Monday, July 08, 2019

The wrong kind of trees?

The government's billion trees program is the sort of policy which could make a real difference to our emissions and the fight against climate change. But climate scientist Jim Salinger isn't convinced:

The Forestry Minister Shane Jones' one billion trees won't reduce carbon emissions, as too few natives are being planted, climate scientist Jim Salinger says.


Forestry New Zealand figures show in the first year, of the 91m trees planted, only 12 percent were native.

The figures are estimates based on the sale and distribution of exotic and native tree seedlings.

Dr Salinger said that ideally 90 percent of the trees planted would be native species as they store more carbon.

"The ratio of storage to carbon between natural forests and plantations like pine trees is 40:1 - so there's a huge difference. The reason being is with plantation forests, if you're going to grow radiata pine, they'll capture carbon for the first cropping cycle but then it gets harvested and it ends up as pulp and paper and ends up back in the atmosphere.

"So I'm afraid Shane Jones' idea of planting a billion trees, well, it might be good for three decades but then the carbon gets back into the atmosphere."

Of course, that assumes that the trees will be cut down. And I'm not sure we can actually assume that. Firstly, because carbon prices are rising, so in thirty years time it might not actually be economic to cut the trees down, in that the cost of carbon would exceed the value of the wood. This only requires carbon costs to triple or quadruple, and people expect that to happen within a decade if the price cap is removed. And secondly, because as the crisis bites, policy is inevitably going to change, so people who plant trees today may find themselves legally forbidden from cutting them down in future.

But there's a real question on which sorts of trees we should be planting. The government wants two-thirds of them to be natives (and is boosting the native seedling industry to cope with the demand), and this has tremendous environmental co-benefits - basicly we'd be beginning to return part of the country to the state it was in before farmers slashed and burned it all to make way for their sheep and cows. But native trees also soak up carbon more slowly than fast-growing exotics, so the quickest way to draw down carbon is to plant pine, or (worse) eucalyptus - which doesn't provide the environmental co-benefits. They're having a similar debate in Ireland, where the government wants to plant trees, but its all spruce rather than native oak.

And on the gripping hand: we no longer have a long-term, so short-term carbon absorption is all that matters. And TBH, at this stage, I think its a case of plant anything, anything at all that soaks up carbon, just get it in the ground and convert land back to forest as quickly as possible. Native trees are nice, but any tree is better than none.