Trees are currently the only mainstream solution for landholders hoping to offset the costs of their emissions under an emissions trading scheme - but this raises another set of challenges.
Massive tree plantings raise a completely new set of problems—not least a "trees-or-food" issue in a world already grappling with food shortages.
Soil carbon has now gained prominence as the other major alternative for carbon sequestration, but the research community and bureaucracies are only now belatedly preparing for serious investigation of its possibilities.
As a result of this delay, Australian farmers will have to wait for the Kyoto II round of talks in 2012 to argue a place for their soil carbon in international emissions trading.
Trees, on the other hand, are already a known quantity.
They are visible, sequester known quantities of carbon, can be assessed on a broad scale, and are acceptable under the (current) Kyoto rules.
But to make a dent in agriculture's emissions bill, extraordinary numbers of trees will have to be planted.
As a rough rule of thumb, hybrid eucalypts growing in a high rainfall zone (higher than 600 mm per year) can sequester 25-30 tonnes a hectare a year of CO2 equivalents.
A cow on pasture produces 1.5-2 tonnes/year of CO2 equivalent, indicating that a hectare of high-rainfall eucalypts offsets the annual belches of 15-20 cows.
An Australian Farm Institute (AFI) paper observed that if an extra 1pc of Australian farmland was sown to trees, it could result in 500–1,000 million tonnes of carbon being sequestered over the 100 years they would need to be in the ground.
That century's worth of sequestration is roughly equivalent to one-fifth to a third of the agricultural sector's greenhouse gas emissions in one year.
Beverley Henry, manager of Meat & Livestock Australia's Environment, Sustainability & Climate Change division, said planting trees to offset emissions, however, raised serious questions about conflicting demands on land use.
"You're looking at tying land up under trees for 100 years, but it's difficult to look 100 years in advance and know in advance what our food requirements will be, or what pressures there will be for more agricultural land," Dr Henry said.
There are other issues with mass tree plantings. CSIRO research has found a 55pc decrease in water flows under forest compared to that under grassland—a substantial issue for already water-stressed catchments.
The AFI has also noted that large-scale emissions-driven forestry could increase bushfire risks—already forecast to increase under climate change—and increase pest and feral animal problems for surrounding farmland.
SOURCE: Science and environment news from Rural Press weekly farm newspapers, updated daily on FarmOnline.
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