POPULATION BIOLOGY AND RATES OF INVASION OF 3 INTRODUCED IMPATIENS SPECIES IN THE BRITISH-ISLES

The rate and extent of spread of three introduced species of Impatiens (I. glandulifera Royle, I. parviflora DC and I. capensis Meerburgh) in Britain was studied. The dates for the first records in each vice-county were obtained, and used to estimate rates of spread in England since their introduction. I. glandulifera was estimated as having a rate of spread of up to 38 km yr1, compared to a rate of up to 24 km yr1 for I. parviflora. The use of vice-county data as opposed to 10 km squares is discussed. Comparative growth experiments were performed both in garden plots and in the field, in an attempt to identify characters which enabled I. glandulifera to be so successful. Frost tolerance and seed output seem to be important factors; there are no doubt others not identified. Occasional long distance dispersal events, probably aided by man, are considered to be responsible for the rapid spread of I. glandulifera. Impatiens glandulifera is a pest plant because it forms dense monospecific stands in damp woodland, swamping all other plants. It is able to do so because of early germination and rapid growth to a height higher than any other British annual. Local spread is limited to 2 m yr1 from its own ballistic dispersal and to a small multiple of that from animal spread.