Trees could be a win-win situation

01-09-2010 | Denis Hocking

Recently I helped organise an evening debate on food versus forestry between Professor Jacqueline Rowarth, agricultural advocate extra­ordinaire from Massey, and Dr Wink Sutton, long-time arboreal philosopher and forestry and wood advocate. It was not really a debate, it was a discussion with much agreement about the need for both land uses. They don't compete, they complement.

Some of the arguments are exactly those that I used last month, arguing that there was a potential win/win/win situation available if there was a concerted effort to afforest the million hectares of most highly erodible land still in "pasture". The wins would be in soil conservation (helping protect some of our most valuable food-producing land), carbon sequestration and in many cases a more profitable land use than the existing pastoralism. This last aspect can be uncertain because while a significant portion of this land may be uneconomic for commercial forestry, it is also often losing money under pasture.

One of the key questions here is: Will a larger forestry/wood resource be an asset in future years? There are several reasons to be optimistic here.

As Wink Sutton has long pointed out, we use a lot more wood every day than we do food. The global average consumption is around 850g of wood per capita, versus 700g of wheat, maize, potatoes and sugar combined, much of which goes into animals before it gets to humans.

The wood is used in a variety of ways - structural timber, paper and packaging, fuel, etc, not all of which are equally profitable for growers, I might add. All these roles can be substituted with non-wood products, but wood has significant advantages. Most notable here are:

It has very low embodied energy. In other words, growing, harvesting, processing and installing wood in a building takes far less energy than producing and installing competing products such as steel, concrete or aluminium - see table 1.

When the carbon dioxide sequestered in wood products is compared with the carbon dioxide released from fossil fuel producing the item then wood products invariably wind up as net carbon stores. All other building materials, except perhaps straw, represent net carbon dioxide emissions - large quantities with steel and aluminium. In other words, wood in a building represents carbon dioxide removed from the atmosphere, all other materials represent carbon dioxide released.

[Figures from A. Alcorn, 2001, "Embodied Energy and CO2 Co-efficients for NZ Building Materials", Centre for Building Performance Research, Victoria University, Wellington.

Negative, red figures represent net carbon dioxide storage in the product. Note that most sawn timber today is "bio-dried" in kilns fuelled by wood waste].

As a source of energy, forests and woods are largely carbon neutral, provided the forests are replanted, because they are merely recycling atmospheric carbon dioxide, which explains the difference between the bio-dried snf gas-dried wood in the table. There may be (at present there will be) fossil fuel used in harvesting, but otherwise the carbon dioxide released was in the atmosphere 20-30 years ago and will be back in trees in a few years.

These properties are exactly what you would be looking for in an energy and carbon-constrained world, though we haven't really entered such a world yet, and are the reasons why forestry can do more to combat greenhouse gas emissions than just sequester carbon dioxide in plantations. We need to be harvesting and using most of this timber to get take full advantage. But don't expect competing materials to defer to wood graciously; rather I predict continuing obfuscation and of course oil and coal interests have been supporting the "climate change denial" business.

Wood and trees have other virtues: Trees will grow quite happily in soils too infertile to carry worthwhile pastures. If Olsen phosphate levels are the commonly quoted key indicator for likely pasture performance, it is worth noting that radiata pine and many eucalypts grow well at low Olsen Ps (well below 10). With their mycorrhizal associations they can mobilise and use bound phosphate not available to pasture species. On most sites trees require little, if any fertiliser, though sometimes trace elements such as boron are required. Some species are more fertility demanding but never at the levels required for pasture.

As one soil scientist put it - a tree crop needs no more fertiliser for a 30-year rotation than a forage crop needs for just one season. And, contrary to some belief, trees such as radiata pine don't ruin the soil. Converting forest soils to pasture does require large fertiliser inputs but only because pasture species are so much more demanding of nutrients than the trees that preceded them and which grew vigorously for years without any fertiliser. If you can't afford to apply phosphate or other fertiliser trees become an even more competitive option.

These low-nutrient requirements mean, of course, that streams and ground water coming out of planted forests have good water quality. As well, trees don't defecate in the waterways; they just drop needles and leaves.

Other gains include the soil conservation and greater indigenous biodiversity advantages of afforestation.

So far I haven't even mentioned carbon credits and the ETS, but the advantages of some early cash flow to cover forest establishment and silviculture are considerable. Not having to carry compounding costs for 25-30 years dramatically improves forest profitability. So why worry about foreigners coming in and "grabbing" our land for carbon forestry. There is such a strong case for landowners to get out and plant that low productivity, highly erodible land themselves, get some revenue out of the ETS and maintain the viability of their operations.

Recognition of this case by Federated Farmers would be a great start - if only.

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