Forests and Wildlife

Forests

Of course, the forests incinerated by these intense bushfires also suffer great damage. Unlike the usual description employed in the media, most native forests are not “destroyed” by wildfire. Some are. Ash-type eucalypt forests are killed in this way, as the 1939 Victorian fire disaster clearly demonstrated. Drier forest types, such as jarrah in WA are not destroyed, although they are severely damaged and many trees are killed by high intensity bushfires.

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Jarrah forest defoliated by a bushfire

Although some individual trees may die, the forest cover is not removed in a wildfire. In a large bushfire, however, the total number of trees killed can be very large. In the 2005 Perth Hills fire, for example, it was estimated that over 1.5 million trees were killed outright. As the image above shows, the forest environment, so important for so many aspects of biodiversity, is completely lost for some time, until the trees are able to reform their crowns,

Most eucalypts have a number of specialised features that enable recovery from intense fires. The remaining trees are, however, damaged in a number of ways. The cambium (the growth layer under the bark) may be killed in one side of the bole, resulting in “dry sides” which are subsequently prone to insect attack, degrading the timber for almost any use. Rots also gain entry via dry sides and burnt limbs.Trees that already have “hollow butts” will often burn out completely and fall, and new hollow butts will be created when a dry log burns alongside a standing tree. The upper parts of saplings and small trees are often killed so that the stems become malformed, thus reducing their potential commercial value, as well as permitting access by damaging fungi and insects.

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These two images show how trees with hollow butts are damaged by severe bushfires.

 

In the case of pine plantations, on which we are now so dependent for timber supplies, the trees are killed by high intensity fires.The logs may also be degraded for certain end uses by charcoal. Destruction of immature plantations disrupts the flow of future timber supplies, with adverse impacts on local employment. In blue gum plantations, we can expect that high intensity fires will kill most trees and, due to their small size, the degradation of logs by charcoal will render them useless for pulpwood, their intended market.

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A burning pine forest

Wildlife

Intense bushfires cause the death, by incineration or smoke suffocation, of large numbers of native animals and insects that are unable to avoid the flames. Microsites (i.e. small areas of different nature from the general area) that do not burn under low intensity burns are incinerated and there are thus no refugial areas left for fire sensitive flora or fauna, or for subsequent recolonisation after the fire. Any animals that are able to take refuge in holes in the ground or in logs are usually quickly lost after a bushfire as they no longer have any cover from predators.

By contrast very little damage is caused by a mild fuel reduction burn. The usual objective is to burn only about 70% of an area, so that there is a patchwork of small areas unburnt in which insects and animals take refuge and from which later move out to recolonise the surrounding regenerating area. Unburnt plants in these patches also seed into adjacent areas.

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 Quokka killed by a wildfire

The large areal extent of severe bushfires means that, unlike low intensity fuel reduction burning where any fauna losses are quickly made up from surrounding unburnt forest, there are wholesale fauna losses. The potential for total loss of a rare and endangered species is clear.

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A ringtail possum caught in a bushfire.

The larger native fauna generally outrun a wildfire, but sometimes even they are caught.

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It is not only terrestrial fauna that is adversely affected by bushfires. If extensive areas of a catchment are covered by a bushfire, the aquatic fauna is also affected, as shown by the study reported by Batini and Barrett in Impacts>Wider Catchment Impacts on this website.