Tuesday, July 21, 2015

The biodiversity of topography

The central Australian desert is an extreme arid environment.  For 20 million years, the continent has been drying, its rivers turning to playas, its ground water salting up, its inland plains and plateaus slowly disappearing under waves of sand.  The plant kingdom has not abandoned the continent, though, and thousands of drought-tolerant plants inhabit the red centre of Australia.  This aridity is a fickle thing, however.  In this wide brown land we call home, a slight increase in water availability, or a bit of shade from the noonday sun can make a big difference to a tropical, moisture loving plant.

A stunning example of this is the cycad.  As this global distribution map shows, cycads are mostly found in tropical to sub-tropical forests, and in Australia, they hug the wetter coastal areas.  But there is one species not shown on this map.

In the central Australian Macdonnell ranges, Macrozamia macdonnelli is found in ravines, at the base of south facing cliffs, and in rare desert oases, where ground water and sun protection allow it to cling to life as the continent dried out.  1500 km from the ocean and about as far from its nearest living relative, these cycads are found through the MacDonnell and Hartz ranges of the Northern Territory, where steep ravines channel water and shade the plants which grow within. Like an outlawed bushranger on the run from the law, this plant and its pollinator sidekick have been hiding out from the sun in the secret mountain waterholes for millions of years.  

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