Farmers and small woodlot owners are missing out on thousands of dollars in carbon payments due to carbon estimation, or look-up tables, falling well short on trees’ actual carbon storage ability.
Forest owners with over 100ha use Field Measurement Assessment (FMA) data, an actual in-forest sampled measurement to assess carbon sequestration. But those with less than 100ha use the Ministry of Primary Industries’ (MPI) look-up tables that offer estimates of carbon storage by species.
MPI’s latest FMA data averaged across the country highlights the significant disparities between actual averages and the look-up tables.
For example, at year 28 Douglas fir averages 636 tonnes of carbon per hectare based on FMA data, compared to look-up tables’ estimate of 468t/ha, leaving foresters well short of what their carbon payments should be.
Common Pinus radiata averages only 700t/ha in the look-up tables, compared to averaged FMA data of 1041t/ha, a variance of almost 50%.
Recent work by Scion researcher Dr Michael Watt also highlights the contrast between how much redwood trees sequester, based on modelled multi-data sources compared to look-up tables.
“The look-up tables are too conservative in their estimates of redwoods’ sequestration. Our study found carbon to be at least twice as high as the values in the look-up tables for all North Island regions,” Watt said.
The look-up data for redwoods, cypress and some other exotic species is not regionalised to allow for the climatic differences that exist along New Zealand’s 1600km length.
For woodlot owners and farmers planting less than 100ha, the look-up tables’ data is central for estimating carbon sequestration, therefore cashflow values, and the value of putting the right tree in the right place.
Graham West, president of the NZ Farm Forestry Association, said there would be many small woodlot owners and farmers in NZ who are receiving significantly less than they should for their forestry planting efforts due to the discrepancy.
“The tables are incredibly conservative and for some species like exotic softwoods (including redwoods) they are miles out. It behoves government to get on and fix this.”
He said the association has made submissions to the government’s ETS review process to have the tables updated.
The Government’s climate emergency response fund released earlier this year includes an allocation of $30 million over four years to forestry to specifically include changes to the ETS look-up tables, to reflect carbon stock changes more accurately.
But West is concerned that the Government’s focus is mainly on understanding native tree carbon sequestration, when it is exotic softwoods that are going to do more of the early work in carbon capture, and will be more popular with farmers.
“Our data shows the tables are conservative for exotics, but overly optimistic for natives, and these are only based off mānuka and kānuka data.”
Native forest sequestration at year 28 is put at 242t/ha in the tables – but the FMA data puts it at only 178t/ha.
Further into the forest’s life, at year 50 the tables estimate stored carbon at 323t/ha in native stands, against the FMA data of only 239t/ha.
Euan Mason, professor of forestry at Canterbury University, said the tables’ disparities need to be addressed sooner rather than later and will require greater exactness than a simple average for the entire country.
“The idea there can be a table for any given species that applies across the country is ridiculous,” Mason said.
“The three factors influencing carbon sequestration that have to be considered are species, site quality, and management. You need to be able to account for all three in any evaluation of sequestered carbon ability,” said Mason.
In Canterbury, Mason’s own work has found a divergence of 60% between what pines actually sequester in carbon and what the look-up tables claim.
“There will be winners and losers if you use an average that does not allow for those variances,” he said.
“The risk is people will learn to game the system, choosing poorer land that can’t meet the average carbon storage, but being able to claim the average that is set out.”
In the meantime, those in better growing areas will not receive full payment for their above average sequestering forest’s ability.
Dave Janett of Forest Management Group said he was hopeful the Government will be upgrading the tables based on the flood of new forest assessment data now pouring in.
“The question will come, are we going to have a national average, or regional averages. This will have to be mulled over,” Janett said.
MPI acknowledged the “significant variation” within each species and forest type in the measured data, and how this variance was a major driver for government investment in the budget bid.
Officials pointed to the government-funded initiative in this year’s budget for research to link forest carbon storage to management actions and enable changes to ETS look-up tables to reflect carbon stock changes more accurately.