BAD NEWS FOR RURAL TREES

Prime Australian hardwood forest scene
Prime Australian hardwood forest scene
Will climate change rob rural forest of its growth rate advantage? Photo: ©Tony Neilson

It seems counter-intuitive, but trees are apparently better off living in the bustling environment of a big city than the peace and quiet of the countryside.

There is fresh scientific evidence that city trees grow fastest – and that their country cousins are in for a rough ride.

According to a Science magazine report http://www.sciencemag.org/news/2017/11/city-trees-grow-more-quickly-their-rural-cousins-here-s-why the ‘warming’ benefits to trees of climate change are fast diminishing.

Climate change researchers have analysed the growth of about 1400 trees in 10 different major cities across the globe. By taking core samples and estimating age and growth using tree rings, they measured how trees grew going back about 150 years.

Brisbane CBD across river
Study suggests urban tree are growing much faster than rural cousins. Photo ©Tony Neilson

25% faster growth

Climate change has generally been beneficial to trees because warmer temperatures stimulate photosynthesis and extend the growing season. But the research shows that after 1960, urban trees grew faster by as much as 25% compared with trees of the same age in the countryside.

This could be because of the urban ‘heat island’ effect, which causes temperatures in the city to rise as much 10°C compared with those in surrounding areas.

Stagnation threat

However, if the urban climate today is what rural regions may see tomorrow, the trend does not bode well, according to the study. There may come a point when the global tree growth rate stagnates and perhaps even declines under warming climates.

(Or you could close your mind, adopt the Donald Trump/Tony Abbott position on climate change and pretend it simply isn’t happening. Ed.)

SAVE OUR FORESTS

View across hardwood log stockpile to gum forest
View across hardwood log stockpile to gum forest
Early forest thinning creates more climate change resistance. Photo: ©Tony Neilson

Cut down more trees

One of the best ways to save our forests is to cut down more trees! Sounds like a red rag to a preservationist bull, but the science and history confirm it works.

In a former life, I spent many years representing the public image of forestry companies under severe pressure from politicians and the environmental lobby.

At issue was the widespread perception that all forest logging was bad and that the trees (yes, even those in plantations and grown to be harvested) should be left to die of natural causes.

Indigenous people and professional foresters down the ages know only too well that controlled burning, thinning and selective logging can benefit  the overall health of forest eco systems.

Now, as global forests feel the heat from climate change, there is fresh support for the ‘log-to-save’ approach.

View inside an American oak forest
Natural forests like these American oaks capture up to 20% of US carbon emissions. Photo: ©Tony Neilson

Science Magazine reported in April that in places like the American West, rising temperatures and drought mean less water for trees, sometimes shrivelling swaths of woodland. (Exactly that has recently happened to thousands of hectares of mangrove forest in Australia’s Gulf Country.)

Scientists have found that thinning early in forest growth creates tougher trees that can endure climate change, the respected journal reports. Even better, these thinned forests can suck carbon out of the air just as fast as dense forests.

“When it comes to carbon sequestration and climate change adaptation, we can have our cake and eat it too,” says Andrew Larson, forest ecologist at the University of Montana in Missoula and author of the new study. “It’s a win-win.”

US forests capture up to 20% of the country’s carbon emissions annually. But if trees get too crowded, they compete for light and water—and stressed trees are more susceptible to drought and insect attacks. Removing some trees, says the study, can ease the competition, letting the remaining trees grow big and healthy.

Natural Images 2017©

SUSTAINING ‘THE SLEEPER’

Fallen blackwood trees, now slowly decomposing in the wet forest
Wide view of a blackwood seed tree reserve
Blackwood seed can lay dormant in the ground for decades until a regenerating fire comes though. Photo: ©Tony Neilson

Tasmanian blackwood – a prized ‘fancy’ hardwood

Writing anything positive about sustainable forestry in Tasmania is fraught with danger.

Not because we fear attack from the island’s army of notoriously uncompromising environmental activists.

But because of the precariousness of virtually everything about the wood business in Tassie, so volatile is the political sentiment there.

So we apologise in advance for any dated references in the following piece about a wonderfully rich native Australian timber species sometimes known as the ‘music tree’.

Blackwood log being broken down in the sawmill
Chocolate growth rings and straw-coloured sapwood give Tasmanian blackwood exceptional figure. Photo: ©Tony Neilson

Poisonous plant list

Tasmanian blackwood (Acacia melanoxylon) is native to eastern Australia and is also referred to as: black wattle, blackwood, hickory, mudgerabah and sally wattle, among others. Interestingly, it also appears on the International Poisonous Plants Checklist by D Jesse Wagstaff, CRC Press.

Blackwood is one of the best-known and most widely used Tasmanian specialty timbers. It is produced in moderate commercial volumes and grows across a broad range of forest types.

Sawn and stacked timber drying outdoors
Air-drying sawn blackwood – popular with Tasmanian boat-builders for internal fit-outs. Photo: ©Tony Neilson

The biggest, straightest and tallest trees come from the wet forest and swamps of northwest Tasmania. These almost pure stands in the Smithton area have been the primary source of sustainably harvested blackwood for well over a century.

Awaken the ‘sleeper’

The tree thrives in a moist atmosphere but is generally short-lived. It regenerates easily from seeds that can lay dormant in the soil for decades until after they are activated by fire. Perhaps it should be called ‘the sleeper’?

Nearly 40% of Tasmania’s blackwood forest types are reserved. Around 8000 ha of swamp forest is harvested on a sustained yield basis – generally at 70-year rotations.

After harvest, regeneration treatment involves burning to encourage germination, and fencing to protect seedlings from browsing wildlife.

Rear view of blackwood back on Taylor Guitar
Tasmanian blackwood is favoured by Taylor Guitars for its 300 Series

Beautifully figured

Blackwood is almost always beautifully figured and is a prized ‘fancy’ hardwood for furniture, decorative veneers and flooring.

Sapwood can range in colour from straw to grey-white, with clear demarcation from the heartwood. Heartwood is golden to dark brown, with chocolate growth rings.

Applications include: flooring, lining and cladding, furniture, windows, doors and stairs, fittings and trim, bench tops and joinery, musical instruments, craft items and turnery.

REFERENCES: Tasmanian Timber Promotion Board (TTPB), Wikipedia, Island Specialty Timbers and A Field Guide to Australian Trees by Ivan Holiday.)

(Editor: This item is in keeping with the raison d’etre of Natural Images – ‘Thinking about Sustainability’. It is not an advertorial.)

©Natural Images 2017