The aliens have landed! What are the justifications for ‘native only’ policies in landscape plantings?

Interest in landscaping with native plants has grown rapidly in recent decades, but there is also a rise in ‘native only’ policies where attempts are made to exclude introduced and exotic species from landscape schemes. This paper reviews the issues associated with the use of native and exotic plants in the landscape by looking at a range of philosophical as well as technical issues. The definitions of native and alien status reveal that the concept is not founded on hard science, as often implied, but reflects a set of value judgements about the timescales of environmental change and forms of human impact regarded as acceptable within the landscape. However, the definitions can be said to generate conflicts that cannot be resolved as environmental change and human impacts are inevitable. Native plants are believed to be superior to introduced species because of their better growth, reduced likelihood to become invasive, their indirect and direct biodiversity value and their contribution to local sense of place. In all cases there are exceptions where non-native species play an important role.