Abstract
Information on the origin (status) and regeneration of plant species improves our understanding of native distributions and the establishment of non-native species. However, current categories used to record status in Britain and Ireland, whilst conceptually informative, rely on a knowledge of persistence that is impossible to assess objectively during a single (one-off) recording visit. We propose five alternative categories that focus on origin (how a species arrived at a site) rather than persistence. The first two categories apply to nationally native taxa: (1) populations that are unequivocally native and (2) those that are likely to have been introduced and/or are spreading for reasons that are obscure. The other three categories cover the occurrences of any taxon, native or non-native, that is known or suspected to have been introduced to a site: (3) introductions with unknown/obscure origins; (4) deliberate introductions; and (5) accidental introductions. For the introduced categories 3-5 we recommend that botanists also record signs of regeneration, i.e. seedlings or widely scattered patches, as a more objective measure whether a species is likely to be self-sustaining in a given locality.
Highlights
Botanists distinguish between native species that evolved in the British Isles or arrived there naturally from a native region entirely independent of human agency, from alien species that were introduced by man, either intentionally or by accident, since the start of the Neolithic period some 6,000 years ago (Webb, 1985; Preston, 2002, 2009; Preston et al, 2002; Preston, Pearman & Hall, 2004; Stace & Crawley, 2015)
For the New Atlas of the British and Irish flora, Botanical Society of the British Isles (BSBI) recorders were asked to assess whether native taxa were native or introduced within each 10-km grid square in Britain and Ireland, that is to decide, using their own knowledge and experience, whether a given species could be accepted as native (Preston et al, 2002)
For the New Atlas recorders were asked to assess the extent to which introduced taxa were established at a given location using four categories proposed by Macpherson et al (1996), hereafter referred to as the ‘Macpherson scheme’ (Macpherson, 1997): planted, a taxon which has been deliberately planted in a ‘wild’ situation and is not established; casual, a taxon which is briefly, i.e. for less than five years, or intermittently present; surviving, a taxon which has been present in the wild for at least five years and is neither spreading vegetatively nor reproducing effectively by seed; and established, a taxon which has been present in the wild for at least five years and is spreading clonally or effectively reproducing by seed
Summary
Botanists distinguish between native species that evolved in the British Isles or arrived there naturally from a native region entirely independent of human agency, from alien species that were introduced by man, either intentionally or by accident, since the start of the Neolithic period some 6,000 years ago (Webb, 1985; Preston, 2002, 2009; Preston et al, 2002; Preston, Pearman & Hall, 2004; Stace & Crawley, 2015). For the New Atlas recorders were asked to assess the extent to which introduced taxa were established at a given location using four categories proposed by Macpherson et al (1996), hereafter referred to as the ‘Macpherson scheme’ (Macpherson, 1997): planted, a taxon which has been deliberately planted in a ‘wild’ situation and is not established; casual, a taxon which is briefly, i.e. for less than five years, or intermittently present; surviving, a taxon which has been present in the wild for at least five years and is neither spreading vegetatively nor reproducing effectively by seed; and established, a taxon which has been present in the wild for at least five years and is spreading clonally or effectively reproducing by seed These four categories captured information on origin, i.e. whether a taxon had been intentionally or unintentionally introduced, persistence, i.e. how long a taxon had been present, and regeneration, i.e. whether there was evidence of seed dispersal and recruitment or clonal spread. I Any taxon known or suspected of having been origin unknown introduced to a locality where the origin and/or the mechanism by which it arrived is unknown
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