think climate. think change.
Department of Climate Change
Prepared for the Australian Greenhouse Office and Environment Australia by CSIRO Forestry and Forest Products, September 2003
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Use of fossil fuels is the main cause of the increase in atmospheric CO2, which in turn is a major cause of global warming. Sustainable firewood production systems have the potential to reduce fossil fuel use and attendant CO2 emissions. Within a specified period of time, the net greenhouse gas (GHG) benefit of burning firewood to displace other forms of energy depends on:
(i) growth rate of the forest;
(ii) management system used;
(iii) quantity of fossil fuel required for processes such as establishment and harvesting of trees, and transporting the firewood to households, and;
(iv) efficiency with which the firewood is burnt.
The aim of this project was to use the AGO’s FullCAM model to explore the effects of these factors on net CO2 emissions from the following example firewood production systems within the 600–800 mm annual rainfall zone of eastern Australia:
(i) remnant woodland near Armidale, New South Wales that was dominated by Eucalyptus melliodora (yellow box) where periodic (i.e. every 5 years) collection of dead wood from the ground was contrasted to annual collection of both dead wood and dead trees;
(ii) sustainably managed native forest near Armidale, New South Wales that was dominated by Eucalyptus laevopinea (silvertop stringybark), where collection of harvest residues for firewood together with periodic (i.e. every 5 years) collection of dead wood from the ground was contrasted with collection of both harvest residues and the annual collection of dead wood and dead trees, and;
(iii) a new plantation of Eucalyptus cladocalyx (sugar gum) established on ex-farmland (i.e. afforestation) near Lismore in Victoria, where the use of thinnings and harvest residues (from a system managed primarily for sawlogs) was compared with a plantation grown using a coppice system solely for firewood production.
Comparisons of CO2 emissions were made both within and between these systems. It was beyond the scope of this study to assess the effect of these ecosystems and their management on net emissions from other greenhouse gases, and on other environmental attributes such as biodiversity and land management for remediation of water quality and soil salinity and acidification.
The FullCAM model was used to calculate CO2 emissions resulting from tree growth and decomposition of debris and products. In addition, emissions associated with establishment of trees and the harvest and transport of firewood were calculated. Transport distances ranging from 50 to 800 km were examined. As expected, emissions were reduced by commercial rather than small scale harvesting, and by short rather than long transporting distances.
Net emissions were calculated by adding together the net change in storage of carbon as a result of establishment of trees, changes in tree biomass, debris and harvested products, and emissions resulting from harvest and transport operations. Net emissions may be positive if less carbon is sequestered in biomass than is lost to decomposition and operations such as establishment, harvest and transport, but negative if more carbon is sequestered than lost. We calculated that when firewood was used for domestic heating, the net amount of greenhouse gas emitted per unit of heat energy produced was:
(i) 0.11 kg CO2 kWhr-1 when firewood was periodically collected from dead wood on the ground under woodlands;
(ii) 0.07 kg CO2 kWhr-1 when firewood was collected annually from both dead trees and dead wood on the ground under woodlands;
(iii) 0.03 kg CO2 kWhr-1 when firewood was collected from harvest residues and from the annual collection of both dead trees and dead wood on the ground under native forests;
It should be noted that given the many assumptions made when simulating these case studies, these results are only semi-quantitative, and as such simply provide a comparison of contrasting ecosystems and management options. However, these results do indicate that in terms of limiting net greenhouse gas emissions, firewood is generally more favourable for domestic heating than other sources of domestic heating such as gas and electricity (which generally produce at least 0.31 kg CO2 kWhr-1, excluding solar-, wind- or hydro- electricity), particularly when firewood was collected from the thinnings, slash and other residues of a commercially grown plantation.
However, sensitivity analysis indicated that it was quite possible that using firewood from woodlands could actually be less favourable than some other forms of domestic heating if growth rates were somewhat lower than assumed (i.e. by 30%), or if mortality of trees was slightly higher than assumed (i.e. 1.2% per year), or if the firewood was burnt in an open fireplace (with an efficiency of only 10%). Therefore it may not always be beneficial to utilise woodlands for firewood collection, particularly those woodlands that are valuable in terms of maintaining biodiversity.
In contrast, there is generally little CO2 produced per unit of energy from burning firewood collected from harvest residues and other material from beneath a native forest, while there is actually a net sequestration of carbon per unit of energy produced from burning firewood collected from a coppiced plantation. However, collecting firewood from the thinnings, harvest residues and other material from beneath a plantation grown for sawlog production provided the greatest benefits in terms of carbon sequestered per unit of energy produced.
