The Effect of Latitude, Litter and Vegetation type on the Performance of the Invasive Species Impatiens glandulifera
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- Institutt for biologi 
Background and Aims Impatiens glandulifera is a blacklisted invasive alien plant species that exhibits high phenotypic variation along latitudinal gradients in its invaded range in Europe, with a preference for riparian, roadside and other moist or disturbed habitats. However, limited information exists on how different latitudinal populations perform in contrasting vegetation types. Furthermore, the impact of I. glandulifera litter on the performance of co-occurring species within different vegetation types has not been assessed. Methods In a greenhouse experiment, we compared performances of different latitudinal populations of I. glandulifera in two vegetation types (roadside vs. riverside) and with or without litter using a life-history trait-based approach. Key Results Performance of I. glandulifera was much lower in graminoid-dominated roadside vegetation turfs than in the herbaceous-dominated riverside vegetation turfs. Although the northern plants exhibited faster onset of flowering, they had lower growth rates, height at maturity and biomass than individuals from central and southern latitudes. Especially the northern plants had lower performance in the highly competitive roadside vegetation compared to the rest of the populations. Interestingly, I. glandulifera litter facilitated the performance of the invader but did not limit the biomass accumulation of the co-occurring species. Conclusions Our findings indicate that the performances of contrasting latitudinal populations of I. glandulifera depend on the invaded vegetation type. The southern and central latitudinal populations of I. glandulifera exhibited higher performances than the northern population. Although litter of I. glandulifera did not limit the performance of native species in invaded vegetation in our study, we show that litter can facilitate the invader s performance. Key words Competitive limitation, Himalayan Balsam, Impatiens glandulifera, invasiveness, invasibility, latitudinal gradient, life-history traits, litter, vegetation type.