Altered fire regimes

2016

The Land report describes how fire frequencies have increased in Australia during the past decade. Alteration in fire regimes is considered a major threat that has contributed to the extinction of 6 mammal species, and is a significant pressure on 35 threatened and 22 near threatened mammal species identified in The action plan for Australian mammals 2012 (Woinarski et al. 2014). Changed fire regimes are increasing in importance as a threat for mammals through much of Australia. In particular, fire regimes in northern Australia have changed significantly since European arrival; they are now dominated by very large fires occurring at shorter fire return intervals. These changed regimes (frequency and extent) have been implicated in the decline of small mammals in northern Australia during recent decades (Griffiths et al. 2015, Lawes et al. 2015). Recurrent wildfire also threatens forest-dwelling mammals in much of southern and eastern Australia (Lindenmayer 2015).

Alteration in fire regimes is also considered a significant pressure on many threatened bird species, especially in northern Australia. The increase in the intensity, area and timing of fire (late dry-season versus early dry-season fires) has affected birds in northern Australia and is an ongoing issue (Garnett et al. 2011). A recent review concluded that the current fire regime in northern Australia is suboptimal for many bird species, especially grain-eating and fruit-eating birds, and hollow-dependent and ground-nesting species. The review recommended that, in northern Australia, at least 25 per cent of the savanna landscape should be unburned for at least 3 years and at least 5 per cent should be unburned for at least 10 years (Woinarski & Legge 2013).

Changed fire regimes may be increasing in importance as a threat for birds in southern Australia. An example is the endangered eastern bristlebird (Dasyornis brachypterus) of eastern Australia, for which extensive wildfire is considered the main threat. Research in semi-arid shrubland of the Murray Mallee region of Victoria showed that 16 of 30 bird species for which there were enough data to model responses showed significant variation in probability of occurrence with time since fire. Of these 16 species, all but 1 occurred more frequently in vegetation where there had been more than 20 years since the last fire. The study concluded that birds displayed a limited response to time since fire; therefore, greater time between fires should allow the provision of suitable vegetation for most species (Watson et al. 2014).

Increased fire frequency can affect the viability of some plant species by damaging or destroying individuals before they reproduce. The ‘minimum tolerable fire interval’ is the minimum period between fires required to allow species within the area to reach reproductive maturity. This is set by the key fire-response species, which take the longest time to reach maturity. These species are adversely affected when fires are too frequent. In Victoria in 2012, 40 per cent of native vegetation was estimated to be below minimum tolerable fire intervals, with 3 per cent above the maximum interval. Only 18 per cent of native vegetation assessed was found to be within the required interval to maintain vegetation communities. The tolerable fire interval could not be calculated for 39 per cent of native vegetation because of a lack of fire history.

Pencil pine (Athrotaxis cupressoides) ecosystems burned in the wildfire at Lake Mackenzie (Tasmanian Wilderness World Heritage Area) in January 2016. Photo by Chris Emms

Pencil pine (Athrotaxis cupressoides) ecosystems burned in the wildfire at Lake Mackenzie (Tasmanian Wilderness World Heritage Area) in January 2016

Photo by Chris Emms

Cresswell ID, Murphy H (2016). Biodiversity: Altered fire regimes. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/biodiversity/topic/2016/altered-fire-regimes, DOI 10.4226/94/58b65ac828812