Research highlights the extent of fuels consumed by fire

The effect of fuel load and structure on fire severity across Australian wet eucalypt forests has been investigated by research conducted through the Bushfire and Natural Hazards CRC’s funding for quick response.  

Findings from a suite of projects led by Dr James Furlaud and Prof David Bowman from the University of Tasmania—Remeasurement of Burnt TERN Ausplots in New South Wales, Remeasurement of burnt permanent plots in Tasmanian wet eucalypt forest – 2019 and Immediate post-fire vegetation re-measurement of TERN plots burnt during 2015/16 fire season—report on the measurement of four Terrestrial Ecology Research Network (TERN) Forest Ausplots across Australia that burned in different bushfires and planned burns between 2016 and 2020.

Wet eucalypt forests are the most complex and poorly documented forest ecosystem in Australia – the combination of a highly-flammable eucalypt overstorey and a less-flammable understorey of Gondwanan rainforest or sclerophyllous shrubs make it unique worldwide. However, due to the contrasting flammabilities of this vegetation, fire behaviour is poorly understood in these forests. The TERN Ausplots were set up to measure carbon and fuel dynamics in structurally mature wet eucalypt forests across Australia. In the 2019-20 fire season, eight Ausplots burned—four in southern NSW and four in northern NSW. This research specifically looked at the four plots in southern NSW.

The main goals of this study were to obtain empirical measurements of fuel load, structure and hazard within the first two years after a fire to complement the measurements of fuel loads taken directly before the fires. This allowed the research team to not only precisely quantify the fuel loads consumed by a range of fires, but also provides a baseline measurement of fuel loads. This baseline can be used to anchor measurements of fuel accumulation in wet eucalypt forests that are part of related CRC studies attempting to measure both the effects of climate and stand age on fuel accumulation in wet forests.

This study revealed that a consistent effect of low-moderate severity fires in tall, wet Eucalyptus forests is to kill, but not consume, the fire-sensitive understorey due to the effect of heat. This resulted in a new deposition of fine surface fuels (leaf litter) within the first 10 months after a fire, and substantial amount of dead standing coarse fuels, which will eventually fall to the surface. Meanwhile, it was found that high-severity fires consumed most of the elevated layer but resulted in a pulse of regenerating biomass. In all cases, the thinning of elevated fuels due to understorey death was found to likely dry out the understorey, potentially leaving these forests vulnerable to future fires.

This project represents the culmination of three different quick response projects to compile a detailed database of pre- and post-fire vegetation and fuels data. This database will allow researchers to better understand how wet eucalypt forests respond to low and high severity bushfires and to further identify how vulnerable resprouter forests are to successive fires, as well as to continue to improve fire behaviour models.

Access the full summary report of findings here.