Positive severity feedback between consecutive fires in dry eucalypt forests of southern Australia

James W Barker,Owen F Price

doi:10.1002/ecs2.2110

Abstract

AbstractFire regimes have long‐term effects on ecosystems which can be subtle, requiring study at a large spatial scale and temporal scale to fully appreciate. The way in which multiple fires interact to create a fire regime is poorly understood, and the relationship between the severities of consecutive fires has not been studied in Australia. By overlaying remotely sensed severity maps, our study investigated how the severity of a fire is influenced by previous fire severity. This was done by sampling points at 500‐m spacing across 53 fires in dry eucalypt forests of southeast Australia, over a range of time since fire spanning every major fire season for 30 yr. Generalized additive models were used to determine the influence of previous severity on the probability of crown fire and understory fire, controlling for differences in time since fire, topography, and weather. We found that a crown fire is more than twice as likely after a previous crown fire than previous understory fire, and understory fire is more likely after previous understory fire. Our findings are in line with the results of studies from North America and suggest that severe fire promotes further fire. This may be evidence of a runaway positive feedback, which can drive ecological change, and lead to a mosaic of divergent vegetation, but research into more than two consecutive fires is needed to explore this. Our results also suggest that a low‐severity prescribed fire may be a useful management option for breaking a cycle of crown fires.

Highlights

Wildfires are a heavily studied natural phenomenon, but many studies treat them as discrete disturbance events, when they are an ongoing natural process (Bowman et al 2009)
By overlaying remotely sensed severity maps, our study investigated how the severity of a fire is influenced by previous fire severity
We found that a crown fire is more than twice as likely after a previous crown fire than previous understory fire, and understory fire is more likely after previous understory fire

Summary

Introduction

Wildfires are a heavily studied natural phenomenon, but many studies treat them as discrete disturbance events, when they are an ongoing natural process (Bowman et al 2009). This process is termed the fire regime, which represents the history of all fire at a location, comprising the number, severity, and seasonality of fires (Gill 1975). High-severity fire will be more damaging to resprouting plants than low-severity fire and may result in plant death. This would be expected to reduce post-fire recovery. High-severity fires can stimulate germination in some

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