Remains of a virgin Amazon rainforest are seen after it was cleared for its wood in Brazil. The study says old trees are dying due to several factors, such as logging, fires and extreme weather caused by climate change. (Lunae Parracho/Reuters)

The world's biggest and oldest trees are dying at an alarming rate, according to a report by three leading ecologists.

Death rates among trees 100 to 300 years old, living organisms that also sustain birds and other wildlife, are accelerating in many parts of the world including savannahs, woodlands, forests, farming areas and even cities.

"Large old trees are critical in many natural and human-dominated environments. Studies of ecosystems around the world suggest populations of these trees are declining rapidly," said the study’s lead author, David Lindenmayer of Australian National University, who wrote the report — published in the journal Science — with colleagues Bill Laurance of James Cook University in Australia, and Jerry Franklin of Washington University in the U.S.

The three ecologists are considered to be the top experts in their field.

"Research is urgently needed to identify the causes of rapid losses of large old trees and strategies for improved management. Without … policy changes, large old trees will diminish or disappear in many ecosystems, leading to losses of their associated biota and ecosystem functions."

The scientists say they were first tipped off about the trend after analyzing forestry records from Sweden dating back to the 1860s. They compared the data to a 30-year study of mountain ash forest in Australia, which suggested the trees were dying at 10 times the normal rate in years that didn’t have fires. The Australian trees were perishing due to several causes including logging, drought and extreme temperatures.

'Very, very disturbing trend'

The ecologists decided to look at other regions of the world – examining tree populations on African savannahs, Brazilian rainforests, California’s Yosemite National Park, European forests, the boreal forests of the North, and those in cities.

“It is a very, very disturbing trend,” said Laurance, referring to the discovery that old trees everywhere are dying at a rapid rate – more than the previous norm.

“Big trees supply abundant food for numerous animals in the form of fruits, flowers, foliage and nectar. Their hollows offer nests and shelter for birds and animals … and their loss could mean extinction for such creatures.”

The scientists say the decline appears to be caused by a combination of factors including land clearing, logging, insect attacks, changes in how fires are fought, severe wildfires and extreme weather brought on by climate change.

They liken the loss of large trees to that of the road to extinction of some of the world’s animals, such as rhinos, whales and elephants.

The ecologists are urging immediate action to assess the extent of the loss of big trees and identify areas in the world they might have a chance to survive and thrive.

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