Scientists call them the Big Five, the five biggest mass extinctions that have dramatically changed life on the Earth. The first occurred 450 million years ago, ice ages and subsequent reduction of the seas led to the extinction of about 85% between invertebrates and fish. Then there was the Kellwasser event: 377 million years ago asteroids hit the Earth generating new extinctions. The third or the worst: 251 million years ago, Earth's largest extinction killed 50% of all families, perhaps because of a huge meteorite or due to a drastic increase in volcanic activity. Subsequently, another 76% of living species disappeared 203 million years ago due to a rise in temperature to 5°C. The last and the most popular: 66 million years ago dinosaurs disappeared. Today many researchers announce the sixth one: no meteorite is coming, but only 'men' ready to destroy 75% of living species, and not just animals – as it would be easy to think – but especially trees.
According to the disturbing reports issued by the Botanic Gardens Conservations International, thousands of tree species are under threat of extinction. The UK-based organization, whose members include hundreds of botanical institutions worldwide, said it pulled data from more than 500 published sources to create the online database GlobalTreeSearch, the world’s first global, authoritative list of tree species. It identified 60,065 tree species currently living on Earth. Of that number, more than half were found to only occur in a single country, which could suggest an increased vulnerability to threats. In addition, we know the conservation status of only about 20,000 tree species, or 30 percent of the world’s trees. But of those assessed, almost half ― or 9,600 tree species ― are considered threatened with extinction. Of this 15%, 300 are critically endangered, with only 50 - and in some cases even less - trees on the planet.
Today who should we get in the hypothetical Noah's Ark? Surely the Karomia gigas (also known as Chinese Hats), now on the brink of extinction due to an excessive use in the construction sector and present only in Tanzania with 6 specimens. But also the Loulou from Hawaii, the Rubber Tree of Santa Helena (also symbol of the island), the Mgpingo from Tanzania and the Dragon Tree from Cape Verde.
Compile a list of tree species required a huge undertaking, a scientific effort that includes the discovery, collection and description of tens of thousands of species of plants. An effort done not only by the botanists of today, but also thanks to those of the past, who first recorded and cataloged the various species. Certainly the database will be a great tool – still to be implemented – to understand how to best conserve these trees slowing or preventing the extinction.