Nola Marino (Forrest, Liberal Party) Share this | Hansard source

The greatest practical carbon sink available to the world right now is that of biosequestration, which is in the world's soils and plants. It is currently the only effective offset. We have spent a great deal of time and money on the alternative, geosequestration; however, the ability to store carbon dioxide deep underground as a liquid or in solution remains commercially unviable. Whilst the optimists continue to pursue it, something I support, there is no guarantee that geosequestration will become an economically viable option

We do know, however, that biosequestration is both practical and viable. Not only that, we have been practising it for generations. We may have called it revegetation, or perhaps agroforestry or plantation farming. We have done it to prevent erosion, to reduce salinity, to improve production, to protect the environment and to retain native species. Governments have done it, farmers have done it, community and environmental groups have done it and lots of private individuals have done it and are doing it. The fact that we can do it is not actually in question. The questions are: how do we increase it; how do we measure it; and how do we make it viable for landholders to engage in?

There are two forms of biosequestration covered in this bill. The first is plant carbon. Sequestering carbon into vegetation such as trees is the easiest to do and certainly the easiest to measure. We know how to plant trees and we know approximately how much carbon is stored in each tonne of wood that grows or in each hectare of plantation. It will range from three tonnes of CO2 equivalent per hectare depending on tree and soil types and the rainfall. The age of trees also matters. A young tree sequesters far more carbon than an older one.

In the south-west of Western Australia the iconic jarrah trees live up to 450 years. Studies of jarrah, karri and other eucalypts across Australia have shown that eucalypt trees rarely exceed 400 years in age. Most of their carbon storage happens in the first 150 years, peaking in years 10 to 30. From 150 to 300 years carbon storage in jarrah trees actually flatlines. In their last 150 years they often contribute more carbon back into the atmosphere than they absorb.

The requirements of the Kyoto agreement restrict measurable carbon to plantings after 1990 on land that was cleared before 1990 and the requirement to leave trees in place for 100 years needs to be considered in this context. One hundred years may be appropriate for many tree species like jarrah but may well be inappropriate for faster growing, shorter lived trees. Those species that only live on average 100 years may only be effective in storing carbon for the first 50 and emitting carbon after 80. If those trees were to be harvested and their carbon stored for the longer term, for example as structural timber, and the area replanted with trees, the amount of carbon stored would be maximised. I note that the CSIRO recently commented as follows:

To achieve the full benefits of carbon storage, carbon forests need to be managed according to natural cycles of death and decay, including the periodic impact of fire. The long term aim might be to manage forests of a range of ages.

Tree planting should not be considered in isolation from other environmental issues. Reforestation of cleared land uses a lot of water and frequently drives water tables down. Whilst this is a good thing, in fact the desired outcome of planting can be to reduce the impacts of salinity, it may have detrimental effects on farming and native forest nearby if it pushes fresh groundwater deeper and out of the reach of drought sensitive species.

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