The felling of giant trees can be disastrous from the ecological perspective, possibly triggering a vicious cycle of more forest shrinkage and carbon emissions.
Big old trees face a dire future globally from agriculture, logging, habitat fragmentation, exotic invaders, and the effects of climate change, warn leading scientists.
William Laurance, professor of ecology at James Cook University, Australia, reveals a dramatic decline among the world's "biggest and most magnificent" trees and the range of threats they face, the journal Science reported.
"Their demise will have substantial impacts on bio-diversity and forest ecology, while worsening climate change. To persist, big trees need a safe place to live and long periods of stability but time and stability are becoming very rare commodities in our modern world," he said, according to a James Cook statement.
Giant trees offer critical shelter and food for innumerable species of mammals, birds and insects, while emitting massive amounts of water through their leaves, contributing to local rainfall.
Old trees also lock up large amounts of carbon and thereby help to slow global warming. But their ability to store carbon and provide other vital services is threatened by human activities, according to Laurance and his co-authors David Lindenmayer at ANU in Canberra and Jerry Franklin at the University of Washington, US.
Some of the world's largest trees are particularly targeted by loggers.
The oldest trees are among the most valuable and therefore the first to be cut in "virgin" forest areas. Big trees are also sensitive to habitat fragmentation, which exposes them to stronger winds and drier conditions.
Laurance's research in the Amazon rain forest has shown substantial die-off of canopy giants in small forest fragments.
Their susceptibility seems counter-intuitive given big trees' life histories, which invariably include periods of drought and other stress.