Aim We tested whether the distribution and cover of alien plant species in Europe was related to human disturbance and microclimate.
Location Surveys were conducted at 13 sites across Europe, each containing a pair of landscapes with different land-use intensities.
Methods Sampling locations were chosen based on land use and microclimate at two scales: land use was characterized at the patch and landscape scale; climate was expressed as regional and local temperature. The slope of each sample location was derived from a digital elevation model. Cover of plant species was measured using point counts and analysed using mixed effect models. Species were classified as native, archaeophytes and neophytes (pre- versus post-ad 1500 immigrants). Due to the zero inflation observed in the alien groups, their cover was analysed conditional on their presence.
Results Anthropogenic disturbance was a significant explanatory variable, increasing the presence and cover of alien species and decreasing the cover of native species. Alien presence was increased in sites under agricultural management, while their cover responded to land use at both local and landscape scales (and to their interaction), such that only natural habitats in semi-natural landscapes had low alien cover. Microclimate was important for neophytes, with presence concentrated around mesic conditions. Slope was relevant for archaeophytes and native species, suppressing the former group and promoting the latter one.
Main conclusions We found that, at the European scale, the distribution of alien plants is related to anthropogenic disturbance more than to microclimatic differences. The presence of neophytes, however, was influenced by climate at local and regional scales, with the highest incidence under mesic conditions. The different patterns observed for the presence and cover of alien species suggest different mechanisms acting during their establishment and spread. They also suggest that to counteract the expansion of alien species natural habitats may need to be maintained at landscape scales.