Invasion patterns of Heracleum mantegazzianum in Germany on the regional and landscape scales

SummaryHeracleum mantegazzianum Somm. et Lev. is an invasive tall forb in Europe with implications for human health (photo-dermatitis), recreational and economic interests, and local biodiversity. This paper presents invasion patterns of the species in Germany on the regional and landscape scales and assesses the species’ impacts on native habitats. We conducted a survey addressing the nature conservation authorities of all 440 German districts and carried out our own field studies in the most heavily invaded landscapes in Germany. The survey indicated that H. mantegazzianum is present and perceived as a potentially dangerous invader in about two-thirds of German districts, while actual or short-term hazards can be assumed for only about 15% of districts. The latter were concentrated in the natural geographic region ‘western low mountain ranges’. In the field studies, dominant stands of H. mantegazzianum, which bear the highest potential for adverse effects on native biodiversity, accounted for 36% of all large stands of the species. Invasion success was highest in abandoned grasslands, grassland and field margins, and corresponding tall-forb stands. The saturation (% area covered) of these preferred habitats with H. mantegazzianum was 8.7%. The invasion percentage (% area invaded) was 18.5%. In conclusion, our results suggest that today H. mantegazzianum has only moderate impacts on the regional and landscape scales even in most heavily invaded regions of Germany.