Assessment of the invasive Himalayan balsam (Impatiens glandulifera) distribution in Sweden : The effects of latitudinal location and land cover on the distribution

Abstract: Invasive alien species are recognized as a major problem worldwide. They affect native flora and fauna negatively, resulting in loss of biodiversity and increased economic costs of the species’ themselves and management efforts. One of the most widely distributed invasive plant species – the Himalayan balsam (Impatiens glandulifera) – is inflicting damage to native plants in Sweden by overshadowing due to its tall stature and capacity to increase population numbers quickly over long distances. The purpose of this study was to examine the distribution of Himalayan balsam in urban versus rural areas in south, central, and northern Sweden. Five land cover classes were also compared to investigate potential differences in where Himalayan balsam is frequently observed. Species observations from Species Observation System (Artportalen by SLU Swedish Species Information Centre) were combined with land cover data from the Swedish Environmental Protection Agency to assess the distribution of Himalayan balsam over different cover classes. The results showed no significant differences for urban versus rural areas nor latitude, but some of the land cover classes were significantly different from one another. Himalayan balsam observations in forests on wetlands are significantly more reported compared to all other classes, and exploited lands and open lands had more reported observations than forests outside wetlands. Observations by the public are often characterised by opportunistic reporting behaviour, ultimately leading to bias in which species are reported. In conclusion, this study tested means to assess the distribution of Himalayan balsam among land cover classes and its results are consistent with other studies showing Himalayan balsam favours in moist habitats over other land cover classes.