Impacts of changed fire regimes on tropical riparian vegetation invaded by an exotic vine

Authors


*Present address: Department of Environment and Conservation WA, PO Box 942 (Lot 248 Ivanhoe Rd), Kununurra, WA 6743, Australia (Email: ian.radford@dec.wa.gov.au)

Abstract

Abstract  Riparian habitats are highly important ecosystems for tropical biodiversity, and highly threatened ecosystems through changing disturbance regimes and weed invasion. An experimental study was conducted to assess the ecosystem impacts of fire regimes introduced for the removal of the exotic woody vine, Cryptostegia grandiflora, in tropical north-eastern Australian woodlands. Experimental sites in subcatchments of the Burdekin River, northern Queensland, Australia, were subjected to combinations of early wet-season and dry-season fires, and single and repeated fires, with an unburnt control. Woody vegetation was sampled using permanent quadrats to record and monitor plants species, number and size-class. Sampling was conducted pre-fire in 1999 and post-fire in 2002. All fire regimes were effective in reducing the number and biomass of C. grandiflora shrubs and vines. Few woodland or riparian species were found to be fire-sensitive and community composition did not change markedly under any fire regime. The more intense dry-season fires impacted the structure of non-target vegetation, with large reductions in the number of sapling trees (<5 cm d.b.h.) and reductions in the largest tree size-class and total tree basal area. Unexpectedly, medium-sized canopy trees (10–30 cm d.b.h.) appear to have been significantly benefited by fires, with decreases in number of trees of this size-class in the absence of fire. Although the presence of C. grandiflora as a vine in riparian forest canopies changed the nature and intensity of crown combustion patterns, this did not lead to the initiation of a self-perpetuating weed–fire cycle, as invaders were unable to take advantage of gaps caused by fire. Low intensity, early wet-season burning, or early dry-season burning, is recommended for control of C. grandiflora in order to minimize the fire intensity and risk of the loss of large habitat trees in riparian habitats.

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