@article {bnh-7889, title = {Optimisation of fuel reduction burning regimes for fuel reduction, carbon, water and vegetation outcomes {\textendash} final project report}, number = {648}, year = {2021}, month = {03/2021}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Fire managers often have multiple objectives for a given prescribed burn centred around risk reduction and conservation of biodiversity. The ability to predict the effects of prescribed burning on the capacity of forests to deliver ecosystem services such as clean air, carbon sequestration, and a reliable and high-quality supply of water is becoming increasingly more important.

The body of research detailed in this Synthesis Report represents a concerted effort to understand the effect of prescribed burning on water quantity and carbon losses and gains in forested ecosystems in south-eastern Australia. We collected empirical data from over 100 sampling sites treated with a recent prescribed burn. The sampling strategy we used was consistent over time with target sampling variables included for estimation of overstorey and understorey biomass and direct sampling of surface and near surface fuel loads. Site selection was stratified to accommodate as much site variability as possible and to take full advantage of prescribed burn plans.

Data collected from the field was used in a variety of modelling assignments to capture the effect of prescribed burning on changes in water availability and transformation of carbon pools. Using a mixture of models and empirical sampling and analysis, we showed that there are few risks to long-term carbon and water cycles when prescribed burning is conducted on cycles of 10 or so years. Critical to this analysis is the frequency of bushfires {\textendash} if the inter-fire interval of unplanned fires becomes short (e.g., \<50 years) then ecosystem losses of carbon and reductions in water yield are likely to become semi-permanent features.

Our modelling endeavours ranged from relatively complex process-based models describing water and carbon balances through to simple response surface models. By exploring the transformation of carbon pools in surface fuels during prescribed burning, we developed robust yet simple-to-use models for predicting changes in total carbon and biomass in this fuel fraction. The novel application of FullCAM, a well-established model used for carbon accounting, was tested for its ability to incorporate often subtle changes in forest growth and carbon transformation associated with prescribed burning. We found this model to be relatively sensitive and recommend it to fire managers for applications such as estimation of carbon emissions. Based on our key findings, we advocate for continued research and evidence-based application of prescribed burning as a valuable land management approach.

Data assembled from peer-reviewed publications and researchers worldwide was mined for changing trends in publications concerning prescribed burning, global patterns of litterfall and standing litter, and water use efficiency of forests. These summative studies informed our research direction and chartered our progress.

A considerable number of student projects have been supported during the course of this project contributing to the training of the next generation of researchers and land managers.

}, keywords = {burning regimes, carbon, fuel reduction, optimisation, vegetation, water}, issn = {648}, author = {Bell, Tina and Adams, Mark A. and Mathias Neumann and Danica Parnell and David Pepper and Malcolm Possell} } @article {bnh-7029, title = {Estimating carbon stocks and biomass in surface fuel layers}, number = {586}, year = {2020}, month = {07/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

In this report we describe a simple model that can be used to estimate carbon

(C) stocks in surface fuel layers for C accounting purposes. We used empirical data collected from dry sclerophyll forests from a range of sites in Victoria, New South Wales and the Australian Capital Territory. This information was used to develop an easy-to-use tool to improve estimates of C emissions from prescribed burning. Models developed using data from each state have been reported previously {\textendash} here we present an evaluation of a universal model developed using the complete empirical dataset for all sites in all three states, and two separate models ({\textquoteleft}universal{\textquoteright} models) developed using data from all the sites burnt by prescribed fires and nearby unburnt sites.

Samples of the near-surface fuel layer were separated into three fractions: fine fuel (\<9 mm diameter), intact leaves, and twigs and other material such as fruits, flowers and bark. The dry weight and C content of each fraction was determined. To model biomass and C content of surface fuels, a mixture design was used. For each site, the proportion of the total fuel load of each of the three surface litter fractions was used as an independent factor (x1, x2, and x3), and the corresponding total fuel load (t ha-1) or C content (t C ha-1) was used as the dependent factor. A response surface was fitted to the mixture design using a Generalised Blending Mixture model (GBM) and a polynomial equation for each response was generated by running the GBM with varying numbers of terms included in the response surface equation. To determine the best fitting equation, Akaike information criterion (AICc) was used as a measure of the relative quality of the response surface for a given set of data in relation to other model iterations. Data were randomly assigned into an 80:20 split for training and testing of the response surface of the model. Models were also validated against a second set of data collected from high and low productivity forest sites. This additional information improved data spread and, thus, model testing.

The response surfaces fitted to data showed reasonable agreement with the data but the universal model (burnt and unburnt data from all sites combined) tended to be unreliable with both over- and underpredictions depending upon which dataset was being used for testing or validation. Universal models created using data from all burnt or unburnt sites were better than other trained models for predicting of biomass or C content in relation to fire history.

}, keywords = {biomass, carbon stocks, estimates, surface fuel layers}, issn = {586}, author = {Danica Parnell and Malcolm Possell and Bell, Tina} } @article {bnh-7030, title = {Model predictions for fuel reduction burning of eucalypt open forest in the greater Blue Mountains region}, number = {587}, year = {2020}, month = {07/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Prescribed burns are a land management tool used for reducing fuel loads in terrestrial ecosystems. Under extended drier, hotter weather conditions they might be used increasingly and more widely to help manage risk of wildfire and subsequent damage to life, property and natural assets. They also represent a form of disturbance to ecosystems, including their biodiversity and biogeochemistry. From a biogeochemistry perspective, we apply the FullCAM carbon accounting model to eucalypt open forest sites in the greater Blue Mountains region that underwent prescribed burns and fieldwork campaigns in 2019. Field data were used to derive values and estimates that guided model calibration and helped to explore the suitability of FullCAM for simulating the effect of prescribed burning on this ecosystem type. The diameter at breast height of overstorey and understorey trees, leaf area index and surface litter fractions were key measurements for estimating production, allocation, turnover (litter input to surface debris) and breakdown (output from surface debris) of carbon pools of forest components and hence, for calibrating FullCAM. Measurements for paired burnt/unburnt plots were key to estimating loss of carbon from forest component pools to the atmosphere due to prescribed fire. Simulation of unburnt forest component pools were reasonable as a calibration, although improvements in simulating fractions of surface litter would probably improve simulations of the effect of prescribed fire on forest component pools. Recommendations related to collection of field data and to model structure are made to improve alignment between model-data comparisons.

}, keywords = {Blue Mountains, eucalypt, Fuel reduction burning, modelling, open forest, predictions}, issn = {587}, author = {David Pepper and Bell, Tina and Malcolm Possell and Danica Parnell} } @article {bnh-6907, title = {Near infrared spectroscopy as a new fire severity metric}, number = {568}, year = {2020}, month = {05/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Samples of leaves, twigs and bark representing typical surface fuels from forests and woodlands were systematically heated until combusted under controlled conditions in the laboratory. Change in colour of residue was described using R-conversion of the Munsell colour system and compared to colours generated from near infrared (NIR) scanning. Regardless of the method of heating used, there was very little change in physical properties or colour of residues when heated at low temperatures to 200

{\textdegree}C. Surface fuel samples began to thermally degrade when heated at 300 {\textdegree}C, which was reflected in much darker coloured residues that were mostly uniform in colour for different fuel types when determined from NIR spectroscopy. When surface fuels were combusted at temperatures between 400 and 600 {\textdegree}C, residues were much lighter in colour regardless of the type of fuel burnt. Again, residue colours were more uniform when described using NIR spectroscopy compared to the Munsell colour system, although differences in the consistency of residues (heterogenous production of charred material and ash) were still reflected in variations in shading. In several instances, colours resulting from NIR scans were closer to the actual colour of residues suggesting that it is a more accurate system than colour matching by eye using the Munsell colour system.

This study indicates that there is potential for NIR technology to be used to determine fire severity according to the colour of residue after fire. While the general method of colour matching is not new, the use of NIR spectroscopy can reduce inaccuracies associated with subjective colour matching and poor colour correlation when using some forms of automated colour conversion. As shown, spectroscopic methods such as NIR can also be used to assess chemical changes in fuels during thermal decomposition. This includes quantitative losses of carbon and nitrogen and estimating fire intensity according to the temperature that were required to form a particular residue.

}, keywords = {fire severity, infrared, metrics, spectroscopy}, issn = {568}, author = {Danica Parnell and Bell, Tina and Malcolm Possell} } @article {bnh-6978, title = {Quantifying the conversion of vegetation to ash for soil carbon fingerprinting}, number = {572}, year = {2020}, month = {06/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Samples of leaves, twigs and bark representing typical surface fuels from forests and woodlands were systematically heated and combusted under controlled conditions. Very little biomass, carbon (C) and nitrogen (N) was lost when heated at low temperatures to 200 {\textdegree} and greatest losses occurred between 400 and 600

{\textdegree}C, regardless of the type of fuel burnt. Losses of C and N varied considerably with temperature. Carbon was lost when fuels were heated at temperatures of 300 {\textdegree}C or more. Nitrogen was relatively more abundant when heated at 400 {\textdegree}C, albeit at very low levels (less than 5\%). When heating time was varied there were noticeable differences in patterns of weight loss and changes in proportions of C and N. This indicates that both fire intensity and residence time is likely to be important in understanding losses of C and nutrients during fire, particularly during low intensity prescribed burning.

The use of colour of residues after heating surface fuel has the potential to determine fire severity. Existing technology such as near infra-red scanners can measure ash colour, not only indicating fire severity but also, by association, C and N losses from fire. Combustion studies done in a well-controlled laboratory environment could be used to interpret fireground conditions in relation to fire intensity and residence time, according to the nature and amount of charred material, charcoal and ash that remains after fire.

}, keywords = {Ash, milestone, soil carbon fingerprinting, vegetation}, issn = {572}, author = {Danica Parnell and Bell, Tina and Malcolm Possell} } @article {bnh-6980, title = {Sampling and data analysis of field sites of 40 prescribed burns}, number = {573}, year = {2020}, month = {06/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

This report provides a summary of the main features of the sites sampled as burn units in the Blue Mountains, NSW to characterise the biomass, carbon and nitrogen held in vegetation/fuel in unburnt and burnt sites. Sites sampled in Victoria and NSW for refinement and testing of current surface fuel models is also provided. Details of how empirical data collected from the field has been used in our modelling efforts and in student projects has been provided.

}, keywords = {data analysis, field sites, prescribed burns, sampling}, issn = {573}, author = {Bell, Tina and Danica Parnell and Malcolm Possell} } @article {bnh-5033, title = {Sampling and data analysis of field sites in NSW}, number = {419}, year = {2018}, month = {10/2018}, institution = {Bushfire and Natural Hazards CRC}, abstract = {

Fuel reduction burning (FRB) is used as a risk mitigation strategy for unplanned fires by altering fuel loads and changing fire behaviour. This involves temporary removal of accumulated fuels of the near-surface and surface fuel layers (Fernandes and Herminio 2003). As the main intention of FRB is to reduce the risk to life and property, associated environmental impacts are often overlooked (Sohngen and Haynes 1997; Gharun et al. 2017a). Fire has a major role in altering biodiversity, carbon and hydrological balances, and can be the cause of soil erosion. As such, changes due to disturbance caused by FRB need to be investigated, and, where practical, integrated into management operations (Gharun et al. 2017a). As planning by fire agencies becomes more sophisticated and accountable, environmental management objectives for FRB need to consider maintenance of high-quality water sources, reduction of carbon dioxide (CO2) emissions and conservation of biodiversity.

}, author = {Bell, Tina and Danica Parnell and Malcolm Possell} }