Bushfires: The effects on the environment.
Severe bushfires are occurring more often than ever before, both in Australia and around the world. As global warming produces more droughts and high fire danger weather conditions, these bushfires are expected to become even more frequent and intense.
Fires release huge quantities of stored carbon, and this carbon might not be resequestered because the regrowth of vegetation is prevented by ongoing drought conditions or by human intervention. Burnt and damaged vegetation and communities, such as forests, take hundreds of years to recover.
Deforestation fires are occurring on a massive scale throughout regions of the world and have been estimated to account for approximately 20% of anthropogenic greenhouse gas emissions. Landscape fires thus have the potential to further accelerate global warming, driving more serious fires.
Negative effects of fire:
Severe bushfires have the potential to produce numerous economic, social and environmental impacts, which can range from short-term inconveniences to long-term life-changing impacts. While it is easy to observe the negative impacts typically found within the economic and social categories, the environment generally requires bushfires to remain healthy and support the rich diversity of flora and fauna.
Fire can have an impact on native animals through injury and loss of habitat. In most cases, populations will not be affected because native animals from surrounding areas will recolonise a burnt area after a fire. When the distribution of a species is limited, or the species is listed as vulnerable or endangered, a significant fire event can impact these populations.
Animals escaping fire:
Native animals can escape fire by fleeing to ‘unburnt islands’ within a burn area or to surrounding unburnt vegetation. Insects, reptiles and small mammals may be able to hide underground, and animals that live in trees can move to treetops and escape low-to-moderate intensity fires.
Birds are least impacted by fire as they can fly away, but chicks and eggs can be impacted depending upon the season of the fire.
The impact of prescribed burning on native wildlife is carefully considered during fire planning and detailed in environmental impact assessments.
Animals injured by a fire may only be rescued and cared for by licensed rehabilitation organisations or individuals. This is because: injured animals can be dangerous to handle injured animals may cause them further stress and fire-affected areas can be unsafe.
Depending on the temperature of the fire, the effect on soil can occur at the biological, chemical or physical level. A proportion of soil nutrients and chemicals is removed from the site by the fire directly through the transfer of gases, particulate matter and ash to the atmosphere in the form of smoke. In addition, soil can be removed from a site once the fire has been extinguished through the erosive processes of wind or rain. In some cases, severe bushfires induce water repellency within the soil, making it even more susceptible to erosion.
The hydrology of a landscape and the resultant quality of watercourses are significantly affected by severe bushfires. The removal of the vegetation encourages large-scale erosion that eventually flows into streams and rivers, causing sedimentation of these waterways and a deterioration in water quality.
Even in areas where waterways have been severely impacted by large quantities of sediments, these sediments are typically flushed out over three to five years. On the catchment scale, the restoration of hydrological processes back to pre-fire conditions can take up to 150 years if a large proportion of the vegetation is removed, as growing trees require much more water than when they are mature.
The smoke produced from severe bushfires contains a number of chemicals, including plant nutrients. Nitrogen in particular is highly susceptible to being lost to the atmosphere, but is eventually returned to the soil through a number of processes, such as nitrogen fixation. Greenhouse gases (e.g. carbon dioxide and nitrogen oxides) CO2 emissions can be really high, causing issues for the environment and global warming.
Many Australian vegetative species have evolved to depend on fire for their ongoing survival, and therefore the persistence of whole ecological communities. In order to take full advantage of this element, plants have developed mechanisms that allow them to survive the initial fire front or reproduce once the fire has passed, which are: storing seed on the plant, storing seed in the soil, resprouting through lignotuberous buds (buds at the base of the tree), resprouting through epicormic buds (buds just under the bark) or spreading vegetatively through rhizomes (underground stems).
Fire can be seen as a positive element; however, if it is applied to the landscape outside its natural tolerances (e.g. too frequently or intense, not frequently or intense enough), then some species are in danger of becoming locally extinct.
In the event bushfires enter a natural landscape outside its natural tolerances, however, the impacts could also be adverse and long-lasting.