Polygonum cuspidatum Sieb. & Zucc. (=Fallopia japonica (Houtt. Dcne.) (herb, shrub)

Ecology Distribution Management Info Impact Info References and Links Contacts

General Impact Polygonum cuspidatum threatens open and riparian areas where it spreads rapidly and forms dense near monoculture stands, which compete with and displace native vegetation and prohibiting their regeneration. It dramatically reduces species diversity and alters habitat for wildlife. A study found that plots adjacent to P. cuspidatum stands had 1.6-10 times as many species. A total of 63 species were found outside knotweed stands, of which 78% were native. Only 13 species, 58% of which were native, were found within stands. Invasion by P. cuspidatum can also reduce invertebrate biodiversity by half or more and reduce the quality of ecosystems for amphibians, reptiles, birds and mammals whose diets are largely composed of arthropods. For example, the Green frog (Rana clamitans) was found to experience decreased foraging in knotweed stands. In raparian habitats P. cusidatum may also increase the risk of flooding and river bank erosion as it establishes monospecific stand that die back in the winter leaving banks exposed. Its tough shoots can break through gravel, tarmac, and even concrete. Prolific rhizome and shoot growth can damage foundations, walls, pavements, drainage works, and flood prevention structures. Its dead stems and leaf litter decompose very slowly and form a deep organic layer, which prevents native seeds from germinating and alters natural succession. The UK Governments Department for Environment, Food and Rural Affairs has estimated a cost of £1.5 billion to control this invasive in United Kingdom alone. In Germany, annual costs for knotweed control and subsequent restoration of waterways and watercourses have been put at almost €30 million; yearly control along only 1% of the total railway system has been calculated at €2.4 million (Aguilera et al, 2009; Gerber et al, 2008; Kurose et al, 2009a; Maerz et al, 2005; Pysek, 2006; ANHP, 2006).          Location Specific Impacts: France   Agricultural: Blockages in rivers caused by F. japonica impacts on irrigation to fields. Interaction with other invasive species: The hybrid Fallopia X bohemica is common in France, produced by crosses of Fallopia japonica and F. sachalinensis. Modification of hydrology: F. japonica contributes to the erosion of riverbanks and causes blockages to rivers in autumn when dry stems are carried by the current. Modification of successional patterns: F. japonica disturbs the natural regeneration of alluvial forests (alders, willows, ashes). United States (USA)   Competition: Remaley (1997) states that it spreads quickly to form dense thickets that exclude native vegetation and greatly alter natural ecosystems. Modification of nutrient regime: Seiger (1991) states that it contributes to the development of the ecosystem, in part, by acting as a nutrient reservoir. Modification of successional patterns: It is a dominant pioneer in the primary succession of volcanic slopes and is frequently a coloniser in secondary succession (Hirose, 1984, in Seiger, 1991). Other: Its early emergence and great height combine to shade out other vegetation and prohibit regeneration of other species (Sukopp and Sukopp 1988, in Seiger, 1991). Thus, it reduces species diversity and damages wildlife habitat (Palmer 1990, Scott and Mars 1984, Wiegman pers. comm., in Seiger, 1991).