaf nutrient analyses were conducted by the CSBP Analytical Laboratory, Perth, Western Australia. Isotope ratio analyses were conducted by the Research School of Biological Sciences laboratory, the Australian National University, Canberra.
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