The Effect of a Bushfire on Earth’s Spheres

BIOSPHERE

Plants:
Fire is a common occurrence in Australian ecosystems and has been for a long time. As such many native species have adapted to not only withstand fire but to benefit from it also. [1] For example, much of the Australian and more specifically, South Australian vegetation consists of fire-adapted eucalyptus. [2] Some other plant species, such as the Banksia plant found commonly in the Mount Lofty Ranges, also rely on fire for germination and reproduction, as their seeds are unable to be released from the their fruit until it is completely dried out or burned. [13][14]

 

mushroom

flower
Images 6 & 7: The image on the top shows the dried fruit of the ‘Banksia Laricina’ plant. The fruit contains the seeds required for reproduction. [15] The image below shows a ‘Banksia Marginata’ plant photographed in Sandy Creek Reserve, Mount Lofty Ranges. [14]

On the contrary, bushfire can also have devastating effects on the biosphere.  It does not destroy the environment as it is commonly thought, but it can act as a major and irreversible disturbance to some plant communities.  If fires are too frequent and of high intensity it can limit the number of seeds left in the soil for reproduction therefore leading species toward extinction. [1]

Soil: 

The fertility of soil can be drastically effected following a bushfire and the extent of damage is dependent on fire intensity and the condition the soil was originally in.  Bushfire commonly burns and consumes organic matter at the surface of the soil resulting in the deficiency of key components such as nitrogen. [16] Nitrogen is essential for plant growth as it allows plants to produce proteins and chlorophyll.  Without nitrogen plant leaves are often yellowed and growth is stunted. [17]

leaf
Image 8: The image on the right depicts the effects of nitrogen deficiency in soil on a corn leaf

Fire damage to soil also increases the risk of erosion. [5] When a fire moves slowly it generates a gas from the combustion of plant materials, which then cools and condenses into the soil.  This creates a waxy film atop the soil which causes the soil to repel water.  This phenomena is known as ‘hydrophobicity’ and results in dehydrated, barren soil. [18] As the soil is so dry the likelihood of erosion then increases. [5]

 

dirt
Image 9: The photo above shows water pooling on top of soil as a result of hydrophobicity. [19]

Wildlife:

Animals are also affected by bushfire and the effect it can have on population sizes and ecosystems can be catastrophic.  Wildlife that is not able to move quickly and that is restricted to localised and specific habitats can be severely effected by fast moving, intense fires. [1] These animals may be killed by the fire itself or may die later from injuries sustained such as burns, smoke inhalation and dehydration.  Loss of numbers from a population can lead to decreased reproduction rates which can negatively influence the stability of the ecosystem of which it belongs. [20]

koala
Image 10: The image to the left is a well-known photo taken during the Black Saturday bushfires in Victoria, 2009. Dehydration is a common cause of death of wildlife caught up in a bushfire. [20][21]

The loss of flora and fauna from an ecosystem can also upset the equilibrium of that system which is often hard to re-establish.  When trees and plants are damaged it not only effects the plant life but also the animals that depend on it to survive. [20] Many small marsupials shelter and feed in the underbrush of shrubs whilst many bird species and other animals such as koalas depend on the trees for food and shelter.  When food and shelter is lost it can be difficult for animals to find new, suitable habitats which can lead to further loss of life. [1]

HYDROSPHERE

Water ways and catchment systems can be negatively impacted by bushfire. [1] The amount of damage caused is usually determined by the intensity and size of the fire. [5]

When a large-scale, high intensity bushfire burns through a vegetated area it releases nutrients, metals and other toxins from within the soil and vegetation.  If a significant rain event occurs soon after the fire has ceased then these nutrients are washed and eroded away into waterways such as streams, rivers, catchments and reservoirs. [5] This is undesirable as the excess nutrients in the water can potentially make it unfit for human and agricultural consumption. [1][5]

Exposure of top soil from lost vegetation post bushfire can also have a negative effect on the hydrosphere.  When top soil is exposed it is easily eroded into waterways via wind and rain.  This increases sediment build up in waterways and increases the likelihood of siltation occurring.

It is nice to note though, that even without human intervention freshwater catchment systems are usually able to regenerate to pre-fire conditions within 5-25 years. [5]

hydrosphere
Figure 3: The above cartoon depicts the possible post-fire changes to a water catchment system [5]

ATMOSPHERE

As a bushfire burns through vegetation, ash and smoke is produced and released into the atmosphere.  This combination is known to negatively affect health and visibility.

The smoke from fire is a known respiratory irritant.  When inhaled the heat from the smoke can burn your respiratory tract causing coughing, vomiting, nausea and confusion.  If left untreated, smoke inhalation can lead to death as the carbon monoxide and cyanide (combustion products) in the smoke can act as poison and can also induce pulmonary irritation and swelling.

Smoke and ash can also majorly effect visibility as it is able to be transported in the atmosphere over hundreds of kilometres via wind.  This not only exposes harmful smoke to an increased number of humans and animals but can also lead to an increase in motor vehicle accidents as visibility to motorists can be decreased. [5]

The video link above shows real life footage of an ember attack through the eyes of a driver during the Canberra 2003 bushfires.  You can see throughout the video that visibility is very low as a result of smoke and ash in the atmosphere. [22]

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