The existence of some of the “largest organisms that have ever lived” – 3,000-year-old sequoias, the 2,000-year-old giant redwoods, big trees around the world in Amazonia, Africa and central America — is in danger as never before, says New Scientist magazine. We human beings who build roads, farms and settlements are certainly to blame. But longer and more extreme droughts and the introduction of new pests and diseases are also contributing to big trees’s demise with repercussions for the climate.
When older trees die, forests “release their stored carbon, prompting a vicious circle of further warming and forest shrinkage,” says William Laurance, a research professor at James Cook University in Cairns, Australia. Big trees comprise only 2 percent of any forest’s trees but they are crucial to their ecosystem as they provide a quarter of the biomass and also seed large areas. Says Laurance:
“With their tall canopies basking in the sun, big trees capture vast amounts of energy. This allows them to produce massive crops of fruits, flowers and foliage that sustain much of animal life in the forests. Their canopies help moderate the local forest environment while their understory creates a unique habitat for other plants and animals,” said Laurance.
In some parts of the world, Laurance said, populations of big trees are dwindling because their seedlings cannot survive or grow. “In southern India an aggressive shrub is invading the understorey of many forests, preventing seedlings from dropping on the floor. With no young trees to replace them, it’s only a matter of time before most of the big trees disappear.”
Due to having tall, inflexible trunks, the biggest trees located at the edges of the forest are especially susceptible to wind turbulence and to being uprooted.
Furthermore, to achieve their vast heights, big trees need lots of time to grow but, in some parts of the world, their seedlings are unable to survive. In India, says Laurance, an “aggressive shrub” is to account for this: The shrub has taken over the understoryof the forest and is preventing seedlings from reaching the ground. In other countries, exotic species sold at garden centers are the source of bacterial infections that can be harmful to native plants.
Equally alarming is that the biggest trees in communities around the world are in danger. Laurance points out that Dutch elm disease killed off “many of the stateliest trees in Britain in the 1960s and 70s”; in the US, the disease almost completely killed all the elms of Connecticut’s “Elm City,” New Haven, in the 1930s.
I still remember the feeling of awe I had on seeing the giant sequoias in California when I was a child in the 1970s. The forest ranger spoke of how people had lived in the trees and how the roots were big enough to drive a car through. Walking beneath trees that seemed even taller than any buildings filled me with awe and the memory has stayed with me. For the sequoias to be over 3,000 years old means that they had been alive since the late Bronze Age, when the legendary events of the Trojan War may have taken place. Are the sequoias and the redwoods doomed to become history, to be the stuff of legends and stories of how “things used to be”?
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