Two faces of parks: sources of invasion and habitat for threatened native plants

To study the role that public parks play as sources of invasions, we surveyed 89 sites in the Czech Republic, comprising chateau parks in urban areas and countryside in various landscapes and socioeconomic contexts, in order to build complete inventories of alien taxa spontaneously spreading outside cultivation in parks or from their surroundings. We describe the richness, diversity, status, frequency and abundance of park floras, explore the relationship between alien taxa, site factors and management practices used in the parks, and assess the invasion potential of the recorded taxa and their interaction with threatened native taxa occurring in the parks. We found that (i) the numbers of escaping invasive species are relatively low, and their population sizes are limited despite the great number of taxa cultivated in parks; (ii) many invasive plants arrived in parks from the surrounding urban and rural landscapes; and (iii) many parks act as refugia for threatened native taxa and vegetation types. We recorded 242 alien taxa, of which 21 were recorded for the first time outside cultivation, representing additions to the national alien flora, seven were cultivars of native taxa, and 26 were native taxa growing outside their natural distribution area in the Czech Republic. The most abundant taxon was the native Hedera helix, which often thrives in its natural habitats; the most abundant alien taxa included the invasive neophytes, Impatiens parviflora and Robinia pseudoacacia. Alien taxa classified as naturalized or invasive in the Czech Republic were recorded as escaping from cultivation in 69% of the parks sampled and casual aliens in only 18%. We recorded 100 Red List taxa, including four critically threatened. Our study shows that parks play a similar role in invasions as other sites in urbanized landscapes, but they also provide habitats for many native taxa. The conservation effect is made possible by regular management primarily focused on aesthetic functions, e.g. removing shrub and tree saplings in specific habitats to maintain open sites and steppe localities.