Although there are many species of ancient trees, only a few grow for centuries to reach 50, 100 and up to 115 meters that some specimens of red sequoia exceed. There is no well-defined category of what botanists call LOT, Large Old Trees. There is also no set minimum height or span to determine what a large tree is. An objective data is the central character they play in their ecosystem. And a subjective fact is the majesty that humans inspire.
That is why LOT are the two species of redwoods that grow on the west coast of the USA, the mountain ash (Eucalyptus regnans) that grows for 400 years to 100 or more meters or the Petersianthus quadrialatus, a species of rosewood that grows In Philippines. But old and large trees are also the firs of more than 50 meters that are in the very old Bialowieza Forest (Poland) or the African baobab that in some species reaches 30 meters in height and more than 10 in circumference. Almost all of them are in retreat.
A study published in 2013 gave only a few decades to two of the baobab species present in Madagascar. In Yosemite National Park (California, USA), home to the redwoods and other giants like the American royal pine, which can reach 70 meters in height, other research showed in 2009 that the density per hectare of these large trees is it had reduced by 25% since the 1930s. Meanwhile, the tallest flowering tree in the world, the Australian mountain ash, will go from a ratio of 5.1 trees per hectare that it had at the beginning of the century to just 0.7xHa in 2070.
"The decline has accelerated in many ecosystems," says Australian National University ecologist David Lindenmayer. This researcher, who specializes in large trees, recalls that these species are particularly susceptible to droughts, but they have also suffered and still suffer from unsustainable logging in many areas. "In some ecosystems in northern Europe, there has been an increase, but they started from very small populations," he adds.
The new threat is global warming. "Climate change brings climatic conditions to levels outside the normal range of the ideal niche for the growth and development of the tree", explains Lindenmayer. "For example, reduced rainfall in southeastern and southwestern Australia will prevent these large, old trees from growing back to the height and size they used to. In other cases, the conditions when they first germinated 500 years ago are so different today that they will not be able to germinate again in the same areas where they grow now, "he adds ..."
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