Planting boom hangover on its way: get more trees in the ground, starting now

In the latest episode in Hot Topic’s election coverage, forestry consultant Piers Maclaren looks at a forestry issue that seems to be missed by all the major parties.

New Zealand faces a major carbon problem in the period from 2023-2038, resulting from the imbalanced age-class structure of our plantation forest estate. Let me explain.

Forestry is a cheap and easy way to sequester carbon, but it is not a total global solution because at best it could possibly offset some 10% of the carbon the planet is likely to emit over the next 100 years from the burning of coal. Afforestation is merely the converse of deforestation, which has been responsible for something like 20% of the increase in atmospheric carbon dioxide since the industrial revolution. Afforestation can help reverse some of that portion.

Afforestation takes a landscape of low carbon density (for example, pasture or short scrub) and changes it to one of high carbon density – a forest. If the forest consists of an even balance of trees of all ages, then it will be in a steady-state situation — neither a carbon sink nor a carbon source, but
carbon neutral — and will remain in that state in perpetuity. The act of establishing a forest therefore constitutes a sink, but the maintenance of a forest is carbon neutral. This applies to all types of forest, and it is irrelevant whether the trees are felled with a chainsaw or by storm damage; whether the trees are removed from the forest, converted to some product and ultimately oxidised, or whether the biomass decays within the forest; or whether the trees are removed in clusters, or are widely spaced individuals. The point is that the removal of some component of the forest — for example a harvestable block of trees within the estate — is exactly counterbalanced
by the growth of all the other blocks.

New Zealand’s problem is that we had a massive planting boom in the 1990s followed by very little planting in subsequent years. The National Party’s “Environment and Climate Change” statement [PDF] quite brazenly states in their very first “key fact” that “more trees have been planted” but this is put in perspective by their graph on page 4 that net tree planting is still negative, though admittedly less negative than in previous years. But Steve Wakelin from Scion has calculated that we would need to plant about 50,000 hectares of new land every year, starting in the winter of 2012, to avoid our forest estate becoming a massive carbon source in the period 2023-2038. Why will it become a source? Because this is the logical result of a harvesting boom following one standard rotation after the planting boom of the 1990s.

To put this in perspective, if a miracle occurred and New Zealand totally stopped burning coal or oil by 2023, and destroyed all its livestock, this country as a whole would still be a carbon deficit situation for 15 years. Our forests would pump out up to eighteen million tonnes of CO2-equivalent per year for some of those years. We will curse our forest “sinks”!

What can we say? All parties have been advised of this problem for more than two decades now, and have done nothing about it. A consistent government-led policy of continuing afforestation would have totally avoided the problem and, indeed, been of considerable carbon and other benefit. How sustainable would that have been? New Zealand has up to 5 million hectares of marginal, steep, erosion-prone or weed-infested country that should never have been cleared of trees in the first place. It yields nothing, and has never yielded anything, to our economy. At 50,000 ha/yr of afforestation (a figure that was achieved throughout the 1990s) this would equate to a hundred years of afforestation. After then? We would no long have any plantable land remaining, but if the world hasn’t discovered alternatives to fossil fuels by then we are all in deep trouble anyway.

The most important climate-relevant policy that relates to forestry is to get more trees in the ground, starting now. Don’t crow about trivial plantings, we need to repeat the massive planting boom of the 1990s but this time keep it up year upon year.

2 thoughts on “Planting boom hangover on its way: get more trees in the ground, starting now”

  1. The problem with government is that when talking trees they can only think in terms of the forestry industry where the trees are cropped after twenty years and the carbon released again. We need a program which encourages land owners to plant native trees for the good of the land by stopping soil erosion and cleaning waterways. Planting trees on poor quality farm land and around rivers is good farming practise but it needs government leadership.

  2. PIERS : I agree, there’s numbers of reasons for “GETTING PLANTS IN THE GROUND, i.e. Carbon derived from green SHOOTs, …. I agree with your description of a transition of C / photosynthetic inputs / energy SOURCES from small to tall plant biomes, or from pasture to shrubs or brush, … to forests
    What role do you think of for C SINKS in plant roots, rhizospheres, & soil micro biota. ???
    What of potential C sequestration effects in mature trees from root morphology transplanting effects. Bare-rooted seedlings are customarily undercut before wrenching. As a plant biologist I understand that undercutting of deep plant roots may possibly be linked to restricting the life span of resulting mature trees, i.e. as a result of restricted root depth / plant anchoring ability resulting from what foresters may call ‘root plates”. i.e. we could extend 20-30/35 year old lifespan of exotic plantation plants, by transplanting seedlings with uncut roots
    We need to get our heads around CARBON CYCLING, including a diversity of labile and resilient SOIL CARBON, plant, fungal, humus, bacteria, soil structure & “soil-biological fertility”

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