@article {bnh-8321, title = {Informing post-fire recovery planning of northern NSW rainforests}, number = {721}, year = {2022}, month = {03/2022}, institution = {Bushfire and Natural Hazards CRC}, address = { Melbourne}, abstract = {

In historic times rainforests have comprised less than 2\% of the total forested area of NSW (Baur 1987) yet they have played a pivotal role in the states early timber industry, and the development of conservation policy, and are the only plant community in NSW to have been included in the name of a World Heritage property. The Gondwanan rainforests evolved in an environment of dependable rainfall and low fire frequency. They have persisted through multiple climate oscillations and glacial/inter-glacial cycles in refugia scattered through the Great Escarpment uplift landform. They now represent a collection of relictual species whose origins can be traced to the Eocene Epoch 55-37 million years ago when cool temperate taxa such as Nothofagus first appears in the fossil record.

In northern New South Wales, temperate rainforests are typically considered to be vulnerable to climate-change related natural hazards such as extended spring droughts and wildfires. Numerous reviews predict that extreme climatic events are likely to increase in frequency and/or intensity in coming decades (CSIRO 2019, 2020) and that wildfires will become larger, more intense, and more frequent. The vulnerability of temperate rainforests to fire is assumed to be the result of their limited intrinsic post-fire regenerative capacity, their susceptibility to canopy scorch and bark damage, and extrinsic factors such as their landscape position as patches within extensive areas of elevated fuel hazard in wet sclerophyll forest and woodland plant communities. The impacts of wildfires on temperate rainforests are heightened because wildfires are naturally infrequent, the vegetation is poorly adapted to fire, and fuel biomass is abundant and contiguous in the surrounding landscape.

During the 2019/20 wildfire season, 18.1\% of the extent of NSW{\textquoteright}s rainforest vegetation classes experienced either low, moderate, high, or extreme severity wildfire, a scale un-anticipated in earlier land management risk planning. While the proportion of each class varied, the greatest impacts occurred in Dry Rainforest and Northern Warm Temperate Rainforest. Across the Gondwana Rainforest of Australia World Heritage property (Gondwana Rainforests), 16 of the 28 reserves in the NSW section saw some fire impacts. This resulted in 8.6\% of the 112,145 ha of rainforest in these reserves experiencing either low, moderate, high, or extreme severity wildfire. The extent of the fire impacts was greatest in the Hastings-Macleay, New England, and Washpool-Gibraltar Range sections of the Gondwana Rainforests. The focus of the current study is the Hastings-Macleay section.

The 2019/20 wildfire season coincided with the lowest annual rainfall recorded in the Hastings-Macleay study area since local records commenced in 1959. Soil moisture deficits in rainforest were at their lowest recorded levels at the end of an extended spring drought in northern NSW. An analysis using data from a decade of soil moisture monitoring indicated that when soil moisture in rainforest reached 10-20\%, the rainforests become susceptible to fuel ignition and sustaining a wildfire.

In November 2019 multiple ignitions and running wildfires were occurring across northern NSW, and fire-fighting resources were prioritised to life and property protection. On November 9th 2019, an unprecedented seventeen wildfires were at Emergency Warning level on the same day in NSW, fire behaviour was erratic and rainforests were igniting and sustaining running fires. The wildfires impacted directly on long-term research plots established in 1959 in Werrikimbe and Willi National Parks in landscapes with extensive localised climate monitoring equipment. Resources were rapidly deployed within weeks of the wildfire impacting the research infrastructure to capture key elements of fire behaviour and commence post-fire assessments. With the financial support of the Bushfire and Natural Hazards CRC and NSW NPWS, citizen science volunteers began to measure the impacts of the wildfires and describe the recovery trajectory of the rainforest stands within the parks.

The long-term research plots provide a baseline to understanding pre-fire rainforest stand dynamics and condition. The 60 years of accumulated data highlighted the high biomass, slow growth rates, and highly episodic nature of tree regeneration in these rainforests. Annualized tree mortality was less than 1\%, and canopy dieback was associated with previous selective harvesting in the 1960s. Fine fuel biomass is low and inputs are strongly seasonal. Basal fire scars were present on trees across the stands surveyed prior to the 2019/20 wildfire season, indicating past wildfires had occurred in these rainforests during the past century, and it appears the majority of established trees were resilient to their effects. Evidence from char heights indicates the predominant fire behaviour experienced by the larger rainforest trees is low-intensity litter fires that progress slowly through the rainforest stands. This was corroborated in discussions with fire managers who had witnessed fires across multiple northern NSW rainforest reserves. Evidence from archival fire reporting and mapping suggests that the typical fire season in the 1950s peaked in November and now peaks two months earlier. These rainforests are approaching the driest months in early spring when lightning ignitions are also at their seasonal maximum.

Wildfires entered rainforest from front or flank spread leading to attrition of trees on rainforest margins. Monitoring dominant trees for 12 years in smaller rainforest stands demonstrated that they can tolerate multiple fires until their structural integrity weakens and fails. In 2019/20 ember attack was widespread in rainforest, but generally led to the ignition of small, localised areas (\<100 m2) or of individual trees. Mortality rates associated with the wildfires were 20-30\% across all tree species, with the proportion increasing with the severity of the wildfire event. This figure may prove to be an underestimate as lagged tree mortality effects from wildfires have been reported elsewhere for rainforests. The majority of burnt trees regenerated with basal coppicing. Seedling regeneration of tree species was infrequent due to the lack of a soil or canopy seed bank. Coppicing was more abundant where fire severity was low. Large trees with well-developed buttress hollows and scars were more likely to ignite due to the accumulation of dry wood and fuel at their base compared to smaller trees. Larger, older trees that had more pre-existing fire scars were more likely to die and collapse after burning. This is potentially an age effect where older and larger (diameter and height) trees have been subjected to more fire-induced wounds and hollows.

The temperate rainforests of northern NSW have been subject to wildfires in the past, and have a level of resilience to them. However, the susceptibility of the canopy dominant rainforest trees to basal wounding and collapse is a concern due to the longevity and age of these trees, their role in maintaining the rainforest microclimate, and their importance as habitat to a very diverse cargo of epiphytic bryophytes. Options to manage wildfire risk using conventional zoning and fuel hazard management may be limited. Fuel hazard was not particularly high during the 2019/20 wildfire season in the Hastings-Macleay section of Gondwana Rainforests, with most areas burnt in 2019 also having been burnt in 2013. Regardless, landscape-level fuel hazard management will not address the risk of individual mature rainforest tree ignition during conditions of significant ember attack when rainforest fine fuel biomass is naturally low.

A range of proposals are made to improve the knowledge base to better inform the spatially explicit wildfire risk assessment process trialled following the 2019/20 wildfire season. The central recommendation is the scoping of a systematic Monitoring, Evaluation and Reporting (MER) system for the Gondwana Rainforests of Australia World Heritage property (Gondwana Rainforests) that focuses on establishing a baseline to track trends in the nominated World Heritage outstanding universal values or criteria. The system will require an integrated remote sensing and ground-based plot monitoring approach stratified by rainforest type and location. The monitoring plots established for this study can be readily integrated into the proposed MER system, and can be used to test the significance of ongoing or lagged tree mortality and to validate models of post-wildfire tree mortality and regeneration.

The current study has informed post-fire recovery planning by assessing the significance of the impacts of the 2019/20 wildfire season on rainforest stand structure, composition, tree mortality, and regeneration strategies. While the field measurements were in progress, recovery planning workshops hosted by the Commonwealth and NSW governments were attended and preliminary results were provided. The availability of existing long-term rainforest monitoring experiments dating from the 1950s, sections of which were burnt in November 2019, was critical to providing preliminary results within months of the fire event (Peacock 2020) to inform post-fire recovery planning. This outcome alone underscores the critical role long-term ecological monitoring systems have in rapidly supporting land managers information needs when responding to widespread natural hazards such as landscape-scale wildfires.

}, keywords = {nsw, Planning, post-fire, rainforests, recovery}, issn = {721}, author = {Ross Peacock and Baker, Patrick} } @article {bnh-8328, title = {Post-fire impact assessment of Tasmanian sphagnum bogs}, number = {724}, year = {2022}, month = {03/2022}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

In the summer of 2015-2016 several large dry lightning storms ignited wildfires that burned across Western Tasmanian landscapes desiccated by the combination of severe spring drought and above average summer temperatures. Approximately 20 000 ha of the Tasmanian Wilderness World Heritage Area burnt including Sphagnum moss communities, or {\textquoteleft}sphagnum bogs{\textquoteright}, and other significant areas of high conservation value Gondwanan refugia. The scale of the fires prompted the Tasmanian government to fund research in techniques to rehabilitate fire-impacted Gondwanan refugia, including sphagnum bogs, in the Lake Mackenzie area of the Northern Central Plateau. A key step in sphagnum bog restoration is the development of rapid, broad-scale, cost-effective and low impact survey techniques to identify sites in need of rehabilitation. We trialled unmanned aerial systems (UAS) with visible spectrum sensor technology to map fire extent and severity.\  Three sphagnum bogs were used to develop an ENVI classification workflow based on a training data set of burn severity categories and other ecological surface cover measurements to map burn severity.\  These maps were validated using ocular assessments of ground cover and burn severity in pre-existing permanently marked quadrats. We found poor to moderate agreement between the UAS and field fire severity with considerable variation amongst the sampled bogs. Total burnt area sphagnum bog maps were then produced by combining burnt severity categories for five bogs, including the three used for fire severity mapping, The congruence between Sphagnum burn extent maps with field data collected by differential Global Positioning System was found to range from substantial to poor according to Cohen{\textquoteright}s Kappa index. Multivariate analysis of the quadrat ground cover assessments showed that high grass cover was most strongly associated with poor field validation agreement (low Kappa scores), whereas acceptable field validation agreement (high Kappa scores), were associated with high cover of Sphagnum. A major constraint of this study was the two-year time gap between the fire and remote sensing mapping and field survey. Higher accuracy fire severity mapping and area burned mapping would be possible if imagery was acquired immediately after a fire event. In light of our findings, we provide recommendations for future UAS surveys of fire impacted sphagnum bogs, the most critical of which is acquiring remote sensing and field data in the same growing season as the fire.

}, keywords = {bogs, impact assessment, post-fire, sphagnum, Tasmanian}, issn = {724}, author = {Morgan Harding and Darren Turner and Grant Williamson and Scott Nichols and David Bowman} } @article {bnh-8081, title = {Understanding post-fire fuel dynamics using burnt permanent forest plots}, number = {674}, year = {2021}, month = {06/2021}, institution = {Bushfire and Natural Hazards CRC}, address = {MELBOURNE}, abstract = {

The main goal of this study is 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 will not only allow us to precisely quantify the fuel loads consumed by a range of fires, but it will also give us a baseline measurement of fuel loads.\  We can use this baseline to anchor measurements of fuel accumulation in wet eucalypt forests that are part of related TERN and BNHCRC studies attempting to measure both the effects of climate and stand age on fuel accumulation in wet forests.

Current state of knowledge

The flammability of tall wet eucalypt forests is poorly understood. A globally unique forest type, these forests consist of a highly-flammable Eucalyptus overstorey and a moist, non-flammable understorey consisting of rainforest and broadleadf trees and shrubs. As a result, these forests are rarely available to burn, and almost no data exists on flammability and fire behaviour. While current fire behaviour models assume that fuel load and hence flammability increase asymptotically as a function of time since previous fire,\ there is much debate over whether this is the true trajectory of flammability in these forests. Understanding how fire severity is influenced by fuels and time since fire is a critical question in these forests.

As the rate of spread and intensity of a fire is a function of fuels, fire weather and topography, and as only the latter can be physically manipulated, the effect of fuel load and structure on fire behaviour, and the subsequent reduction in fuels, is extremely important to understand.\  Planned burning, the intentional use of low-severity fire, is the most commonly employed fuel reduction technique in Australia.\  The underlying concept is that burning off fuel loads across a landscape leads to an increased encounter rate with low fuel load areas.7 While reducing fuel ages has been shown to reduce both the extent and incidence of unplanned fires, the effect of low severity fires on actual fuel loads has not been explicitly quantified, especially in wet forests where planned burning is less commonly practiced than in dry forest.\  Further, low-severity fires have historically been overlooked in wet forests, as high-severity fires are though to be the important disturbance type due to the serotinous nature of many eucalypts. But recent research indicates that low-severity fires could play a more important role that previously realised.

Related projects

This study is building a large dataset of pre- and post-fire permanent plot measurements to complement existing studies on the fire regime of wet eucalypt forests. As mentioned above it utilised infrastructure set up as part of the TERN forests Ausplots network, and the Warra Chronosequence plots. Such a dataset will allow for analyses such as\  the validation of fire behaviour models, analysis of the resilience wet forests to wildfire, and help understand how fire severity affects subsequent fire hazard. Data from this study has already added a valuable validation section to a study providing the first-ever explicit description of the fire regime of mature wet Eucalyptus forests across Australia.26\ 

This project has also contributed a valuable high-resolution field-based validation for the BNHCRC project Using pre and post fire LiDAR to assess the severity of the 2019 Tasmanian Bushfires. This project will create, among other things, a high-resolution fire-severity map of the Riveaux Road Fire. With these data, we will be able to perform geospatial analyses to untangle the drivers of fire severity during this bushfire. Importantly the area burned in the fire includes the WARRA silvicultural experiment, in which a number of silvicultural treatments were trialled in a small area. This will allow an investigation into the effects of different silvicultural practices on flammability and fire severity in tall wet Eucalyptus forests.

Research questions

This study plans to focus on three major research questions:

}, keywords = {burnt, dynamics, forest, fuel, permanent, plots, post-fire}, issn = {674}, author = {Furlaud, James M. and David Bowman} } @article {bnh-8165, title = {Using pre- and post-fire LiDAR to assess the severity of the 2019 Tasmanian bushfires}, number = {698}, year = {2021}, month = {08/2021}, institution = {Bushfire and Natural Hazards CRC}, address = {MELBOURNE}, abstract = {

In January 2019, over 64,000 ha of bushland burned in the Riveaux Road fire in Tasmania{\textquoteright}s southern forests. Most of area burned occurred in tall wet eucalypt forest. These forests are considered to be highly flammable in dry conditions, but fires are infrequent due to the generally cool, wet climate in which they grow. As a result, limited data exists on the behaviour and effects of wildfire in these forests. Prior to these fires, extensive areas of these southern forests have been studied in-depth. In 2014, a large area of the forests that burned were mapped with aerial LiDAR, a remote-sensing technology that can characterise three-dimensional forest structure. Further, in 2016, detailed field-based measurements of fuel load, structure, and hazard were taken at 12 permanent plots which subsequently burned in 2019. Hence, the 2019 fires in Tasmania represent a globally-rare opportunity to characterise the severity of a large wildfire using pre-fire and post-fire data. In October 2019, the Department of Primary Industries, Parks, Water and Environment (DPIPWE) in Tasmania, along with five other BNHCRC end-users and the University of Tasmania, launched a project to use remote-sensing and field-based data to create a detailed case study of the 2019 Riveaux Rd. Fire, and to untangle the drivers of fire severity in tall wet eucalypt forests.\  To do this we (i) remeasured plots to assess tree mortality and changes in fuel loads post fire; (ii) acquired LiDAR data from a transect across a burned buttongrass-forest boundary on the Weld River enabling comparison with pre-fire LiDAR data; (iii) established baseline postfire LiDAR buttongrass-forest boundary transect on the Huon River at Blakes Opening.\  Here we describe the data sets and report some preliminary analyses.

}, keywords = {Bushfire, fire severity, Lidar, post-fire, pre-fire, Tasmania}, issn = {698}, author = {Furlaud, James M. and Arko Lucieer and Scott Foyster and Anna Matala and David Bowman} } @article {bnh-6929, title = {Understanding post-fire fuel dynamics using burnt permanent forest plots}, number = {569}, year = {2020}, month = {05/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The main goal of this study is to obtain empirical measurements of fuel load, structure and hazard within the first year after a fire to complement the measurements of fuel loads taken directly before the fires. This will not only allow us to precisely quantify the fuels consumed by these relatively low-severity fires, but it will also give us a baseline measurement of fuel loads. We can use this baseline to anchor measurements of fire severity and fuel accumulation in wet eucalypt forests related to other BNHCRC studies attempting to measure both fuel accumulation and the drivers of fire severity in wet forests.

The flammability of tall wet eucalypt forests is poorly understood. A globally unique forest type, these forests consist of a highly-flammable Eucalyptus overstorey and a moist, non-flammable understorey consisting of rainforest and broadleadf trees and shrubs.[i], As a result, these forests are rarely available to burn, and almost no data exists on flammability and fire behaviour. While current fire behaviour models assume that fuel load and hence flammability increase asymptotically as a function of time since previous fire, there is much debate over whether this is the true trajectory of flammability in these forests. Understanding how fire severity is influenced by fuels and time since fire is a critical question in these forests.

As the rate of spread and intensity of a fire is a function of fuels, fire weather and topography, and as only the latter can be physically manipulated, the effect of fire on fuel loads is extremely important to understand.\  Low-severity fires are known to reduce surface fine fuels loads across a landscape in certain forest types, so intentionally lighting low-severity fires (i.e. planned burns), will increase the encounter rate of wildfires with low fuel load areas.7 However the effect of low-severity fires in wetter forests is mostly unstudied. While reducing fuel ages has been shown to reduce both the extent and incidence of unplanned fires, the effect of low severity fires on actual fuel loads has not been explicitly quantified.\  While the period of effectiveness of a planned burn has been generally reported to be 5-6 years,8,\ these studies have looked at the empirical probability or size of unplanned fires as a function of fuel age, no studies that we could find in Australia measured fuel loads directly after a low-severity fire.

}, keywords = {eucalypt forest, fuel dynamics, permanent forest plots, post-fire}, issn = {569}, author = {Furlaud, James M. and David Bowman} }