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Invasive alien species can arrive in a new region or country
in many ways. Natural boundaries such as oceans, mountain
ranges and deserts provide no barrier at all in this age of
world trade and global travel.
Some arrive hidden on ships, in bales of hay, in packing
materials or in crop seed. Some are deliberately brought in
to the country as ornamental plants for gardens, or as medicinal
or food plants. Given the right conditions they can spread
along the same avenues that we use for transportation –
roads, railways and canals! Plants that become invasive often
have high growth rates and produce many seeds, which if adapted
to be dispersed by the wind can easily spread over a wide
area. They are often also resistant to tough conditions in
some way, such as drought, grazing, fire or wind. All of these
attributes are an advantage in colonising disturbed soil such
as on agricultural or waste land. From here colonisation of
natural habitats can take place and the invasive alien species
can compete with native and naturalised plants.
The landscapes most altered by invasive alien species are
tropical oceanic islands such as the Hawaiian Islands, St
Helena, and Mauritius. However continental areas suffer also,
for example in Australia, America and South Africa.
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alien plants and the changing UK flora >>>
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