Spread of alien invasive Impatiens balfourii in Europe and its temperature,light and soil moisture demands

Impatiens balfourii was introduced in the beginning of the 20th century from the Himalayas to Southern Europe where it was able to establish. In recent years an increasing number of more northern situated occurrences were recorded. An overview about the current distribution of Impatiens balfourii in Europe is given and new records for Germany are presented. To explore the range of potential habitat conditions, vegetation relevés and autecological experiments were conducted. Gas exchange measurements showed an optimum of net photosynthesis at 24–32 °C and light saturation above 700 μmol m⁻¹ s⁻¹ PPFD without any signs of photoinhibition. A moisture gradient experiment showed that Impatiens balfourii prefers fresh soils of moderate dampness. In contrast to the native I. noli-tangere and to the alien species I. glandulifera and I. capensis, which prefer moister or even wet habitats, Impatiens balfourii resembles in its soil moisture demands the alien Impatiens parviflora which originates also in Central Asia and which is invasive in Europe. But in contrast to I. parviflora and to all other established Impatiens species in Europe, I. balfourii is able to colonize even open habitats with high light intensities. Against this background, a further expansion of Impatiens balfourii in Europe appears to be likely.