Weeding out the risks of carbon offset programs

A study into the potential risks of carbon offset programs has identified invasive high-biomass weeds, such as gamba grass, as a possible threat and deterrent for landholders wishing to get involved in such programs.

Lead author Dr Vanessa Adams noted that Australia’s savannahs cover 25% of the continent and experience severe late-season fires which account for 3% of our annual greenhouse gas emissions. Relating this to programs like the Carbon Farming Initiative, she said, “If a farmer sells carbon offsets for trees he’s planted and a fire takes out those trees, he might be liable to pay back those lost offsets.”

A new offset program called savannah burning has been set up to combat this threat; burning savannah early in the season to reduce the total amount of land burned and emissions released. “But when native savannahs are invaded by weeds such as gamba grass,” said Dr Adams, “fuel loads are dramatically increased and fires can burn up to five times hotter than a native wildfire.”

For this reason, said Dr Adams, “any land that is invaded by a grass like gamba grass has to be excluded from savannah burning, so that’s lost income.” But the risk of an uncontrolled fire will still be very much present, and “a fire coming off a gamba grass patch might be very intense and spread onto neighbouring land … [resulting] in additional fire and therefore additional emissions.”

The researchers found that of the land that’s eligible for savannah burning in northern Australia, 75% is highly suitable for gamba grass. They also found that the cost of controlling gamba grass in one hectare of land is $40 a year - whereas the maximum revenue a landholder could gain from savannah burning in one hectare is $1.92 a year.

“This means that a landholder controlling one hectare of gamba grass would need to enrol an additional 290 hectares of land into savannah burning just to recuperate the cost of that management activity,” noted Dr Adams.

The study did have some good news though. It found that 75% of properties are currently not invaded by gamba grass; that in the Northern Territory, only about 20% of properties that could run profitable savannah burning programs had gamba grass; and 16% of these had small infestations.

“A one-off investment of $200,000 would eradicate these infestations and, for the majority of properties that are gamba free, an effective control program would safeguard them into the future,” said Dr Adams, suggesting that such an investment could come from the government. And eradication would mean that those landholders could viably participate in savannah burning and generate an income.

“If we want landholders to participate in these programs, we need to be giving them the same advice and support and insurance against risks that we would for any other farming industry,” said Dr Adams.

The study has been published in Environmental Research Letters.

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