There can be little disagreement that the common aim of conservationists everywhere is the long-term safeguarding of the natural environment. This being so, the very minimum requirement of conservation is that nature remain recognisably nature. From this point onwards, opinions concerning the role of conservation begin to diverge, not least because there is no set standard with regard to what should count as properly representative of nature. Nevertheless, there is a powerful body of opinion which holds that conservation ought to concern itself only with species and other entities that have a 'natural history' in a place and not with species that have arrived there by means of human intervention, intentional or otherwise. This idea is expressed as the belief that native (or indigenous) but not introduced (or alien) species are worthy of being conserved. As noted by Peretti (1998, pp. 183-184), '[t]he protection and restoration of native species is one of the major foci of conservationists' attempts to protect biodiversity. Biological nativism pervades the environmental movement'. Peretti mentions, for example, the proliferation of native plant societies in the United States 'encouraging the exclusive use of indigenous plants in urban gardens'. A British equivalent is the organisation 'Flora for Fauna' which encourages the public to plant native flora in their gardens in order to support native animals and birds and to this end, provides lists of native plants for each postcode area in Britain. In the same vein, Peretti notes that '[s]ince 1963, the United States national parks have attempted to follow the Leopold Report's directive to re-create original ecological conditions - including the restoration and protection of native species' (p. 184).