Shrubland Fire Research Articles

Fuel Drivers of Fire Behaviour in Coastal Mallee Shrublands

Coastal mallee shrubland wildfires present challenges for accurately predicting fire spread sustainability and rate of spread. In this study, we assess the fuel drivers contributing to coastal mallee shrubland fires. A review of shrubland fire behaviour models and fuel metrics was conducted to determine the current practice of assessing shrubland fuels. This was followed by workshops designed to elicit which fuel structural metrics are key drivers of fire behaviour in coastal mallee shrublands. We found that height is the most commonly used fuel metric in shrubland fire models due to the ease of collection in situ or as a surrogate for more complex fuel structures. Expert workshop results suggest that cover and connectivity metrics are key to modelling fire behaviour in coastal mallee shrublands. While height and cover are frequently used in fire models, we conclude that connectivity metrics would offer additional insights into fuel drivers in mallee shrublands. Future research into coastal mallee fire behaviour should include the measurements of fuel height, cover, and horizontal and vertical connectivity.

Rising wildfire risk to houses in the United States, especially in grasslands and shrublands.

Wildfire risks to homes are increasing, especially in the wildland-urban interface (WUI), where wildland vegetation and houses are in close proximity. Notably, we found that more houses are exposed to and destroyed by grassland and shrubland fires than by forest fires in the United States. Destruction was more likely in forest fires, but they burned less WUI. The number of houses within wildfire perimeters has doubled since the 1990s because of both housing growth (47% of additionally exposed houses) and more burned area (53%). Most exposed houses were in the WUI, which grew substantially during the 2010s (2.6 million new WUI houses), albeit not as rapidly as before. Any WUI growth increases wildfire risk to houses though, and more fires increase the risk to existing WUI houses.

Fuel treatments in shrublands experiencing pinyon and juniper expansion result in trade-offs between desired vegetation and increased fire behavior

BackgroundNative pinyon (Pinus spp.) and juniper (Juniperus spp.) trees are expanding into shrubland communities across the Western United States. These trees often outcompete with native sagebrush (Artemisia spp.) associated species, resulting in increased canopy fuels and reduced surface fuels. Woodland expansion often results in longer fire return intervals with potential for high severity crown fire. Fuel treatments are commonly used to prevent continued tree infilling and growth and reduce fire risk, increase ecological resilience, improve forage quality and quantity, and/or improve wildlife habitat. Treatments may present a trade-off; they restore shrub and herbaceous cover and decrease risk of canopy fire but may increase surface fuel load and surface fire potential. We measured the accumulation of surface and canopy fuels over 10 years from ten sites across the Intermountain West in the Sagebrush Steppe Treatment Evaluation Project woodland network (www.SageSTEP.org), which received prescribed fire or mechanical (cut and drop) tree reduction treatments. We used the field data and the Fuel Characteristic Classification System (FCCS) in the Fuel and Fire Tools (FFT) application to estimate surface and canopy fire behavior in treated and control plots in tree expansion phases I, II, and III.ResultsIncreased herbaceous surface fuel following prescribed fire treatments increased the modeled rate of surface fire spread (ROS) 21-fold and nearly tripled flame length (FL) by year ten post-treatment across all expansion phases. In mechanical treatments, modeled ROS increased 15-fold, FL increased 3.8-fold, and reaction intensity roughly doubled in year ten post-treatment compared to pretreatment and untreated controls. Treatment effects were most pronounced at 97th percentile windspeeds, with modeled ROS up to 82 m min−1 in mechanical and 106 m min−1 in prescribed fire treatments by 10 years post-treatment compared to 5 m min−1 in untreated controls. Crown fire transmissivity risk was eliminated by both fuel treatments.ConclusionsWhile prescribed fire and mechanical treatments in shrublands experiencing tree expansion restored understory vegetation and prevented continued juniper and pinyon infilling and growth, these fuel treatments also increased modeled surface fire behavior. Thus, management tradeoffs occur between desired future vegetation and wildfire risk after fuel treatments.

Mapping fireline intensity and flame height of prescribed gorse wildland fires

Wildfires currently represent an imminent danger to communities around the world due to their increasing severity and frequency. It is critical to expand current knowledge on wildfire behaviour to improve risk management practices, firefighting operation and engineering design in the Wildland Urban Interface (WUI). This paper reports 2D high resolution measurements of Byram's fireline intensity generated during a 150 × 200 m2 gorse shrub burn generated from visual and infrared video footage of the prescribed fire, and Light-Detection-and-Ranging (LiDAR) data of the vegetation canopy, both acquired using Unmanned Aerial Vehicles (UAV) technology. The results show that the fireline intensity was highly variable across the plot, reaching localized peak values over 40,000 kW/m and an averaged intensity of 14,300 kW/m approximately. An empirical correlation for estimating the average flame height was derived from the fireline intensity maps and from experimental measurements carried out during the prescribed burn. The correlation was used to produce a 2D detailed map of the average flame height of the prescribed fire, achieving a 11% of error compared to in-fire measurements. The findings from this research suggests that non-linear variabilities of fireline intensity should be carefully considered to adequately describe wildifire behavior of shrubland fires.

Global methyl halide emissions from biomass burning during 2003-2021.

Methyl halides (CH3Cl, CH3Br, and CH3I) are ozone-depleting substances. Biomass burning (BB) is an important source of methyl halides. The temporal variations and global spatial distribution of BB methyl halide emissions are unclear. Thus, global methyl halide emissions from BB during 2003-2021 were estimated based on satellite data. A significant decreasing trend (p<0.01) in global methyl halide emissions from BB was found between 2003 and 2021, with CH3Cl emissions decreasing from 302 to 220Ggyr-1, CH3Br emissions decreasing from 16.5 to 11.7Ggyr-1, and CH3I emissions decreasing from 8.9 to 6.1Ggyr-1. From a latitudinal perspective, the northern high-latitude region (60-90° N) was the only latitude zone with significant increases in BB methyl halide emissions (p<0.01). Based on an analysis of the drivers of BB methyl halide emissions, emissions from cropland, grassland, and shrubland fires were more correlated with the burned area, while BB emissions from forest fires were more correlated with the emissions per unit burned area. The non-BB emissions of CH3Cl increased from 4749Ggyr-1 in 2003 to 4882Ggyr-1 in 2020, while those of CH3Br decreased from 136Ggyr-1 in 2003 to 118Ggyr-1 in 2020 (global total CH3I emissions are not available). The finding indicates that global CH3Cl and CH3Br emissions from sources besides BB increased and decreased during 2003-2020. Based on our findings, not only searching for unknown sources is important, but also re-evaluating known sources is necessary for addressing methyl halide emissions.

Post-Fire Recovery of Plant Biodiversity Changes Depending on Time Intervals since Last Fire in Semiarid Shrublands

Fire is a key disturbance affecting plant biodiversity patterns and evolution. Although a wide range of studies have shown important impacts of fire on vegetation, most have focused on taxonomic diversity, with less emphasis on other aspects of biodiversity, such as functional and phylogenetic diversity. Therefore, we assessed the recovery of biodiversity facets across different times since the last fire in semiarid shrublands in Northeast Iran. We quantified changes in plant biodiversity facets, including taxonomic, functional, and phylogenetic diversity, and the diversity of seven functional traits in five ecologically comparable sites that have experienced wildfire disturbances at short-term (1 and 4 year sites) and long-term (10 and 20 year sites) intervals, in com- parison to an unburnt site. Our results showed significant changes in all biodiversity facets related to the year since the last fire, with a significant increase in biodiversity and diversity of functional traits under long-term rather than short-term conditions, and in comparison to the unburned site. We conclude that wildfire influences the presence of plant species with distant functional and evolutionary relatedness and causes an increase in plant species and diversity of functional traits de- pending on time intervals. Therefore, wildfire can promote positive effects on the recovery of bio- diversity aspects and the evolution of vegetation in semiarid shrublands.

Dynamic Response of Shrubbery Fire to Meteorological Changes in Yunnan Province

This paper takes shrubland fires as the research object and selects typical shrubland forest fire cases that occurred throughout Yunnan Province from 1954 to 2018 as the research samples, and the shrubland fire loss elements and meteorological data are studied by SPSS correlation analysis and MATLAB gray prediction model to analyze shrubland fires and meteorological elements. The results showed that there were significant correlations between shrubland fires and meteorological data; the shrubland fire over fire area, forest damage area, and economic loss composite data index showed positive correlations with annual maximum temperature, annual average minimum temperature, annual average temperature, and annual sunshine hours; the annual average relative humidity, precipitation days, and the composite index of the same day meteorological data showed significant negative correlations, etc. In exploring the main meteorological factors affecting the distribution of forest fires, we establish a meteorological fire model to provide a real and credible scientific basis and theoretical foundation for future forest fire prevention and prediction.

GIS-Based Modeling for Vegetated Land Fire Prediction in Qaradagh Area, Kurdistan Region, Iraq

This study aims to estimate the susceptibility of fire occurrence in the Qaradagh area of the Iraqi Kurdistan Region, by examining 16 predictive factors. We selected these predictive factors, dependent on analyzing and performing a comprehensive review of about 57 papers related to fire susceptibility. These papers investigate areas with similar environmental conditions to the arid environments as our study area. The 16 factors affecting the fire occurrence are Normalized Difference Vegetation Index (NDVI), slope gradient, slope aspect, elevation, Topographic Wetness Index (TWI), Topographic Position Index (TPI), distance to roads, distance to rivers, distance to villages, distance to farmland, geology, wind speed, relative humidity, annual temperature, annual precipitation, and Land Use and Land Cover (LULC). To extract fires that occurred between 2015 and 2020, 121 scenes of satellite images (most of them are scenes of Sentinel-2) were used, with the aid of a field survey. In total, 80% of the data (185,394 pixels) were used for the training dataset in the model, and 20% of the data (46,348 pixels) were used for the validation dataset. Conversely, 20% of these data were used for the training dataset in the model, and 80% of the data were used for the validation dataset to check the model’s overfitting. We used the logistic regression model to analyze the multi-data sites obtained from the 16 predictive factors, to predict the forest and vegetated lands that suffer from fire. The receiver operating characteristic (ROC) curve and the area under the curve (AUC) were used to evaluate the accuracy of the proposed models. The AUC value is more than 84.85% in all groups, which shows very high accuracy for both the model and the factors selected for preparing fire zoning maps in the studied area. According to the factor weight results, classes of LULC and wind speed gained the highest weight among all groups. This paper emphasizes that the used approach is useful for monitoring shrubland, grassland, and cropland fires in other similar areas, which are located in the Mediterranean climate zone. Besides, the model can be applied in other regions, taking the local influencing factors into consideration, which contribute to forest fire mitigation and prevention planning. Hence, the mentioned results can be applied to primary warning, fire suppression resource planning, and allocation work. The mentioned results can be used as prior warnings of the outbreak of fires, taking the necessary measures and methods to prevent and extinguish fires.

Extension of the Balbi fire spread model to include the field scale conditions of shrubland fires

The ‘Balbi model’ is a simplified rate of fire spread model aimed at providing computationally fast and accurate simulations of fire propagation that can be used by fire managers under operational conditions. This model describes the steady-state spread rate of surface fires by accounting for both radiation and convection heat transfer processes. In the present work the original Balbi model developed for laboratory conditions is improved by addressing specificities of outdoor fires, such as fuel complexes with a mix of live and dead materials, a larger scale and an open environment. The model is calibrated against a small training dataset (n = 25) of shrubland fires conducted in Turkey. A sensitivity analysis of model output is presented and its predictive capacity against a larger independent dataset of experimental fires in shrubland fuels from different regions of the world (Europe, Australia, New Zealand and South Africa) is tested. A comparison with older versions of the model and a generic empirical model is also conducted with encouraging results. The improved model remains physics-based, faster than real time and fully predictive.

Increasing forest fire emissions despite the decline in global burned area.

Satellites have detected a global decline in burned area of grassland, coincident with a small increase in burned forest area. These contrasting trends have been reported in earlier literature; however, less is known of their impacts on global fire emission trends due to the scarcity of direct observations. We use an atmospheric inversion system to show that global fire emissions have been stable or slightly decreasing despite the substantial decline in global burned area over the past two decades caused by the carbon dioxide emission increase from forest fires offsetting the decreasing emissions from grass and shrubland fires. Forest fires are larger carbon dioxide sources per unit area burned than grassland fires, with a slow or incomplete follow-up recovery—sometimes no recovery due to degradation and deforestation. With fires expanding over forest areas, the slow recovery of carbon dioxide uptake over burned forest lands weakens land sink capacity, implying positive feedback on climate change.

Fire in Semi-Arid Shrublands and Woodlands: Spatial and Temporal Patterns in an Australian Landscape

Semi-arid landscapes are of interest to fire ecologists because they are generally located in the climatic transition zone between arid lands (where fires tend to be rare due to lack of fuel, but are enhanced following large rainfall episodes) and more mesic regions (where fire activity tends to be enhanced following severe rainfall deficits). Here we report on the characteristics of the contemporary fire regimes operating in a semi-arid region of inland south-western Australia with rainfall averaging around 300 mm per annum. To characterize fire regimes, we analyzed a geodatabase of fire scars (1960–2018) to derive fire preferences for each major vegetation type and fire episode and used known fire intervals to model fire hazard over time and calculate typical fire frequencies. We also used super epoch analysis and correlations to explore relationships between annual fire extent and rainfall received before the fire. We found fires strongly favored sandplain shrublands, and these tended to experience hot crown fires once every 100 years (median fire interval), with fire hazard increasing linearly over time. In contrast, fires were rare in eucalypt woodland and other vegetation types, with a median interval of 870 years and broadly consistent fire hazard over time. Annual fire extent was most strongly linked with high rainfall in the year prior to fire, and this was particularly so for eucalypt woodlands. Large-scale fires in shrublands tended to favor areas burnt in previous large fires, whereas in woodlands they favored edges. In conclusion, we found divergent fire regimes across the major vegetation types of the region. Sandplain shrublands were similar to Mediterranean shrublands in that they experienced intense stand-replacing wildfires which recovered vigorously although slowly, meaning burnt shrublands did not experience fires again for at least 25 and 100 years on average. In contrast, eucalypt woodlands were fire sensitive (trees readily killed by fire) and experienced fires mostly around the edges, spreading into core areas only after large rainfall events elevated fuel levels. Overall, both vegetation types subscribed to typical arid-zone fire regimes where elevated rainfall, and not drought, promoted fires, although the role of fuel accumulation over time was more important in the shrublands.

Biomass burning spatiotemporal variations over South and Southeast Asia

In this study, Moderate Resolution Imaging Spectroradiometer active fire and land use products were integrated to extract and classify biomass burning (BB) data for South Asia (SA) and Southeast Asia (SEA). Several trend and geographic distribution analyses were conducted at the grid (0.25° × 0.25°) and regional scales. As the principal local form of BB, crop residue burning (CRB) in SA increased by 844 spots/yr, and the Mann–Kendall (MK) τ reached 0.61. Additionally, the CRB in Punjab-Haryana, a region a well-known for severest CRB, presented a significant declining trend. BB in mainland SEA was much more intense and was dominated by forest and shrubland fires. Forest fires in mainland SEA declined at a rate of −209 spots/yr, and shrubland fire conversely grew at a rate of 803 spots/yr, which was likely related to the dramatic land cover change induced by the local swidden agriculture. Unlike other regions, BB in equatorial SEA primarily occurred in the second half of the year (August to October), and it was extremely vulnerable to El Niño events. When the annual sea surface temperature anomalies within the Niño 3 region improved by 1 °C, the annual BB spots and fire radiative power in equatorial SEA increased by 5.18 × 104 and 2.40 × 106 MW, respectively. Although the interannual variations in equatorial SEA were dramatic, the robust Siegel’s repeated median estimator still revealed that equatorial SEA BB significantly declined by −1825 spots/yr. This regional decline reflects government endeavors to curb indigenous BB. However, regions with enhanced BB still need to draw more attention, and it is imperative for the Indonesian government to take substantial measures to reduce anthropogenic fire sources during El Niño events.

Exploring the utility of Sentinel-2 MSI derived spectral indices in mapping burned areas in different land-cover types

The difference in structure and composition of landcover types requires accurate mapping of burned areas for post-fire ecological assessments. Spectral indices for burned area mapping are mostly hard-coded to particular environments. However, the best post-fire spectral index to use for burned area mapping in most unstudied landcover types is not known. In this study, out of nine burned mapping indices optimised using the red-edge band, we tested which index outperformed the others in different land cover types. We used the Random Forest (RF) classifier to detect burned areas from Sentinel 2A imagery in four study sites and assessed the classification accuracy. We found out that, the Burned Area Index (BAI) and Global Environmental Monitoring Index (GEMI) spectral indices outperformed other indices in open shrublands, evergreen forest and in needle-leaved and semi-deciduous forests. The lowest performing spectral indices in the four study sites were Optimised Soil Adjusted Vegetation Index (OSAVI), Normalise Burn Ratio (NBR), and Normalise Difference Vegetation Index (NDVI). We recommend that for future studies, researchers and ecologists should use BAI and GEMI in mapping fires in open shrublands, evergreen, needle-leaved and semi-deciduous forests. Our results provide necessary insight for burned mapping algorithms and the accurate estimation of post-fire carbon emission with uni-temporal spectral indices in open shrublands, evergreen, needle-leaved and semi-deciduous forests.

Influence of biomass burning on local air pollution in mainland Southeast Asia from 2001 to 2016

In this study, various remote sensing data, modeling data and emission inventories were integrated to analyze the tempo-spatial distribution of biomass burning in mainland Southeast Asia and its effects on the local ambient air quality from 2001 to 2016. Land cover changes have been considered in dividing the biomass burning into four types: forest fires, shrubland fires, crop residue burning and other fires. The results show that the monthly average number of fire spots peaked at 34,512 in March and that the monthly variation followed a seasonal pattern, which was closely related to precipitation and farming activities. The four types of biomass burning fires presented different tempo-spatial distributions. Moreover, the monthly Aerosol Optical Depth (AOD), concentration of particulate matter with a diameter less than 2.5 μm (PM2.5) and carbon monoxide (CO) total column also peaked in March with values of 0.62, 45 μg/m3 and 3.25 × 1018 molecules/cm2, respectively. There are significant correlations between the monthly means of AOD (r = 0.74, P < 0.001), PM2.5 concentration (r = 0.88, P < 0.001), and CO total column (r = 0.82, P < 0.001) and the number of fire spots in the fire season. We used Positive Matrix Factorization (PMF) model to resolve the sources of PM2.5 into 3 factors. The result indicated that the largest contribution (48%) to annual average concentration of PM2.5 was from Factor 1 (dominated by biomass burning), followed by 27% from Factor 3 (dominated by anthropogenic emission), and 25% from Factor 2 (long-range transport/local nature source). The annually anthropogenic emission of CO and PM2.5 from 2001 to 2012 and the monthly emission from the Emission Database for Global Atmosphere Research (EDGAR) were consistent with PMF analysis and further prove that biomass burning is the dominant cause of the variation in the local air quality in mainland Southeast Asia.

Estimation of emissions from biomass burning in China (2003–2017) based on MODIS fire radiative energy data

Abstract. Biomass burning plays a significant role in air pollution and climate change. In this study, we used a method based on fire radiative energy (FRE) to develop a biomass burning emission inventory for China from 2003 to 2017. Daily fire radiative power (FRP) data derived from 1 km MODIS Thermal Anomalies/Fire products (MOD14/MYD14) were used to calculate FRE and combusted biomass. Available emission factors were assigned to four biomass burning types: forest, cropland, grassland, and shrubland fires. The farming system and crop types in different temperate zones were taken into account in this research. Compared with traditional methods, the FRE method was found to provide a more reasonable estimate of emissions from small fires. The estimated average annual emission ranges, with a 90 % confidence interval, were 91.4 (72.7–108.8) Tg CO2 yr−1, 5.0 (2.3–7.8) Tg CO yr−1, 0.24 (0.05–0.48) Tg CH4 yr−1, 1.43 (0.53–2.35) Tg NMHC yr−1, 0.23 (0.05–0.45) Tg NOx yr−1, 0.09 (0.02–0.17) Tg NH3 yr−1, 0.03 (0.01–0.05) Tg SO2 yr−1, 0.04 (0.01–0.08) Tg BC yr−1, 0.27 (0.07–0.49) Tg OC yr−1, 0.51 (0.19–0.84) Tg PM2.5 yr−1, 0.57 (0.15–1.05) Tg PM10 yr−1, where NMHC, BC, and OC are nonmethane hydrocarbons, black carbon, and organic carbon, respectively. Forest fires are determined to be the primary contributor to open fire emissions, accounting for 45 % of the total CO2 emissions (average 40.8 Tg yr−1). Crop residue burning ranked second place with a large portion of 39 % (average 35.3 Tg yr−1). During the study period, emissions from forest and grassland fires showed a significant downward trend. Crop residue emissions continued to rise during 2003–2015 but dropped by 42 % in 2015–2016. Emissions from shrubland were negligible and little changed. Forest and grassland fires are concentrated in northeastern China and southern China, especially in the dry season (from October to March of the following year). Plain areas with high crop yields, such as the North China Plain, experienced high agricultural fire emissions in harvest seasons. Most shrubland fires were located in Yunnan and Guangdong provinces. The resolution of our inventory (daily, 1 km) is much higher than previous inventories, such as GFED4s and GFASv1.0. It could be used in global and regional air quality modeling.

Why is the effect of live fuel moisture content on fire rate of spread underestimated in field experiments in shrublands?

Live fuel moisture content (LFMC) influences fire activity at landscape scale and fire behaviour in laboratory experiments. However, field evidence linking LFMC to fire behaviour are very limited, despite numerous field experiments. In this study, we reanalyse a shrubland fire dataset with a special focus on LFMC to investigate this counterintuitive outcome. We found that this controversy might result from three causes. First, the range of experimental LFMC data was too moist to reveal a significant effect with the widespread exponential or power functions. Indeed, LFMC exhibited a strong effect below 100%, but marginal above this threshold, contrary to these functions. Second, we found that the LFMC significance was unlikely when the number of fire experiments was smaller than 40. Finally, an analysis suggested that 10 to 15% measurement error – arising from the estimation of environmental variables from field measurements – could lead to an underestimation by 30% of the LFMC effect. The LFMC effect in field experiments is thus stronger than previously reported in the range of LFMC occurring during the French fire season and in accordance with observations at different scales. This highlights the need to improve our understanding of the relationship between LFMC and fire behaviour to refine fire-danger predictions.

A generic fuel moisture content attenuation factor for fire spread rate empirical models

Aim of study: To develop a fuel moisture content (FMC) attenuation factor for empirical forest fire spread rate (ROS) models in general fire propagation conditions.Methods: The development builds on the assumption that the main FMC-damping effect is a function of fuel ignition energy needs.Main results: The generic FMC attenuation factor was successfully used to derive ROS models from laboratory tests (n = 282) of fire spread in no-wind and no-slope, slope-, and wind-aided conditions. The ability to incorporate the FMC attenuation factor in existing field-based ROS models for shrubland fires and grassland wildfires (n = 123) was also positively assessed.Research highlights: Establishing a priori the FMC-effect in field fires benefits the proper assessment of the remaining variables influence, which is normally eluded by heterogeneity in fuel bed properties and correlated fuel descriptors.

Wildfires as a source of airborne mineral dust – revisiting a conceptual model using large-eddy simulation (LES)

Abstract. Airborne mineral dust is a key player in the Earth system and shows manifold impacts on atmospheric properties such as the radiation budget and cloud microphysics. Investigations of smoke plumes originating from wildfires found significant fractions of mineral dust within these plumes – most likely raised by strong, turbulent fire-related winds. This study presents and revisits a conceptual model describing the emission of mineral dust particles during wildfires. This is achieved by means of high-resolution large-eddy simulation (LES), conducted with the All Scale Atmospheric Model (ASAM). The impact of (a) different fire properties representing idealized grassland and shrubland fires, (b) different ambient wind conditions modulated by the fire's energy flux, and (c) the wind's capability to mobilize mineral dust particles was investigated. Results from this study illustrate that the energy release of the fire leads to a significant increase in near-surface wind speed, which consequently enhances the dust uplift potential. This is in particular the case within the fire area where vegetation can be assumed to be widely removed and uncovered soil is prone to wind erosion. The dust uplift potential is very sensitive to fire properties, such as fire size, shape, and intensity, but also depends on the ambient wind velocity. Although measurements already showed the importance of wildfires for dust emissions, pyro-convection is so far neglected as a dust emission process in atmosphere–aerosol models. The results presented in this study can be seen as the first step towards a systematic parameterization representing the connection between typical fire properties and related dust emissions.

Biofuels from broom clearings: Production and combustion in commercial boilers

Abstract Shrub lands could provide an almost unexplored biomass resource of increasing potential in the EU, particularly in Mediterranean countries. Its collection and transformation into solid biofuels will help to reduce the adverse effects associated with frequent shrub land fires. The objective of this study is to examine the pre-treatment and combustion of biomass obtained from broom plant clearings to assess the feasibility of utilising it as a fuel in commercial combustion applications. Above ground broom biomass was collected with a harvester-baler machine. Afterwards, in a milling installation and a pilot pelletisation plant two fuels were obtained: 30 mm milled material and pellets, which were used in two commercial grate boilers (40 kWth and 500 kWth). We conclude that biomass from broom clearings could be used to produce solid biofuels for commercial boilers. Milling and pelletisation did not entail difficulties and the pellets could be classified as B (ISO 17225-2:2014). During combustion, no operating problems related to the fuel were observed. However, due to its high potassium content, special attention should be paid to the tendency to produce deposits and to particle emission and it would be advisable to control the working temperature to avoid slag formation in the burner.

Structural determinants of increased susceptibility to dehydration-induced cavitation in post-fire resprouting chaparral shrubs.

It is well established that transpiration and photosynthetic rates generally increase in resprouting shoots after fire in chaparral shrublands. By contrast, little is known about how plant hydraulic function varies during this same recovery period. We hypothesized that vascular traits, both functional and structural, would also shift in order to support this heightened level of gas exchange and growth. We examined stem xylem-specific hydraulic conductivity (Ks ) and resistance to cavitation (P50 ) for eight chaparral shrub species as well as several potential xylem structural determinants of hydraulic function and compared established unburned plants and co-occurring post-fire resprouting plants. Unburned plants were generally more resistant to cavitation than resprouting plants, but the two groups did not differ in Ks . Resprouting plants had altered vessel structure compared with unburned plants, with resprouting plants having both wider diameter vessels and higher inter-vessel pit density. For biomechanics, unburned plants had both stronger and denser stem xylem tissue than resprouting plants. Shifts in hydraulic structure and function resulted in resprouting plants being more vulnerable to dehydration. The interaction between time since disturbance (i.e. resprouting versus established stands) and drought may complicate attempts to predict mortality risk of resprouting plants.