- In Australia, old-growth forest is defined as ecologically mature forest where the effects of disturbances are negligible. Old-growth forests contain trees which can be 120 years to as many as 1,000 years of age, depending on species and degree of forest disturbance.
- The loss of old growth forest has the duel, detrimental effect in regard to efforts to halt and reverse global warming. The capacity to extract greenhouse gas from the atmosphere is lost and vast quantities of carbon currently locked in forest are made available for release into the atmosphere.
- Under the Kyoto Protocol and subsequent climate change action agreements, old-growth forests have not been adequately protected by international laws or treaties.
- Governments, companies and non-government organisations have entered into a voluntary, UN action to halve de-forestation by 2020 and eliminate it by 2030. These undertakings were further ratified at the UN 2015 Paris Climate Conference.
Old-growth forest can be defined as mature forest where human disturbances are negligible. In terms of age, old-growth can broadly be defined as from 120 to as much as 500 years old with individual trees estimated to have reached 1,000 years old. Old-growth forest has an important role to play in efforts to halt and reverse climate change. It has the capacity to both remove atmospheric greenhouse gases and to permanently store these gases in the form of carbon. Even with an international, voluntary agreement to halve de-forestation by 2020, and eliminate it by 2030, old growth forest continues to be lost at an alarming rate. Protection of remaining forest and reforestation in areas where it has been lost is vital for global climate stability.
Definition of Old-growth Forests
The United Nations Food and Agriculture Organisation (FAO), defines primary or old-growth forests as ‘forests of native species, in which there are no clearly visible indications of human activity and ecological processes are not significantly disturbed’. The FAO also states that primary forests exist ‘where there has been no known significant human intervention or where the last significant human intervention was long enough ago’. In Australia the old-growth forest is defined as ‘ecologically mature forest where the effects of disturbances are negligible’. In terms of age, old-growth can broadly be defined as from 120 to as much as 500 years old with individual trees estimated to have reached 1,000 years old. In Australia, as a consequence of a high frequency of bushfires, eucalyptus trees rarely exceed 350 years of age. Some Tasmanian huon pines, however, are estimated to be up to 4000 years old.
Old-growth Forests in Australia
Australian old-growth forests are usually identified in stands larger than two or three hectares (see Figure 1.). Disturbances are often not well recorded and must be determined from forest structure, tracks, stumps, fire scars and other evidence of disturbance. On-ground inspection can be augmented by aerial photography and digital analysis. As a consequence, a relatively small area of Australia’s forests (mostly tall, wet forests in southern areas) has been assessed for old-growth value in accordance with the Regional Forest Agreements (RFA) Act (2002). To date, much Australia’s northern regions have not been extensively mapped and assessed though old-growth forest is known to occur in the tall eucalypt open forests and the tropical savannas north of the 20o latitude.
Figure 1: Regions of Australia with a completed RFA. Source: https://www.oren.org.au/campaign/politics/westrfadead.htm
Old-growth Forest Ecology
Old-growth forest is vitally important for its ecological biodiversity. It’s unique structure, size, maturity and varying canopy layers provide habitat for a wide range of organisms. A forest that has been undisturbed for hundreds of years will sustain the life cycles of organisms ranging from the microscopic to large birds, mammals and reptiles. Large forest trees die and fall, creating further niche habitats, while other organisms benefit from a usually deep litter layer and from ground cover grasses, mosses ad lichens. Of added biological and ecological benefit, is the forest’s capacity to retain moisture.
Old-growth forest is one of the few land features that produce topsoil instead of degrading or destroying it. Forests also have an important role in the water and air purification cycles.
Old-growth Forests, Carbon Sequestration and Carbon Sinks
In conjunction with their ecological and conservation value, old-growth forests can play a significant role in mitigating the causes of climate change. One of the principle atmospheric greenhouse gases (GHG) contributing to climatic warming is CO2. The process whereby CO2 is captured from the atmosphere and stored for indefinite or long periods of time is known as carbon sequestration. The places where the carbon is stored, for example oceans, soil and vegetation for example, are known as carbon sinks. Forest, and old growth forest in particular, are identified as important carbon sinks. Through photosynthesis, CO2 is absorbed by plants and processed into sugars and other chemical compounds from which the plant derives its nourishment. This process has the potential to take up some 30 per cent of atmospheric CO2 emissions. The sequestered carbon is contained in live woody tissue and organic matter in soil litter. When a plant dies, the absorbed carbon is locked in slowly decomposing soil organic matter; the older the growth, the greater the capacity for the carbon to remain in the soil.
Old-growth forest removes CO2 from the atmosphere at rates that vary with geography and climate. Research conducted in Australia determined that old-growth forests in southern Victoria, which contains trees in excess of 350 years old, store up to 1,900 tonnes of carbon per hectare. Forests in tropical regions, however, typically contain 200–500 tonnes per hectare. The variation is attributed to slower rates of organic matter decomposition in the temperate forest.
Until recently it was believed only young forests sequestered atmospheric carbon in early growth and that old-growth forests were only sinks in which the carbon was stored. Recent studies, however, have identified that intact old-growth forests continue to take up carbon from the atmosphere even past the point at which they reach maturity. By measuring growth rates, researchers have identified that carbon sequestration in trees increases continuously because the overall leaf area increases as they grow, enabling bigger trees to absorb more carbon from the atmosphere. Older, larger deciduous trees reproduce more new leaves, thus capturing the most carbon from the atmosphere.
Protection of Old-growth Forest
The Kyoto Protocol is an international treaty which extends the 1992 United Nations Framework Convention on Climate Change (UNFCCC) that commits signatory nations to reduce GHG emissions, based on the premise that global warming exists and man-made emissions have contributed to it. The Kyoto Protocol was adopted in Kyoto, Japan, on 11 December 1997 and entered into force on 16 February 2005. There are currently 192 parties to the Protocol.
The Kyoto Protocol intended to force the international community into action to set mandatory limits on GHG emissions. It does not include the protection of old-growth forests. This is due, in part, to the differing scientific judgements on the capacity of old-growth forests to sequester and store carbon. The scientific opinion in 1997 has been superseded by general scientific agreement that old-growth forests continue to take up and sequester carbon and may account for as much as 10 per cent of the global uptake of CO2. A UN Climate Summit recognised changing scientific opinion and, as a consequence, governments, companies and non-government organisations entered into a voluntary action to halve de-forestation by 2020 and eliminate it by 2030. These undertakings were further ratified at the UN 2015 Paris Climate Conference (COP21).
Loss of Old-growth Forests
Over 30 per cent of existing global forest area is unmanaged and, therefore, poorly protected. As stated above, these forests store vast amounts of carbon that would otherwise contribute to climate change. When old-growth forest is degraded or destroyed the carbon stored above and below ground in organic matter is released to the atmosphere as CO2. Current estimates suggest that globally, old-growth forests store nearly 300 billion tons of carbon in their living parts, or roughly 30 times the annual amount of emissions created by burning fossil fuels.
In stable systems forests naturally re-generate. Individual trees and plants will die naturally and be replaced by new plants that emerge from seed or root stock. Regeneration can be related to, or result from a weather event; wind or drought, fungus, disease, geological factors or wildfires.
The commercial (and at times illegal) practice of de-forestation is the most significant cause of the loss of old-growth forests. De-forestation is occurring extensively in South East Asian and in South American countries surrounding the Amazon Basin. In Indonesia, scientific measurement and analysis determined that between 2000 and 2012, over 6 million hectares of old-growth forest were lost to logging and cropping for palm oil. Furthermore, by 2012, clearing rates had reached the point of outpacing Brazil. Critically, nearly 40 per cent was cleared in areas that are supposed to be subject to restrictions on forest clearing, including 16 per cent in protected forests and preserves. In the islands in the Pacific, old-growth forests are being decimated for a handful of commodities, including palm oil, soya, paper and pulp. In Australia, Tasmania records show industrial-scale logging operations have resulted in the loss of as much as 10,000 hectares of tall-eucalypt old-growth forest since 1996.
While not as destructive as deforestation, selective logging in old-growth forests continues globally. The removal of usually bigger, older trees releases stored carbon into the atmosphere contributing to GHG emissions and removes the important carbon sequestration function.
Globally, records indicate that deforestation practices, convert some 90,000 km2 (or 0.2 per cent) of all old-growth forest to other uses; the amount of carbon released is equal to 17-25 per cent of annual global fossil fuel emissions. At the current rate of loss in the Amazon Basin, more than 30,000 teragrams (30 billion tonnes) of carbon could be released from deforestation by 2050.
While there is wide-scale logging of old-growth forests, efforts are being undertaken to re-establish forests in order to reduce GHG through carbon sequestration. In Chile under the UNFCCC, commencing in 1998, the Rio Condor Carbon Sequestration Project seeks to preserve 272,880 hectares of old-growth forest that would have been logged for conversion into younger, managed stands of trees to be used for timber; the aim is to avoiding CO2 emissions of approximately 15 million tonnes over a 60 year period.
An example of a project to re-establish forests currently underway in Western Australia is the Yarra Yarra Biodiversity Corridor Project. This long-term native reforestation project has the objective of removing 1.257 million tonnes of carbon from the atmosphere in a region where over 90 per cent of the old-growth woodland had been cleared for agriculture, but which no longer supports viable farming practices.
Figure 3: Logging in Indonesia. Source: econews.com.au
In landscapes where old-growth is limited or denuded through land clearing, maintaining existing areas is by far the best strategy to providing old-growth habitat, vital to carbon sequestration and storage. Conservation, management and restoration strategies need to be tailored to the particular type of old-growth consistent with the landscape and climate conditions. This is particularly true of long-lived old-growth types which are both relatively stable and which take long periods to develop (e.g. eucalypts forest in Australia).
Long-term strategies for old-growth conservation require the identification of areas that will provide future old-growth patches and landscapes which are protected from damage such as cutting or prescribed burning, over significant periods of time, in excess of centuries. The challenge is monumental in scale but the consequence of inaction could be globally devastating.
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