Search

There is a public perception that large high-severity wildfires decrease biodiversity and increase fire hazard by homogenizing vegetation composition and increasing the cover of mid-story vegetation. But a growing literature suggests that vegetation responses are nuanced. LiDAR technology provides a promising remote sensing tool to test hypotheses about post-fire vegetation regrowth because vegetation cover can be quantified within different height strata at fine scales over large areas. We assess the usefulness of airborne LiDAR data for measuring post-fire mid-story vegetation regrowth over a range of spatial resolutions (10 x 10 m, 30 x 30 m, 50 x 50 m, 100 x 100 m cell size) and investigate the effect of fire severity on regrowth amount and spatial pattern following a mixed severity wildfire in Warrumbungle National Park, Australia. We predicted that recovery would be more vigorous in areas of high fire severity, because park managers observed dense post-fire regrowth in these areas. Moderate to strong positive associations were observed between LiDAR and field surveys of mid-story vegetation cover between 0.5-3.0 m. Thus our LiDAR survey was an apt representation of on-ground vegetation cover. LiDAR-derived mid-story vegetation cover was 22-40% lower in areas of low and moderate than high fire severity. Linear mixed-effects models showed that fire severity was among the strongest biophysical predictors of mid-story vegetation cover irrespective of spatial resolution. However much of the variance associated with these models was unexplained, presumably because soil seed banks varied at finer scales than our LiDAR maps. Dense patches of mid-story vegetation regrowth were small (median size 0.01 ha) and evenly distributed between areas of low, moderate and high fire severity, demonstrating that high-severity fires do not homogenize vegetation cover. Our results are relevant for ecosystem conservation and fire management because they: indicate that native vegetatio

There is a public perception that large high-severity wildfires decrease biodiversity and increase fire hazard by homogenizing vegetation composition and increasing the cover of mid-story vegetation. But a growing literature suggests that vegetation responses are nuanced. LiDAR technology provides a promising remote sensing tool to test hypotheses about post-fire vegetation regrowth because vegetation cover can be quantified within different height strata at fine scales over large areas. We assess the usefulness of airborne LiDAR data for measuring post-fire mid-story vegetation regrowth over a range of spatial resolutions (10 x 10 m, 30 x 30 m, 50 x 50 m, 100 x 100 m cell size) and investigate the effect of fire severity on regrowth amount and spatial pattern following a mixed severity wildfire in Warrumbungle National Park, Australia. We predicted that recovery would be more vigorous in areas of high fire severity, because park managers observed dense post-fire regrowth in these areas. Moderate to strong positive associations were observed between LiDAR and field surveys of mid-story vegetation cover between 0.5-3.0 m. Thus our LiDAR survey was an apt representation of on-ground vegetation cover. LiDAR-derived mid-story vegetation cover was 22-40% lower in areas of low and moderate than high fire severity. Linear mixed-effects models showed that fire severity was among the strongest biophysical predictors of mid-story vegetation cover irrespective of spatial resolution. However much of the variance associated with these models was unexplained, presumably because soil seed banks varied at finer scales than our LiDAR maps. Dense patches of mid-story vegetation regrowth were small (median size 0.01 ha) and evenly distributed between areas of low, moderate and high fire severity, demonstrating that high-severity fires do not homogenize vegetation cover. Our results are relevant for ecosystem conservation and fire management because they: indicate that native vegetatio

High severity wildfires pose threats to human assets, but are also perceived to impact vegetation communities because a small number of species may become dominant immediately after fire. However there are considerable gaps in our knowledge about species-specific responses of plants to different fire severities, and how this influences fuel hazard in the short and long-term. Here we conduct a floristic survey at sites before and two years after a wildfire of unprecedented size and severity in the Warrumbungle National Park (Australia) to explore relationships between post-fire growth of a fire responsive shrub genera (Acacia), total mid-story vegetation cover, fire severity and fuel hazard. We then survey 129 plots surrounding the park to assess relationships between mid-story vegetation cover and time-since-fire. Acacia species richness and cover were 2.3 and 4.3 times greater at plots after than before the fire. However the same common dominant species were present throughout the study. Mid-story vegetation cover was 1.5 times greater after than before the wildfire, and Acacia species contribution to mid-story cover increased from 10 to 40%. Acacia species richness was not affected by fire severity, however strong positive associations were observed between Acacia and total mid-story vegetation cover and severity. Our analysis of mid-story vegetation recovery showed that cover was similarly high between 2 and 30 years post-fire, then decreased until 52 years. Collectively, our results suggest that Acacia species are extremely resilient to high severity wildfire and drive short to mid-term increases in fuel hazard. Our results are discussed in relation to fire regime management from the twin perspectives of conserving biodiversity and mitigating human losses due to wildfire.

High severity wildfires pose threats to human assets, but are also perceived to impact vegetation communities because a small number of species may become dominant immediately after fire. However there are considerable gaps in our knowledge about species-specific responses of plants to different fire severities, and how this influences fuel hazard in the short and long-term. Here we conduct a floristic survey at sites before and two years after a wildfire of unprecedented size and severity in the Warrumbungle National Park (Australia) to explore relationships between post-fire growth of a fire responsive shrub genera (Acacia), total mid-story vegetation cover, fire severity and fuel hazard. We then survey 129 plots surrounding the park to assess relationships between mid-story vegetation cover and time-since-fire. Acacia species richness and cover were 2.3 and 4.3 times greater at plots after than before the fire. However the same common dominant species were present throughout the study. Mid-story vegetation cover was 1.5 times greater after than before the wildfire, and Acacia species contribution to mid-story cover increased from 10 to 40%. Acacia species richness was not affected by fire severity, however strong positive associations were observed between Acacia and total mid-story vegetation cover and severity. Our analysis of mid-story vegetation recovery showed that cover was similarly high between 2 and 30 years post-fire, then decreased until 52 years. Collectively, our results suggest that Acacia species are extremely resilient to high severity wildfire and drive short to mid-term increases in fuel hazard. Our results are discussed in relation to fire regime management from the twin perspectives of conserving biodiversity and mitigating human losses due to wildfire.

We analysed the influence of weather, time since fire (TSF) and topography on the occurrence of crown fire, as mapped from satellite imagery, in 23 of the largest wildfires in dry sclerophyll forests in eastern Australia from 2002 to 2013. Fires were analysed both individually and as groups. Fire weather was the most important predictor of crown consumption. TSF (a surrogate for fuel accumulation) had complex nonlinear effects that varied among fires. Crown fire likelihood was low up to 4 years post-fire, peaked at ~10 years post-fire and then declined. There was no clear indication that recent burning became more or less effective as fire weather became more severe. Steeper slope reduced crown fire likelihood, contrary to the assumptions of common fire behaviour equations. More exposed areas (ridges and plains) had higher crown fire likelihood. Our results suggest prescribed burning to maintain an average of 10 years' TSF may actually increase crown fire likelihood, but burning much more frequently can be effective for risk reduction. Our results also suggest the effects of weather, TSF and slope are not adequately represented in the underlying equations of most fire behaviour models, potentially leading to poor prediction of fire spread and risk.

We analysed the influence of weather, time since fire (TSF) and topography on the occurrence of crown fire, as mapped from satellite imagery, in 23 of the largest wildfires in dry sclerophyll forests in eastern Australia from 2002 to 2013. Fires were analysed both individually and as groups. Fire weather was the most important predictor of crown consumption. TSF (a surrogate for fuel accumulation) had complex nonlinear effects that varied among fires. Crown fire likelihood was low up to 4 years post-fire, peaked at ~10 years post-fire and then declined. There was no clear indication that recent burning became more or less effective as fire weather became more severe. Steeper slope reduced crown fire likelihood, contrary to the assumptions of common fire behaviour equations. More exposed areas (ridges and plains) had higher crown fire likelihood. Our results suggest prescribed burning to maintain an average of 10 years' TSF may actually increase crown fire likelihood, but burning much more frequently can be effective for risk reduction. Our results also suggest the effects of weather, TSF and slope are not adequately represented in the underlying equations of most fire behaviour models, potentially leading to poor prediction of fire spread and risk.

Structurally complex forest provides important habitat for a diverse array of vertebrate fauna. Frequent fire can simplify forest structure, though topographic mitigation of fire effects could potentially preserve structurally more complex habitat within certain topographic locations of fire prone landscapes. Our study assessed whether the effects of fire frequency on forest structure (tree hollows, log volume, vegetation complexity) varied with topographic position. The effect of wildfire severity and intensive logging were also examined. Frequent fire reduced vegetation cover on ridges, but not in gullies. The risk of collapse (i.e. presence of fire scars) increased for large trees on frequently burnt ridges, but remained suppressed in gullies. Crown fire reduced hollow presence in dead trees (i.e. snags), but increased hollow presence in trees with a healthy crown. The volume of extensively decomposed logs was three times greater in gullies than ridges, but was unaffected by fire frequency. Intensive logging reduced the number of hollow bearing trees and increased the volume of extensively decomposed logs, though future declines in log volume are predicted due to bottlenecks in log input. Our results suggest that gullies may play a critical role in preserving structurally complex stands within frequently burnt temperate eucalypt forests. Protecting gullies from land clearing and intensive logging is likely to be an important step in maintaining key habitat features and associated fauna in these landscapes.

Log hollows provide important habitat for a range of vertebrate fauna. Despite this, little is known about the impact fire regimes have on this resource, or the role topography may play in preserving hollows through the mitigation of fire intensity. This study examined the effect different combinations of fire frequency and topography have on (i) the number of hollow bearing logs and (ii) the presence and size of hollows within logs. The influence of wildfire severity and logging were also examined. Hollow availability (i.e. density of hollow bearing logs and hollow presence within logs) was greatest at sites burnt at ‘low’ frequency. The density of hollow logs was greater in gullies, though the effect of fire frequency did not vary with topographic position. Hollows showing signs of internal fire charring typically had a greater entrance width than unburnt hollows, which suggests fire plays an important role in creating large hollows. The number of hollow bearing logs increased with logging intensity, due to unmerchantable timber being left in situ. Wildfire severity had little effect on log hollows. The results indicate that frequent burning may reduce hollow availability, though it is likely that gullies will still retain a high density of hollow bearing logs irrespective of burning, and may play an important role in preserving connectivity of this resource across landscapes.

Log hollows provide important habitat for a range of vertebrate fauna. Despite this, little is known about the impact fire regimes have on this resource, or the role topography may play in preserving hollows through the mitigation of fire intensity. This study examined the effect different combinations of fire frequency and topography have on (i) the number of hollow bearing logs and (ii) the presence and size of hollows within logs. The influence of wildfire severity and logging were also examined. Hollow availability (i.e. density of hollow bearing logs and hollow presence within logs) was greatest at sites burnt at ‘low’ frequency. The density of hollow logs was greater in gullies, though the effect of fire frequency did not vary with topographic position. Hollows showing signs of internal fire charring typically had a greater entrance width than unburnt hollows, which suggests fire plays an important role in creating large hollows. The number of hollow bearing logs increased with logging intensity, due to unmerchantable timber being left in situ. Wildfire severity had little effect on log hollows. The results indicate that frequent burning may reduce hollow availability, though it is likely that gullies will still retain a high density of hollow bearing logs irrespective of burning, and may play an important role in preserving connectivity of this resource across landscapes.

Structurally complex forest provides important habitat for a diverse array of vertebrate fauna. Frequent fire can simplify forest structure, though topographic mitigation of fire effects could potentially preserve structurally more complex habitat within certain topographic locations of fire prone landscapes. Our study assessed whether the effects of fire frequency on forest structure (tree hollows, log volume, vegetation complexity) varied with topographic position. The effect of wildfire severity and intensive logging were also examined. Frequent fire reduced vegetation cover on ridges, but not in gullies. The risk of collapse (i.e. presence of fire scars) increased for large trees on frequently burnt ridges, but remained suppressed in gullies. Crown fire reduced hollow presence in dead trees (i.e. snags), but increased hollow presence in trees with a healthy crown. The volume of extensively decomposed logs was three times greater in gullies than ridges, but was unaffected by fire frequency. Intensive logging reduced the number of hollow bearing trees and increased the volume of extensively decomposed logs, though future declines in log volume are predicted due to bottlenecks in log input. Our results suggest that gullies may play a critical role in preserving structurally complex stands within frequently burnt temperate eucalypt forests. Protecting gullies from land clearing and intensive logging is likely to be an important step in maintaining key habitat features and associated fauna in these landscapes.

Structurally complex forest provides important habitat for a diverse array of vertebrate fauna. Frequent fire can simplify forest structure, though topographic mitigation of fire effects could potentially preserve structurally more complex habitat within certain topographic locations of fire prone landscapes. Our study assessed whether the effects of fire frequency on forest structure (tree hollows, log volume, vegetation complexity) varied with topographic position. The effect of wildfire severity and intensive logging were also examined. Frequent fire reduced vegetation cover on ridges, but not in gullies. The risk of collapse (i.e. presence of fire scars) increased for large trees on frequently burnt ridges, but remained suppressed in gullies. Crown fire reduced hollow presence in dead trees (i.e. snags), but increased hollow presence in trees with a healthy crown. The volume of extensively decomposed logs was three times greater in gullies than ridges, but was unaffected by fire frequency. Intensive logging reduced the number of hollow bearing trees and increased the volume of extensively decomposed logs, though future declines in log volume are predicted due to bottlenecks in log input. Our results suggest that gullies may play a critical role in preserving structurally complex stands within frequently burnt temperate eucalypt forests. Protecting gullies from land clearing and intensive logging is likely to be an important step in maintaining key habitat features and associated fauna in these landscapes.

Log hollows provide important habitat for a range of vertebrate fauna. Despite this, little is known about the impact fire regimes have on this resource, or the role topography may play in preserving hollows through the mitigation of fire intensity. This study examined the effect different combinations of fire frequency and topography have on (i) the number of hollow bearing logs and (ii) the presence and size of hollows within logs. The influence of wildfire severity and logging were also examined. Hollow availability (i.e. density of hollow bearing logs and hollow presence within logs) was greatest at sites burnt at ‘low’ frequency. The density of hollow logs was greater in gullies, though the effect of fire frequency did not vary with topographic position. Hollows showing signs of internal fire charring typically had a greater entrance width than unburnt hollows, which suggests fire plays an important role in creating large hollows. The number of hollow bearing logs increased with logging intensity, due to unmerchantable timber being left in situ. Wildfire severity had little effect on log hollows. The results indicate that frequent burning may reduce hollow availability, though it is likely that gullies will still retain a high density of hollow bearing logs irrespective of burning, and may play an important role in preserving connectivity of this resource across landscapes.