THE IMPACT OF TEMPERATURE ON THE NORTHERN DISTRIBUTION-LIMITS OF THE INTRODUCED SPECIES FALLOPIA-JAPONICA AND IMPATIENS-GLANDULIFERA IN NORTH-WEST EUROPE

This paper tests the predictions of sensitivity analysis performed on two matrix population growth models, for annual and perennial vegetati on (Woodward, 1988). Climatic correlations have been established for t wo introduced invasive plant species Fallopia japonica (Japanese knotw eed) and Impatiens glandulifera (Himalayan balsam) in north-west Europ e. These two species represent examples of perennial and annual vegeta tion respectively. In accordance with the model predictions, the north ern distribution limit of F. japonica was found to be controlled by tw o climatic variables-the length of the growing season, measured in day -degrees, and the minimum temperature-while for I. glandulifera only t he length of the growing season was critical. Experimental verificatio n of the results is crucial for understanding the mechanisms operating to limit plant distributions. By use of the predictions established b y the climatic correlations for I. glandulifera and F. japonica, maps have been produced forecasting the potential northward spread of both species on the basis of a 1.5-degrees-C and a 4.5-degrees-C rise in gl obal mean surface air-temperature. These temperatures represent the mi nimum and maximum increases predicted to occur by general circulation models for a doubling of CO2 concentration in the atmosphere. For a gl obal temperature increase of 1.5-degrees-C the maps demonstrate a maxi mum northward spread of F. japonica from a latitude of 63-degrees to 6 8-degrees-N and for I. glandulifera from 64-degrees up to 69-degrees-N . The greater temperature increase of 4.5-degrees-C indicates a consid erable potential for expansion in the range of F. japonica in Norway a nd Sweden but a distribution which was restricted along the eastern co ast of Sweden and southern Finland. In contrast, I. glandulifera could colonize the whole of the Fennoscandinavian area. The predictions are made assuming no migrational lag and no soil 'incompatibility'. Geogr aphical differences in the patterns of spread between the species were explained with reference to the different factors affecting perennial and annual vegetation.