More than 600,000 tonnes of carbon were lost to the atmosphere in recent fires at two of New Zealand’s most important wetlands, highlighting the importance of keeping wetlands wet, a new study finds.
If these losses had to be paid for, the estimated cost would be about $32 million based on current carbon markets.
The Department of Conservation, working with scientists at Manaaki Whenua Landcare Research (MWLR), in a statement this week said it had published a report on carbon emissions from the 2022 fires in the Kaimaumau-Motutangi wetland in Northland and the Awarua wetland in Southland.
At the Awarua fire’s peak, several ground crews from Canterbury, Otago and Southland fought the blaze, while up to nine helicopters attacked the fire from the air.
But high winds later grounded the helicopters, delaying the fire being brought under control from the air.
Both wetlands are "peatlands" which have an incredible ability to store carbon in peat, built up over tens of thousands of years.
In Kaimaumau the burnt area was more than 2900ha, while at Awarua it was 980ha.
Both fires were caused by humans.
Natural peatland fires occurred in New Zealand before humans arrived but the increased frequency due to human activities was concerning, the statement said.
Doc freshwater scientist Hugh Robertson said calculating carbon loss really brought home the impact of wetland fires on New Zealand’s stores of carbon.
"Carbon emissions from the 2022 fires were large, estimated at more than 515,000 tonnes of carbon dioxide emissions from Kaimaumau and more than 104,000 tonnes from Awarua.
"All of that carbon was released into the atmosphere."
MWLR scientist Jack Pronger said the loss of carbon due to the two fires represented about 5% of New Zealand’s annual target for the 2026-2030 emissions reduction period.
"Year-on-year vegetation growth in peatlands removes carbon dioxide from the atmosphere and stores it as peat soil," Mr Robertson said.
"Fire stops this process by releasing carbon back into the air, which then contributes to greenhouse gas emissions."
Peat soils were highly flammable, particularly when they were dried out.
"If we reduce drainage and protect our wetlands, we’re supporting an important nature-based solution to climate change.
"Re-wetting our wetlands will make them less likely to burn and will reduce greenhouse gas emissions."
"Recovery and restoration of the Kaimaumau and Awarua wetlands will require extensive weed control, as the bare, burnt ground allows exotic plants to establish."
Wetlands were not currently included in New Zealand’s emissions trading scheme, or carbon accounting, but the research highlighted the significant potential of wetlands to contribute to New Zealand’s response to climate change.
The research was the first detailed study on peatland fire carbon emissions completed in New Zealand.
There was a degree of uncertainty in the carbon loss estimates and it was probably higher than calculated.
