Patterns of flammability after a sequence of mixed‐severity wildfire in dry eucalypt forests of southern Australia

Abstract

Fire severity is the impact of a fire on the landscape, particularly the physical impact on vegetation. Previous studies have established that the severity of a fire can be influenced by the severity of previous fires. Many of these studies were conducted in mixed‐conifer forests, while little is known of this process in temperate eucalypt forests. Barker and Price in their 2018 publication (“Positive severity feedback between consecutive fires in dry eucalypt forests of southern Australia,” Ecosphere 9:e02110) found that high severity fire promotes high severity fire in eucalypt forests, but how is the severity of a fire in these systems affected by the severity of two sequential previous fires? This was investigated using remotely sensed and mapped fire severity data. We found that high severity fire is more likely after at least one previous high severity fire, regardless of its position in the sequence. A sequence of low or moderate severity fire followed by low severity fire resulted in the lowest proportion of high severity in the response fire. Our results suggest that low severity fire maintains the structure of forest fuels, so flammability remains relatively constant. A single high severity fire drives change, altering the structure and flammability of the vegetation and promoting more severe fire. However, the effects were small, so a cycle of high severity fire may be easily broken due to the influence of other variables, such as weather. Repeated high severity fire may also result in a decline in the ability of plants to recover from fire, leading to a compositional and structural change and potentially reducing the flammability of a forest.

Self-thinning forest understoreys reduce wildfire risk, even in a warming climate

“…A recent study found that the median severity of prescribed burns in Eastern Australian eucalypt forests was 'high' (complete crown scorch, (Price et al 2022)), compared to a median severity of 'moderate' in wildfires for the same region (Collins et al 2021a). Given that positive severity feedbacks in that region have been most pronounced following high severity fire (Barker et al 2021), it is possible that a regime dominated by wildfires may have a less pronounced peak in flammability. Cultural burning practices have been shown to both consume less surface litter and burn at a significantly lower severity than prescribed burns (Price et al 2022), potentially reflecting their very small scale and locationspecificity (Lullfitz et al 2020).…”

Method of Wildfire Risk Assessment in Consideration of Land-Use Types: A Case Study in Central China

“…The land-use types have a significant impact on wildfire occurrence, as they influence vegetation characteristics, quantity, structure, and continuity, ultimately affecting the probability, spread rate, fire size, and environmental impacts of wildfires [52,84,85]. Generally speaking, forested, grassland, and farmland areas typically accumulate combustible vegetation, such as dry leaves and grass, making them more prone to fire occurrence and less equipped with natural and artificial fire prevention measures.…”