Effect of environmental factors on size and fecundity of field populations of Impatiens glandulifera

Background: Impatiens glandulifera, an annual species native to the Himalayas, is the tallest annual plant in Europe, where it has become invasive and destabilises riverbanks. Aims: This study explored between- and within-site trait variation in the invasive range of I. glandulifera to identify trait relationships that underlie the large size and local invasion success of this species. Methods: Leaf chlorophyll content, vegetative growth traits (plant height, leaf length, leaf width, number of side branches, leaves and nodes), the number of reproductive units (sum of flower buds, flowers and seed pods) and seed pod length were determined for five I. glandulifera stands in the south-west of Ireland. Results: Plant vegetative growth traits and the number of reproductive units were positively correlated, with the highest trait values observed at a shaded site with high disturbance. Chlorophyll content in the upper leaves declined with an increasing number of reproductive units at sites with low soil nitrogen, suggesting that nutrient allocation to the reproductive sinks is prioritised over photosynthetic capacity of the upper leaves. Conclusions: The ability to grow to a remarkably large size under shaded, disturbed conditions contributes to the invasion success of I. glandulifera.