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It’s a billion-dollar question: could a massive possum-eradication programme boost native forests and fight global warming?
As well as increasing native bird, lizard and insect populations, pest control programmes could be having another positive effect: allowing trees to grow more quickly and absorb more greenhouse gas.
Charity Zip – which has eradicated introduced predators such as possums, stoats and rats in large areas of the South Island – will measure the carbon dioxide sucked in by trees in pest-free and unmanaged areas, which effectively cools the planet.
It hopes to convince the Government to spend billions on pest control at home rather than giving the cash to other countries to reduce emissions on its behalf.
Zip has paired up with scientists from Niwa, Scion and government ministries – and received $250,000 in funding from Crown-owned Predator Free 2050.
The charity’s work eliminating possums, stoats and rats on the West Coast means it can take advantage of innovative technology to measure carbon absorption.
The coastal South Ōkārito site, near Franz Josef, has no polluting factories nearby and is exposed to fresh air coming off the Tasman Sea, said Niwa scientist Gordon Brailsford.
When it’s moving west to east, the air will be monitored to see how much carbon dioxide is being absorbed by the trees.
A forest with unrestrained numbers of possums, rats and stoats will tell the scientists how much carbon this type of landscape absorbs.
That will be compared to Zip’s pest-controlled bush nearby. The team hope to find that predator-free forest absorbs significantly more greenhouse gas.
Beginning in 2021, Zip dropped non-toxic pellets as lures followed by 1080 pellets to target the introduced mammals in the 20,000-hectare Ōkārito site. Traps were placed to eliminate the remaining possums, stoats and rats, said Zip development director Tom Agnew.
Thermal imaging cameras detect pest species and alert the team. Waterways are tested for the presence of pest DNA to see if a stray animal has slipped through the net.
Each area of bush will have two air-monitoring stations. One right on the coastline will test how much carbon dioxide is in the fresh air coming from the Tasman Sea.
The second, inland station will track how much carbon dioxide remains once the air passes over the forest.
It will also track the type of gas that’s leftover. Trees prefer to absorb, essentially, the lightest form of carbon dioxide, Brailsford said. Therefore, if the lightest carbon is typically being captured between the coast and the outer edge of the forest, the scientists will be even more confident the trees are responsible.
Liz Carlson/Stuff
The picturesque forest around Ōkārito will be host to a unique study on the benefits of pest control.
This is a new way to track carbon absorption. But the project will also use more traditional methods: scientists will survey the growth of wood in sample plots and use aerial scans to track the amount of vegetation.
Selected trees will be fitted with special sensors to measure trunk growth. Wood is stored carbon. The more wood the forest holds, the more greenhouse gas it has absorbed.
Other forest features, including soil and peat, can also absorb carbon, Brailsford said – so the air measurements should capture this effect as well.
SUPPLIED
A curious kia stays safe during field trials of new AI-enabled pest control tools from research and development company Critter Solutions. This clip was Filmed at the Auckland Zoo.
The project will run for two years, but the air-monitoring stations will send data every hour to scientists.
Since pest-controlled forest is only expected to absorb a tiny amount of extra carbon, the project could require years of measurements to observe an effect, Brailsford said. “You’re not going to get good data every day. You’ve got to wait for the condition where the air blows from the coast to the inland site.”
Agnew expects the managed bush to outperform the comparison area. “Possums are prolific browsers of native and exotic vegetation. We look to a place like the Ruahines, places that don’t have a history of predator work, and you can see the forest is in pretty dire straits.”
The exact different between the two forests could convince the Government to ramp up its investment in pest control.
That’s because it has promised to halve national emissions (albeit in a controversial apples-to-oranges comparison) by 2030. Action at home is projected to make a minor contribution – so the Government is expected to buy the equivalent of between 88 and 114 million carbon offsets. Treasury estimated the bill could cost anywhere from $3.3 to $23.7 billion.
But if predator control is shown to be a cost-effective way to absorb extra carbon dioxide, the Government might invest some of that cash at home, Agnew said.
“If we can sequester approximately 50g of carbon per square meter [of forest] year-on-year, then this work would begin to pay for itself. We’re talking a pretty minimal uplift in forest health.”
Peter Meecham/Stuff
Zip’s Tom Agnew with the amount of wood that a forest would need to produce to fund pest control.
While Agnew describes the work as a feasibility study that will need to be replicated, Brailsford said the science will be robust. The aim is to publish a paper in a scientific journal.
Predator Free 2050 science director Dan Tompkins said pest control offered many benefits – any climate gains would just be one. “We also get biodiversity benefits and support local communities and businesses… creating jobs in the regions.”
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