Fire frequency and biodiversity conservation in Australian tropical savannas: implications from the Kapalga fire experiment

Abstract

Every year large proportions of northern Australia's tropical savanna landscapes are burnt, resulting in high fire frequencies and short intervals between fires. The dominant fire management paradigm in these regions is the use of low-intensity prescribed fire early in the dry season, to reduce the incidence of higher-intensity, more extensive wildfire later in the year. This use of frequent prescribed fire to mitigate against high-intensity wildfire has parallels with fire management in temperate forests of southern Australia. However, unlike in southern Australia, the ecological implications of high fire frequency have received little attention in the north. CSIRO and collaborators recently completed a landscape-scale fire experiment at Kapalga in Kakadu National Park, Northern Territory, Australia, and here we provide a synthesis of the effects of experimental fire regimes on biodiversity, with particular consideration of fire frequency and, more specifically, time-since-fire. Two recurring themes emerged from Kapalga. First, much of the savanna biota is remarkably resilient to fire, even of high intensity. Over the 5-year experimental period, the abundance of most invertebrate groups remained unaffected by fire treatment, as did the abundance of most vertebrate species, and we were unable to detect any effect of fire on floristic composition of the grass-layer. Riparian vegetation and associated stream biota, as well as small mammals, were notable exceptions to this general resilience. Second, the occurrence of fire, independent of its intensity, was often the major factor influencing fire-sensitive species. This was especially the case for extinction-prone small mammals, which have suffered serious population declines across northern Australia in recent decades. Results from Kapalga indicate that key components of the savanna biota of northern Australia favour habitat that has remained unburnt for at least several years. This raises a serious conservation concern, given that very little relatively long unburnt habitat currently occurs in conservation reserves, with most sites being burnt at least once every 2 years. We propose a conservation objective of increasing the area that remains relatively long unburnt. This could be achieved either by reducing the proportion of the landscape burnt each year, or by setting prescribed fires more strategically. The provision of appropriately long unburnt habitat is a conservation challenge for Australia's tropical savanna landscapes, just as it is for its temperate forests.

Experimental evidence that fire causes a tree recruitment bottleneck in an Australian tropical savanna

“…This study was part of a landscape-scale experiment in Kapalga examining the effect of fire treatments on flora, fauna and soils of north Australian mesic savannas, described in detail by Andersen et al (2003Andersen et al ( , 2005. It compared annual early dry-season (June) fires, annual late dry-season (September) fires, and no fire (control; Williams et al 1999Williams et al , 2003.…”

“…This reflects the logistical difficulties of undertaking landscape-scale fire experiments in tropical savanna environments. The Kapalga fire experiment in a north Australian savanna (Andersen et al 2005) provides a globally rare opportunity to test for the existence of a fire-mediated recruitment bottleneck in a mesic savanna. The key elements of the fire-mediated recruitment bottleneck are (1) abundant juveniles, which are able to persist even when fire frequencies are high (generally through resprouting); (2) vulnerable saplings, with high fireinduced stem loss, and adults that are fire-tolerant relative to the sapling size class; (3) low rates of recruitment from saplings into the small-adult size class; and (4) removal of fire leads to an increase in tree cover, i.e.…”

Is there an inherent conflict in managing fire for people and conservation?

“…A fire regime considers the frequency, intensity, extent, seasonality, heterogeneity and size of fires in a given landscape (Gill 1975;Whelan 1995). Changes to natural fire regimes (or the variability therein) can result in significant ecological impacts on some populations, species and communities (Fox 1982;Russell-Smith et al 2003;Andersen et al 2005;Clarke 2008;Driscoll and Henderson 2008;Nimmo et al 2012;Nimmo et al 2014;Sitters et al 2014).…”

Geographic patterns and correlates of the decline of granivorous birds in northern Australia

“…The general trend has been for decreased frequency in pastoral areas and increased frequency in the higher-rainfall nonpastoral areas of the far north. These changes have important implications for biodiversity (Williams et al 2002;Andersen et al 2005). In particular, fire regimes demonstrably affect grass composition, productivity and the seed resources it yields (e.g.…”