The impact of gigafire on vegetation structure, terrestrial vertebrate abundance, and diel activity

Fire regimes are shifting around the world due to climate and land-use
change, resulting in an increased frequency of large and severe wildfires.
However, the impact of extreme wildfire events on animal species remains
poorly understood. Particularly lacking is an understanding of how fire
affects animal behaviour. By examining how distinct vertebrate groups
respond to wildfire, we capture variations in resilience mechanisms that
further our understanding of fire ecology and aid conservation strategies
in increasingly fire-prone landscapes. Across an area of 180,110 ha, we
investigated the effects of the 2019–2020 Australian ‘Black Summer’
wildfires on vegetation structure (a proxy for vertebrate habitat), the
number of independent detections (as an indicator of abundance), and diel
activity of a range of terrestrial animals in Eucalypt forests of
south-eastern Australia. We examined the influence of fire severity on
vegetation structure, using wildlife cameras, animal species abundance,
and how burnt or unburnt areas and fire severity affect species’ diel
activity patterns 20 months post-fire. Areas subject to high severity
fires (in comparison to low–moderate) had less canopy cover and leaf
litter, and higher vegetation cover at measured (0 to >2 m)
understory heights, as well as greater abundance of logs. Fire severity
had a limited effect on the abundance of animal species, with differences
in abundance observed in eight of 29 species. A greater impact occurred
following high severity fire, where 8/29 species were affected, compared
to 3/29 in areas burnt at lower severity. However, only 4/29 species (high
severity) and 1/29 (low severity) responded negatively, demonstrating a
general resilience among many species to fire. Areas that burnt at high
severity had higher introduced mammal richness and reduced native mammal
diversity, suggesting the potential for introduced species to establish in
severely burnt areas. The diel activity patterns in areas subject to fire
differed for seven of 17 species with sufficient data, with these species
concentrating their activity during specific times in burnt areas compared
to unburnt areas. Such behavioural plasticity may facilitate species
persistence in environments modified by fire by allowing species to
exploit different resources or minimise predation risk. Understanding how
fire affects animal species, including animal behaviour, will be critical
as the world’s fire regimes continue to change.