Australia is an arid continent that has unique ecosystems and organisms. These unique ecosystems are continually being exposed to natural and human-made events. Bushfire, drought and flood are the three main events that affect Australia's ecosystems. These events can devastate various ecosystems but there can also be some positive outcomes. This chapter looks at the effects of bushfires on Australia's ecosystems.
Fire has been a part of the natural cycle of ecosystems in Australia for millions of years. Before the arrival of the Indigenous peoples, fires were started by lightning strikes. These bushfires destroyed and changed many ecosystems with the result that plants and animals either adapted to the fires or gradually died out from the area.
When the Indigenous peoples arrived in Australia over 50 000 years ago, they began using fire to manage the land and to ensure a plentiful food supply. Many native plants and animals adapted to bushfires by developing special characteristics that enabled them to survive during and after a fire. These specialised characteristics mean that some native plants require fire to regenerate or to release their seeds.
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The Indigenous peoples changed the natural pattern and timing of fires. Previously the fires started by lightning were sporadic. The Indigenous peoples began to light fires every few years which created different ecosystems and changed the landscape of many parts of Australia.
The Indigenous peoples used fire to burn areas of bush for a number of reasons. The fire could trap prey making them easier to catch. Regular burning of the bush helped keep the undergrowth clear and reduced the danger of fires burning out of control. Fires which were out of control (termed bushfires) produced more intense heat and destroyed even the fire-tolerant plants. Fire also encouraged the growth of fresh leaves and shoots which attracted kangaroos and other animals which the Indigenous peoples could then more easily hunt.
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When the Europeans arrived in Australia, they broke the pattern of frequent, low heat bushfires. The open bush began to be replaced by dense bush which provided the fuel for more intense fires. Today, the fire brigades regularly use control burning in an effort to reduce undergrowth and reduce the threat of large bushfires.
By lighting fires regularly, the Indigenous peoples created an open scrub ecosystem. This ecosystem provided a habitat for many plants and animals that needed to adapt to a bushfire prone area. One of the specialised characteristics that native plants have for surviving a fire is housing their seeds in woody seed pods that provide protection from a fire. Some native plants, however, require the heat from a fire to split open the seed pods and release their seeds. The Banksia fruit, for example, open and release their seeds only when heated by fire and the seeds of some wattles need the heat from fires to germinate.
Many eucalypts also have buds underneath their thick, fire-resistant bark. The bark protects the living cells inside the trunk. After a fire, these buds sprout and new green shoots rapidly grow. Eucalypts also have swollen parts on their roots called lignotubers. These lignotubers also contain buds and sprout soon after a fire. In these ways the eucalypt recovers from fire damage while other types of plants are killed.
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Native animals are often caught in a fire. Some quicker animals such as kangaroos and birds are able to move away from a fire, but slower animals such as echidnas, reptiles and wombats take shelter in burrows or logs. Many animals and insects are killed in fires and it takes years before the population reaches the level it was at before the fire.
A bushfire in Australia has both negative and positive effects on the ecosystem. The fire destroys some adult trees and burns the branches, trunks and leaves of others. It also burns the undergrowth. The positive effects of this means that more sunlight can then reach the soil and seeds that were waiting for a fire release them can germinate. Young plants can thrive due to an increase in light.
A fire can change the structure of the soil by making it finer but it also releases stored nutrients in the soil that act as a fertiliser. This provides suitable conditions for seeds to germinate, but also makes it easier for the soil to be washed or blown away.
A bushfire reduces the number of animals in a region. Animals are either killed or escape to a safer area. They are unable to return until food becomes available again. The food web is significantly damaged and may take years to recover.
In the next chapter, the impact of drought on Australia's ecosystem will be explored.