European map of alien plant invasions based on the quantitative assessment across habitats

Recent studies using vegetation plots have demonstrated that habitat type is a good predictor of the level of plant invasion, expressed as the proportion of alien to all species. At the scale of a few to hundreds of square meters, habitat types explain much more variation in the level of invasion than climate or alien propagule pressure. Moreover, it has been shown that patterns of habitat invasion are consistent among European regions with contrasting climates, biogeographical affinities, history and socio-economic background. These findings make a solid background for mapping the level of plant invasion, based on the projection of the habitat-specific levels of invasion onto land-cover maps. We used 52,480 vegetation plots from Catalonia (NE Spain), Czech Republic and Great Britain to quantify the levels of invasion by neophytes (alien plant species introduced after AD 1500) in 33 EUNIS habitat types. Then we estimated the proportion of each of these habitat types in CORINE land-cover classes and calculated the level of invasion for each class. The highest levels of invasion were predicted for agricultural, urban and industrial land-cover types, low levels for natural and semi-natural grasslands and most woodlands, and the lowest levels for sclerophyllous vegetation, heathlands and peatlands. We projected the levels of invasion on the European land-cover map, extrapolating Catalonian data to the Mediterranean bioregion, Czech data to the Continental bioregion, British data to the British Isles, and combined Czech-British data to the Atlantic and Boreal bioregions. The resulting map predicted high level of invasion in lowland areas of the temperate zone of western and central Europe and low level in the boreal zone and mountain regions across the continent. Low level of invasion was also predicted in the Mediterranean region except its coastline and areas with irrigated agricultural land