Thesis
The ecological consequences of rainforest expansion into fire-excluded open forests of eastern Australia
Southern Cross University, Forest Research Centre
Doctor of Philosophy (PhD), Southern Cross University
2021
DOI:
https://doi.org/10.25918/thesis.158
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Abstract
The expansion of rainforest pioneer trees into long-unburnt open forests is a global phenomenon and widely reported in high rainfall regions of Australia. However, impacts on Australian open forest biodiversity have been little studied beyond the tropics. In this thesis, I asked whether an invading midstorey of rainforest pioneers had adverse impacts on communities of open forest flora and fauna, and on ecosystem function, by examining heathy Eucalypt forest with contrasting fire frequencies and levels of rainforest-invasion in the Bundjalung Wilderness Area of northern NSW.
Where rainforest pioneers dominated the midstorey, understorey plant species richness was halved, and ground cover and density of open forest specialists were reduced by ~90% compared to the uninvaded state. Rainforest-invaded open forest also had lower insectivorous bat activity (63% lower) and species richness (35% lower). Forest flammability was also sharply reduced by rainforest pioneers through near-elimination of dense grassy (graminoid) and heathy understorey fuels in exchange for sparse rainforest saplings with less-flammable foliage and crown structure.
These findings suggest that rainforest pioneers are ecosystem engineers that modify open forest fuel properties, initiating a positive fire-suppression feedback that facilitates their persistence and the continued transition to a fire-resistant closed forest.
I also examined fire-resilience traits among 228 taxa of woody rainforest plants burnt in the extensive 2019-20 bushfires of eastern Australia to determine the reversibility of rainforest-invasion when fire ultimately returns to long-unburnt open forest. Most taxa survived fire by resprouting and/or fire-cued seedling recruitment, and resprouting rates were high across all size classes, including in small rainforest plants (≤1 cm DBH, ≤1m tall).
These findings suggest that rainforest plants which invade long-unburnt open forests may quickly become resistant to removal by future fires, allowing rapid re-establishment of midstorey cover from established root stocks.
The observed declines in open forest flora, fauna and ecosystem function occurred well before recommended maximum fire-intervals for dry open forest, casting doubt on the suitability of existing guidelines in high rainfall regions. To conserve open forest biodiversity, this research suggests that fires should be of sufficient frequency to prevent a dense rainforest midstorey from eliminating open forest flora, fauna and the understorey fuels that underpin open forest function.
Details
- Title
- The ecological consequences of rainforest expansion into fire-excluded open forests of eastern Australia
- Creators
- Andrew G. Baker
- Contributors
- Kirsten Benkendorff (Supervisor) - Southern Cross UniversityClaudia Catterall (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University, Forest Research Centre
- Number of pages
- xiii, 172
- Identifiers
- 991012958498102368
- Copyright
- © AG Baker 2021
- Academic Unit
- School of Environment, Science and Engineering
- Resource Type
- Thesis