Underpinnings of fire management for biodiversity conservation in ...

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54 Fire intensity Intensity is the usual fire property considered in relation to immediate fire effects. It reflects the rate of heat release and flame length (Byram 1959; Catchpole 2002), and therefore the exposure to, and direct effects on, plants and animals (Whelan et al. 2002). Crown scorch (and death of firesensitive plants) can be related to intensity (Dickinson and Johnson 2001), while exposed animals in trees would be affected to a similar extent to the leaves and crowns that they live among (Gill and Bradstock 1995a). Intensity is not relevant for fires in peat where rates of spread are extremely slow. The length of time that seeds and roots are exposed to temperatures above lethal levels seems more appropriate, but the three-dimensional nature of the problem, along with the extremely slow rates of spread, make the determination of this difficult. The depth of peat burnt or proportion of depth burnt (some c.f. all) may be better indicators that reflect the length of time of exposure of organs to heat, and what the suitable substrates for plant regeneration are (Miyanishi 2001). Effects of fire regimes The effects of fires on plants and animals depend on a particular fire regime and whether they are adapted to it (Gill 1975). If they are adapted to a particular fire regime or set of regimes, this means that they are not adapted to the complement of possible regimes, and may go extinct if under their influence. Extinction may be local but could also be over a wider area if the regimes that cause extinction are widespread; local niches with different regimes may allow remnants to survive, however. Mistletoes can be locally eliminated by a single fire because their individuals are readily fire killed and they have no seed store; their local extinction may be reversed by seed dispersal by Mistletoe Birds (Dicaeum hirundinaceum) (Gill 1996). In contrast to the extensive literature on the effects of fires on vascular plants and vertebrate animals (Text Box 3.2), there has been little research on the effects of fires on non-vascular plants. Results from the grasslands of Western Victoria suggest that the vascular and non-vascular flora ‘respond in different ways to fire and this should be considered in … conservation planning’ (Morgan 2004). In frequently burned grassland, Morgan (2004) found that there were fewer mat species (non-vascular plants e.g. mosses) in his grasslands, but he noted that vascular plant species’ richness is usually higher in frequently burned areas. In forested south-western Australia, Robinson and Bougher (2003) found that different fire histories ‘result in fungal communities with similar total diversity but different species composition’. Wark (1997) found that non-vascular plants were common colonisers after fire. In a western New South Wales eucalypt shrubland (mallee), Eldridge and Bradstock (1994) found that the ground coverage of cryptogams (algae, mosses and lichens) increased with time since fire, algae being the main early colonisers. The effects of fire regimes on biodiversity are: • Changing species’ presence to the point of plant-population reduction (Bradstock et al. 1997) or even extinction (Gill and Bradstock 1995a); evidence of local extinction may be observed historically or directly through the killing by fire of seedlings establishing in new territory (e.g. Callitris noted by Leigh et al. 1989) or the eventual establishment of adult plants in an area after a change of fire regime. • Changing organic aspects of habitat for native animals, such as forest structure (e.g. Catling 1991; Gill and Catling 2002) or litter structure (York 1999). • Changing inorganic aspects of habitat for plants and animals (including fish and stream invertebrates) through changes in soil chemistry (such as pH), water chemistry and temperature, erosion and sedimentation, and changed soil-moisture regimes. • Changing species’ composition of plant and animal communities as a result of (i), above, and indirectly through various interactions (e.g. burning–grazing and the likelihood of invasions by, or proliferations of, exotic species). Fire and adaptive management Underpinnings of fire management for biodiversity conservation in reserves
Underpinnings of fire management for biodiversity conservation in reserves When regimes change, the effects may take many iterations (a series of successive fires) to reveal ultimate changes (Gill and Bradstock 1995a). For example, a change in greater dominance of the native grass Themeda triandra compared with Cymbopogon plurinodis, another grass, occurred with a program of frequent burning in South Africa. The new quasi-equilibrium took about eight fires to be achieved in the 16 years of observation (Trollope 1996). Our knowledge of the effects of fire regimes on the biota is growing, but is still at an early stage on a national scale in Australia. For example, explicit knowledge of the immediate responses of vascular plant species to fires is incomplete, although no recent census has been conducted. There is a wide variety of information on the direct and indirect effects of fire on animals in a variety of habitats, from streams to forest and desert. The complexity of the food web and the effects of fire regimes on individual components of it is a challenge to our understanding. Computer simulation is one way of exploring possible effects of a fire regime, including prescribed fires (e.g. Bradstock et al. 1998a, 1998b, 2005), especially in a time of dynamic change of climate, fuels or fire regime. Also, effects can be examined empirically using long-term fire experiments that are, by necessity, dominated by lowintensity prescribed fires (e.g. Tolhurst and Flinn (1992) provide a progress report on a range of studies related to the effects of prescribed fires on forest plots in Central Victoria). Text Box 3.2 Literature on the effects of fire regimes There is considerable literature on the effects of fires on biodiversity. Bradstock et al. (2002) and Abbott and Burrows (2003) are recent multi-author books that tackle the subject in Australia. Whelan (1995) is an Australian text on The Ecology of Fire. In the USA, there are substantial recent reviews of the effects of fires on fauna (Smith 2000), flora (Brown and Smith 2000) and air (Sandberg et al. 2002). A range of topics is considered in depth in Forest Fires: Behavior and Ecological Effects (Johnson and Miyanishi 2001). Bond and Van Wilgen (1996) give an authoritative account of the effects of fires on plants, based on their South African experience; while Goldammer and Furyaev (1996) report on Eurasian Boreal forests. There are a number of commentaries on the effects of fires and fire regimes on various Australian animal species, including invertebrates (Brown et al. 1998; and various chapters in Bradstock et al. 2002; especially Whelan et al. 2002; Abbott and Burrows 2003 and Anderson et al. 2003). Despite many advances in our knowledge of fire regimes and their effects throughout the world, a conservation manager may still not know how local species in the local jurisdiction respond to fire regimes. There may be a general lack of local information and answers from one area do not necessarily apply to another (Williams et al. 1994). It behoves the local manager to observe effects of fire regimes on the local environment in light of the literature, and thereby draw and record conclusions. Conclusion Prescribed fires are fires lit by managers of landscapes for specific purposes under specific conditions. These can be contrasted with other fires that are not for management purposes, and which may be ignited by unauthorised people or lightning. In forests, fires prescribed for broad-area fuel modification are generally of low intensity. In some places they may occur at shorter intervals than unplanned fires and occur in different seasons. In other areas they may be relatively rare. In some shrublands fires may burn with a high intensity whenever a fire will carry satisfactorily, and some grasslands may be burnt in mild weather during the usual fire season. There are various methods for assessing a prescribed burning program, such as cost, influence on ease of suppression and ecological effects. Various possible performance criteria for assessing prescribed burning programs may be devised. Effectiveness may be viewed at a number of levels, such as the proportion of area burned, effect on fire suppression or immediate effect on the landscape. The ultimate measure of a program is its contribution to management aims. Fire and adaptive management 55
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