Giant old trees are dying at an alarming rate due to human activity, fire and climate change, an ecologist says.
The accelerated death rate of trees aged between 100 and 300 years seems to be a global problem in all types of forest, says Professor David Lindenmayer of the ARC Centre of Excellence for Environmental Decisions (CEED) and Australian National University.
"Large old trees are critical in many natural and human-dominated environments," he says in a paper with Professor Bill Laurance of James Cook University and Professor Jerry Franklin of Washington University.
Research is urgently needed to identify the causes of rapid losses of large old trees and strategies for improved management, says their paper published in the journal Science on Friday.
"Without policy changes, large old trees will diminish or disappear in many ecosystems, leading to losses of their associated biota and ecosystem functions," they say.
They were tipped off to the increasing loss of big old trees while examining Swedish forestry records going back to the 1860s.
Then a 30-year study of mountain ash (Eucalyptus regnans) forest in Australia confirmed that not only were big old trees dying en masse in forest fires, but also perishing at 10 times the normal rate in non-fire years - apparently due to drought, high temperatures, logging and other causes.
Their study found similar trends at all latitudes.
"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," they said.
"They provide nesting or sheltering cavities for up to 30 per cent of all birds and animals in some ecosystems."
The trees also store huge amounts of carbon, recycle soil nutrients and influence the flow of water in landscapes.
The decline appears to be driven by a combination of forces, including land clearing, agricultural practices, man-made changes in fire regimes, logging and timber gathering, insect attack and rapid climatic changes.