Colonial plants

Published: Saturday 28 February 2009

Down to Earth
Map of Europe showing different levels of risk from invasive plant species
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Invasive species are common in human-modified habitats

introduction of plant species to foreign habitats, by humans or otherwise, often leads to disastrous results. These alien plants usually have no predators in the new habitat and rapidly infest the area, pushing native species out in the process. Such invasive species can bring about significant changes in the ecosystem of an area and are among the biggest threats to biodiversity.

Not all kinds of habitats are vulnerable to such invasions. Some are more likely to have a higher number of invasive species than others. Predicting which environments are more prone to invasive species would help devise mechanisms to take protective steps. Such a predictive map of invasives versus habitats has been created for Europe by researchers from Spain, the UK and the Czech Republic.

The researchers analyzed the proportion of invasive plant species to the total number of species in sample vegetation plots in the three countries, covering a range of climatic zones. The information for a particular habitat was extrapolated to cover similar habitat types in the rest of Europe. For example, the data from Spain's Catalonia, which has a Mediterranean climate, was used to map the invasion level of other Mediterranean climes.

The analysis showed a distinct pattern across Europe; certain habitats had higher levels of plant invasions than others (see map). The level of invasion or the number of invasive plant species was consistently the highest in human-made, frequently disturbed habitats such as urban, industrial and agricultural areas. The level was low in natural grasslands, deciduous forests and coniferous forests. It was the lowest in peat bogs and moors.

Looking into reasons factoring the predictions, the team found that the level of plant invasions depends on the distribution of different ecosystem types across Europe. "High levels of invasion are typical of lowland areas and of humid areas with cool summers as in western and central Europe while low levels are found in northern Europe and mountain regions across the continent", said Petr Py?ek from the Institute of Botany, Academy of Sciences of the Czech Republic.

All the same, regions of high human density (irrespective of the region's ecosystem) have higher levels of invasion, said the research which was published in Diversity and Distributions' January 2009 issue. This can be understood by the fact that higher the number of humans in a particular area, higher is the number of human-introduced (accidental or otherwise) plant species. Sparsely populated Sweden has low levels of invasion.

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