DEAR News Of The Area,

I’D just like to offer a correction to Louise Cranny’s recent letter on the growth rates of trees and their potential carbon storage.

As approximately half of the dry weight of a tree is carbon, its capacity to draw in carbon via photosynthesis is indeed important in combating climate change.

However, a tree’s carbon absorption does NOT accelerate as it ages, in fact, quite the opposite is true.

Eucalypts, which make up the majority of the Australian bush, are extremely shade intolerant and their strategy is to grow as rapidly as they can to outcompete their neighbours in their search for sunlight.

Those that get left behind are soon suppressed by the dominant trees, their growth rates slow down and they become suppressed and even die.

Have a look at any of the eucalypts around where you live and you will see their branches trying to grow away from each other or other shading obstacles. However, the growth rates of even the dominant trees slows as it gets older.

In a study of 87,000 individual trees from 280 plots over seven decades, scientists showed that “stand growth rates of even-aged forests tend to increase during the early life of the forest, but, after a few decades or so, reach a maximum and decline progressively thereafter. Various reviews and texts describe this phenomenon. These trends are evident in whatever measures of tree size are used, measures such as biomass or stem wood volume or characteristics correlated with these, such as stem basal area” (West, 2023).

Louise is also incorrect when she states that when forests are harvested, “their immense stores of carbon are quickly released”.

The trees that are harvested from the forest are either those thinned to allow the younger, faster growing trees to continue to grow rapidly into larger trees or those that have reached maturity and their growth rate is slowing down.

The latter are removed to make way for new vigorous regeneration to absorb carbon once again at the maximum rate that the site will allow.

The timber and wood products produced from each tree is permanently fixed in any number of solid wood products, like telegraph poles, bridge timbers, decking, flooring, fencing, structural timbers and even pallets. Research has shown that even wood fibre converted to paper and cardboard products can store carbon in landfill for decades.

Unlike the rest of the world, we don’t take full advantage of the potential biomass left behind or produced in the conversion of round logs to dimensional timber by converting it into biofuels, biochar, biogas and even electricity. The leaves and fine branches are naturally left behind and are a source of nutrients for the new regeneration and dominant regrowth.

That’s why the United Nations’ own science from the Intergovernmental Panel on Climate Change (IPCC) declares: “A sustainable forest management strategy aimed at maintaining or increasing forest carbon stocks, while producing an annual sustained yield of timber, fibre or energy from the forest, will generate the largest sustained mitigation benefit (IPCC 4th Assessment).”

Kind regards,
Steve DOBBYNS,
Executive Officer,
Forest and Wood Communities Australia.