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Trees may be a better bet than soil for carbon reduction on the land. NFGMan/Flickr

Are farmers the future of carbon management?

Both the current Government and Opposition are relying on agriculture and forestry to bear much of the burden of Australia’s emission reduction. But are they building their hopes on sand?

The way we manage the land can reduce emissions from existing carbon stocks and other greenhouse gases, increase carbon stocks in soils and vegetation or replace fossil fuel emissions by burning biomass or by replacing energy intensive materials with timber.

The land sector enabled Australia to meet its recent Kyoto Protocol emission target despite significant underlying growth in greenhouse emissions from other economic sectors. This was achieved by reducing land clearing and by large-scale reforestation of farmland through Managed Investment Schemes. However, land clearing is likely to recommence in Queensland, and possibly one-third of the investment scheme plantations will be converted back to farmland.

Reducing emissions

Greenhouse gases are emitted from deforestation, ruminant animals and from nitrogen escaping the soil. The main gases are carbon dioxide, methane and nitrous oxide; the latter two being more potent greenhouse gases than carbon dioxide. Total emissions are commonly described as carbon dioxide equivalents (CO2-e). In 2012, agricultural emissions of methane and nitrous oxide represented 16% of Australia’s emissions, and deforestation resulted in another 9%.

The first step is to tackle these sources. While reducing emissions from agricultural activities has had limited success, large reductions from land clearing have been achieved.

In the 1980s, Australia was clearing around one million hectares of land each year. This has since been significantly reduced. In 1990, clearing was estimated to produce 132 Mt CO2-e/year; reducing to 50 Mt CO2-e/yr by 2012. Interestingly, the largest emissions reductions have come from regulation, rather than a market-based approach.

Reducing clearing allowed Australia to meet its target in the Kyoto Protocol. Although some have considered this an accounting trick, it can be argued that reducing land clearing has also been a good thing in terms of conserving biodiversity. This is the thinking behind schemes (such as REDD+) that tie forest preservation to emission reduction outcomes.

Not everyone is happy with this approach - agricultural land-use is often more profitable than retaining forests. Much of Australia’s reduction in land clearing occurred in Queensland, where the government recently relaxed these restrictions. Emissions from renewed clearing will make meeting future emissions targets more difficult.

Increasing carbon stocks

The second approach to carbon mitigation is to change land-use and increase the carbon stored in soil and vegetation. This can include changing agricultural practices such as tillage or grazing. Small additional increments of soil carbon will be stored over large areas, providing a large total carbon store. Although recent results are not promising, collaborative work between Murdoch and Adelaide Universities has shown that clay additions to sandy soils can double soil carbon stores.

Another approach is to plant new forests. These can be plantation timbers, rebuilding woodlands or trees integrated with agriculture, opening up possibilities for restoration of biodiversity and protection of land and water. Australia has major conservation problems – including wind and water erosion and salinity - and a major problem has been matching the scale of need with the funds available for treatment. For large areas there has been no prospect of land treatment because of the cost. Emerging carbon markets have offered some prospects for change.

Like many policies, this could be a two-edged sword. Managed poorly there could be displacement of food production and competition for water resources. A future challenge will be providing food and water for an increasing global population, which is also increasing its per capita consumption.

Is land management the answer?

The land sector has significantly contributed to Australia’s mitigation in the past, but it will become harder. The clearing of bushland and investment plantations will see to that. The hope that soil carbon will make a major contribution appears to be diminishing, and destocking rangelands has had mixed results.

What are the most promising approaches using the land sector? Immediate approaches include preserving carbon in existing forests, and storing more carbon by planting new forests. These can also deliver a range of environmental and water management benefits, although at some stage these will have to be paid for.

Managing agricultural emissions and increasing soil carbon stocks may have potential, but more long-term experimentation is needed. Several activities are possibly not worth pursuing – such as those involving rangelands and managing existing forests – with the risks of emissions likely greater than any benefits.

In any case, using the land should be part of a portfolio approach, rather than considering it a silver bullet that obviates other responses.

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