FLAMMABILITY RESEARCH AT SFS - Barb Lanskey

In the first semester of 2023, students from the SFS (School for Field Studies) Centre for Rainforest Studies, presented their Directed Research at the Yungaburra Community Hall on 29th April. One of the research studies compared the flammability of trees in rainforest, dry rainforest and savanna, in the Australian tropics.

Introduction

“Intense wildfires are occurring in subtropical and tropical regions, and 70-80% of global burned area between 1997 and 2018 were experienced in tropical forests and tropical savannas (Tang et al. 2021).” 

“While wildfires are more prevalent in drier ecosystems, they are expected to become more common in tropical rainforests, such as seasonally dry tropical forests (SDTF) and rainforests, where plants possess fewer adaptations for fire (Meir and Woodward 2010). SDTF and rainforests both fall under the category of ‘tropical forests’, but they differ in their canopy make-up and water availability, as rainforests have much longer rain seasons while SDTF have longer dry seasons. Plants within savannas, however, are adapted to handle wildfires much more than those from rainforests and SDTF (Simon and Pennington 2012), as wildfires are a periodic occurrence in savannas.”

“The findings of this study may contribute to a more comprehensive understanding of the comparative flammability of three vegetation types in northeast Australia, and determine which vegetation types are more at risk in terms of wildfires. Tropical forests are known to be the most species-rich ecosystems on the planet, which provides a vast diversity in natural adaptations to fire and water availability (Sterck et al. 2011). As a result, we expect to see differing levels of flammability between plants within each ecosystem. An understanding of the relative flammability between each ecosystem and within each ecosystem provides vital information for fire management.”

“One such management option is green firebreaks. Green firebreaks are a method of wildfire management that involves the planting of species selected for low flammability traits that are planted at specific locations as a method of slowing or stopping the spread of wildfires (Curran et al. 2017).” 

“We sought to investigate the difference in relative flammability between the different forest types occurring in a similar region and the species within each region. With an overarching hypothesis that the three vegetation types will exhibit different shoot level flammabilities, we predict that savanna trees will be the most flammable and rainforest trees the least flammable. Since the plants in SDTF are often affiliated with rainforest and form closed canopies, like rainforest, we predict that SDTF trees would have shoot flammability more similar to that of the rainforest than savanna. Identifying the levels of relative flammability within each region are important in providing improved understanding for the fire ecology of these different regions and could help land managers to better address and reduce fire risks in a particular region.”

Study Sites

The students used for their rainforest data, the database collected by previous SFS students (Ortiz et al. 2023 unpublished data) in the Fall of 2022, from simple notophyll vine forest. For SDTF forest, they used species collected from Chillagoe National Park in sites dominated by Brachychiton australis emergence and diverse families of other tree and shrub species. The savanna species were collected near Mount Baldy and near Granite Gorge at localities where Corymbia and Eucalyptus spp. frequent.

Species Collection

“At each vegetation type studied, we collected 70cm long branches of the outer canopy of healthy, mature individuals. We also collected subsamples of 20cm in length with a minimum of five leaves for leaf functional trait analysis. We collected branches of 13 SDTF species, with a total of 66 samples, and 10 savanna species, with a total of 54 samples. The previously collected rainforest species database contained 47 species with a total of 235 samples. The SDTF and savanna data was additionally supplemented with species from previously completed databases, with 14 additional SDTF and 21 savanna species being added. In total, we compiled 602 samples from 107 species.”

Experimental Setup

The students used a barbecue grill and a blowtorch to measure burn time etc. “Once the grill had reached 110℃ - 130℃, we placed the 70cm branch sample on the grill for two minutes to replicate drying from an approaching wildfire. After two minutes, a blowtorch flame was applied on the distal end of the branch for 10 seconds. We measured branch flammability traits by recording burnt biomass, total burn time, flame height, and the maximum temperature of burn. We recorded the burn time starting from the first initial flame using a handheld stopwatch, measured maximum flame temperature using a Fluke ‘IR’ Thermometer, and recorded the percentage of burnt biomass via visual analysis. We recorded each burn on an iPhone 14 attached to tripod and reviewed these videos to determine the maximum flame heights, using a meterstick set up on the grill for reference.”

Functional Trait Analysis

“Using the collected subsamples, leaf area and leaf dry matter content (LDMC) were calculated for each individual. The leaves on each subsample were plucked from the leaf and placed on a flat, white sheet. These were pressed under a glass sheet and a picture was taken to upload onto paint.net for leaf calculations. The LDMC was measured by measuring the weight of the fresh leaves. The leaves were then dried in an oven at 70℃ and until they were completely dried, upon which they were re-weighed to find dried leaf mass.”

Results and discussion

“To our surprise, our results were not in line with our expectations, with rainforest trees having maximum temperatures, burnt biomass and burn time being more similar to those of savanna trees than SDTF trees.”

“As expected, the savanna species were found to be highly flammable. Previous studies have identified that drought tolerant plants may make adjustments that can increase plant flammability (Sultana 2022). Due to this, there is the potential that drought tolerant plants are actually more fire sensitive than previously thought, which can be exacerbated by the effects of droughts (Holan et al. 2020). Our results provide support to these points and reaffirm that area with low water access and frequent droughts, such as the savanna, are areas of fire risk. Proper attention and measures, such as green firebreaks, are therefore needed for the savanna.”

“Interestingly, however, was the fact that although rainforest plants are considered to be less flammable, they in fact had high flammability similar to that of the savanna. This is likely due to the lack of fire adaptations that rainforests plants possess (Meir and Woodward 2010), which may be due to their environment. Because of the wet, moist conditions of the rainforest, wildfires are a rarity, and plants have not needed to adapt to survive these fires. Research has found that moisture is an important limitation to rainforest wildfires and thus a drying period from droughts, which we simulated in our experiment, may be detrimental. As droughts increase, however, these drying periods may become more prevalent and thus increase the flammability of these species, making it important to recognise rainforests as fire-risk areas.”

“Our data also provides important data on species that may be effective in green firebreaks for each biome. With the understanding that each of these vegetation areas faces a risk of wildfire, including rainforests, identifying the least flammable and most flammable species in each biome can help determine appropriate species for a green firebreak.”

Conclusion

“Overall, our findings highlight the urgency of fire management practices in the three studied biomes, especially when considering the increasing lengths of droughts. As changing global conditions continue to threaten these vegetation areas, especially rainforests, utilising green firebreaks with native, relatively fire resistant plants is necessary. Improving the land management practices in these areas with the implementation of green firebreaks can be especially helpful in the context of private properties, where a potential lack of resources makes high effective, efficient practices needed. Continued research is needed on the topic of flammability so as to better understand and incorporate this and future information into bio-ecophysiology when addressing the future of wildfire management.”

Research paper: Shoot and leaf flammability of plants in North Queensland Australia

Research authors: Audrey Crawford, Texas Tech University, Amy Marie Gaulke, Brown University, Daniel Ire Kim, Brown University, Owen Chen Tsunoda, University of Southern California

Research Advisors: David Tng, PhD, Centre for Rainforest Studies, Deborah Apgauauana, PhD, Centre for Rainforest Studies

2023 AGM Report - Barb Lanskey

Nearly 30 people attended TREAT’s 41st Annual General Meeting on Friday evening 1st September at the Yungaburra Community Hall. 

Peter Snodgrass gave his Nursery Report as a Power-Point presentation, and this year the wall was used as the screen, to give a better and bigger image. Mandy presented her yearly audited Financial Report and drew attention to some of the larger figure amounts. Angela read her President’s Report - see this newsletter. She noted that both Mandy Bormolini and Dinah Hansman were stepping down this year from the TREAT management committee, and led the applause to show our appreciation of their work.

All committee positions were then declared vacant and Alan Gillanders was invited to chair the election of the management committee for the coming year. A list of nominees and positions had been on display at the nursery for 2 weeks and those nominees were elected. One committee member position was still available, and Angus Emmott was nominated and elected at the meeting.

The committee for the coming year is:

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President - Angela McCaffrey

Vice-president - John Hardman

Secretary - Doug Burchill

Treasurer - Kelvin Brooks

Committee members - Belinda Bogart, Simon Burchill, Christine Eade, Angus Emmott, Irene Gorman, Jemma Horner, Barbara Lanskey, Dave Skelton.

During the year, Carey Robinson moved back to Melbourne and was replaced on the management team by Gemma Horner.

A General Meeting follows the AGM. This year it was extremely short as no issue was raised.

Angela then asked Alan to give us his talk for the evening. This was in place of Nigel Tucker’s talk which Nigel had to cancel due to family matters.

Alan’s talk was about five plants for the garden. He’d brought along samples of some of their foliage, flowers and fruit and used these in his talk as well as pictures on the screen. It was all most informative, and there were quite a few questions asked. While some of the garden trees can grow very large in the rainforest, Alan pointed out that he’d never yet seen a rainforest tree die from pruning. The species he spoke about were: Galbulimima baccata (Pigeonberry Ash), Hicksbeachia pilosa (Red Bauple Nut), Athertonia diversifolia (Atherton Oak), Syzygium fibrosum (Fibrous Satinash) and the fern Microsorum membranifolium (Pimple Fern).

Supper was then held and the last of us left about 9pm.