Over the Hedge: Assessment of the Invasiveness and Potential Distribution of the Barrier Plant, <i>Metrosideros excelsa</i> (Myrtaceae), in South Africa and Beyond

Abstract

ABSTRACT Ornamental plants, including barrier or hedge plants, are important in horticulture. Occurring at the urban to natural barrier, plants are often conflict of interest species. Here, we study the invading ornamental barrier plant Metrosideros excelsa Soland ex Gaertn. (Myrtaceae) and determine the current and potential future distribution and the risk posed to South Africa. Roadside surveys were undertaken in the coastal regions of South Africa, yielding 1541 records. Most records are of large, planted trees, indicating a historical horticultural popularity. The 47 naturalising populations occur mostly in low‐lying, seasonally wet coastal areas within the fynbos biome of South Africa. Globally coastal parts of southern Australia, Tasmania, southern Brazil, Uruguay, Argentina, a few scattered areas in the mountains of northern South America and along the Mediterranean are most suitable, while in South Africa, high environmental suitability was predicted along the southwest and south coast. Eradication of M. excelsa from South Africa is unlikely as the species is widespread, and since it is a popular hedge plant in coastal areas, biological control is advisable to minimise conflicts. The risk analysis for South Africa suggests that the species poses a high risk, has potential moderate environmental and minor socio‐economic impacts and the taxon should be controlled as part of a national management programme. Countries in which M. excelsa is a popular ornamental tree and with similar climates and habitats to invaded areas in South Africa should consider prevention measures.