|1350 year old oak tree|
"It's a worldwide problem and appears to be happening in most types of forest," said the study's lead author, David Lindemayer, a professor at Australian National University and an expert in landscape ecology and forest management.
The research team found that big, old trees are dying at an alarmingly fast clip around the world at all latitudes – Yosemite National Park in California, the African savanna, the Brazilian rain forest, Europe and the boreal forests around the world.
They described the cause as a combination of factors, from a hotter, drier climate in many places to logging, land clearing, changes in fire prevention and management policies, insect attacks and diseases.
The die-off of these 100-to-300-year-old trees raises concern, the researchers say, because they sustain biodiversity to a greater degree than many other components of the forest. "Big, old trees are not just enlarged young trees," said Jerry F. Franklin of the University of Washington, a co-author of the study who has studied old-growth forest for 45 years. "Old trees have idiosyncratic features – a different canopy, different branch systems, a lot of cavities, thicker bark and more heartwood. They provide a lot more habitat and niches."