Japanese knotweed,
a rhizomatous perennial, was introduced from Asia to Europe in the
mid-nineteenth century as an ornamental and fodder plant. It is an
impressive species, which grows to a height of 2-3 meters, with
flecked bamboo-like stems, arching branches and clusters of creamy
white flowers appearing late in the season. The orange to brown
coloured, woody, dead stems persist erect throughout the winter and
new shoots, produced from the extensive rhizome system, grow up
amongst these the following spring to form dense thickets. The dead
stems and leaf litter decompose very slowly and form a deep organic
layer, which prevents native seeds from germinating. Once present
at a site, Japanese knotweed increases in area very rapidly and
soon forms monoculture stands. Specific problems caused by Japanese
knotweed are:
* Damage to paving
and tarmac areas
* Damage to flood
defence structures
* Damage to
archaeological sites
* Reduction of
biodiversity through out-shading native
vegetation
* Restriction of
access to riverbanks for anglers, bank inspection and amenity
use
* Reduction in
land values
* Increased risk
of flooding through dead stems washed into river and stream
channels
* Increased risk
of soil erosion and bank instability following removal of
established stands in riparian areas
* Accumulation of
litter in well established stands
* Aesthetically
displeasing
* Expensive to treat