Chapter 5. Effects of grazing and fire on fauna and flora in Eucalyptus similis tropical savanna woodland. “At length, tracing the dry bed of a creek, (Warrigal Creek, from the many Warrigals or dingoes), he crested the forest-clad Main Dividing Range. A curious sight appeared - trees plastered with yellow earth: these trees, called yellowjacks, are soft wood, so white ants enclose them with earth walls and eat the wood out, leaving shells which first strong wind or bush-fire sweeps away. Around these grew gaudy poison-bush.” (p. 49. Bennett 1928). Introduction There is little argument that fire has profoundly influenced the historical evolution and current patterns of biota on the Australian continent. This is clear from the predominance of fire-dependent and promoting flora (Kershaw et al. 2002). Other indications of the importance of fire include systems of biota inexorably linked to fire age (Williams and Gill 1995), and climatic patterns that result in fierce seasonal electrical storms sparking wildfire (Cook and Heerdegen 2001). There is also strong evidence of a long history of prescribed burning by Aboriginal land managers (Hallam 1985; Crowley and Garnett 2000). However with European settlement, there was a rapid cessation of pre-existing regimes (Bowman 2000; Yibarbuk et al. 2001) and a shift to regimes dictated by pastoral land use and human property protection (Crowley and Garnett 2000). There has been vigorous debate on the extent and importance of traditional Aboriginal burning (e.g. Flannery 1994; Benson and Redpath 1997), though there is general acceptance of an impact on biodiversity (Bolton and Latz 1978; Burbidge and McKenzie 1989; Franklin 1999). This has led to recognition of the value of environmental history to inform current land management (Fensham 1999; Crowley and Garnett 2000; Bowman 2001; Vigilante 2001). Regardless of the detail regarding scale, frequency, season and size of the regime change, a wholesale shift is evident, and at least coarsely, this is coincident with changes in species diversity (Burbidge and McKenzie 1989; Franklin 1999). Many plant and animal populations follow clear trajectories of increase or decline with time since fire (Williams and Gill 1995). It follows from this that fire will promote a change in composition of plant and animal assemblages, and changes in the fire regime may Chapter 5. Grazing and fire well have effects on species diversity. The post-European shift has been from fine-scale mosaic burning to one of greater extremes (Burbidge and McKenzie 1989), typically involving one or other of the following: • deliberate fire exclusion to protect property, stock and ground cover; • secondary exclusion via continuous grazing removing fuel load; • complete abandonment of burning in more remote areas, resulting in occasional large-scale fires; or • a greater frequency of hot, extensive fires. These changes in regime have resulted in homogenisation of plant and animal composition, loss of particular resource dependent species and, in some instances, decline of those species needing a longer time lag between burning (Burbidge and McKenzie 1989; Bowman and Panton 1993; Franklin 1999). The historical effects of grazing on Australian ecosystems contrast with those of fire, but they may be equally significant. Since the Late Pleistocene extinction of megafauna, Australia has lacked large native herbivores. The disappearance of the megafauna may have been due to human impact, although this is still debated (Flannery 1994; Horton 2000; Bowman 2000), but it appears to have had little impact on Australian ecosystems. Rather, it has been argued that invertebrates (e.g. termites, ants and grasshoppers) are this continent’s significant herbivores, with a diversity and biomass beyond other comparable systems worldwide (Andersen and Lonsdale 1990). However the current regulatory influence of invertebrates on ecosystem function is still far from being understood (Andersen and Lonsdale 1990; Andersen 2000). The key event regarding grazing impacts is again post-European change and the massive influx of mammalian herbivores, both hard-hoofed ungulates (sheep and cattle) and rabbits (Lunney 2001). Pastoralism is currently the dominant land use across northern Australia, occupying 60% of the total area (Ash et al. 1997) and was introduced to Queensland savannas as early as the 1860’s (May 1984). Grazing alone causes only moderate localised change (such as the removal of ground cover or compaction of soil), but the increasing density of artificial water-points (foci for intense grazing activity) exacerbates these impacts markedly (James et al. 1995). In intact 2 Chapter 5. Grazing and fire environments, this creates a patchwork of piospheres (gradients of intensity of livestock grazing) and ultimately an undifferentiated environment of consistent low ground cover and low plant species richness with a preponderance of less palatable and disturbance- tolerant species (Landsberg et al. 1997). Refuges of unaffected, heterogeneous resource rich habitat become uncommon as the density of artificial watering points is increased (Landsberg and Gillison 1996). Coupled with more serious transformations of the landscape such as tree clearing for non-native pasture development, remnant vegetation becomes fragmented, degraded and species poor (Barrett 2000; Ford et al. 2001). Bird and mammal species that rely on a dense and floristically diverse ground cover have declined under livestock grazing both in Australia and elsewhere (see reviews in Fleischner 1994; James et al. 1999; Woinarski et al. 2001a). Unfortunately the potential of tropical savanna woodlands for pastoralism has been notoriously romanticised (Smith 1994), despite frequent failure of early and current pastoral enterprises (Bennet 1928; Holmes 1996; Ash et al. 1997). The reports of explorers typically emphasised wet season resource abundance, and ignored the dramatic seasonality of tropical savannas and the key period of scarcity prior to the wet season (Smith 1994). The response of pastoralists to this has been to shift stock type (sheep to English cattle breeds to Brahman cattle breeds), and to consistently try to modify the landscape resources to standardise annual conditions for stock. This has been via the provision of more water points, pasture improvement with introduced grasses, addition of lick to increase use of poor forage, and tree-clearing to promote pasture growth (Gardener et al. 1990; Ash et al. 1997). Paradoxically this generally creates degradation and a shift from mixed pasture to a monoculture of perennial grasses, and finally ephemeral grasses or unpalatable species, accentuating the end of dry season resource slump (Ash et al. 1994; Ludwig et al. 1997). Native fauna are adapted to this pattern of seasonality, and utilise strategies that compensate for climatic uncertainty, such as dispersal and resource tracking, resource switching within a mosaic home range, and localised extinction and contraction to refuges ready for post-rainfall irruption (Woinarski 1999a). Fundamental to this is access to heterogenous habitat, at a variety of scales. There is a clear recognition that economically sustainable rangeland management also equates to ecological sustainability, and that future stewardship of tropical savannas should embrace a 3 Chapter 5. Grazing and fire philosophy of land management that in fact creates environments conducive for biodiversity conservation (Ash 1996). Ironically, the conditions most suitable for viable cattle grazing in tropical savannas partly mirror requirements for native fauna (Ludwig et al. 1997), yet management for “conservation” is anathema to many pastoralists, despite the shared goal of healthy landscapes (Landsberg et al. 1998). Cattle-grazing in the Desert Uplands has a long history and is the dominant land use (Smith 1994; Rolfe et al. 2001). However tree clearing for more intensive production is become more widespread, with the south-eastern parts of the bioregion having undergone some of the highest clearing rates in Queensland (Fairfax and Fensham 2000; Rolfe et al. 2001; Neldner et al. 2002). The largest and central sub-region of the bioregion is the Alice Tableland, dominated by sandstone ranges and deep red sandy soils of intact Tertiary sandsheets (Sattler and Williams 1999). This area is also the least developed in the bioregion, due to low fertility, and therefore has few artesian bores and little other infrastructure, with some parts identified nominally as wilderness (Morgan et al. 2002). A single vegetation type - open E. similis woodland with Triodia pungens ground cover (regional ecosystem 10.5.1 sensu Sattler and Williams 1999) - dominates this area and was chosen to examine the effect of grazing and fire on the vertebrates, ants and plants. Despite the aforementioned low fertility, these areas are still actively grazed. This woodland type is also notable in the region in that many properties have long or permanently ungrazed paddocks due to the presence of heartleaf poison bush Gastrolobium grandiflorum, which is toxic to cattle. This plant can only be removed by intensive mechanical means, and though many areas have been treated and are grazed by cattle, many paddocks are left unutilised, or at least used only in extreme circumstances such as drought. Additionally the presence of dense and highly flammable Triodia ground cover results in intentional and unintentional periodic burning, more regularly than in surrounding woodlands with predominantly tussock grass ground