Alien plants in urban nature reserves: from red-list species to future invaders?

Urban reserves, as other protected areas, are aimed at preserving species richness but the conservation effort in these protected areas is complicated by a high proportion of alien species. We examined which environmental factors determine the representation of alien species in 48 city reserves of Prague, Czech Republic, distinguishing between archaeophytes, i.e. alien species introduced since the beginning of Neolithic agriculture up to 1500 A. D., and neophytes, i.e. modern invaders introduced after that date, with the former group separately analysed for endangered archaeophytes (listed as C1 and C2 categories on national red list). Archaeophytes responded positively to the extent of arable land that was in place at the time of the reserve establishment, and to a low altitudinal range. Neophytes, beside soil properties responded to recent human activities proxied by current proportion of built-up area in the reserves. Endangered archaeophytes, besides the same affinity for past arable land as other archaeophytes, were supported by the presence of current wasteland habitats in the reserve. This suggests that for endangered archaeophytes it might have been difficult to adapt to changing agricultural practices, and ruderal wasteland might act as a refugium for them. From the viewpoint of conservation, ruderal habitats of nature reserves thus can be more important than was previously though. Forty-six of the 155 neophytes recorded in the reserves are classified as invasive. The reserves thus harbour 67% of the 69 invasive neophytes recorded in the country, and particularly warning is that among the most invasive species are many shrubs and trees, a life form that is known to account for widespread invasions with high impacts. Our results thus strongly suggest that in Prague nature reserves there is a warning potential for future invasions.