INVASIVE SPECIES
In part II of his article
PHILIP RUSTED, Director of Research and Development, tcm (r&d) Ltd., looks at the ...
BIG BOYS
In the last issue I wrote about three invasive species, Himalayan Balsam, Ragwort and the Browntailed Moth. This time I would like to bring the two big boys to your attention. Big in physical size, big in national spread and big in terms of cost to clients, landowners, contractors and the environment. These are of course Japanese Knotweed (Fallopia japonica var japonica) and Giant Hogweed (Heracleum mantezaganium). Both of these plants have had huge amounts of publicity this year, with the Japanese Knotweed being the king of all things invasive. Japanese Knotweed is a
rather generic term that seems to cover three different species of Knotweeds that are problematic within the UK and Western Europe. These species are the straight Japanese Knotweed (Fallopia japonica var japonica), Giant Knotweed (Fallopia sachilensis) and Hybrid Knotweed (Fallopia x bohemica). In the eyes of the Public and Environmental Agencies / Bodies, there is little to choose between the three species and they are all subjected to the same regulatory terms and conditions as each other. It was always thought that if Japanese Knotweed could breed sexually then the
entire country would come to a standstill. It is breeding sexually, although not very successfully, hence the fact that the Hybrid Knotweed is in existence in the UK. Historically the
Knotweeds have shown themselves to be the masters of invasion. A single plant brought into Kew Gardens in 1850 has been spread throughout the UK, Western Europe and East Coast America. The majority of this spread has taken place without any viable seeds being produced. Purely through the movement of sections of the plants extensive rhizome network into new areas. Sections of Rhizome weighing fractions
With thanks to the Victorians
of a gramme have the ability to produce new plants that will not be hindered by obstructions standing in their way such as building foundations, concrete, tarmac, brick walls and the like.
The effects of the rapid
growth of Knotweed from this single plant to an approximate area coverage now well exceeding 1200km2 (DEFRA 2003) is startling to stay the least.
So how does it spread so far and so fast without the advantage of seed? The answer lies in the plants incredible growth rate, outcompeting all plants in its areas by producing densely shaded understory
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