The aliens have landed! What are the justifications for ‘native only’ policies in landscape plantings?
Introduction
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 (Kendle and Forbes, 1997). 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. As will become evident, these cannot be separated, indeed it is the determination to do so that is sometimes at the root of many environmental problems and false solutions.
The subject merits an initial consideration of the very concept and definitions of ‘native’. We tend to use the terminology of native and exotic or alien as if these words represent a concrete reality that needs no explanation, but actually there are complex issues that need to be addressed. The very search for a definition that people feel accurately reflects their position tells us much about their implicit values and assumptions, and it is beyond doubt that this is a subject that is heavily value-laden.
Section snippets
What are the definitions of native?
Whilst everyone recognises the broad meaning of the concept of native, finding agreement about the definition in a way that allows for consensus about detail is not easy. Webb (1985) reviewed the issue of how native is defined within the context of the UK and Ireland and proposed the following that seems to encompass the generally accepted usage of the term native in the UK: a native plant is one that has arrived before neolithic times, or has arrived since without human agency.
This definition
Functional implications of nativeness
Of course definitions and philosophies are often muddy when dealing with the complex realities of the natural world and arguably the more important issue is the functional importance of the native/alien classification. Let us, therefore, accept even the most conservative concept of native. Why is the distinction significant?
There are five common arguments that are forwarded concerning the importance of native plants and the dangers of introduced aliens or exotic species (Hitchmough and Dunnett,
Conclusions
The above functional critique of the importance of native plants in the landscape amounts mostly to an illustration of how, in a complex environment superimposed with equally complex human history, culture, values and aspirations, it is impossible to characterise one group of plants as ‘superior’ than others. This is especially true when the classification system is as nebulous and as value-laden as our definition of native. In essence it is clear that all of the arguments given to favour the
Anthony (Tony) D. Kendle is lecturer in landscape management in the Department of Horticulture and Landscape of the University of Reading, UK. He holds a Ph.D. in restoration ecology from the University of Liverpool and a B.Sc. (Hons) in Horticulture from the University of Bath. He is a member of the Institute of Ecology and Environmental Management and sites on the research sub-committee of the Landscape Institute UK. Research interests include restoration of conservation value on degraded
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Anthony (Tony) D. Kendle is lecturer in landscape management in the Department of Horticulture and Landscape of the University of Reading, UK. He holds a Ph.D. in restoration ecology from the University of Liverpool and a B.Sc. (Hons) in Horticulture from the University of Bath. He is a member of the Institute of Ecology and Environmental Management and sites on the research sub-committee of the Landscape Institute UK. Research interests include restoration of conservation value on degraded land and urban nature conservation.
Juliet E. Rose is a Ph.D. research student in the Department of Horticulture and Landscape of the University of Reading, UK. She holds an M.Sc. Degree in Horticulture (Distinction) from Reading, and a B.Sc. (Hons) in Biological Sciences with specialisation in Plant Sciences from Kings College, the University of London. Her areas of research address the restoration of degraded and desertified land on islands, and the response to changing environments and land use capabilities.