Wildfire management in Mediterranean-type regions: paradigm change needed

PerspectiveDuring the last decades, climate and land use changes led to an increased prevalence ofmegafires in Mediterranean-type climate regions (MCRs).Here, we argue that current wildfire management policies in MCRs are destined to fail.Focused on fire suppression, these policies largely ignore ongoing climate warming and landscape-scale buildup of fuels.The result is a ‘firefighting trap’ that contributes to ongoing fuel accumulation precluding suppression under extreme fire weather, and resulting in more severe and larger fires.We believe that a ‘business as usual’ approach to wildfire in MCRs will not solve the fire problem, and recommend that policy and expenditures be rebalanced between suppression and mitigation of the negative impacts of fire.This requires a paradigm shift: policy effectiveness should not be primarily measured as a function of area burned (as it usually is), but rather as a function of avoided socio-ecological damage and lossinfo:eu-repo/semantics/publishedVersio

Effect of thinning on growth and allometry of Eucalyptus diversicolor

Karri (Eucalyptus diversicolor F. Muell.) forest is an endemic forest type of southwest Western Australia (SWWA), noted for having the tallest trees in the region, and providing commercial, ecological and conservation value. To inform management aimed at optimising these values, a thinning trial was commenced in 1992. The aim of this study was to evaluate the effects of thinning on individual tree growth, stand level growth and allometry of karri trees in even-aged stands. Mixed effect models were used to compare the effect of different levels of thinning on individual tree growth and stand level growth of karri. We developed allometric equations modelling the relationship between diameter at breast height (DBH) and height, and tested whether thinning affected this allometric relationship. Thinning enhanced DBH, height and crown width (CW) growth of individual trees by up to 149%, 56% and 108% respectively in heavily thinned stands, with stand basal area growth optimised at retained basal areas of 13 m2 ha−1. Thinning had a significant effect on allometry of DBH with height, height-DBH ratio (HDR) and CW. Reduction in stand density through thinning from below increased diameter growth of individual trees. Stand level basal area growth is optimised at an intermediate level of thinning. Thinning can be a good management tool for even-aged karri forest because it may promote the diameter and thereby basal area growth, good health of individual trees, and potential ecological benefits including accelerated development of larger tree crowns typical of mature forest

Vegetation and landscape connectivity control wildfire intervals in unmanaged semi-arid shrublands and woodlands in Australia

The aim of this study was to determine how spatial variation in vegetation type and landscape connectivity influence fire intervals in a semi-arid landscape with low relief and complex mosaics of woodland and shrubland vegetation

Characterization of landscape pyrodiversity in Mediterranean environments : contrasts and similarities between south-western Australia and south-eastern France

Landscape pyrodiversity encapsulates the range of spatiotemporal variability in disturbance by fire. There is a widely-held view that diversity in fire regimes promotes biological diversity (i.e., the Pyrodiversity– Biodiversity paradigm). However, this relationship needs to be examined more carefully as pyrodiversity at the landscape scale remains poorly defined and difficult to quantify. Here, we used a novel approach to analyze landscape pyrodiversity by selecting and quantifying appropriate descriptors of fire variability at the landscape level. We characterized and classified observed fire mosaics at the 1 km scale using temporal attributes (fire frequency, timesince- fire and mean fire interval) and a variety of spatial attributes derived from landscape metrics. We trialed our approach on a 50-year record of fire patterns in two Mediterranean environments; (1) in southern France where fire regimes are dominated by unplanned (‘wild’-)fires and (2) in south-west Australia, where fire regimes are dominated by planned fires. We found that the landscape pyrodiversity of both regions was expressed by distinct gradients of both fire frequency and spatial diversity of fire patterns. As expected, the two environments were significantly different in landscape pyrodiversity, with contrasting mean fire frequency and mean time-since-fire patterns. However, we also found similarities between southern France and south-west Australia in the composition and configuration of their spatial fire patterns. Our results show that these two Mediterranean environments form a pyrodiversity continuum despite the disparate management regimes. Our findings also demonstrate that a quantitative characterization of pyrodiversity is central to developing new perspectives and practical tools for biodiversity conservation in fire-prone landscapes

Climatic anomalies drive wildfire occurrence and extent in semi-arid shrublands and woodlands of southwest Australia

Variation in the frequency, extent and intensity of wildfires can drive changes in the composition, structure, diversity and functioning of ecosystems in fire-prone regions worldwide. However, relationships between climatic variation and wildfire occurrence remain poorly understood in many fire-prone regions. We investigated fire occurrence and extent across 15,500 km2 of semi-arid southwest Australia in relation to inter-annual and/or seasonal variation in regional climate and broad-scale circulation patterns. Superposed epoch analysis (SEA) was used to determine whether wildfire occurrence was related to anomalously high or low regional rainfall or temperature. In particular, we tested if years of minor fire extent (i.e., 1,000 km2 burnt) occurred under different climatic conditions. We also used SEA to determine if wildfires occurred during or following periods of extremes of drivers of regional climate, including the El Niño southern oscillation (ENSO), the Indian Ocean dipole, atmospheric blocking in the adjacent Southern Ocean, and the southern annular mode (SAM). Fire occurrence was linked to dry and hot conditions typically associated with the El Niño phase of ENSO, with few or no fires in years with cool and wet summers. However, major fire years tended to occur during drought conditions that followed wet and cool conditions in spring and summer of the preceding year. These wet and cool periods were typically associated with the presence of blocking highs in the Southern Ocean to the south of Western Australia. We hypothesise that high rainfall in spring and summer favours the growth of ephemeral plants while subsequent drought conditions promote fuel drying, resulting in more continuous and highly flammable fuel beds capable of sustaining larger fires. Regional climatic patterns are likely driven by interactions among the SAM, atmospheric blocking, and decaying tropical cyclones. As climatic extremes are expected to increase in intensity and frequency in the future, it is likely that the occurrence of extensive wildfires in semi-arid southwest Australia will also increase, potentially driving changes in the distribution and composition of fire-sensitive plant communities

Climatic anomalies drive wildfire occurrence and extent in semi-arid shrublands and woodlands of southwest Australia

Variation in the frequency, extent and intensity of wildfires can drive changes in the composition, structure, diversity and functioning of ecosystems in fire-prone regions worldwide. However, relationships between climatic variation and wildfire occurrence remain poorly understood in many fire-prone regions. We investigated fire occurrence and extent across 15,500 km2 of semi-arid southwest Australia in relation to inter-annual and/or seasonal variation in regional climate and broad-scale circulation patterns. Superposed epoch analysis (SEA) was used to determine whether wildfire occurrence was related to anomalously high or low regional rainfall or temperature. In particular, we tested if years of minor fire extent (i.e., 1,000 km2 burnt) occurred under different climatic conditions. We also used SEA to determine if wildfires occurred during or following periods of extremes of drivers of regional climate, including the El Niño southern oscillation (ENSO), the Indian Ocean dipole, atmospheric blocking in the adjacent Southern Ocean, and the southern annular mode (SAM). Fire occurrence was linked to dry and hot conditions typically associated with the El Niño phase of ENSO, with few or no fires in years with cool and wet summers. However, major fire years tended to occur during drought conditions that followed wet and cool conditions in spring and summer of the preceding year. These wet and cool periods were typically associated with the presence of blocking highs in the Southern Ocean to the south of Western Australia. We hypothesise that high rainfall in spring and summer favours the growth of ephemeral plants while subsequent drought conditions promote fuel drying, resulting in more continuous and highly flammable fuel beds capable of sustaining larger fires. Regional climatic patterns are likely driven by interactions among the SAM, atmospheric blocking, and decaying tropical cyclones. As climatic extremes are expected to increase in intensity and frequency in the future, it is likely that the occurrence of extensive wildfires in semi-arid southwest Australia will also increase, potentially driving changes in the distribution and composition of fire-sensitive plant communities

Scale-dependent thresholds in the dominant controls of wildfire size in semi-arid southwest Australia

We aimed to characterize the size distribution of naturally occurring wildfires and to determine how fuel characteristics influence wildfire size in a vegetation mosaic of shrublands and woodlands in semi-arid southwest Australia. The shape of frequency-size distributions of fires can be used to elucidate shifts in the dominant drivers or constraints of fire size. We modeled the cumulative frequency-size distribution of wildfires in southwest Australia using a segmented linear model with two break points. Three fire size categories were defined by the break points of the segmented model: “small” (41,020 ha). Break points were interpreted as thresholds in fire size that may represent shifts in the dominant controls of fire spread. We tested whether the influence of fuel characteristics on fire spread varied among fire size categories by comparing the composition of vegetation types and fuel ages among burnt and adjacent unburnt areas using selection ratios (ωx). Small and medium fires burnt shrub-dominated vegetation types in proportion to their availability (ωx ≈ 1), but tended to burn smaller proportions of sparsely-vegetated woodlands (ωx 30 years) burnt in proportion to their availability (ωx ≈ 1). Fire size in semi-arid southwest Australia is generally limited by fuel mass in recently burnt areas and by fuel continuity in sparsely vegetated woodlands. However, following unusually wet years and subsequent growth of ephemeral plants, fuels in woodland vegetation likely become spatially continuous and capable of supporting the spread of large fires

Scale-dependent thresholds in the dominant controls of wildfire size in semi-arid southwest Australia

We aimed to characterize the size distribution of naturally occurring wildfires and to determine how fuel characteristics influence wildfire size in a vegetation mosaic of shrublands and woodlands in semi-arid southwest Australia. The shape of frequency-size distributions of fires can be used to elucidate shifts in the dominant drivers or constraints of fire size. We modeled the cumulative frequency-size distribution of wildfires in southwest Australia using a segmented linear model with two break points. Three fire size categories were defined by the break points of the segmented model: “small” (41,020 ha). Break points were interpreted as thresholds in fire size that may represent shifts in the dominant controls of fire spread. We tested whether the influence of fuel characteristics on fire spread varied among fire size categories by comparing the composition of vegetation types and fuel ages among burnt and adjacent unburnt areas using selection ratios (ωx). Small and medium fires burnt shrub-dominated vegetation types in proportion to their availability (ωx ≈ 1), but tended to burn smaller proportions of sparsely-vegetated woodlands (ωx 30 years) burnt in proportion to their availability (ωx ≈ 1). Fire size in semi-arid southwest Australia is generally limited by fuel mass in recently burnt areas and by fuel continuity in sparsely vegetated woodlands. However, following unusually wet years and subsequent growth of ephemeral plants, fuels in woodland vegetation likely become spatially continuous and capable of supporting the spread of large fires