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Williams PR, Congdon RA, Grice AC, Clarke PJ (2004) Soil temperature and depth of legume germination during early and late dry season fires in a tropical eucalypt savannah of north-eastern Australia. Austral Ecology 29, 258-263. 146 Chapter 8 General conclusions Introduction This thesis sought to examine the effects of fire regime on the vegetation dynamics in spinifex grasslands in central Australia. This chapter synthesizes the results of this research and puts forward the hypothesis that plants within spinifex grasslands possess adaptations that have been selected for under a fire regime characterised by periodic, summer fire. It also summarizes the management implications of these findings, and points towards potential future research directions. Spinifex fire regimes Chapter 2 showed that contemporary fire regimes in spinifex grasslands are characterised by extensive wildfire events that occur in response to fuel accumulations after extreme rain. During these events, the scale of fires can be enormous, with one fire during the 1980s burning over 6000 km2 of sand dune and range country. The almost complete absence of fires during inter-event periods was also striking, with less than 1% (~ 80 2 km ) of the study area burning during the entire period from 1985-2000. The main season of fire occurrence in spinifex grasslands is over the late spring and summer months, when air temperatures are highest and humidity levels are low. The potential for fires during these months is enhanced by the increased likelihood of summer lightning strikes (Griffin, Price et al. 1983). Chapter 2 also showed that spinifex grasslands are occasionally subjected to short fire intervals, and that these fires occur when sufficient rains fall soon after initial fires. It is suggested that these short interval fires are fuelled by inter-hummock grass species, such as Aristida holathera and A. inaequiglumis, as these species were common in the seed bank (see Chapter 5) and Triodia fuels are virtually absent during early stages of post-fire succession (see Chapter 4). Chapter 3 showed that these short interval fires are of lower intensity and severity than initial Triodia-fuelled fires (see Chapter 6), but as was demonstrated in Chapters 4 and 5, their ecological impact can still be significant. 147 While the data from this thesis only pertain to the very recent history of fires, it was suggested in Chapter 2 that the contemporary relationship between rain and widespread fire in spinifex grasslands may also have prevailed prior to the arrival of humans in Australia. Such a hypothesis may be plausible, given that fires in arid environments across the globe are constrained by low biomass levels, and that opportunities for fire only ever occur when high rainfalls promote substantial fuel accumulation (Frost 1985; Kitzberger, Swetnam et al. 2001; Veblin, Kitzberger et al. 1999). At this stage no data are available to directly validate this hypothesis, although it could be tested in the future using research techniques similar to those of Atahan et al. (2004) and Dodson et al. (2005), who used Pliocene charcoal records from palaeo-lakes to show that pre-human fire regimes in south-western Australia were characterised by fires that were highly seasonal and frequent. In Chapter 2 it was also suggested that the seasonality of fires in spinifex grasslands may not have changed considerably since pre-human times, as fuel combustibility during these times would still have been highest in summer. This hypothesis has previously been put forward by Suijendorp (1981), who also postulated that pre-human fire regimes may have been even more seasonal than contemporary ones, owing to the absence of anthropogenic ignition sources and the dependence on summer lightning strikes to initiate fires. If these hypotheses hold, then it can be presumed that the spinifex flora has spent a considerable portion of its evolutionary history adapting to fire regimes characterised by infrequent summer fires that occur in response to