Old forests may not be the CO₂ saviour we think they are

Many of Victoria’s forestry workers have long moved on to other vocations, but the onflow of other businesses has been affected.

Some companies have sourced wood from NSW and overseas, allowing furniture builders and the like to continue.

Machinery companies are now wary of a glut of three-year-old logging vehicles flooding the market.

One Victorian sawmill operator has moved his entire business to Tasmania, while others have simply closed.

The ludicrous importing of timber from Brazil where 90 per cent of forestry is illegal is a thoughtless irony I’ll save for another day.

What should interest regional communities is the research behind forestry cycles and their impact on carbon storage.

It’s complex and there is no ideology involved, just a lot of science.

Trees store carbon and in one sense should be left alone to do just that.

Australian Forest Products Association non-executive director Joel Fitzgibbon claims from credible sources that fast-growing replanted timber forests will store more than a long-standing patch.

If you add this to locking carbon up in housing and furniture timber by taking logs away, then regrowing a forest makes sense for sequestering CO₂.

Either option can seem better than the other.

Sufficient scientific papers on carbon capture of long-standing forests in Europe show that carbon absorption continues when atmospheric CO₂ is elevated.

Other reports find that Australian forests do not suck in as much CO₂, seeming to have saturated their ability to store it.

And so replacing either forest types with newly growing forests after logging can be a better or worse option.

It really is a matter of horses for courses, and the ‘courses’ are often the amounts of phosphorus in the soil.

This is the best physiological justification for stopping logging in the Strathbogie Shire in 2017, despite not being the reason for it.

World-renowned forest ecologist Professor David Ellsworth has studied Eucalyptus forests in NSW and by using the most sophisticated technology imaginable for enveloping a single forest tree with its own private ‘cloud’ of increased carbon dioxide, he found that old forests might not be the heroes we think they are.

“The trees will not capture any additional CO₂ when it goes up in the atmosphere because they are constrained by the level of phosphorus in the soil,” Professor Ellsworth told Country News.

“The trees in our study took in half a metric ton of CO₂ per hectare of forest, but that didn’t increase at all when increasing the CO₂ around the tree.”

Phosphorus is crucial for a tree’s growth and reproduction despite taking up a mere tenth of a per cent of its mass.

However, phosphorus has a finite supply.

“Phosphorus comes from weathering of rocks which is an incredibly slow geological process,” Prof Ellsworth said.

“Nitrogen can be rebuilt up (from the atmosphere) but phosphorus cannot.

“Every time you make a removal of your trees, you also take with it a lot of phosphorus.

“And our Australian soils are generally well-weathered compared to the northern hemisphere (soils) and therefore very low in phosphorus.

“In fact, forests in the northern hemisphere can often be nitrogen constrained.”

The speed at which phosphorus depletes is site dependent.

Prof Ellsworth said shallow sandstone soils had very little of the element.

“But there are parts of Gippsland that have high levels of; it really depends on where you are.”

What is the solution?

It depends on the problem, and Prof Ellsworth’s research may have produced a new one if it suggests Australian forests won’t contribute to carbon storage as has been long assumed.

When politics ignores the science that strongly hints at needing more research, a state-wide blanket ban certainly doesn’t cut it.

How can it, with such diversity in carbon storage between regions?

Andy Wilson writes for Country News. He is a pre-peer review science editor in a range of fields and has a PhD in ecology from the University of Queensland.