Does temperature limit the invasion of Impatiens glandulifera and Heracleum mantegazzianum in the United Kingdom?
The extent to which climate, as experienced along an elevational gradient, might limit the geographic distribution of the two invasive plants Impatiens glandulifera and Heracleum mantegazzianum (both on the EPPO List of Invasive Alien Plants) was examined. Seeds of both species were sown (in plastic bags to prevent their escape in the wild) in six elevation stations established across a representative elevational gradient in north-east England (10 to 600 m above sea level), including sites outside the current range of the species. Both species germinated readily at all elevations, even in areas well above their current limits within the study area. However, the plants were smaller at higher altitudes. H. mantegazzianum expressed high germination, seedling and adult survivorship across a wide range of elevation. This result is consistent with the species’ native montane habitat, where cold winters occur. While climate may determine the absolute distribution of a species, this study indicates that the current lowland distribution of H. mantegazzianum in the UK may primarily reflect dispersal limitations and human influences, rather than climatic limits. Impatiens glandulifera produced fewer seeds with increasing elevation. For both species, overwinter survival of seeds was not related to winter temperatures or frost days. The results suggest that, of the two species, only I. glandulifera is currently limited by temperature, although this is not the only factor determining the distribution of the species.
Sources
Willis SG, Hulme PE (2002) Does temperature limit the invasion of Impatiens glandulifera and Heracleum mantegazzianum in the UK? Functional Ecology 16, 530-539.