1BT: Native tree numbers unknown
Wednesday 16 Oct 2019
The Government’s tree planting agency, Te Uru Rakau, says it can’t estimate what proportion of the one billion trees programme will be native species, saying a previous figure it gave to Newsroom was meant to be purely "illustrative”.
The illustrative figure was used to calculate the estimated climate benefit from the tree scheme, which Te Uru Rakau has put at 384 million tonnes of carbon dioxide over the trees’ lifetimes.
The Government plans to foster planting of half a billion new trees over a decade, using a mixture of grants, education and co-funding forestry projects with other entities.
The one billion figure that gives the programme its catchy name was reached by counting another half a billion plantation pine trees in existing pine forests. These likely would have been replanted anyway by commercial foresters after harvesting, and these trees won’t receive any government assistance.
Te Uru Rakau has a goal of funding two-thirds of native trees, but the agency has clarified that this target applies to only a small proportion of the trees: an estimated 60 million that could be paid for by $120 million in grants to landowners, from money set aside from the Provincial Growth Fund.
If the two-thirds target is met, that means roughly 40 million of the trees planted with direct landowner grants will be native species - roughly 4 percent of the billion trees programme, or 8 percent of the half a billion genuinely new trees that will arise during the programme.
That's just one part of the mix. As for the overall proportions of new trees, the agency says that’s largely up to landowners who will choose what trees they want. It expects people to continue voluntarily planting natives with no subsidies, but the agency says it's impossible to forecast how many indigenous trees we will end up with.
Te Uru Rakau previously told Newsroom it had estimated the carbon sequestration benefits of the billion trees scheme (by assuming the total mix of species) would be 70 percent exotic and 30 percent indigenous, equating to 384 million tonnes of CO2 sequestered over the forests’ lifetimes.
The mix of native and exotic species is important for working out the carbon sequestration, because pine absorbs more carbon, by forestry scientists’ measurements.
That’s despite pine usually being harvested and replanted about every 27 years, which allows native forest to slowly catch up with the pine over more than a century. (These greenhouse estimates don’t count everything - for example, they exclude how much heat the forests absorb or reflect, and the carbon cost of harvesting machinery and trucking, something native forest advocates argue should be studied and factored in properly).
To work out how much carbon the scheme would sequester, the agency assumed the average carbon stock of pine was reached at age 21, while indigenous forests’ maximum storage is reached at maturity (after 200 or so years). Te Uru Rakau also assumed indigenous forest had twice as many trees per hectare. Despite that, it put pine’s average carbon sequestration at 650 tonnes per hectare compared to indigenous forests’ 257 tonnes.
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