Legislative Assembly for the ACT: 2009 Week 08 Hansard (Thursday, 25 June 2009) . . Page.. 2988 ..
proportion of trees in a semi-mature state, compared to its existing structure, which has a majority of mature to over-mature trees. The report indicates that there is maximum carbon potential in leaving the tree logs whole. However, other research demonstrates the benefits of having mulch to reduce water use and improve the soil. These elements need to be assessed together to maximise the benefits of the urban forest.
Actew, as part of its expansion of the Cotter Dam environmental impact statement process, also audited the effect of the expansion of the Cotter Dam inundation. However, the carbon emissions reported in the ANU and Actew reports do not correlate. Both the ANU and Actew reports use the fullCAM methodology. However, the fullCAM methodology still involves significant user-derived assumptions to be made. All the assumptions made by the ANU are not identified in the report and hence cannot be fully investigated without further discussion with the ANU authors, which Actew will be pursuing.
Assumptions that are listed in the ANU report that are different from those assumptions made by Actew, and may be the sources of the discrepancy, include growth rates of vegetation based on soil structure and fertility, fire severity and impacts, and the level of resolution used for vegetation identification in the inundation area.
The ANU report identifies that decomposition of inundated vegetation is poorly understood, and hence has adopted a worst-case scenario of total and immediate emission of carbon in its report. This is identified as a pessimistic scenario by the report’s authors. Actew considers this to be too conservative. Actew’s assumptions were based on the accounting of available carbon, not total carbon as per the ANU report. This means that, for example, large tree trunks were not accounted for, nor were large woody roots. This assumption holds throughout the ECD EIS in that large tree trunks are to be retained in the reservoir as fish habitat. It is not expected that breakdown, and hence carbon emission from this source, will occur to any significant extent. This assumption can be evidenced through the large, undecomposed vegetation—mature trees—which can still be seen in the reservoirs of the Snowy Mountains scheme, some 40 years after inundation of those reservoirs.
A carbon sequestration audit of vegetation biomass in the Australian Capital Territory is a unique report in Australia. It is the first attempt to audit the vegetation biomass and its carbon sequestration for an entire state or territory. The report strongly urges the establishment of permanent research plots to monitor ecological variables related to predictions of carbon stock, sequestration and the ongoing after-effects of the 2003 bushfires. Further research in this area will contribute to the government’s goal of zero net emissions. I commend the report to the Assembly.
Debate (on motion by Mr Rattenbury) adjourned to the next sitting.
ACT greenhouse gas abatement scheme—operation
Paper and statement by minister
MR CORBELL (Molonglo—Attorney-General, Minister for the Environment, Climate Change and Water, Minister for Energy and Minister for Police and