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) i n Britain was studied. The dates for the first records in each vice-co unty were obtained, and used to estimate rates of spread in England si nce 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 f or I. parviflora. The use of vice-county data as opposed to 10 km squa res is discussed. Comparative growth experiments were performed both i n 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 n ot identified. Occasional long distance dispersal events, probably aid ed 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 limite d to 2 m yr1 from its own ballistic dispersal and to a small multiple of that from animal spread.