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Ascension Island – how trees can make it rain

November 1, 2010

..to date, scientists have been deaf to the parable of Ascension Island. – Howard Falcon-Lang, BBC Science Correspondent, BBC website September 2010

This true story of a remote island in the Atlantic shows that planting trees in an arid area could induce rainfall over time. The 500 year history of man’s exploitation of this place may have a message for the modern world

Trees can make it rain!A tiny island was discovered by Portuguese sailors in the middle of the Atlantic Ocean, half way between Africa and South America on Ascension Day 1503. The mariners named ‘Ascension’ after the Christian celebration of the ascension of Jesus Christ to heaven.

The age of discovery

The uninhabited island was a convenient stop off point, so the Portuguese released goats to eat the small scrubby ferns. The animals provided fresh meat at first, but over the years they multiplied and consumed all the native flora.

The dark ages

The volcanic island became totally arid. The little rain that fell evaporated away. It was described by a visitor in 1775 as “a ruinous heap of rocks.” It was littered with the bones of sailors who had been left cast away as a punishment for on-board crimes. They usually died of thirst.

The age of empire

In 1815 the strategic position of the island was noted by the British, who established a garrison. They pronounced it a ‘Stone Frigate’ and called it HMS Ascension and a small population took hold. In 1836 Charles Darwin visited. He noted that there was almost no rainfall so inhabitants kept themselves alive by conserving water carefully in tanks. He described the island as being like a ‘a cinder’.

The age of science

Then in 1846, botanist John Hooker of Kew Gardens visited the island and deduced that it had potential for forestation. Hooker arranged for many species of tree to be imported from the Kew and planted on the mountainous island. Some trees planted took hold and spread across the centre of the Island, creating a growing ‘cloud forest’ and a increasingly wet microclimate.

A forgotten experiment rediscovered

Long after John Hooker’s death the result of this long term ‘experiment’ was realised in June 2005, when the first National Park on Ascension Island was opened. Non-indigenous plants teem there, and he crown of Island is now called ‘Green Mountain’ with more green spreading over the entire terrain.

Because Ascension Island remained a strategic British Overseas Territory inhabited only by RAF, NASA and US Air Force staff, few scientists have been to island to observe the miracle of the man-made rainforest. One of them is Dr David M. Wilkinson Biological and Earth Scientist from Liverpool John Moores University

He wrote: “On Green Mountain, the eco-system has gone from species-poor fern-dominated hillsides to species-rich cloud forest in around 150 years.”*

Dr Wilkinson researches viability of “terra-forming” – long term investment into the improvement of natural environments by human activity.

The BBC’s science correspondent Howard Falcon-Lang published an article on the BBC website on September 1 2010,  entitled ‘Charles Darwin’s ecological experiment on Ascension isle’. Read more

* Source:  The parable of Green Mountain: Ascension Island, ecosystem construction and ecological fitting David M. Wilkinson Biological and Earth Sciences, Liverpool John Moores University  Journal of Biogeography 31, 1–4, ª 2004 Blackwell Publishing Ltd.

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