Invasive plant species: prime suspects Max Wade RPS Ecology

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Invasive plant species prime suspectsMax
WadeRPS Ecology
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380,000 forthree years of Giant Hogweed
management
1.56 billion to eradicate Japanese Knotweed
from UK
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What is Japanese Knotweed and why is it regarded
as such a problem? How do Giant Hogweed
and Himalayan balsam compare with it?What about
other species such as Water Primrose and Tree of
Heaven?
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How should an invasive weed forum respond to such
species?Risk assessmentPrevention of invasion
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Japanese Knotweed
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Spring shoots

• Green to red/purple with leaves rolled back
• When the shoot extends, the leaves unfurl

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Summer stems

• Form dense clumps
• Grow up to 3 m tall, stem diameter reach up to 40
  mm

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Summer stems

• Hollow, green, with red/purple flecks and
  distinct nodes like bamboo

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Leaves

• Young leaves light green and rolled back
• Fully grown leaves shield-shaped with a flat
  base, up to 120 mm (5 in) long

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Winter stems

• Deep orange/brown and woody
• Take up to three years to decompose
• Produce large quantities of debris

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Crown with buds
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Rhizomes

• Perennial
• Underground system can extend up to 7 m (23 in)
• Dark brown exterior
• Bright orange interior
• Break easily like carrot

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Methods of dispersal and spread
Rhizome and stem regeneration

• A piece of rhizome with two nodes can grow into a
  new plant
• Stem material regenerates in both terrestrial and
  aquatic media

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Flowers

• Male and female flowers on separate plants
• In UK only female flowers
• Cream / white coloured
• In clusters 80-120 mm long

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Seeds

• Enclosed in thin, papery, three-winged achene
• Dark brown and shiny

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Seeds

• Triangular, 3 mm long
• Not found in UK

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Habitats in introduced areas

• Stream and river banks
• Road verges, railway lines and river banks
• Vacant lots, neglected gardens, churchyards
• Spoil heaps, fly tipping

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Problems caused by Japanese knotweed
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Built environment

• Shoots able to push up through asphalt, damaging
  pavements, car parks

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Problems for Developers

• Rhizomes penetrate brickwork and other hard
  landscaping
• Deep rhizome must be carefully followed during
  excavation
• Early identification can widen the range of
  available control options and save money

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Eradication and associated costs

• A conservative estimate of 9.5 million would be
  needed to control the current Japanese knotweed
  infestation in Swansea

• Approximately 400,000 to resurface a car park
  damaged by Japanese knotweed

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Biodiversity

• Dense canopy restricts growth of ground flora
• Prevents growth and establishment of native
  species
• Replaces existing vegetation, including other
  rhizomatous species (e.g. bracken)

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Landscape, safety and recreation

• Reduces visibility on roadsides and railways
• Stands of the plant encourage urban litter and
  decay
• Difficult access for anglers and walkers along
  river banks

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Flood defence

• Dense stands impede flow and may exacerbate
  flooding
• In autumn/winter the bare soil is easily washed
  away, increasing erosion
• Rhizome and shoots can break apart masonry used
  to retain river bank

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Built environment

• Rhizome can penetrate foundations and other
  walls, land drainage works and lift interlocking
  concrete blocks

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Archaeology

• Rhizomes lift and disturb archaeological remains

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Advantages of Japanese knotweed

• Used as a medicine in the Far East
• Used for stabilisation of sand dunes and mine
  spoils
• Stems used as a basis for a vegetable dye
• Source of nectar late in the season for insects
  including bees
• Dense stands in urban areas can provide a
  pseudo-woodland habitat

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Dig and dump
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Dig and dump
1m2 of Japanese Knotweed
Total Volume 15m x 15m x 3m 675m3 Tonnes per
m3 1.6 tonnes Cost per tonne 50 Cost of 1m2
JK 54,000
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What risks are posed by this species?Undertake
a risk assessment local and national
perspectives
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Himalayan Balsam
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Problems caused by Himalayan Balsam- erosion
along river banks- exacerbating flooding-
displacement of native vegetation
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What risks are posed by this species?Undertake
a risk assessment local and national
perspectives
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Giant Hogweed
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What risks are posed by this species?Undertake
a risk assessment local and national
perspectives
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Problems caused by Giant Hogweed- erosion
along river banks- exacerbating flooding-
displacement of native vegetation- health
hazard- restriction of access, e.g. to river
bank
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Tree of Heaven
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What risks are posed by this species?Undertake
a risk assessment local and national
perspectives
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Problems caused by Tree of Heaven-
disturbance to building structures-
displacement of native vegetation- spoiling
urban landscape
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Water Primrose
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Keeled Garlic
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3,586 species (non-grasses) 885 of which are
establishedplus 710 grass species
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50-100 new alien species being found annually in
the wild in Britain and Ireland (BSBI News)
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Lag phase for these species in Great Britain can
be measured in decades
Japanese
Knotweed
Giant Hogweed
Gunnera
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Risk assessment species
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Risk assessment pathways
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Legislation and policy starts the clock ticking
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City and County of Swansea Local Plan Policy NE
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Full details of a scheme for the eradication
and/or control of Japanese Knotweed shall be
submitted to and approved by the Local Planning
Authority prior to the commencement of work on
site and the approved scheme shall be implemented
prior to the use of the building commencing
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Risk management - the wide awake phase-
eradication from a site- eradication from a
river corridor- eradication from a county-
eradication from a country
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Rapid response time to wake up phase- which
species to watch?- trigger point for sleeper
species- decision to take action-
co-ordination and capacity to act- extermination
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Water Primrose
Are its days numbered?
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Prevention setting the alarm clock- which
species to watch? - where to watch them?- what
pathways to watch?
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Prevention
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An introduction to Japanese Knotweedand a
comparison with Himalayan Balsam and Giant
Hogweed Dont forget other species which are
not yet a problemUndertake risk assessment
before taking actionPrevention is best
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• St Ives, Cambridgeshire
• PE27 5JL
• ( 01480 466335
• wadem_at_rpsgroup.com
• 8 www.rpsgroup.com

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Surveillance site/local
county/regional
national international
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Revegetation
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Risk Assessment
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Research- risk assessment- novel control
measures- detailed studies of individual
species and groups of species
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Nymphaea mexicana in Lake Ohakuri
Number of colonies reported per year Source
Johnstone 1992
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Scottish Statutory Instrument 2005 No. 308
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20 speciesCabombaSalviniaPistiaAilanthusHydr
ocotyleLudwigia
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