Holidays provide opportunities to travel and enjoy our native bush. It’s an interesting exercise to combine the two to see how planting trees might soak up travel carbon emissions.
Tane’s Tree Trust, whose motto is “native forests for our future”, has an online calculator for such things. It shows that absorbing the emissions generated by a return flight between Auckland and Christchurch requires 604 two-year-old native trees and shrubs. Fortunately, trees’ ability to sequester carbon increases astonishingly as they grow. Just 23 trees and shrubs will stash away those emissions over 10 years. After 50 years, two trees will have done the job.
The delay is longer than for fast-growing exotic species like Pinus radiata, which is reflected in the Emissions Trading Scheme’s forestry settings. But those settings probably give native forests less credit than is due – and therefore small-forest owners receive less money. Forest biometrician Mark Kimberley of Tane’s Tree Trust explains: “If you’re a small grower with fewer than 100 hectares, you use a default look-up table to work out how much carbon you’re sequestering. For natives, there’s just one table that’s based on regenerating native forest, or scrubland, which grows more slowly than a well-maintained planted stand.
“The look-up table for natives says you’re sequestering around 6.5 tonnes a year of carbon dioxide on average. But a stand of kauri or tōtara planted on a reasonable forestry site – where you’ve matched the species to the site and it’s being managed in terms of animal pests, weeds and stock fencing – is probably doing at least twice that, maybe 15 tonnes a year.” That management is crucial to getting decent survival and growth from planted or naturally regenerating native trees, he says.
Te Uru Rākau ‒ New Zealand Forest Service is researching native forest sequestration, including differences between naturally regenerating, restoration planting and indigenous plantation forests. Any look-up table updates could be implemented by 2026, says its forestry systems director, Olivia O’Sullivan.
But inevitably, compensatory tree planting for a holiday flight takes years to become effective. Yvette Dickinson, a silvicultural scientist at Scion, agrees timing is an issue. “The climate crisis is right now, and we’re trying to reduce net emissions as fast as we can, as well as trying to have the biggest reductions that we can. So timing is important, and that’s reflected in goals to be net zero by 2050.”
When choosing which trees to plant, she encourages landowners to think about their values as well as forests’ multiple benefits. There’s wood if they choose to do some harvesting, soil and water protection, recreational space and habitat.
But there’s no guarantee of enduring storage. “Droughts or fire or big winds might disturb or kill trees, and that can release that carbon back into the atmosphere.” However, she points out trees’ huge upsides. “They are not the single solution to climate change. But we can plant them right now. We don’t have to develop a new technology or system, and in geological timescales, they can absorb carbon quite rapidly.”
Kimberley proposes a timely solution. “Suppose parents or grandparents decide to plant enough trees to cover their child’s expected lifetime carbon dioxide emissions. They’d need to plant 498 tōtara, 349 kauri or 208 red beech trees. With exotics, they’d achieve the goal with 169 radiata pine, 114 Eucalyptus regnans or just 99 redwood trees.” Always, of course, on an appropriate site with good management. That would absorb an 80-year life’s worth of today’s average emissions, although it omits methane from agricultural products. “You’d need to double the tree numbers for that,” estimates Kimberley. “It is surprising how few trees are needed, native or exotic.”
