Germination and establishment of invasive and native Impatiens species

Impatiens glandulifera (Balsaminaceae) is one of the most widely distributed invasive alien plants in Europe. In the Czech Republic, it first colonized open riverbank habitats and more recently less humid and more shaded habitats where it comes in contact with two congeners, the native I. noli-tangere and ear-lier invader I. parviflora; both these species are likely to be affected by competition with I. glandulifera. A reciprocal sowing experiment was established to explore the performance and possible microsite dif-ferentiation of the three Impatiens species in the field. Three triads of plots, each dominated by one Impatiens species, were established in surroundings of a river with a fine-grained mosaic of woody and meadow vegetation in southern Bohemia, Czech Republic. The plots were protected from the natural input of seed by cutting the vegetation 20 cm above the soil surface and covering the surface with a cloth during the period of seed release. Each plot consisted of a subplot sown with a mixture of seed of all three species collected at the same locality and a control subplot with no seed added. Sites dominated by I. noli-tangere and I. parviflora were suitable for germination of all Impatiens species; the I. parviflora sites were more suitable for the establishment and further development of Impatiens plants. This indi-cates that I. noli-tangere was outcompeted from sites currently dominated by I. parviflora and further spread of I. glandulifera into sites occupied by the other Impatiens species is likely. Experimental plots in sites dominated by I. glandulifera were unsuitable for growth of all species, including its own seedlings