- A Man-Made rainforest that should have taken millennia
to evolve has baffled scientists by springing up in just 150 years.
- Rainforests should take millions of years to develop
the highly complex, interactive ecosystems for which they are famed, in
which every species fills an essential niche.
- But the forest on Green Mountain, Ascension Island, in
the mid-Atlantic sprung up chaotically from a mixed bag of botanical scrap
brought in by the Royal Navy in 1843.
- And the introduced species have thrived at a rate that
has stunned experts and could trigger a rethink of conventional ecological
theory, New Scientist magazine reports today.
- When Charles Darwin stopped off at Ascension Island in
1836 on the home stretch of his long journey on the Beagle, he described
it then as "entirely destitute of trees". Lying 1,200 miles from
the nearest continent, the volcanic island was almost barren because of
its remoteness, with only about 20 plant species, mainly ferns.
- But in 1843, an ambitious British scheme for revitalising
the island began, with Royal Navy troops planting thousands of trees a
year, using seedlings from Argentina, South Africa, and the Royal Botanical
Gardens at Kew.
- Soon the bare white mountain was cloaked in vegetation
and renamed Green Mountain. By the early 20th century the mountain's slopes
were covered in guava, banana, wild ginger, the white-flowered Cleroden
drum, Madagascan periwinkle and eucalyptus from Australia. A thick bamboo
forest crowned the summit.
- Now Green Mountain is a thriving tropical forest, yet
it grew from species collected randomly. Conventional theory suggests complex
ecosystems only emerge through a slow evolution in which different organisms
develop in tandem to fill particular niches.
- But Green Mountain suggests that natural rainforests
may be constructed more by chance than by evolution.
- Dissident theorists call this "ecological fitting".
It says species do not so much evolve to create ecosystems as make the
best of what they have.
- "The Green Mountain system is a spectacular example
of ecological fitting," David Wilkinson, from Liverpool John Moores
University, told New Scientist. "It is a man-made system that has
produced a tropical rainforest without any co-evolution between its constituent
- But Alan Gray, an ecologist at the University of Edinburgh,
argues that the few surviving endemic species on Green Mountain would still
be co-evolving and may form the framework of the new ecosystem, meaning
the newcomers may be structurally irrelevant.
- Even the new species may not be such a random collection.
- "Many of the imports may have come from the same
place, importing their co-evolutionary relationships," said Gray.
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