Most risk analysis studies in invasion biology have focused on the invasiveness of non-native species, even though some native species also can pose a high risk to the environment and human well-being. This is especially true under current global change, which may cause dominant native species to expand their range of distribution and have substantial effects on the ecosystem. In this study, the risk of invasiveness of five non-native and five native plant species in Turkey was evaluated using a standard risk screening protocol. All ten species selected for screening are known to be invasive in several parts of the world, i.e. non-native Ailanthus altissima, Cuscuta campestris, Phytolacca americana, Robinia pseudoacacia and Sicyos angulatus, and native Cirsium arvense, Hedera helix, Onopordum acanthium, Phragmites australis and Sorghum halepense. The Australian Weed Risk Assessment decision-support tool adapted to Turkey’s geographical and climatic conditions was used for screening the study species based on their biological traits, ecology and management approaches. All species were classified as high-risk, with R. pseudoacacia among non-natives and P. australis among natives achieving the highest scores followed by S. halepense, C. campestris, C. arvense, O. acanthium, P. americana, S. angulatus, A. altissima and H. helix. Based on their risk scores, all non-native species were classified as invasive and all native species as ‘expanding’ for Turkey. An ordination based on the risk scores showed similarities between invasive and expanding species. The outcomes of this study indicate that species can have several risk-related traits resulting in high risk scores irrespective of their origin. Such species can modify their environment and interact with other species with severe consequences for biodiversity. It is argued that dominant species with highly negative environmental and socioeconomic impacts in their habitats should be included in priority lists for management measures irrespective of their origin (i.e. native or non-native). More studies are needed to evaluate the magnitude and prevalence of the present findings for other regions worldwide.
