Why some trees evolved to live underground (BBC)
With the exception of wildlife film makers, arboriculturalists and a few scientists, most of us don't spend much time in the leafy upper reaches of tree canopies. But in the underground forests beneath the savannahs of southern Africa and South America, it's an experience open to all.
With most of their branches safely underground and just their leaves and perhaps some twigs poking up above the surface, these subterranean versions of their above ground ancestors are close to indestructible. Some can live for more than 10,000 years.
Recent research into when and why these underground trees first evolved is starting to shed light on how the savannahs in which they live came into being.
Savannahs are ecosystems in which trees are widely spaced enough for plenty of light to penetrate, allowing grasses to dominate at ground level. They cover around 20% of the vegetated surface of the Earth.
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Most recently, researchers have hit upon another potential key factor in the origin and rapid growth of the savannahs - one that also led to the origin of the underground forests. Not only did these new ecosystems spread like wildfire, they say, but they were also born from wildfire.
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more: http://www.bbc.com/earth/story/20141103-why-some-trees-live-underground
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