Learning how species become extinct may help prevent further die-offs
Grace Chua, Straits Times 24 Oct 09;
AN INTERNATIONAL team of botanists, including one from Singapore, has carried out the first large-scale analysis of how cities drive plants extinct.
Both the rate of landscape change and the number of native plants left will affect plant survival in future, they found.
Understanding how vegetation goes extinct will help scientists predict - and hopefully stem - further die-offs, said National University of Singapore biologist Richard Corlett, a co-author of the study.
Dr Corlett and botanists from Australia, New Zealand, the United States and the United Kingdom compared extinction rates in three groups of cities.
In the first group are cities where the native plant life started to be transformed more than 400 years ago, such as Hong Kong, Vienna and Zurich.
Singapore, New York City and Auckland fall into the second group, where transformation took place after 1600 but before any plant surveys were done.
And the third group comprises younger cities such as Melbourne and San Diego, where native plants were surveyed but later transformed by urban development.
Cities in the first two groups had the highest extinction rates due to agriculture and urban development.
But where a greater proportion of native vegetation - over 30 per cent - was left, the extinction rate was lower.
For instance, New York City, founded in the 1600s, has lost perhaps half of its original species, whereas Durban in South Africa, founded in 1824 and with 60 per cent of its native vegetation cover left, has lost fewer species.
The botanists' study is published in the current issue of the journal, Ecology Letters.
In Singapore, about 30 per cent of plant species recorded since the 19th century have gone extinct, and studies have predicted that up to three-quarters of the original species are gone.
Singapore has about 1,500 plant species now.
Dr Corlett said that Singapore still had a wide range of plants and animals though this biodiversity was under threat from climate change and global warming.
'But you've only got to look at a map of Singapore to see that it's not a good place to be a wild species,' he added.
Natural habitats here are cramped, so there may be an extinction debt - gradual, delayed die-offs of species whose populations are too small to be sustained.
With 60 per cent of the world's population set to be living in cities by 2030, up from 50 per cent now, the importance of such studies is likely to rise.
'It's part of a growing recognition that we live in a human-dominated landscape,' Dr Corlett said.
National University of Singapore plant ecologist Edward Webb commented: 'The article points out how important it is to retain native vegetation in urban areas - and by vegetation I do not mean single trees but habitat such as forest and high-diversity parks like Bukit Timah, the Singapore Botanical Gardens, Sungei Buloh and Pulau Ubin.'
Managing the vegetation of natural systems such as terrestrial forest and coastal mangroves, and cultivating urban landscapes with native species could help minimise the extinction debt, he added.
