Friday, March 29, 2024

GHG study a ‘snapshot analysis’

Neal Wallace
A study concluding most NZ sheep and beef farms are carbon neutral is a snapshot in time and does not mean a farm’s greenhouse gas inventory will not change.
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Climate change experts have welcomed the independently prepared report for Beef + Lamb NZ ( B+LNZ) which found sheep and beef farms are close to carbon neutral, with farms offsetting between 63% and 118% of their emissions.

The midpoint is 90%.

NZ Agricultural Greenhouse Gas Research Centre (NZAGRC) director Harry Clark praised the report, describing it as rigorous, but tempering his enthusiasm by noting it only provides a static snapshot of a farm’s greenhouse gas inventory.

Sequestration rates will change over time, such as when exotic trees are harvested.

“The issue with all carbon sequestering is you have to look at carbon sequestration over time,” he said.

“You can have a high sequestering rate at one point in time but over time as vegetation matures, sequestering goes to zero.

“Net zero may apply today but does it apply in the future?”

Report author Bradley Case from the Auckland University of Technology’s ecology department agreed.

“We did not consider sequestration rates through time and how they might change overall,” he said.

“It is indeed a static snapshot analysis.

“The idea here is that it’s a picture of where things stand at the moment, spatially, across the sector.”

Managing the cycle of exotics for example, will change a farm’s net emissions.

“The story can change quite a bit in any given year, depending on what gets harvested and replanted,” Case said.

Exotic plantations account for about 17% of vegetative area on sheep and beef farms but contribute up to 50% of a farm’s carbon sequestration.

“What happens to them in the future is quite important, and we need to consider this and what the impact on the net carbon balance may be as these get harvested and also in terms of when they get harvested,” he said.

B+LNZ’s environmental policy manager Dylan Muggeridge says the next step is to develop technology and a system so individual farmers can calculate and manage their greenhouse gas emissions and sequestration.

Clark says because they grow rapidly, exotic trees sequester carbon at 22 to 31 tonnes/ha/year compared to slower growing natives at three to six tonnes/ha/year.

Carbon is released once an exotic plantation is harvested and to balance that the harvested block has to be replanted and another block of trees grown to compensate for the released carbon and to continue sequestration.

Clark welcomed the B+LNZ study as the first significant attempt to quantify the carbon status of sheep and beef farms.

Victoria University weather and climate researcher Professor James Renwick has not studied the report, but says regular farm monitoring was needed to account for vegetation changes such as tree harvesting.

He says the report shows NZ potentially has more carbon sinks than has been acknowledged, but he is uncertain as to what that will mean to the country’s carbon inventory.

Muggeridge says the report’s findings do not automatically mean farmers will have carbon credits to trade as legal issues remain such as the definition of qualifying vegetation as well as how to measure emissions and sequestration.

“There is a lot of sequestering happening with vegetation on-farm and vegetation that does not meet the definition under the Emissions Trading Scheme,” he said.

According to the report, sheep and beef farms have 1.52m ha of native bush and woody vegetation and 0.48mha of exotic vegetation.

Muggeridge says the study addresses several issues facing farming: emissions and sequestration, which is potentially a game changer for the sector’s greenhouse gas inventory, a boost for biodiversity and an opportunity to underpin the marketing of carbon-neutral NZ meat.

“This is not only about the sequestration value from vegetation but also contribution to managing biodiversity and similar aspects available on-farm,” he said.

The study also honours the sector’s obligation to He Waka Eke Noa, the agreement between industry and government to address on-farm greenhouse gas emissions.

“I certainly think this is significant in terms of how we think the contribution from sheep and beef farmers makes towards climate change and carbon sequestering on their farms,” he said.

The carbon that is being sequestered by woody vegetation is not currently acknowledged by international agreements as carbon sinks, which Muggeridge is an issue that needs to be addressed at an inter-government level.

Muggeridge says as the study’s release coincided with the election, government feedback has been limited.

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