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Invading plants overtake and replace native species, causing wetland disturbance

Yale University : 22 March, 2002  (New Product)
A non-native strain of the common reed Phragmites australis, found along roadways and marshes all over New England, has been introduced and spread undetected along the eastern seaboard, resulting in dramatic changes in plant populations and altering species diversities, a Yale researcher has found.
'This invasion has eliminated almost all native strains of the species along the Atlantic coastline,' said principal investigator Kristin Saltonstall, graduate student in ecology and evolutionary biology at Yale. 'It has changed marsh communities and could affect rare plant species that have specific habitat requirements. It can also have an impact on wildlife such as ducks, that don't migrate into the dense foliage of the reed.'

Published in the February 19 issue of Proceedings of the National Academy of Sciences, the study analyzed DNA sequences of chloroplast genes found in modern Phragmites leaves collected worldwide. Saltonstall compared the sequences of these modern-day samples with historical samples from 18th-century North American herbarium collections to get a sense of how the genetic structure in the population has changed. She identified 11 different native North American types that were widespread centuries ago and one non-native type that was historically found only in coastal sites.

'In Connecticut and Massachusetts by the 1940s, there were only invasive types, indicating that they have outcompeted the native plants,' said Saltonstall. 'The native strains can still be found in parts of the Midwest and western United States and Canada. Only a few native populations are left on the eastern coastline.'

While they are very similar, the non-native strain of the plant grows more densely and typically in a monoculture, whereas the native strains grow in mixed-plant communities. The non-native strain can also change the flow of water by increasing sediment deposits.

Saltonstall said it is hard to pinpoint when the non-native strain was introduced, but Phragmites was used as packing materials on ships in the 1800s. She theorizes that it could have taken root after being discarded along the coastline.

'Invasions like this can be happening without our knowledge,' said Saltonstall. 'There could be more invasive species that we just don't know about. People can tell there is something different about the species, but they can't quite put a finger on it.'
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