Fallopia japonica (Houtt. Ronse Decraene) (syn. Reynoutria japonica syn. Polygonum cuspidatum, Japanese knotweed) is an aggressively invasive alien weed in the United Kingdom (UK) and throughout its introduced range. Its presence can herald considerable costs, both in terms of its ecological impact as a threat to biodiversity and economically due to the physical damage caused to property and the associated costs of treatment and disposal of the plant. There is therefore increasing interest in eradicating this alien species and as a result many different management techniques have been applied to try and control its spread. It is important to ascertain which of these are most appropriate in any given situation and so tools that can test the impact and efficiency of these techniques both quickly and cheaply would be extremely useful. In this thesis mathematical models are developed for the spatial spread of F. japonica on a local scale in the UK.

Höga kvävenedfall och förändringar inom jord- och skogsbruk har lett till igenväxning av svenska sandmarker. Sand- och grustäkter kan fungera som tillflyktsort för kärlväxtarter som är beroende av de torra och näringsfattiga markförhållanden som finns i sandmarker. Vapnö grustäkt i Hallands län undersöktes 2010 och visade sig ha en hög biologisk mångfald med bland annat 145 kärlväxtarter, varav fyra rödlistade. Syftet med den här studien var att se hur artsammansättningen av kärlväxter ser ut idag, sju år senare. Området inventerades vid tio tillfällen från april till augusti och samtliga kärlväxtarter noterades. Resultatet blev en lista på 224 arter varav 63 var återfynd från 2010 och 161 var nya arter för området. Det fanns fem rödlistade arter: Knippnejlika (Dianthus armeria) (EN), hårginst (Genista pilosa) (NT), backtimjan (Thymus serpyllum) (NT), skogsalm (Ulmus glabra) (CR) och naverlönn (Acer campestre) (CR). Det totala antalet arter och rödlistade arter har ökat sen 2010, vilket tyder på en positiv utveckling av områdets biologiska mångfald. Den höga artmångfalden beror troligen på det öppna, varierande landskapet och de rödlistade arterna växer där tack vare den alltmer ovanliga sandmarken. Områdets mångfald av kärlväxter hotas av igenväxning samt konkurrens från de invasiva arterna blomsterlupin (Lupinus polyphyllus) och parkslide (Fallopia japonica). Detta kan motverkas av störningar i form av slåtter, uppgrävning, naturvårdsbränning eller bete. / Nitrogen deposition and changes in agriculture and forestry have led to a decrease of sandy habitats in Sweden due to regrowth of vegetation. Sand- and gravelpits can act as refuges for vascular plants that require the dry and nutrient-poor conditions of sandy soils. Vapnö gravelpit in Halland county in Sweden was surveyed in 2010 and proved to hold a high biodiversity including 145 species of vascular plants, of which four were red-listed. Now, seven years later, the purpose of this study was to see how the composition of vascular plants has changed since then. The area was studied on ten occasions from April to August, and all species of vascular plants were noted. The study resulted in a list of 224 species, of which 63 were remaining since 2010 and 161 were new species for the area. There were five red-listed species: Dianthus armeria (EN), Genista pilosa (NT), Thymus serpyllum (NT), Ulmus glabra (CR) and Acer campestre (CR). The total number of species and red-listed species have increased, suggesting a positive development of the biodiversity of the area. The high species diversity is probably due to the open, varied landscape and the presence of the red-listed species due to the increasingly rare sandy habitat. The diversity of vascular plants in the area is threatened by regrowth of vegetation, as well as the invasive species Lupinus polyphyllus and Fallopia japonica. These threats can be counteracted by disturbance in the form of mowing or digging up plants, prescribed burning or grazing.

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Fallopiajaponica (Houtt.) Ronse Decraene (Japanese knotweed), an introduced, invasive, rhizomatous perennial plant, has become an increasing problem for nature conservation and land management in both rural and urban areas in the British Isles. In the native range of the plant, Japan, Taiwan and northern China, a number of varieties are recorded. Three congeners of F. japonica are present in the British Isles, F. sachalinensis, F. japonica var. conipacta and F. baldschuanica in addition to a hybrid F. x bohemica. An investigation by postal survey of the distribution of the hybrid F. x bohemica has identified 131 records for the British Isles. Both male and female plants of F. x bohemica have been recorded. Current understanding suggests that only female plants of F. japonica are present in the British Isles, inferring that the only means of reproduction is through vegetative regeneration. High rates of regeneration were recorded in this study for stem and rhizome material for both F. japonica and F. x bohemica in an aquatic and terrestrial environment. Implications of vegetative regeneration are discussed in terms of current management practices and future methods of control. A combination of digging with a mechanical excavator followed by spraying with the herbicide glyphosate decreased the time required to achieve an effective level of control of F. japonica compared to spraying alone. Fragmentation of the rhizome system through digging resulted in an increase in stem density allowing a more effective delivery of herbicide. Implications in terms of costs for F. japonica treatment on sites awaiting re-development are discussed. Analysis of data collated from surveys of F. japonica in Swansea using a Geographical Information System suggest that the primary habitats infested are waste ground and stream and river banks. Results suggest that disturbance, both by natural means and by human intervention has been the primary cause of spread of F. japonica in the British Isles. Management strategies are proposed which take account of these results and measures are put forward to help prevent future infestations.