Fire

Another scourge of the Australian bush is the forest fire. Every year, bushfires ravage thousands of hectares of wombat habitat, the eucalypt forests of eastern Australia. No doubt the wombat has a better chance of survival than most other forest animals. Often the floors of small valleys and gullies are unburnt, as a fire will jump right across the top of a gully

Figure 7.1 A few remnants of vegetation remained in this gully after a severe bushfire had swept through the forest.

leaving the vegetation and animals untouched (Figure 7.1). But some bushfires are more intense; an uncontrolled wildfire rarely leaves a blade of greenery in its path.

In December 1972 a severe and extensive wildfire ravaged the Nadgee Nature Reserve in south-eastern New South Wales. A study of the effects of this fire on 20 species of animals was made by a group of research workers led by Alan Newsome and including John Mcllroy. They assessed the abundance of the larger animals by observing and counting their tracks on carefully prepared plots of soil, which were located at intervals along 40 kilometres of dirt roads, walking tracks and beaches. These counts, which were made before and after the fire, showed that while other large herbivores, the kangaroos and wallabies, survived poorly, wombats survived the fire well. Earth is a good insulator; G.E. Lawrence found that the temperature 15 centimetres down rodent burrows reached only about 72°C during a fire measured at 360-555°C, so it is likely that the temperature several metres down a wombat burrow would be relatively low. Newsome's study showed an increase in the number of wombat tracks recorded after the fire, but this was probably due to the wombats feeding more often along the roads where grasses recovered well after rain.

Although burrows provide some degree of safety during bushfires, an intensely hot fire will deprive the air of oxygen so severely that even the wombats deep in their burrows suffer and a number die. Some of the burrows themselves are completely destroyed in a severe fire, especially those dug beneath uprooted trees; when these burn, the whole structure usually collapses. When fire destroyed 221 000 hectares of forest in East Gippsland in 1983, part of the coastal forest adjacent to my home was burnt out. Before the fire there were nine frequently used wombat burrows in 80 hectares of this burnt area, which were used by at least four different wombats: a large female, two smaller wombats of unknown sex and a hand-reared male, then seven years old. All of these wombats also sometimes frequented a part of the forest that was not burnt, and had other burrows there. On checking the burrows in the burnt area a few days after the fire, I found that three of them had been destroyed: two, dug under old fallen logs, had collapsed at the entrances and for some distance along the tunnels as the logs burned; the third had been flattened by a fire-fighting bulldozer. All of the wombats had disappeared; the hand-reared male was seen shortly after the fire in the unburnt forest, but the others were not seen again. It is not known whether they died in the fire or left the area completely.

Some wombats do survive even the hottest fire, only to emerge to find a completely changed world. All the familiar features of the wombat's limited landscape have gone; all familiar scents and signs have been eliminated. Worse still, so has most of the food - the grasses that form the major part of the diet have been reduced to grey ash. If the fire has devastated a large area, and wildfires usually do, the nearest green food source may be many kilometres away, well beyond the wombats' usual limits. Some of them manage to exist by eating roots and bark; and when rain falls, fungi of many kinds usually appear before the grasses and herbs begin to grow, providing another temporary food supply. Other wombats travel long distances in search of food, encountering more dangers as they do so. Wombats living nearer to the perimeter of a bushfire have a better chance of survival, but if they move into new country they are not welcomed by any wombats residing there, and the resulting fights can be savage and harmful.

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