Invasive Impatiens parviflora has negative impact on native vegetation in oak-hornbeam forests

- Impact of invasive I. parviflora was studied with the use of removal experiment.
- Number and cover of native species was increasing after invader removal.
- Species composition significantly changed after invader removal.
- Suppressed plants were mostly small plants flowering in early spring.

Impatiens parviflora (Balsaminaceae) is one of the most widespread invasive plant species in Central Europe. Nevertheless, both mechanisms and consequences of its invasion are still poorly understood. In this study we attempt to understand the impact of this species on native vegetation.The impact of I. parviflora on native vegetation was studied using removal experiment on permanent plots in oak-hornbeam forests in central Bohemia, Czech Republic. Nine pairs of plots were established in invaded vegetation, one plot in each pair stayed invaded and the other served as removal plot and all I. parviflora individuals were repeatedly removed from the plot. Species composition in 4 subsequent years was recorded in the plots. Species response to I. parviflora removal was correlated to plant traits to reveal trait characteristics of species suppressed by the invasion.Significant increase in both numbers and cover of native species was observed in removal plots in comparison with invaded plots during the experiment, with the greatest change in first two years after invader removal. Species composition also significantly differed between invaded and removal plots. Species with high affinity to removal plots, i.e. species that are most restricted by I. parviflora invasion, were mostly species with small releasing height and early start of flowering.Our results indicate that I. parviflora has negative impact on native vegetation but that the vegetation can recover within few years after the invader removal. Due to its extensive distribution and high turnover, removal of the species from larger plots is, however, not realistic in practice.