Scientists Friday warned of an alarming increase in the death rates of the largest living organisms on the planet, the giant, old trees that harbour and sustain countless birds and wildlife.

Research by universities in Australia and the United States, published in Science, said ecosystems worldwide were in danger of losing forever their largest and oldest trees unless there were policy changes to better protect them.

"It's a worldwide problem and appears to be happening in most types of forest," said David Lindenmayer from the Australian National University, the lead author of a study into the problem.

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

Lindenmayer, along with colleagues from the James Cook University in Australia and Washington University in America, undertook their study after examining Swedish forestry records going back to the 1860s.

They found alarming losses of big trees, ranging from 100 to 300 years old, at all latitudes in Europe, North America, Africa, Asia, South America, Latin America and Australia.

The trees at risk included mountain ash in Australia, pine trees in America, California redwoods, and baobabs in Tanzania.

The study showed that trees were not only dying en masse in forest fires, but were also perishing at 10 times the normal rate in non-fire years.

The study said it appeared to be down to a combination of rapid climate change causing drought and high temperatures, as well as rampant logging and agricultural land clearing.

"It is a very, very disturbing trend," said Bill Laurance of James Cook University.

"We are talking about the loss of the biggest living organisms on the planet, of the largest flowering plants on the planet, of organisms that play a key role in regulating and enriching our world."

Large old trees play critical ecological roles, providing nesting or sheltering cavities for up to 30 percent of all birds and animals in some ecosystems.

They also store huge amounts of carbon, recycle soil nutrients, create rich patches for other life to thrive in, and influence the flow of water within landscapes.

"Big trees supply abundant food for numerous animals in the form of fruits, flowers, foliage and nectar," said Laurance.

"Their hollows offer nests and shelter for birds and animals... and their loss could mean extinction for such creatures."

The scientists said policies and management practices must be put in place that intentionally grow such trees and reduce their mortality rates.

"Targeted research is urgently needed to better understand the key threats to their existence and to devise strategies to counter them," they added.

"Without such initiatives, these iconic organisms and the many species dependent on them could be greatly diminished or lost altogether."