Fire exclusion and the changing landscape of Queensland’s Wet Tropics Bioregion 1. The extent and pattern of transition

Summary

The vegetation and geology of the Wet Tropics Bioregion of North Queensland, covering 1 998 150 ha, were mapped at a scale of 1:50 000. The resulting geographic information system (GIS) data base provided an unprecedented opportunity to examine vegetation condition across the entire bioregion. Mapping used colour aerial photography at 1:25 000, informed by ground truthing. Vegetation type, nature of the understory and ground cover, degree and type of disturbance, and the presence of secondary vegetation were described by a coding system, with codes marked directly on the aerial photos.

Analysis of these data has confirmed a picture, which emerged from ground truthing, of large areas of sclerophyll woodland and forest being invaded by a rainforest understory that prevents regeneration of the sclerophyll canopy. Fifty-three per cent of the native vegetation of the bioregion consists of non-rainforest vegetation types, dominated in both area and number by sclerophyll woodlands and forests. Seventeen per cent of the 735 713 ha of sclerophyll woodland and forest types were assessed as having suffered irreversible change. Between 25% and 79% of individual forest vegetation types were judged to have been affected by irreversible change. No climatic changes, or changes in the environment, apart from those related to changing fire regimes, were identified as causative factors. Changed fire regimes, predominantly fire exclusion, are considered to be the most likely cause.

Keywords:

• geology
• mapping
• geographical information systems
• habitats
• regions
• forests
• rainforests
• fire
• fire regimes
• fire effects
• change
• Queensland

Acknowledgements

This paper, and a complementary one, would never have been completed without the encouragement of Ian Bevege, Roger Underwood and Jeremy Russell-Smith. Their critical comments on a first draft led to major changes in presentation and a better product. The blame for any deficiencies now lies entirely with the authors. Peter Stanton would also like to express his gratitude to his wife, Karen, who typed his handwritten manuscripts and provided much needed quality control.