October 29, 2011

Palm trees older than we thought

Our forests were already diversifying 100 million years ago

According to biologists from the French Institute for Research for Development (IRD), forests began to form more than 100 million years ago, shortly after the extinction of the dinosaurs. The previous most accepted theory was that this process began much more recently, just 35 to 45 millions years ago, at the time when many mountains, including the Andes, were formed. IRD’s work resulted in the first complete genus-level evolutionary history of one of the most characteristic plant families found in tropical rain forests (TRFs) today – the palms (Arecaceae or Palmae). There are 2 500 palm species of which 90 % are restricted to the TRFs.

Using a molecular dating method, based on DNA sequences, they traced this history back to the middle of the Cretaceous period. Evidently, the immense wealth of species found in TRFs is a consequence of constant diversification. During the ice ages and times of major glaciations, the TRFs were refuge zones. These days, they themselves are under threat from human activities.

Tropical rainforests together are the richest terrestrial ecosystem, containing an estimated 50 % of all known species of plants and animals, as well as one-third of the globe’s forest formations. Where and when they were formed and how their rich biodiversity developed is a crucial issue for their conservation. The research showed that the major palm lineages emerged gradually over geologic time, a process of constant diversification in an ecosystem that had persisted right from its origin with many of the same initial and principal lineages having survived throughout, constantly diversifying and generating the high levels of biodiversity we see today.

The first palm forests actually arose in the Northern Hemisphere, on Laurasia -the supercontinent made up of what is now North America and Eurasia- not in the Equatorial latitudes (i.e. the Tropics). In the Cretaceous period, the climate in Equatorial latitudes was too hot and dry for humid forests. Today, TRFs cover some 7% of Earth’s surface and provide the livelihoods of several hundred million people.



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