The decline and fall of the forest’s grand old masters

Big old trees, as we know are as rare as hen’s teeth, but far more important for forest ecosystems globally.

They are necessary for all sorts of wildlife and processes that have evolved with large old trees. They are now a small part of any forest (if they exist at all) but can account for 50% of the carbon captured within trees. This latest study shows that the world’s biggest giants are now more vulnerable than ever on more fronts than ever.

RESEARCHERS have put the globe’s big old trees on a par with animals such as whales, lions and tigers that have low populations and are vulnerable to decline.

Following a stocktake of the world’s large old trees, Australian and American researchers have found that such trees – the largest living organisms on the planet – are declining at all latitudes.

” Just as large-bodied animals such as elephants, tigers and cetaceans [such as whales] have declined drastically in many parts of the world, a growing body of evidence suggests that large old trees could be equally imperilled,” the authors conclude.

Variously informed by logging, land clearing, fire and agricultural intensification, the trend has been documented in a range of environments – from urban environments in Europe to temperate savannah in southern Africa and tropical forests in Asia, South and Central America.

Australian National University ecologist David Lindenmayer worked with colleagues from James Cook University and the University of Washington to map the decline internationally .

” It’s turned out to be a global problem that has been overlooked before,” he said. ” While we better understand it in [Victoria’s ] mountain ash forests because they’re so well documented, it’s happening worldwide.”

Just 1 per cent of Victoria’s central highland forests are made up of old growth trees that pre-date the 1939 fires. Those old trees – some dating back to the 1700s – are under constant threat of fire. After the Black Saturday firestorm, 79 per cent of large trees with cavities died.

In a paper published in the journal Science this month, Professor Lindenmayer forecasts that the mountain ash are set to decline from 5.1 trees per hectare in 1997 to 0.6 trees per hectare in 2070.

” Big trees have massive implications for how ecosystems work,” he said.

Considered the ” keystone structures” , large old trees provide refuges and nests for wildlife. In Victoria’s highland forests the old mountain ash trees are home to about 40 species of invertebrates, including the endangered Leadbeater’s possum. The trees remain sought after long after they have died.

But the plight of large old trees is not a uniquely Victorian problem.

” Big trees are vulnerable in our tropical savannahs of the Northern Territory, in woodland and agricultural areas of New South Wales and Victoria and in the tropical rainforests of northern Australia,” Professor Lindenmayer said.

In California’s Yosemite National Park, density of the largest trees declined by 24 per cent between the 1930s and 1990s. Similarly, in southern Sweden, trees witha trunk diameter greater than 45 centimetres have declined in number from historical densities of about 19 per hectare to about one per hectare now.

” Now we recognise for the first time that big trees are also vulnerable to decline,” he said. ” And there are really big implications for that.”

Bridie Smith
Science and technology reporter
The Age

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