Nurseries and garden centres act as hubs of alien plant invasions: a case study from Hungary

The growing global horticultural trade has a key role in the introduction of alien plant species into new areas, partly because it also entails the unintentional dispersal of many contaminant species over large distances. However, apart from sporadic reports of such contaminant species, this phenomenon is largely understudied. In order to study this, a systematic field survey of garden centres in Hungary was carried out to assess their role in unintentionally introducing invasive alien species. Twelve garden centres were surveyed in spring, summer and autumn and all individuals of alien species recorded. In addition to the pots and containers of plants for sale, all indoor and outdoor areas, such as flowerbeds, bare and covered surfaces, cracks in the pavement, lawns and other vegetated areas were surveyed. A total of 93,788 individuals of 67 alien species were recorded, seven of which were recorded for the first time in this country. Despite their small area, the studied garden centres hosted a large percentage of the local alien flora, indicating that they strongly accumulate alien species. There were large populations of many alien species, suggesting that garden centres can act as invasion hubs. Trait differences between the alien species in the garden centres and the regional alien flora indicate that the species most successful at colonizing garden centres are both good dispersers and possess an effective resource-acquisitive strategy. Thus, populations of alien plants in garden centres may be the source of local invasions. Moreover, individuals and seeds in the containers of ornamental plants are likely to be transported to distant areas by customers. Despite the limited spatial extent of this survey, the findings indicate that the horticultural trade may act not only as a source of plant introductions, but can also potentially influence the subsequent stages of the invasion process. Thus, there is a need for further studies on the role of species contaminating horticultural stock in alien plant invasions.