Teacher background information
Year 9 Science Content Description
Chemical sciencesChemical reactions, including combustion and the reactions of acids, are important in both non-living and living systems and involve energy transfer (ACSSU179 - Scootle )
Many chemical reactions require the input of energy to initiate them. In cases, such as combustion, the exothermic nature of the reactions themselves provides sufficient energy to sustain the ongoing reaction. Fire, the result of a combustion reaction, is important in ecosystems, such as the tropical savanna regions of northern Australia, as it promotes the recycling of nutrients. This process is well-known by Aboriginal and Torres Strait Islander peoples and as such, fire has been used for millennia to control the transfer of matter and energy through the ecosystem in a practice known as firestick farming.
The Sun’s energy is captured and trapped in plant material through the process of photosynthesis. This energy is primarily utilised through the process of respiration and as it is transferred through food webs it sustains all life in an ecosystem. During fires, the energy stored in biomass is released through the process of combustion. The process of burning biomass releases a wide range of products, some of which can act as nutrients or contribute to the cycling of nutrients in the environment. Others, such as methane and dioxins, are harmful to the environment. Which products are produced, and in what quantities, can be significantly affected by the temperature at which the biomass is burnt. Studies have found that the temperature of the fire also has an impact on the physical, chemical and biological properties of soils.
Over millennia, Aboriginal and Torres Strait Islander peoples have amassed knowledge about the variables that affect the control and intensity of fires. This knowledge is applied to regulate the frequency and timing of fires in order to ensure the efficient recycling of nutrients, thus creating and shaping a patchwork of resources at different stages of regrowth in a convenient and predictable manner. Fires that are burning too hot result in a greater loss of volatile nutrients from the ecosystem and have detrimental effects on the soil. Aboriginal and Torres Strait Islander peoples understand this fact well. Hence, burns are conducted in the early dry season, whilst plant matter still contains moisture, resulting in smaller scale and cooler fires. This method of harnessing fire in strictly controlled fire regimes is known as firestick farming and is the oldest known farming practice in the world.
The successful transfer of nutrients is highly dependent on fire temperature. An essential factor in controlling fire temperature is the time when these fires occur. In recognition of this, Aboriginal and Torres Strait Islander communities in the tropical savanna areas of northern Australia purposefully light fires in the early dry season (March-April) to prevent the occurrence of hotter burning fires in the late dry season (October-November). These low-intensity fires recycle nutrients from the biomass into new growth, allow for the selective distribution of fire-tolerant and fire-sensitive plants, foster the regrowth of crop plant species, and encourage the migration of target game species to the new regrowth zones of the recently burnt areas. At the same time, the mosaic nature of burnt and unburnt areas provides a balanced environment for game species to find food and shelter.
Students could research the chemical reactions of photosynthesis, respiration, the complete combustion of simple hydrocarbons in an ample supply of oxygen and the incomplete combustion of simple hydrocarbons. They could compare the products of these combustion reactions with those produced in the combustion of the more complex compounds involved in biomass fuels, and the effect of high temperature fires on the production of greenhouse gases such as methane and nitrogen oxides.
In investigating the context suggested in this elaboration students will gain a deeper understanding of the role combustion reactions play in the accessibility and recycling of nutrients through the ecosystem and how these reactions have been employed and controlled by Aboriginal and Torres Strait Islander peoples in the agricultural practice of firestick farming.
In the construction of this teacher background information, a list of consulted works has been generated. The consulted works are provided as evidence of the research undertaken to inform the development of the teacher background information. To access this information, please read and acknowledge the following important information:
Please note that some of the sources listed in the consulted works may contain material that is considered culturally offensive or inappropriate. The consulted works are not provided or recommended as classroom resources.
I have read and confirm my awareness that the consulted works may contain offensive material and are not provided or recommended by ACARA as classroom resources.
The following sources were consulted in the construction of this teacher background information. They are provided as evidence of the research undertaken to inform the development of the teacher background information. It is important that educators recognise that despite written records being incredibly useful, they can also be problematic as they are often based on non-Indigenous interpretations of observations and records of First Nations Peoples’ behaviours, actions, comments and traditions. Such interpretations privilege western paradigms of non-First Nations authors and include, at times, attitudes and language of the past. These sources often lack the viewpoints of the people they discuss and can contain ideas based on outdated scientific theories. Furthermore, although the sources are in the public domain, they may contain cultural breaches and cause offence to the Peoples concerned. With careful selection, evaluation and community consultation, the consulted works may provide teachers with further support and reference materials that could be culturally audited, refined and adapted to construct culturally appropriate teaching and learning materials. The ability to select and evaluate appropriate resources is an essential cultural capability skill for educators.
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Boerner, R. (2000, March). Effects of fire on the ecology of the forest floor and soil of central hardwood forests. Paper presented at the workshop on fire, people, and the central hardwoods landscape in Richmond, KY, Newtown Square, PA.
Cape York Elders & Community Leaders, George, T., & McConchie, P. (2013). Fire and the story of burning country. Avalon, NSW: Cyclops Press.
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Cook G. D. (1994). The fate of nutrients during fires in a tropical savanna. Australian Journal of Ecology, 19(4), 359-365. doi:10.1111/j.1442-9993.1994.tb00501.x
Department of Primary Industries New South Wales. (2005). Impact of fire on soil life and nutrients. Retrieved from https://www.dpi.nsw.gov.au/content/archive/agriculture-today-stories/ag-today-archives/agriculture_today_february_2006/2006-002/columns/impact_of_fire_on_soil_life_and_nutrients
EnviroNorth. (2006). Fire: Nutrient cycling and national issues. Retrieved from http://environorth.org.au/downloads/Fire nutrient cycling carbon.pdf
Gammage, B. (2011). The biggest estate on Earth: How Aborigines made Australia. Crows Nest, NSW: Allen and Unwin.
Holt, J. A., & Coventry, R. J. (1990). Nutrient cycling in Australian savannas. Journal of Biogeography, 17(4/5), 427-432. doi:10.2307/2845373
Jones, R. (1969). Fire-stick farming. Australian Natural History, 16(7), 224-228.
Kennett, R. (2014). Looking after Country: The NAILSMA I-tracker story. Retrieved from https://www.researchgate.net/publication/325398354_Looking_After_Country_The_NAILSMA_I-Tracker_story
Marschner, P., & Mills, R. (2015, August 25). Fire damage to soils sets back bushfire recovery. University of Adelaide News. Retrieved from https://www.adelaide.edu.au/news/news80262.html
McKenzie, N. (2004). Impacts of fire on soil. Retrieved from https://ewater.org.au/bushfire/downloads/1000003.pdf
Mitchell, T. (1848). Journal of an expedition into the interior of tropical Australia, in search of a route from Sydney to the Gulf of Carpentaria. London: Longman, Brown, Green and Longmans.
Moore, D. R. (1979). Islanders and Aborigines at Cape York: An ethnographic reconstruction based on the 1848-1850 ‘Rattlesnake’ Journals of O. W. Brierly and information he obtained from Barbara Thompson. Canberra: The Australian Institute of Aboriginal Studies.
Raison, R. J. (1980). A review of the role of fire in nutrient cycling in Australian native forests, and of methodology for studying the fire-nutrient interaction. Australian Journal of Ecology, 5, 15-21.
Torres Strait Regional Authority. (2016). Land and sea management strategy for Torres Strait 2016-2036. Land and Sea Management Unit, Torres Strait Regional Authority.
Tulau, M. J., & McInnes-Clarke, S. (2015). Fire and soils: A review of the potential impacts of different fire regimes on soil erosion and sedimentation, nutrient and carbon cycling, and impacts on water quantity and quality. Sydney, NSW: Office of Environment and Heritage, State of New South Wales.
United States Environmental Protection Agency. (2018). Overview of Greenhouse Gases. Retrieved from https://www.epa.gov/ghgemissions/overview-greenhouse-gases