CONTENTS
SOME ABBREVIATIONS USED IN THIS REPORT
iii
SUMMARY
v
INTRODUCTION
Justification for concern about aliens
Definition of aliens
1
1
2
AIMS OF THE AUDIT
Scope of the audit
5
5
METHODOLOGY
Vascular Plants
Bryophytes
Fungi
Mammals
Excluded domestic/feral stock species
Excluded ancient introductions
Undocumented range extensions of native species
Birds
Amphibia
Fish
Invertebrates
7
7
10
11
11
11
11
11
12
13
13
13
AUDIT FINDINGS
Vascular Plants
Numbers and occurrence of alien species
Origins and mode of introduction of alien plant species
Present impact of alien plant species
Bryophytes
Fungi
Mammals
Birds
Amphibia
Fish
Invertebrates
Introduction of alien races of native plants
17
17
17
21
24
33
34
34
36
37
37
38
39
DISCUSSION
The current entry, status and impact of aliens in Scotland
Pathways of entry
Differences between regions and habitats
Historical perspective
Reasons for the success of aliens
Evaluation of the costs and benefits of aliens
Ethical consideration about aliens
Possible measures for dealing with unwanted introductions
43
43
44
45
45
46
47
49
50
REFERENCES IN THE TEXT AND APPENDIX 1
55
i
APPENDIX 1: LISTS OF ALIENS AND KEY DESCRIPTIVE INFORMATION
Vascular plants
Bryophytes (Liverworts)
Bryophytes (Mosses)
Mammals
Amphibia
Fish
Invertebrates
59
64
107
108
109
112
113
115
APPENDIX 2: PROFILES
120
APPENDIX 3: SCIENTIFIC NAMES OF SPECIES APPEARING IN THIS
REPORT
221
ii
SOME ABBREVIATIONS USED IN THIS REPORT
BRC
Biological Records Centre
BSBI
Botanical Society of the British Isles
CEH
Centre for Ecology and Hydrology (formerly the Institute of Terrestrial
Ecology)
cf.
compare
DETR
Department of the Environment, Transport and the Regions
EC
European Commission
MAFF
Ministry of Agriculture, Fisheries and Food
NZ
New Zealand
SNH
Scottish Natural Heritage
spp
species (plural)
UK
United Kingdom
v.
against
SOAEFD
Scottish Office Agriculture, Environment and Fisheries Department
DANI
Department of Agriculture Northern Ireland
WOAD
Welsh Office Agriculture Department
USA
United States of America
iii
iv
SUMMARY
1.
Alien species were defined as ones introduced accidentally or deliberately by
humans.
2.
The terrestrial and freshwater alien plants and animals now occurring in
Scotland were ascertained from atlases for particular groups, from Biological
Record Centre databases, and from trawls through key works listing British
species.
3.
Other basic information about these aliens was assembled from various
sources, and is presented in tables for vascular plants, bryophytes, mammals,
birds, amphibians, fish, and some better-known invertebrate groups.
4.
For each species, information is given on its origin, manner of introduction,
present abundance and distribution, trends in abundance, nature of impact,
significance of present and future impacts, and whether it is naturalised.
5.
Analyses of this basic information were carried out for the five main groups of
biota (vascular plants, mammals, birds, fish and invertebrates) to assess the
current status of aliens. Totals are provided for the whole of Scotland, for
seven geographical regions, and for eight habitat groups into which all
habitats have been classified.
6.
It was found that there are at least 988 alien species occurring in Scotland.
The list consists of 824 vascular plants, 6 bryophytes, 13 mammals, 49 birds
(but only 8 breeding species), 16 fish, 22 insects in better-known groups, 50
molluscs in better-known groups, 5 other invertebrates and 1 amphibian.
Fungi were not systematically assessed.
7.
Most alien vascular plants were introduced as garden outcasts. Other
important modes of origin were accidental carriage in grain imports and seed
mixes.
8.
About 80 per cent of the alien vascular plants are currently infrequent in
occurrence in that they are found in less than 15 per cent of the 10 km
squares in Scotland. Only 92 are widely distributed being found in at least
five of the seven regions of Scotland.
9.
Alien vascular plants are much more numerous in the South and Central Belt
regions than less-populated regions. They are also more frequent in manmade habitats, grasslands and woodlands than in coastal, wetland and
upland habitats.
10.
From their biology, 203 species of alien plant were classed as competitors,
and 142 as habitat damaging, the remainder merely having impact by their
presence. From their behaviour, 77 of the alien vascular plants were
considered to be naturalised, defined as spreading by their own qualities
rather than human interference.
v
11.
The majority of alien vascular plants experienced no change in abundance
between monitorings in the 1950s and 1987-1988, but 103 species increased
and only 13 species decreased.
12.
Successful alien plants in Scotland were considered to have four basic
attributes, namely
 they originate from North Temperate areas with similar climate to the
regions they have colonised;
 they reproduce effectively and have good dispersion;
 they are competitors able to do well in widespread habitat types; and
 they have good defences against herbivory.
13.
The alien mammals are mostly widespread, and ten of these species were
judged to have damaging impacts (American mink, black rat, brown rat, feral
cat, feral ferret, feral goat, fallow deer, sika deer, grey squirrel and rabbit).
Several species were introduced deliberately for sporting purposes, and
several were accidental escapes.
14.
The alien birds have variable abundance, most being recent introductions.
Only two species were rated as having adverse direct impacts (Canada goose
and ruddy duck), but the rearing of pheasants also causes habitat damage.
15.
The alien fish species are mostly restricted in range with occurrences mainly
in the South and Central Belt regions. Several introductions were done
deliberately for the purpose of providing quarry for recreational fishing, and
others were accidental releases of bait fish. Most of the introduced species
came from England.
16.
There are few known invertebrate alien species, the most numerous being
slugs and snails. Only a handful of invertebrates are rated as having
damaging impacts, including the green spruce aphid and flatworms from
Australia and New Zealand, which prey on earthworms.
17.
Some examples of important and representative alien species were chosen
and are presented in two-page profiles; there were 30 plant species
(26 vascular plants, two bryophytes and two fungi) and 19 animal species
(seven mammals, four birds, one amphibian, two fish and five invertebrates).
Information is presented on biology, current status, impacts and control.
18.
Possible measures suggested for tackling alien species include




a publicity campaign about the problems of garden outcasts;
studies on naturalised aliens of reproductive and dispersal capacity so that
likely invaders can be picked out;
greater controls on animal collections and culture; and
more tests on imported materials especially grain, seed mixes and soil,
which could harbour potentially damaging species.
vi
INTRODUCTION
Alien species are defined in this report as ones not occurring naturally in Britain, i.e.
species that have been introduced accidentally or deliberately by humans. This
definition is the same as used by Usher (1999) in a paper discussing the concept of
nativeness. As there are subtle differences between classes of biota in how the
definition is normally applied, to which we have adhered, a fuller treatment is given
later in this introduction.
Great Britain is the basic land unit for which native occurrence has been judged.
Other species native in England or Wales, but alien to Scotland, have additionally
been included in the audit.
The pathways by which alien species reach a new country can be classified as
deliberate or accidental, and often two or more steps are involved in a species
becoming naturalised, one step being deliberate and planned, and another being
accidental and unforeseen. Deliberate introduction includes transport or release for
agriculture, horticulture or silviculture, for domestic or medicinal use, for
conservation purposes, and for game rearing and in fisheries. Accidental entry
includes escape, outcasts from gardens, and carriage on vehicles, animals or
persons moving between countries, or in products such as grain, hay and timber.
Obviously there are potentially many such vectors, but biologists have normally
identified only the more important.
More information will be given about these pathways when the numbers of aliens
having different origins are presented later in the audit.
Justification for concern about aliens
Issues about alien species, their impact, importance, control and management, arise
repeatedly in conservation at the present time, and it is desirable to bring together a
comprehensive account of aliens in Scotland in order to inform policy. This is
especially true now that more decisions about land management and good practice
are being made in Scotland. Moreover, a review on introductions has been called
for as part of the UK Biodiversity Action Plan.
Past examples of alien plants and animals spreading uncontrollably and having
serious effects on habitats and other wildlife species, for instance the impacts of
mink, giant hogweed and rhododendron in Scotland, give ample warning that further
major wildlife impacts due to aliens could occur. But despite a general awareness of
these events, there is little indication that the human attitudes and behaviour which
led to them have changed. Indeed the opportunities for alien species to become
established are probably still increasing, with greater trade, more people travelling,
new crops and management practices, and also climate changes. In particular, the
predicted warming during the next century will open Scotland to invasion from an
increased number of species, warmer regions having greater species diversity than
cooler regions.
1
For several reasons the threat posed by aliens is not normally obvious to those
doing the activities which lead to naturalisation. Most important is that only a small
proportion of the species introduced become pests. A ‘tens rule’ has been put
forward (Williamson & Fitter, 1996a), whereby only 10 per cent of the species
imported into Britain appear in the wild, only 10 per cent of these become
established, and only 10 per cent of these established species become pests, i.e.
0.1 per cent of the species arriving. This low rate of success reflects the
unfittedness of the imported species to the host ecosystems, and the lack of niches
for colonisation, but may well vary greatly between classes of biota. The perceived
improbability of the combination of events and pathways that will lead to
naturalisation actually occurring is what induces complacency.
Another hindrance to managers trying to avoid catastrophic spread by aliens is the
very large number of species involved and the many routes of entry to habitats, all of
which need some monitoring. There is also the long time scale over which
assessments are required, since retrospective studies on major pest species have
quite often shown that they had initially very slow rates of spread.
A topical issue for which current knowledge about aliens is necessary is the genetic
modification of crops, trees and fish. One way in which crop plants are being
modified is to give them genes resistant to herbicides, and there is worry that these
genes could spread to weed species growing with the crops, these species then
becoming much less controllable. Transfers are more likely to allied species, so it is
desirable to know what weeds grow with particular crops, or might grow with them in
the future. Even if the resistant genes spread to just one weed species, the
consequences could be serious.
For plants there is another concern, that of alien races of established native species
being brought into Scotland and changing the genetic constitution of the resident
species. The plants affected include trees, e.g. the Scots pine, and grassland herbs.
The means of introducing them are respectively planting for commercial forestry,
and the sowing of grass/wild flower seed mixes to give cover quickly on roadside
verges. The extent of these practices, and the issues arising, are discussed in the
Audit Findings section of the report, but the species involved are not included in the
main data sets.
Definition of aliens
Botanists have long separated introduced species from native species in their floras,
the former term being used for species brought into a country by humans. These
species are called aliens, perhaps as a verbal short cut instead of saying introduced
species. Species which have arrived naturally from abroad, e.g. by wind dispersal or
carried by animals, are excluded, e.g. in Clement & Foster (1994).
Zoologists usually include all species recently arrived from abroad as aliens
whatever their agency of introduction (deliberate, accidental, or natural), but then
have problems defining ‘recent’. For well-studied groups (birds and mammals),
historic points in time can be stated, e.g. 0 AD, but for other groups it is only possible
to separate out very recent arrivals. Thus entomologists, with very little information
on occurrence and distribution before the nineteenth century, may suspect that
2
species with few records in Britain and many in other countries are aliens, but they
do not certainly class them as this without hard evidence. An example of a species
that has changed from being a Red Data Book rarity to being an alien is the
longhorn beetle (Tetropium castaneum) which is profiled in Appendix 2. For groups
that are not so well-known, the proportion of alien species out of the total number of
species is likely to be an under-estimate.
In practice, British botanists have ruled out very few species from being classed as
alien on the human-involvement criterion, the usual assumption being that if birds,
for example, carry a plant so can humans. One species that is treated as native,
despite obviously being regularly conveyed to Britain from abroad, is the creeping
spearwort (Ranunculus reptans), brought from Iceland to Scottish lochs each
autumn by migrating pink-footed geese (Anser brachyrhynchus) (Gornall, 1987).
Another accepted native is the pipewort (Eriocaulon septangulare) which is confined
to Coll, Skye and the extreme west of Ireland, but which is widespread in North
America; dispersal across the Atlantic is suspected for this species. The number of
these species is minute compared to the 3,586 species considered alien to the
British Isles in Clement & Foster (1994).
Mammalogists have also ruled out very few species from the alien category on the
time-period criterion, the main example being the Orkney vole (Microtus arvalis),
which was probably brought accidentally to Britain by Neolithic settlers around
3500 BC.
In Usher (1999) a division of non-native species into ‘long-established’ and ‘recentlyarrived’ is suggested, the latter being paralleled by a similar sub-division within
native species. Distinction between the two groups of new arrivals depends on the
balance of probability on whether human activity helped in their colonisation, and is
obviously arbitrary. We have followed the opinions of authorities for the biota
classes in our listings, e.g. the collared dove (Streptopelia decaocto) is not included
in the audit although changes in agricultural practices possibly encouraged its
colonisation of Britain. More details are given about the selection of species in the
Methodology section.
3
4
AIMS OF THE AUDIT
The audit aims
 to list all currently known terrestrial and freshwater alien species present in
Scotland (non-native marine species have been reviewed separately by Eno et al.
(1997));
 to give basic facts about these species, their origin, manner of introduction,
current distribution, trends in abundance, habitats and ratings for their current and
future impacts;
 to identify particularly vulnerable habitats or regions;
 to identify alien species that could potentially become serious pests;
 to increase awareness and understanding of key alien species, either because
they are ones likely to become pests or because they typify groups of alien
species;
 to highlight the key issues relating to the introduction of alien species to Scotland;
and
 to suggest ways or measures that will reduce the adverse impacts of aliens.
In fulfilling these aims we have encountered two major problems. First, there is the
very large number of alien vascular plants currently established in Scotland,
considerably greater than we believed before starting the work. Most of these
plants, except for some prominent nuisance species, have received very little
attention from Scottish botanists, and very little is known about their distribution,
performance and status. Secondly, for many less-studied groups such as the
invertebrate classes and some lower plants, it is hard for researchers working on the
group to know what is an alien when numerous apparently native species are still
being newly found in Britain. Even with well scrutinised groups such as birds, there
are problems in compiling a complete inventory. Birds are highly mobile and it is
difficult to determine the provenance of exotics. Some are clearly vagrants, i.e.
displaced migrants, but others could have escaped from captivity. Some may even
have found assisted passage by seeking refuge aboard ships. Where such birds
were thought to be alien, records were not archived until quite recently. We have
therefore little historical information on the occurrence of, for example, budgerigar,
red-cheeked waxbill or Chilean flamingo. Hence, it is probable that many fewer
species have been listed in the audit than the likely totality of the recent and current
flow into Scotland of alien plants and animals. These weaknesses are the result of
real gaps in scientific knowledge rather than consequences of the reporting process.
Scope of the audit
The main task has been to describe the current state of aliens in Scotland,
particularly their abundance, distribution and impact, rather than prescribe
responses to particular problems. So lists of all known aliens and basic facts about
them are presented, and analyses have been made in order to summarise this basic
information. In these analyses, differences between habitats and regions have been
assessed with particular respect to the numbers of species involved and the
importance of their impacts. To help increase awareness of how aliens become
established, have an impact on the environment and how they are controlled, two5
page profiles for 49 alien species are presented in Appendix 2. Information from
these profiles is used to illustrate the conclusions from the all-species analyses
given in the Audit Findings section of the report.
Our approach to the work fits with the Pressure–State–Response model now often
used in environmental auditing. In this model, alien species represent a pressure on
the Scottish environment, the current composition and structure of that environment
are the state, whilst the response includes both actual control activities and potential
management. This audit provides an overview of the scale of potential pressures on
the natural heritage as a result of alien species and reports briefly on the nature and
extent of their present impacts. The Discussion section suggests possible measures
that could be included in a programme to combat the introduction and presence of
alien species in Scotland. Three key numbers which are relevant to the model, and
which also test Williamson & Fitter’s (1996a) ‘tens rule’, are the number of alien
species recently recorded in Scotland, the number of these species considered to be
naturalised, and the number of naturalised species for which control measures are
being actively undertaken at present. These are tabulated for the different classes
of biota in the Discussion section of the report (Table 15).
The structure of the report comprises, following this introduction, sections on the
methods employed, the audit findings and a discussion of these findings and key
related issues. These include the rationale for selective control of aliens and a
consideration of the importance of the parameters which aliens influence or alter,
such as biodiversity, naturalness and genetic integrity. The main report ends with
acknowledgements and a reference list, this including all articles cited in the main
text and Appendix 1.
Much detailed information about Scottish alien species is contained in two
appendices, the first, the audit tables, giving complete lists of aliens for different
groups and basic information on each species (Appendix 1), the second giving the
49 profiles, for 30 plants and for 19 animals (Appendix 2). Because of the
constraints of space on the printed page and the size of legible text, not all of the
information given to SNH has been shown in the tables, the rest being contained in a
spreadsheet database held by SNH and which can be readily manipulated to draw
out required facts. Additionally, there is an introductory summary of column
headings, abbreviations and conventions for Appendix 1, and Appendix 2 has an
index of the names of the profiled species. Appendix 3 provides a list of all of the
scientific and common names for species referred to in the report.
6
METHODOLOGY
The work started with a series of trawls through the recording schemes of the
different groups of biota (vascular plants, bryophytes, fungi, mammals, birds,
amphibians, fish, invertebrates) in order to pick out all the species considered aliens
by group specialists. Major works, which either list British aliens or discuss the
criteria used in their selection, are cited in the text for each group that follows below.
The basic facts required about the alien species were obtained from other published
sources, the key ones also being cited below.
The procedures used differed slightly between the groups of biota because the
bases and timing of each recording scheme varied considerably. There were many
more aliens for vascular plants than for any other group. These procedures and the
criteria adopted in producing the audit appendices, data sets and tables are now
outlined for each group.
To assess current distribution, Scotland has been divided into seven regions based
on the Watsonian vice-counties, and reflecting likely ecological disparities. These
are South, Central Belt, West (Western Highlands and southern, inner Hebrides
Islands), East, North, Outer Hebrides, Orkney and Shetland (Fig. 1). The vicecounties allotted to each region are given in the introduction to Appendix 1.
Vascular Plants
All of the species judged by Clement & Foster (1994) to be alien in the British Isles
were considered for the audit list, but only those species believed to be present in
Scotland after 1986 have actually been included. This cut-off date reflects the start,
in 1987, of a major recording exercise by the Botanical Society of the British Isles
(BSBI), to produce for the millennium a new atlas of the distribution of plants on the
hectad (10 km x 10 km square) scale. The data from this recording scheme are
collected by the Biological Record Centre (BRC) of the Centre for Ecology and
Hydrology (previously known as the Institute of Terrestrial Ecology). By using a start
date of 1987 the list of aliens was considerably shortened, many aliens brought to
Scotland by once-important practices and trades, e.g. shoddy imports, now no
longer occurring.
Species considered alien in Scotland although native elsewhere in the British Isles
have been identified chiefly from the distribution maps given in Perring & Walters
(1962). However, botanists at that time made decisions about native status with little
regard to the boundaries of the component countries within Britain, so the maps
convey the broad pattern of where introductions are likely and could well conceal
minor native populations.
7
Figure 1. The boundaries of the seven regions of Scotland used for reporting the
distribution of the alien species.
8
For the assessments of current status only post-1986 records have been examined,
with division into two scales of abundance, above and below a 15 per cent frequency
of occurrence in hectads (10  10 km square). As only a proportion of the hectads
in a region had had their plant records assimilated by BRC at the time of analysis, a
third, minor level of abundance has been employed; this is for species known to
occur but with no hectad presence in the available data. Information on these
occurrences has been obtained from other published sources, e.g. floras, and from
direct communication with knowledgeable botanists.
The current trends in status of vascular plants have been decided by making use of
the 1987-1988 BSBI Monitoring Scheme. This was a special campaign for the
whole of the British Isles in which every ninth hectad was recorded, giving a total of
118 usable hectads in Scotland excluding some with only fragments of land. The
frequency of occurrence in 1987-1988 was compared with the frequencies recorded
in the 1950s for the production of the 1962 BSBI Atlas (Perring & Walters, 1962),
using exactly the same hectads. Similar comparisons have previously been reported
in Rich & Woodruff (1990), but the calculations on the significance of the changes
were done from a whole-British-Isles standpoint; therefore new comparisons using
Sign Tests (Dixon & Mood, 1946) have been made for this report, based entirely on
Scottish hectads. A significant increase (or decrease) was taken to be one with
<5 per cent chance of occurring. To achieve significance, a species had to have at
least six increases (or decreases) and no hectads having decreases (or increases),
or at least eight increases if there was one decrease, or at least ten increases if
there were two decreases, etc. For species with less clear-cut differences, a further
division was employed, those with small increases (or decreases) having at least
half the number of occurrences needed to attain the 5 per cent level of significance
(i.e. 3 cf. 0 occurrences, 4 cf. 1, etc.). Species with smaller differences were said to
show ‘no or minor trend’.
Statements about the means of introduction and origin of alien plants have been
based on comments in Clement & Foster (1994) and current authoritative floras
(Clapham, Tutin & Moore, 1987; Stace, 1991). Usually all the introduction modes
stated in Clement & Foster are given, and the full geographic range of a species.
Deciding that a species has mostly come from a particular country or by a particular
mode of entry (e.g. in grain imports rather than as a seed contaminant), when
several modes are known requires considerable examination of the evidence and
was beyond the scope of the current work. Manners of introduction given by
Clement & Foster which clearly do not occur in Scotland were ruled out, e.g. species
not being cultivated agriculturally here. Also for species native elsewhere in the
British Isles, but alien in Scotland, the country of origin has normally been given as
the British Isles despite all these species having wider ranges.
The nature of the impacts of alien plants, i.e. if they are competitors, cause habitat
damage, or merely have impact from being present, was assessed from several
biological attributes, chiefly their mean height, growth rates, aggregation, shade and
litter cast, and whether they are perennial, biennial or annual. Competitors were
defined as species growing so tall or vigorously that other species would be lost from
communities, and species causing habitat damage were ones which affected the
ground layer by litter fall or shading, also causing species to be lost.
9
The value of the alien species was judged on a three-point scale (adverse, benign or
beneficial) using criteria based on conservation and aesthetic stand-points; the
evaluation was broad and indicative. Whilst it is acknowledged that many species,
such as conifers, give great benefits yielding fibre, food and other products, this
audit considers foremost their effect on habitats and other species. For a few
species with generally accepted aesthetic value such as cedar trees or lupins we
have changed benign ratings given on conservation criteria to beneficial ratings, but
have not done this for seemingly attractive plants such as rhododendrons given
adverse ratings for other reasons. Similarly, a few species of cultural or antiquarian
interest because they tell of past events and practices, e.g. Magellan ragwort
(Senecio smithii) brought back by whalers operating off the tip of South America,
and butter dock, whose leaves were used to wrap up butter, have been uprated from
a benign ranking to beneficial. These decisions, though given on the basis of the
authors’ subjective opinions, do conform to commonly held views among
conservationists.
The location where the aliens grow considerably affected the value rating given,
semi-natural communities being viewed as unsuitable for aliens, whereas waste
ground, man-made habitats such as lawns, and habitats strongly influenced by
humans, such as the policies around mansion houses, are felt not to suffer from
alien presence. The increase in biodiversity resulting from alien establishment has
not been considered a possible benefit.
The significance of the impact of the alien plants was assessed for the present time
and also for a period 20 years from now. The assessment was made using their
current abundance in the 1987-1998 period, and their likely abundance in 20 years’
time, judged from their change in abundance from the 1950s recording to the 19871988 recording to their abundance now. For alien species having adverse impacts
these ratings give an indication of how important they are now, and also help to pick
out the ones likely to become pests in the future. But these ratings also assess the
importance of benign species. Thus, common aliens such as the slender speedwell
(Veronica filiformis), which gives a summertime blue sheen to many lawns in
Scotland, are classed as having a moderately significant impact even though this is
not adverse; this procedure gives a balanced description of the role of aliens at
present in Scotland.
Bryophytes
Hill & Preston (1998) list 19 species of bryophytes which are regarded as
introductions in the British Isles. These were considered for the current audit, being
checked for recent occurrence in Scotland. The distribution of the species found to
be Scottish was then ascertained for the standard seven regions (Fig. 1). The same
two scales of frequency were used, based on the presence of the species in more or
less than 15 per cent of hectads in a region, as for vascular plants. In calculating
the frequency, records made from 1950 onwards have been included to correspond
with the data presented by Hill et al. (1991, 1992, 1994). A cut-off year of 1987 was
impractical since this would have much reduced the apparent number of records,
there being few bryologist recorders and no special effort began then, unlike for the
vascular plant recording scheme.
10
In addition to the bryophytes regarded as introductions throughout Britain, a few
weedy species (e.g. Lunularia cruciata) could perhaps be introduced in Scotland
although native in England. These have not been included in the tabulation, as the
assignment of taxa to this category would be extremely speculative in the absence
of any detailed historical evidence.
Fungi
For this group no attempt at systematic searching for aliens was made; however, a
few species which are definitely considered to be alien were included as examples.
Mammals
For this group, the native/introduced categorisation has been taken from published
handbooks (Corbet & Harris, 1991) and distribution atlases (Arnold, 1993), while
indications of changes in populations have been taken from Harris et al. (1995). A
review of these publications found 20 species of mammal that are described as
being introduced to Scotland or parts of Scotland, but only 13 have been listed in the
audit table (Appendix 1). The other seven species were excluded from the lists
because of either their domesticated nature, or their ancient occurrence, or their
introductions being undocumented extensions to ranges.
Excluded domestic/feral stock species
There are three excluded domestic/feral stock species:- the horse (Equus caballus)
(free-ranging populations on Shetland and certain Hebridean islands), the reindeer
(Rangifer tarandus) (single managed herd in Cairngorms since 1952), and the feral
sheep (Ovis aries) (the Soay and Boreray breeds confined to Soay/Hirta and
Boreray islands of the St Kilda archipelago, respectively). Division of these species
from the feral goat (Capra hircus), the feral cat (Felis catus), and the two deer
species that are included as aliens (Sika deer (Cervus nippon) and fallow deer
(Dama dama)), is somewhat arbitrary, but the excluded species receive some
management as livestock or are unlikely to spread beyond their present very small
range.
Excluded ancient introductions
Two species are believed to have been introduced long ago to one or more of the
‘remoter’ Scottish islands: pygmy shrew (Sorex minutus), and Orkney/Guernsey vole
(Microtus arvalis). These introductions were probably accidental. The Orkney vole
was probably introduced by Neolithic settlers between c. 3700 and 3400 BC.
Undocumented range extensions of native species
The hedgehog (Erinaceus europaeus), whilst native to Scotland, has been
introduced recently to some islands, probably for aesthetic reasons. Also the stoat
(Mustela erminia) has apparently been deliberately introduced to several islands
fairly recently, e.g. to Shetland, on the assumption that it would help control small
mammal pests; such range extensions are beyond the scope of the audit.
11
Birds
The birds considered by the audit are designated as Category C in the British
Ornithologists’ Union Records Committee list of British birds (Holmes et al., 1998).
Category C is defined as those ‘species that, although originally introduced by Man,
either deliberately or incidentally, have established breeding populations derived
from introduced stock that maintain themselves without necessary recourse to
further introduction’. Four Category C birds are omitted from the alien list as they
were native species which became extinct but have since been re-introduced
(capercaillie (Tetrao urogallus), northern goshawk (Accipiter gentilis), red kite (Milvus
milvus) and white-tailed eagle (Haliaeetus albicilla)). Only birds that have selfsustaining populations in Scotland (Forrester, 1994) have been included in the audit
list, hence vagrants, e.g. white stork (Ciconia ciconia), and non-breeding migrants,
e.g. fieldfare (Turdus pilaris), are excluded.
The criterion of a self-sustaining population is not always easy to determine. Some
species have bred sporadically in Scotland or in small numbers and may ultimately
form a viable long-lasting population, though this is not likely now or in the near
future. Examples include barnacle goose (Branta leucopsis), white-fronted goose
(Anser albifrons), muscovy duck (Cairina moschata) and eagle owl (Bubo bubo).
Another species, the black-crowned night heron (Nycticorax nycticorax hoactli), has
had a long-established free-flying breeding population, but has never spread outside
of Edinburgh and seems to be dependent on the food provided at the Zoo to breed.
None of these species has been listed, although the night heron has been given a
profile in Appendix 2 which helps describe its status. The snow goose (Anser
caerulescens) has had a self-sustaining population for many years and, therefore,
has been included even though it is not yet designated Category C (Vinicombe et al.,
1993); the reason for this delay is that the population has remained small despite an
initial increase.
Species that have both native and introduced components to their Scottish breeding
populations, e.g. greylag goose (Anser anser) and rock pigeon (Columba livia), have
been excluded from the audit table. Also, a few species are excluded when it is
uncertain whether the population established from artificial or natural provenance.
An example is the gadwall (Anas strepera), which was introduced into England, but
its establishment as a Scottish breeding species coincided with a dramatic increase
in the Icelandic population, and so most authorities believe it was a natural
colonisation.
In the appended tables the assessments of abundance have been made for the
same standard regions as used in the vascular plant tables. The same categories
have been employed for the significances of impacts. For the assessments of
trends in status, the 1990s have been compared to the 1950s, making use of recent
surveys and, in particular, the New Atlas of Breeding Birds in Britain and Ireland:
1988-1991 (Gibbons et al., 1993), fieldwork for which took place from 1988 to 1991.
12
Amphibia
A single alien amphibian is known in Scotland, the alpine newt (Triturus alpestris).
An entry for this species follows the bird table in Appendix 1, and uses the same
categories.
Fish
The categorisation of fish as introduced or native in Scotland has been taken from
published reviews and distribution maps (Maitland & Campbell, 1992; Giles, 1994).
A review of these publications suggests that there are 16 species of introduced fish
in Scotland, all of which have been included in the audit tables. Five fish considered
late arrivals to Scotland, but with established populations by 1790 (northern pike
(Esox lucius), roach (Rutilus rutilus), stone loach (Noemacheilus barbatulus), perch
(Perca fluviatilis) and minnow (Phoxinus phoxinus)) have been excluded from the
audit because it seems more likely that they came by natural means, e.g. on the feet
of wildfowl, rather than by human intervention (Maitland, 1994). Because of
sampling difficulties, there are no standard surveys of fish distribution and hence
little information is available on population status. There is also very little information
on the potential threats of these introductions. So the assessments given are
subjective opinions rather than objective facts based on proper survey.
The same regions have been used to report current distribution in Scotland as for
the vascular plants, and the same terms to report change in status and significance
of impact. Much of the information presented is contained in Maitland (1994) and
Maitland & Campbell (1992), having been gleaned by them from many sources.
Invertebrates
The invertebrate part of the project has covered all those taxonomic groups for
which the Biological Records Centre holds suitable computerised data. These are
listed in Table 1, together with the number of species considered by group
specialists to be alien in Scotland. The groups included are diverse and have a wide
ecological range, with representation from the terrestrial and freshwater biomes.
In addition, information on some other known Scottish aliens, belonging to groups
not having Biological Records Centre recording schemes, has been gleaned from
literature and from relevant experts. These species comprise one landhopper, two
flatworms, one aphid and one weevil.
It should be noted that the BRC database of non-marine Mollusca is currently being
reviewed and updated. Information supplied here on the distribution of Scottish
molluscs, a group with many aliens, should therefore be regarded as preliminary, but
the categorisation of status follows Kerney (1999), being given in the notes column
of the Appendix 1 list.
No attempt has been made to exclude a species from consideration if it has not
been recorded in Scotland in recent years. Such apparently extinct species may
merely have been overlooked, given the very small number of active recorders in
these groups compared to botanists and ornithologists. Also, species whose status
13
as aliens has been doubted, for example because they are considered native in
other European countries or because they are now widespread in Britain, have been
included in the Appendix 1 audit list and the counts of alien species. Similarly, some
species may be merely vagrants, brought to Scotland by, for example, unusual
winds rather than carried here by man, but ruling out particular modes of entry is
difficult, especially so when there are few records. To describe the balance of
probabilities for the status of species included in the audit, the notes column of
Appendix 1 employs the following terms – ‘unknown status’, perhaps native,
probably native, perhaps vagrant, and probably vagrant.
Many alien invertebrates survive in association with man in permanently heated
buildings, greenhouses, or in buildings housing grain, bone-meal, or other sources of
food, being known as synanthropic species. While it can be possible to find some of
these outdoors in summer, they do not become established outdoors except in very
artificial situations such as rubbish dumps. This whole suite of species has been
excluded from the audit since they have little if any relevance to ecological
processes in Scotland.
14
Table 1. Groups of invertebrates assessed for the occurrence of Scottish alien
species.
Taxonomic group
English name
Hirudinea
Mollusca (non-marine)
Cladocera
Isopoda (in part)
Decapoda (in part)
Diplopoda
Chilopoda
Odonata
Orthoptera
Dictyoptera
Dermaptera
Phasmida
Neuroptera
Megaloptera
Raphidioptera
Mecoptera
Atomariinae
Coleoptera: Cantharoidea &
Buprestoidea
Coleoptera: Carabidae
Coleoptera: Cerambycidae
Coleoptera: Coccinellidae
Lepidoptera, macro-moths
Lepidoptera, butterflies
Lepidoptera, burnets
Diptera: Sepsidae
Diptera: Ptychopteridae
Diptera: larger Brachycera
Hymenoptera: selected species
freshwater leeches
molluscs
water-fleas
woodlice
crayfish
millipedes
centipedes
dragonflies
grasshoppers and crickets
cockroaches and mantises
earwigs
stick-insects
lacewings
alderflies
snake-flies
scorpion-flies
atomariine beetles
soldier and jewel beetles
Opiliones
ground-beetles
longhorn beetles
ladybirds
Macro-moths
Butterflies
Burnet moths
sepsid flies
ptychopterid craneflies
horse-flies, robber-flies, etc.
110 species of bees, wasps and
ants
harvestmen
15
Number of alien
taxa in Scotland
0
50
0
1
1
0
0
0
0
0
0
0
0
0
0
0
8
0
4
2
3
3
0
0
0
0
0
0
0
16
AUDIT FINDINGS
Vascular Plants
Numbers and occurrence of alien species
About 830 alien vascular plant species have been included in the audit table
(Appendix 1), having been observed in Scotland since 1986. About 10 per cent are
Scotland-only aliens that occur as native elsewhere in Britain (89 species) but the
majority (735 species) are not thought to be native anywhere in the British Isles
(Table 2). This compares with a total of 3,586 alien species, excluding grasses,
listed by Clement & Foster (1994) as having been recorded in the British Isles at
some time. However, substantial numbers of the latter species were probably shortlived introductions, not now present. In comparison, Stace (1991) has approximately
1,400 alien species and Kent’s (1992) check list of the British flora has just
1,057 alien species, reflecting progressively stricter qualifications of permanence for
inclusion in these two works.
Table 2. Numbers of alien vascular plant species currently occurring in Scotland
belonging to different taxonomic groups.
Taxonomic group
Ferns and allies
Gymnosperms
Chenopods
Crucifers
Rose allies
Legumes
Composites
Other Dicotyledons
Total Dicots
Grasses
Other Monocotyledons
Total Monocots
Subtotals
Total Vascular Plants
Aliens in British
Isles
5
27
11
41
96
38
83
331
600
36
67
103
735
Aliens in Scotland but
native elsewhere in
British Isles
0
0
3
3
3
2
5
55
71
4
14
18
89
824
The make-up of the Scottish alien flora in terms of plant families has been compared
to the whole-British-Isles alien flora, using for comparison the BRC list of aliens, this
being based on Kent’s (1992) check list supplemented by some of Stace’s (1991)
extra species. The Scottish alien flora is less rich in chenopods (members of the
Chenopodiaceae (families 43 and 44 in Appendix 1) e.g. goosefoots) and grasses
than the whole-British-Isles alien flora, and richer in gymnosperms, crucifers
(members of the Cruciferae (family 62 in Appendix 1) e.g. mustards and rockets)
and rose allies. The respective percentage occurrences of species in the above
groups in Scotland after 1986, and in the BRC list, are gymnosperms 4 per cent v.
17
2 per cent, crucifers 6 per cent v. 5 per cent, rose allies 13 per cent v. 11 per cent,
chenopods 1 per cent v. 3 per cent, grasses 1 per cent v. 9 per cent.
The size of the group of species alien to Scotland, but native elsewhere in the British
Isles, is somewhat problematic in that some of its species could be native here, or
native in some areas and introduced elsewhere; this is commented on in the ‘Notes’
column of the audit table (Appendix 1). Examples are field maple (Acer campestre)
and white stonecrop (Sedum album). As explained in the Methodology section, the
judgements on native status for the maps in Perring & Walters (1962) could only
have been large scale and arbitrary, but amending them is beyond the scope of the
present audit.
Table 3. Numbers of alien plant species belonging to the four frequency classes of
current distribution, judged on occurrence in hectads in seven regions.
Frequency class
Definition
Aliens in
British Isles
Present
Having less than 15 per
cent frequency of
occurrence in 1-4 regions
583
70
Local
Present in 1-4 regions,
with at least 15 per cent
frequency of occurrence in
at least 1 region
69
10
Widespread
Present in 5-7 regions; if 7
with at least 15 per cent
frequency of occurrence in
3 or fewer regions
66
7
Ubiquitous
Present in 7 regions with
at least 15 per cent
frequency of occurrence in
more than 3 regions
17
2
735
89
Subtotals
Total Vascular Plants
Aliens in Scotland
but native elsewhere
in British Isles
824
Most alien vascular plants in Scotland have very limited ranges and so occur with
low frequency (Table 3). Only 171 species exceeded 15 per cent frequency on a
hectad basis in at least one region, and only 92 species were present in five, six or
seven regions. If recording had been carried out over a longer period, a longer
species list and apparently greater frequencies of occurrence would have resulted,
but this would mask the regular extinction and regular further introduction of species.
Many aliens in Scotland are essentially casuals or survivors, and only 77 species
have been classed as naturalised, i.e. spreading largely by their own qualities rather
than human interference.
The alien plants profiled in Appendix 2 were somewhat atypical in that 15 of the
26 species were either widespread or ubiquitous in Scotland. This obviously
resulted from important species being chosen for profiling in order to illustrate
18
impacts, management and control. However, nine profiled plants were classed only
as present, not exceeding 15 per cent frequency in any region. Some of these were
judged to be benign or beneficial in impact, but others had adverse impacts. The
pirri-pirri-bur (Acaena novae-zealandiae), for example, occurs in just one region, and
could be considered a potential pest. Similarly the damaging freshwater species
New Zealand pigmyweed1 (Crassula helmsii) and Nuttall’s waterweed (Elodea
nutttallii) occur as yet in few regions. Eastern rocket (Sisymbrium orientale), rated
as benign, is typical of many weed aliens occurring mostly in waste places, and
helps to make the profiled species properly representative of Scottish aliens.
Many more alien species are found in the South and Central Belt regions of
Scotland than further north (Table 4). This is true for both the full aliens and the
Scottish aliens native elsewhere in the British Isles. For its area the North region is
particularly poor in alien species, this probably reflecting the large extent of ground
little visited by people and far from habitation. All of the groups distinguished in
Table 4 show similar patterns of regional distribution, one slight variation being that
only gymnosperms do not have more species in the South region than any other
region. The aliens profiled are typical of all Scottish aliens in their regional
occurrence, nearly all of them being present in the South and Central Belt.
However, Senecio smithii is a northern species, and the alpine campion (Silene
quadrifida) occurs only near Ben Lawers.
Aliens are most numerous in the non-semi-natural habitat type which includes arable
land, waste ground, curtilages and gardens (Table 5). Uplands and fresh waters are
the habitat types that have fewest alien plants. The numbers given in this table add
up to greater totals of species down the columns than the totals present in the
regions (Table 4) because species can be listed as occurring in more than one
habitat in the database. The proportions of alien species belonging to particular
habitat types differ little between the regions, although the North region has relatively
few species of non-semi-natural habitats and relatively more species of grassland.
This habitat type includes roadsides, railways, lawns and permanent pasture,
besides semi-natural grasslands. Separating these latter grasslands from manmade ones would have been desirable, but the information sources (floras) do not
usually make the distinction. Woodlands are inhabited by considerable numbers of
alien species particularly in the South region and Central Belt, and several of these
species have been profiled in Appendix 2 (few-flowered garlic (Allium paradoxum),
rhododendron (Rhododendron ponticum), shallon (Gaultheria shallon), Spanish
bluebell (Hyacinthoides hispanica) and Welsh poppy (Meconopsis cambrica).
1
Also referred to as the Australian swamp stonecrop in some literature.
19
Table 4. Regional distribution (see Fig. 1) of alien plant species belonging to
different broad groups.
East
North
Outer
Hebrides
Orkney,
Shetland
3
16
10
37
74
29
61
237
31
45
2
21
1
21
52
16
37
183
14
35
3
19
0
13
25
6
18
105
8
19
2
16
2
17
29
7
23
114
10
22
0
8
0
4
9
3
11
47
3
5
0
4
0
7
7
1
5
29
6
2
0
2
0
10
6
6
8
37
3
7
553
381
216
242
90
61
79
Aliens in Scotland but native elsewhere in British Isles
Ferns & allies
0
0
0
Gymnosperms
0
0
0
Chenopods
3
1
1
Crucifers
2
1
0
Rose allies
2
1
1
Legumes
2
0
0
Composites
5
2
2
Other Dicotyledons
46
34
17
Grasses
3
1
0
Other Monocotyledons
11
9
7
0
0
0
3
1
0
1
22
0
7
0
0
0
0
0
0
0
10
0
1
0
0
0
0
0
0
1
9
0
0
0
0
0
2
1
0
1
8
0
0
34
11
10
12
Aliens in the British Isles
Ferns & allies
Gymnosperms
Chenopods
Crucifers
Rose allies
Legumes
Composites
Other Dicotyledons
Grasses
Other Monocotyledons
All Vascular Plants
All Vascular Plants
74
49
20
West
Central
Belt
Numbers of species present in region
South
Classes of aliens and
taxonomic groups
28
Table 5. Numbers of alien plant species occurring in broad habitat types currently
present in the seven regions of Scotland (includes both full British aliens and
Scottish aliens elsewhere native in the British Isles).
East
North
Outer
Hebrides
186
16
175
126
49
8
20
10
96
9
87
87
35
6
17
11
110
7
102
90
49
10
13
10
40
1
52
36
15
1
4
7
34
2
31
20
11
1
4
4
All
Scotland
West
314
25
237
142
64
10
27
11
Orkney,
Shetland
Central
Belt
Non-semi-natural (MM)
Coasts (CO)
Grasslands (GR)
Woodlands (WO)
Wetlands (MA)
Fresh waters (FW)
Rocks, walls (RO)
Uplands (UP)
Numbers of species occurring in habitat types in region
South
Habitats types and
code
50
3
39
20
17
1
5
2
380
36
301
184
85
14
34
15
Origins and mode of introduction of alien plant species
Most alien plants in Scotland are natives of Europe, this group outnumbering natives
from all other continents (Table 6). Only two species have come from Tropical
Africa, and very few from the Southern Hemisphere. There are only small
differences in the make-up of the alien flora either between Scottish regions or
between the main habitat types.
Garden escapes contribute by far the greatest total of alien plant species (Table 7).
Again, in this table the columns add up to greater totals of species than occur in the
regions or habitat types, since species can have several manners of introduction.
Because the database does not give different modes of introduction for each region
and habitat type, some blurring of the actual patterns has occurred, for instance
grain and wool introductions (from grain spillages at ports and distilleries, and
around shoddy fields) are probably very few in the North, Hebrides and
Orkney/Shetland regions, yet species with these modes occur there, many of them
having other means of introduction. Nevertheless, the overall picture is clear: very
few alien plants nowadays have been introduced from ships’ ballast (e.g. lesser
swine-cress (Coronopus didymus)), from seed contamination (e.g. corncockle
(Agrostemma githago)), and from soil transport (e.g. red goosefoot (Chenopodium
rubrum)). Some modes with only a handful of examples, e.g. accidental import
(American speedwell (Veronica peregrina) was supposedly brought to Britain in a
consignment of plants for cultivation in a nursery), have been omitted from the table.
Species deliberately planted outside gardens are few in number but include some
prominent ones, for example snowdrop (Galanthus nivalis) and laburnum (Laburnum
anagyroides) on roadsides, and Hyacinthoides hispanica in woodland. Into this
category has been placed the planting of silver lady’s-mantle (Alchemilla conjuncta)
and purple colt’s-foot (Homogyne alpina) in Angus glens, and in total there are three
deliberately planted species recorded in the upland habitat types (Table 7).
21
Table 6. Numbers of alien plant species from different world regions currently
occurring in the seven regions of Scotland and the eight broad habitat types.
Geographical area
and habitat types
Europe
Asia
Region
South
Central Belt
West
East
North
Outer Hebrides
Orkney, Shetland
264
180
84
131
46
28
39
80
54
37
30
8
12
10
90
64
44
49
19
8
12
31
24
19
7
5
3
4
1
0
2
0
0
0
0
8
7
3
3
0
0
0
15
9
6
6
2
1
3
351
109
117
41
2
13
25
165
9
151
73
34
1
22
8
44
6
34
22
13
1
5
1
41
3
35
41
22
5
1
3
21
6
9
8
3
2
0
2
1
0
0
1
0
0
0
0
5
2
2
1
1
2
1
0
13
4
8
1
2
1
1
0
Scotland
Habitat type
Non-semi-natural
Coasts
Grasslands
Woodlands
Wetlands
Fresh waters
Rocks, walls
Uplands
Number of species with origin
North
South
Tropical South
Americ
Americ
Africa
Africa
a
a
22
Australasia
Table 7. Numbers of alien plant species with different modes of introduction that currently occur in the seven regions of Scotland and
the eight broad habitat types.
+
º
East
Outer
Hebrides
Orkney,
Shetland
Non-seminatural
Coasts
Grasslands
Woodlands
Wetlands
Fresh waters
Rocks, walls
Uplands
59
31
18
28
9
9
20
48
3
30
7
4
0
1
0
69
Deliberate (horticulture)*
15
12
10
12
6
2
4
3
0
5
8
3
2
0
3
22
Deliberate (silviculture)
29
28
27
25
14
8
5
6
0
10
31
2
0
0
6
35
40
28
19
24
10
10
9
26
2
20
12
4
0
0
1
47
Garden escapes
436
327
174
191
76
42
49
222
27
230
157
74
11
31
7
530
Seed contaminant
36
14
7
13
5
3
5
31
0
16
2
1
0
0
0
41
Birdseed ingredient
78
30
14
20
6
6
13
81
1
14
0
0
0
0
0
83
Carried in grain
61
15
8
14
2
4
7
62
0
14
1
2
0
0
0
69
Carried with timber
4
1
1
2
1
1
0
4
0
2
1
0
0
0
0
5
Carried with wood
64
23
13
19
4
6
8
65
2
16
0
1
0
1
0
72
Carried with other products
48
17
9
10
1
1
5
51
0
7
1
0
0
0
0
54
Ship ballast
4
2
2
2
0
1
2
4
1
0
0
0
0
0
0
4
Soil transport
9
5
1
2
0
2
1
10
1
0
0
0
0
0
0
10
+
North
West
Total
Species
Central Belt
Habitat
Deliberate (food, vegetable)
Deliberate (other)
*
Region
South
Manner of introduction
Includes only horticultural planting outside gardens, e.g. roadsides, woodlands
Includes deliberate planting for fisheries, game preservation, domestic uses, windbreaks, etc
Includes outcasts and relics
23
Some sharp differences can be seen between habitats in the modes of introduction
of their alien plants (Table 7). Aliens carried in grain, wool and other products (e.g.
soya beans) are far more frequent in man-made (non-semi-natural) habitats than
elsewhere (Sisymbrium orientale is an example profiled in Appendix 2), and garden
escapes are particularly frequent in the grassland, roadsides and woodland habitats
(Allium paradoxum and Meconopsis cambrica are examples profiled).
Present impact of alien plant species
The majority of alien plants have apparently changed little in abundance between
the 1950s and 1987-1988 (Table 8). However, significant increases far exceed
significant decreases, and the plants experiencing these increases are much more
evenly distributed between the regions than the plants with minor change. To some
extent this results from only plants with at a least moderately wide distribution having
a good chance of showing significant change (at least six increases or decreases
are required in 118 hectads). A few species with negligible occurrence in the 1950s
have increased spectacularly, for example butterfly bush (Buddleja davidii)
(4 hectads in the 1950s compared with 16 in 1987-1988) and American willowherb
(Epilobium ciliatum) (0 compared with 41 hectads); Epilobium ciliatum was actually
present in the 1950s, having first been observed in 1957 (Appendix 2), but none of
these localities was in the one ninth sample of hectads used for the tests on trends.
Table 8. Numbers of alien plant species showing different classes of change in
abundance, classified by region and broad habitat type.
Geographical area
and habitat types
Small
Increase
Significant
Increase
Small
Decrease
Significant
Decrease
South
Central Belt
West
East
North
Outer Hebrides
Orkney, Shetland
No or
minor
trend
512
322
159
180
47
39
56
45
41
28
32
15
8
8
58
58
53
56
37
21
24
6
3
1
6
1
0
2
5
5
3
2
1
3
1
Non-semi-natural
Coasts
Grasslands
Woodlands
Wetlands
Fresh waters
Rocks, walls
Uplands
334
36
250
139
70
11
26
8
16
0
21
15
8
1
2
0
22
0
22
29
6
1
6
7
5
0
4
1
0
1
0
0
3
0
2
0
1
0
0
0
The grassland and woodland habitats hold proportionately more of the alien species
that show significant increases than non-semi-natural habitats. Woodlands are
especially rich in alien vascular plants showing significant increases, examples
24
profiled including Allium paradoxum Hyacinthoides hispanica, Meconopsis cambrica
and Rhododendron ponticum (Appendix 2).
Aliens plants judged to be competitors or which damage habitats were considerably
fewer in number than aliens whose impact is due to their presence (Table 9). This
was true in all regions and in all habitats except wetlands. The non-semi-natural and
rocks-wall habitats had the greatest frequency of ‘presence aliens’, many species in
the former habitat being annual weeds. Three examples of annual weeds, wild oat
(Avena fatua), Epilobium ciliatum and Sisymbrium orientale, have been profiled
(Appendix 2). These have been judged to belong to the ‘presence’ class even
though non-conservationists could consider them damaging, particularly Avena fatua
because it contaminates grain. The grasslands, wetlands and woodland habitats
had the highest contribution of competitive and damaging species, many of them in
the latter habitat being trees or shrubs considered to damage the field layer by their
litter and the shade they cast.
Table 9. Numbers of alien plant species considered to have effect by presence,
competition and habitat damage, classified by region and broad habitat type.
Geographical area and
habitat types
South
Central Belt
West
East
North
Outer Hebrides
Orkney, Shetland
Non-semi-natural
Coasts
Grasslands
Woodlands
Wetlands
Fresh waters
Rocks, walls
Uplands
Presence
Competition
368
210
114
152
47
36
51
151
128
70
72
25
16
25
Habitat
Damage
108
92
60
52
29
19
15
259
21
154
79
33
9
29
6
89
9
82
41
35
5
2
0
32
6
65
64
17
0
3
9
The 77 species judged to be naturalised and therefore likely to become pests are
listed in Table 10. The decisions about naturalisation were inevitably arbitrary given
the infinite gradation between established, surviving and casual species. At one
extreme there are highly successful species increasing their range rapidly by their
own reproduction and dispersion, e.g. New Zealand willowherb (Epilobium
brunnescens) and Epilobium ciliatum (Appendix 2). Then there are other successful
species reproducing and increasing their range, but being obviously aided in part by
people, e.g. Hyacinthoides hispanica and Sitka spruce (Picea sitchensis)
(Appendix 2). Then there are species obviously reproducing yet hardly spreading,
e.g. Senecio smithii and Sisymbrium orientale. There are also species reproducing,
but apparently declining in extent. Many alien vascular plants belong to the two
25
intermediate categories, but only those species reproducing themselves more than
enough to replace natural losses have been classed as naturalised. Hence, an
ability to spread unaided to new situations was a criterion for being naturalised, and
this perhaps qualified more grassland and woodland species than waste-ground
species. Many ruderals such as goosefoots (Chenopodium spp.) and Sisymbrium
orientale have stayed restricted to waste ground in recent decades and, though
reproducing, have only held their ground or declined in range. This partly reflects
the increasing rarity of waste ground in Scotland, and may also result from a lack of
dispersion pathways between tracts of waste ground, when these are isolated as in
most of Scotland outwith the Central Belt.
Most of the 77 naturalised species have widespread or ubiquitous occurrence
(Table 10). Many are classed as competitors or habitat damaging, and have been
rated as having moderate or highly significant impacts. Sixteen of them have been
given profiles in Appendix 2.
Species rated as having moderate (M) or highly significant (H) impacts are listed by
habitat type in Table 11. Relatively few come from non-semi-natural habitats partly
because we have rated alien impacts on this type less severely than on more natural
vegetation. Woodland has the largest number of M and H impact alien plant
species, illustrating the extent to which this habitat has suffered from human
interference across Scotland. In the upland habitat type, only trees associated with
large-scale plantation forestry are listed, and fortunately the parts of this habitat
away from plantations have suffered very little impact from alien vascular plants.
26
Table 10. List of species considered to be naturalised (i.e. spreading by their own qualities rather than human interference).
Notes:
z
27













Uplands
Rocks, walls
Fresh waters







Value
of
impact
X
X
X
X
X
X
X
X
X
X
X
X
Significance future
n
n
n
Wetlands
E
x
H
Woodlands
w
w
w
x
hab dam.
hab dam.
hab dam.
hab dam.
hab dam.
hab dam.
hab dam.
presence
competitor
hab dam.
hab dam.
hab dam.
Grasslands
C
C
C
C
n
n
N
n
n
<<
<<
<<
<<
<<
<<
<<
O
<<
O
<
O
Habitats occupied
Coasts
x
E
E
E
E
E
e
Mode of
impact
Non-semi-natural
W
W
W
W
W
W
W
Orkney, Shetland
x
C
C
C
C
C
C
Current
trend in
status
Significance present
s
s
s
S
S
S
s
s
s
s
s
s
Outer Hebrides
European silver-fir
Douglas fir
Western hemlock-spruce
Sitka spruce
Norway spruce
European larch
Western red-cedar
Green hellebore
Monk's-hood
Barberry
Darwin's barberry
Hedge barberry
North
Abies alba
Pseudotsuga menziesii
Tsuga heterophylla
Picea sitchensis
Picea abies
Larix decidua
Thuja plicata
Helleborus viridis
Aconitum napellus
Berberis vulgaris
Berberis darwinii
Berberis darwinii x
empetrifolia (B. x
stenophylla)
Regional occurrence
East
English name
South
Scientific name
West



The table shows their regional occurrence, recent trend in status, and the nature and significance of their impacts.
The codes for regional occurrence are given in Fig. 1.
Regional occurrence is indicated by
Uppercase – occurrence of species in more than 15 per cent of hectads for which records were available from BRC;
Lowercase – occurrence of species in less than 15 per cent of hectads for which records were available from BRC; and
x – species known to occur in the region, based on local floras, but no records yet held by BRC.
The current status is indicated by << for a significant increase, < a small increase and O for no trend or a minor trend.
The value of the impact is shown as X for a predicted impact and 0 if judged to be benign.
The present and future impacts are discussed in the text.
Central Belt



M
L
L
M
M
M
L
L
L
L
L
L
M
M
M
M
L
M
L
L
M
L
M
L
S
S
s
S
S
S
S
s
S
s
s
S
S
s
C
C
C
C
C
C
C
C
C
w
W
w
W
w
w
w
W
W
w
W
W
W
E
E
x
E
E
e
x
x
e
n
n
n
n
n
x
H
h
Z
n
n
h
<<
<<
<
O
<<
O
<<
<
O
O
<
<<
<<
O
presence
hab dam.
hab dam.
hab dam.
hab dam.
presence
competitor
hab dam.
presence
hab dam.
hab dam.
presence
presence
hab dam.
S
S
s
C
C
O
<<
<<
O
competitor
presence
presence
presence
c
C
C
W
W
x
x
e
E
E
E
z
h
h
h
Z
z
Z
n
N
h
H
Z
28











































Significance future
presence
hab dam.
presence
hab dam.
competitor
presence
Significance present
<<
O
<<
<<
<
<<
X
X
X
X
X
0
M
M
M
M
L
L
M
M
H
H
M
L
0
X
X
X
X
0
X
X
X
X
X
0
X
X
M
H
L
L
L
L
L
L
L
L
L
L
L
L
M
H
M
L
M
L
M
M
M
L
M
M
M
L
0
0
0
X
L
L
M
L
L
L
M
L
Uplands
z
z
Z
Z
Z
z
Rocks, walls
h
h
h
H
h
Value
of
impact
Fresh waters
n
N
n
n
n
Wetlands
E
E
E
E
E
E
Woodlands
W
W
W
W
w
w
Grasslands
C
C
C
C
C
C
Coasts
S
S
s
S
S
S
z
Habitats occupied
Non-semi-natural
Orkney, Shetland
Outer Hebrides
Nootka lupin
American willowherb
New Zealand willowherb
Large-flowered evening
primrose
North
Brassica napus
Rhododendron ponticum
Gaultheria shallon
Ribes rubrum
Ribes sanguineum
Sedum album
Tolmiea menziesii
Rubus spectabilis
Alchemilla mollis
Cotoneaster frigidus
Cotoneaster integrifolius
Cotoneaster horizontalis
Cotoneaster simonsii
Cotoneaster frigidus x
salicifolius (C. x
watereri
Lupinus nootkatensis
Epilobium ciliatum
Epilobium brunnescens
Oenothera glazioviana
Mode of
impact
East
Welsh poppy
Beech
Pink purslane
Japanese knotweed
Dame's violet
Medium-flowered winter
cress
Rape
Rhododendron
Shallon
Red currant
Flowering currant
White stonecrop
Pick-a-back-plant
Salmonberry
Garden lady's mantle
Tree cotoneaster
Small-leaved cotoneaster
Wall cotoneaster
Himalayan cotoneaster
Hybrid tree cotoneaster
Current
trend in
status
West
Meconopsis cambrica
Fagus sylvatica
Claytonia sibirica
Fallopia japonica
Hesperis matronalis
Barbarea intermedia
Regional occurrence
Central Belt
English name
South
Scientific name
Significance present
Significance future
s
O
presence


X
L
L
s
O
presence

X
L
L
x
C
w
O
O
hab dam.
hab dam.

s
X
X
L
L
L
M
Norway maple
Field maple
Sycamore
Indian balsam
Sweet cicely
Alexanders
Ground elder
Giant hogweed
S
S
S
S
S
s
S
S
C
C
C
C
C
x
C
C
w
w
W
W
w
W
w
E
e
E
E
E
x
E
E
<<
O
O
<<
O
O
O
<<
presence
presence
presence
competitor
presence
presence
competitor
competitor

X
0
X
X
0
0
X
X
M
M
M
M
M
L
M
H
M
M
M
M
M
L
M
M
Russian comfrey
S
C
W
E

X
M
M
Peppermint
S
C
w
E

X
L
L
Butterfly bush
Garden privet
Monkeyflower
Ivy-leaved toadflax
S
s
S
S
C
C
C
C
W
w
W
W
e

0
X
X
0
L
L
M
M
M
L
M
M
Purple toadflax
S
C

0
L
L
E
E
N
n
n
h
H
Z
z
Z





H
n
H
Z
<<
competitor
H
Z
<
competitor
<<
<<
O
O
competitor
competitor
competitor
presence


<<
presence

h
h
z
x
29


n
x
h
n
n
Z
Uplands
L
Rocks, walls
L
n
Value
of
impact
Fresh waters
X
e
Habitats occupied
Wetlands

Griselinia littoralis
Ilex aquifolium x perado
(I. x allaclerensis
Acer platanoides
Acer campestre
Acer pseudoplatanus
Impatiens glandulifera
Myrrhis odorata
Smyrnium olusatrum
Aegopodium podagraria
Heracleum
mantegazzianum
Symphytum asperum x
officinale (S. x
uplandicum)
Mentha aquatica x spicata
(M. x piperita)
Buddleja davidii
Ligustrum ovalifolium
Mimulus guttatus
Cymbalaria muralis
subsp. muralis
Linaria purpurea
Mode of
impact
Woodlands
Coasts

Oenothera cambrica
Current
trend in
status
Grasslands
Non-semi-natural
presence
Orkney, Shetland
O
Outer Hebrides
s
North
Intermediate evening
primrose
Common evening
primrose
Small-flowered evening
primrose
New Zealand broadleaf
Highclere holly
East
Oenothera x fallax (O.
biennis x glazioviana)
Oenothera biennis
West
Regional occurrence
Central Belt
English name
South
Scientific name











S
S
s
S
S
s
s
s
c
C
C
C
C
c
W
w
w
W
w
x
E
N
n
n
n
C
E
E
x
x
x
H
<
O
O
<
<<
<
O
O
O
<<
<<
O
competitor
presence
presence
competitor
competitor
competitor
competitor
presence
presence
presence
presence
presence



Z
z
x
h
z
w
s
S
C
C
w
x
E
x
x
n
Z
z
30





















Significance future
Early goldenrod
Pineappleweed
Oxford ragwort
Leopard's bane
Canadian waterweed
Nuttall's waterweed
Swamp meadow grass
Oat
Highland bent
Spanish bluebell
Few-flowered garlic
Silvery crocus
Z
Significance present
n
h
0
0
0
X
X
X
X
X
0
L
M
M
L
M
L
L
L
L
L
M
M
M
M
L
L
M
M
X
0
0
X
X
X
X
0
0
X
0
X
L
M
L
M
M
L
L
L
L
M
L
L
L
M
L
M
M
M
L
L
L
M
M
L
Uplands
E
E
Z
Z



Rocks, walls
w
w
H
h
presence
presence
presence
hab dam.
hab dam.
competitor
competitor
competitor
presence
Value
of
impact
Fresh waters
C
C
n
n
n
n
O
O
<<
<<
<<
<
O
<<
O
Wetlands
e
E
E
E
E
Woodlands
w
W
W
w
W
w
Habitats occupied
Grasslands
x
C
C
C
C
c
Mode of
impact
Coasts
s
S
S
S
S
s
s
S
S
Current
trend in
status
Non-semi-natural
East
American speedwell
Common field-speedwell
Slender speedwell
Red-berried elder
Snowberry
Himalayan honeysuckle
Californian honeysuckle
Common blue sow thistle
Fox-and-cubs
Orkney, Shetland
West
Veronica peregrina
Veronica persica
Veronica filiformis
Sambucus racemosa
Symphoricarpos albus
Leycesteria formosa
Lonicera involucrata
Cicerbita macrophylla
Pilosella aurantiaca
subsp. carpathicola
Solidago gigantea
Matricaria discoidea
Senecio squalidus
Doronicum pardalianches
Elodea canadensis
Elodea nuttallii
Poa palustris
Avena sativa
Agrostis castellana
Hyacinthoides hispanica
Allium paradoxum
Crocus biflorus
Outer Hebrides
Central Belt
Regional occurrence
North
English name
South
Scientific name
Table 11. Lists of alien plant species classed as having moderate or highly
significant impacts, grouped by broad habitats and showing their regional
distribution. The codes for the regions are shown in Fig. 1.
Note:
Regional occurrence is indicated by
Uppercase – occurrence of species in more than 15 per cent of hectads for which
records were available from BRC;
Lowercase – occurrence of species in less than 15 per cent of hectads for which records
were available from BRC; and
x – species known to occur in the region, based on local floras, but no records yet held
by BRC.
Horse chestnut
Darwin's barberry
Perennial cornflower
Snow-in-summer
Common blue-sow-thistle
Himalayan cotoneaster
Montbretia
Dame's violet
Yellow archangel
Sweet cicely
Fox-and-cubs
Japanese rose
Steeple bush
31
Orkney,
Shetland
s
Outer
Hebrides
Pirri-pirri-bur
North
Coasts
Acaena novae-zealandiae
East
Ground elder
Rape
Butterfly bush
Japanese knotweed
Giant knotweed
Pineappleweed
Himalayan knotweed
Slender speedwell
Common field-speedwell
West
Non-semi-natural habitats
Aegopodium podagraria
Brassica napus
Buddleja davidii
Fallopia japonica
F. sachalinensis
Matricaria discoidea
Persicaria wallichii
Veronica filiformis
V. persica
Grasslands (including roadsides)
Aesculus hippocastanum
Berberis darwinii
Centaurea montana
Cerastium tomentosum
Cicerbita macrophylla
Cotoneaster simonsii
Crocosmia x crocosmiiflora
Hesperis matronalis
Lamiastrum galeobdolon
Myrrhis odorata
Pilosella aurantiaca ssp
carpathicola
Rosa rugosa
Spiraea douglasii
Regional occurrence
Central
Belt
English name
South
Habitat type and species
S
S
S
S
s
S
s
S
S
C
C
C
C
C
C
c
C
C
W
w
W
W
w
W
w
W
W
E
E
e
E
n
n
H
H
Z
Z
n
Z
E
e
E
E
N
H
h
H
n
n
h
H
Z
Z
S
s
s
S
S
S
S
S
S
S
S
C
C
C
C
C
C
C
C
C
C
C
W
w
w
w
w
W
W
w
W
w
w
E
n
n
n
n
n
h
z
h
H
h
Z
Z
S
s
C
c
W
w
e
e
E
e
E
e
E
E
E
E
n
n
n
n
n
Z
Z
h
Z
e
x
E
x
c
Fresh waters
Azolla filiculoides
Crassula helmsii
Elodea canadensis
Elodea nuttalli
Water fern
New Zealand pigmyweed
Canadian waterweed
Nuttall's waterweed
s
x
S
s
C
c
w
W
w
Walls, rocks
Cotoneaster horizontalis
Cotoneaster integrifolius
Cymbalaria muralis
Wall cotoneaster
Small-leaved cotoneaster
Ivy-leaved toadflax
S
s
S
C
c
C
W
W
W
European silver-fir
Field maple
Norway maple
Sycamore
Garden monk`s-hood
Few-flowered garlic
Grey alder
Pink purslane
Leopard's-bane
Beech
Shallon
Spanish bluebell
s
S
S
S
s
S
s
s
S
S
s
s
S
s
S
S
S
S
s
s
S
S
s
S
S
S
S
x
C
C
C
x
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
W
w
w
W
w
w
W
W
w
W
w
Woodlands
Abies alba
Acer campestre
A. platanoides
A. pseudoplantanus
Aconitum x cammarum
Allium paradoxum
Alnus incana
Claytonia sibirica
Doronicum pardalianches
Fagus sylvatica
Gaultheria shallon
Hyacinthoides hispanica
H. hispanica x non-scripta
Ilex x altaclerensis
Larix decidua
Lysimachia punctata
Meconopsis cambrica
Pentaglottis sempervirens
Pseudotsuga menziesii
Rhododendron luteum
R. ponticum
Ribes sanguineum
Rubus spectabilis
Sambucus racemosa
Saxifraga x urbium
Symphoricarpos albus
Tolmiea menziesii
Highclere holly
European larch
Dotted loosestrife
Welsh poppy
Green alkanet
Douglas fir
Yellow azalea
Rhododendron
Flowering currant
Salmonberry
Red-berried elder
London pride
Snowberry
Pick-a-back-plant
32
W
W
W
W
W
w
W
w
W
w
w
W
w
x
E
x
e
E
E
x
x
x
E
E
E
x
E
x
e
E
e
E
E
E
x
E
E
x
E
e
E
e
n
Orkney,
Shetland
x
Outer
Hebrides
C
s
North
East
Spiraea x psuedosalicifolia
West
Regional occurrence
Central
Belt
English name
South
Habitat type and species
z
x
x
n
h
h
h
z
h
n
N
n
n
n
n
N
n
H
Z
z
h
h
Z
h
z
Z
Z
n
H
z
z
n
n
n
h
h
n
n
n
n
h
h
Z
n
h
Z
Z
East
North
Western hemlock-spruce
Lesser periwinkle
s
S
C
C
W
w
E
E
n
n
Wetlands
Aconitum napellus
Alchemilla mollis
Epilobium brunnescens
Heracleum mantegazzianum
Impatiens glandulifera
Lysichiton americanus
Mimulus guttatus
Petasites albus
Symphytum x uplandicum
Monk's-hood
Garden lady's-mantle
New Zealand willowherb
Giant hogweed
Indian balsam
American skunk-cabbage
Monkeyflower
White butterbur
Russian comfrey
s
S
S
S
S
s
S
s
S
C
C
C
C
C
x
C
C
C
w
W
W
w
W
w
W
n
n
N
x
n
H
W
E
e
E
E
E
e
E
E
E
n
n
n
h
h
H
Upland
Larix kaempferi
Larix x marschlinsii
Picea abies
P. sitchensis
Pinus contorta
Japanese larch
Hybrid larch
Norway spruce
Sitka spruce
Lodgepole pine
s
S
S
S
s
C
C
C
C
C
W
W
W
W
W
e
E
E
E
E
n
n
n
N
n
Tsuga heterophylla
Vinca minor
Orkney,
Shetland
West
Outer
Hebrides
Regional occurrence
Central
Belt
English name
South
Habitat type and species
z
Z
z
z
Z
h
z
Bryophytes
The number of bryophytes which have become established as introductions in
Britain, 19, is small in comparison to the total bryophyte flora (Hill & Preston, 1998).
Of these aliens, only six species are known in Scotland (Appendix 1). Two of them,
Campylopus introflexus and Orthodontium lineare, are mosses from the Southern
Hemisphere which are now widely established in western Europe; they have invaded
Scotland as part of this process of natural spread following an initial introduction
elsewhere, as described in the profiles in Appendix 2.
Two Southern Hemisphere liverworts belonging to the genus Lophocolea are
established in Scotland following accidental introduction with garden plants but
currently have very restricted distributions. However, the history of one of these
species in England suggests that it may eventually become more widespread in
Scotland. Lophocolea bispinosa was collected on Tresco, Isles of Scilly, in 1962,
and for nearly 30 years no other English locality was known until in 1991 when the
species was discovered in Dorset; since then it has been found elsewhere in
southern England. Finally, two Hennediella species are thought to be introductions
originating from the Southern Hemisphere (though H. stanfordensis has not yet been
discovered in its native range!).
33
Fungi
Only a few species of fungi are definitely considered alien, two of which have been
profiled in Appendix 2 (red cage fungus and larch bolete). As a systematic search
for alien lichens was not undertaken, they are not listed in Appendix 1.
Mammals
A total of 13 mammals are considered to be alien in Scotland (Table 12) (see
Methodology section – Mammals). Most of these alien mammals are widespread,
occurring in many regions (Table 13) and many have had damaging impacts
(Table 14). The species are diverse and have a variety of origins, some being
deliberate releases for sporting purposes, others being accidental escapes.
Table 12. Numbers of alien animal species belonging to the different main classes,
and classified by their frequency of occurrence.
Taxonomic group
Mammals
Birds
Amphibians
Fisho
Insects
Crustaceans
Molluscs
Other invertebrates
Present
2
4
1
14
20
2
27
2
Local
1
0
0
1
0
0
1
0
Widespread
6
3
0
1
1
0
13
0
Ubiquitous
4
1
0
0
1
0
9
1
Total
13
8
1
16
22
2
50
3
includes 10 species introduced from England
Four species are of domestic/feral origin: the domestic/feral cat (Felis catus), the
feral ferret (Mustela furo), the feral goat (Capra hircus) and the American mink
(Mustela vison). Domestic cats and American mink are perceived as threats to
native fauna through predation on birds and small mammals. Also, in the case of
the domestic cat, introgression with the European wildcat (F. silvestris) has resulted.
Feral ferrets have been introduced to some parts of the Western Isles to control
rabbits, but there is a lack of information about their occurrence elsewhere in
Scotland and the rest of Britain. Feral goats occur usually in small discrete
populations in hilly areas and on several islands. The American mink is most
notorious for its presumed impact on the water vole, which has become very
severely reduced in numbers in Scotland. Only remnant populations of water voles
now survive in the headwaters of rivers, where mink have not become established.
Four species have been long established in Scotland, first arriving between the Iron
Age and c. 1800 AD, and are either ubiquitous (rabbit (Oryctolagus caniculus),
house mouse (Mus domesticus), and common/brown rat (Rattus norvegicus)) or are
very widespread (brown hare (Lepus europaeus)). A considerable amount of
information is available on many aspects of their ecology.
34
Table 13. Occurrence of alien animal species, classified by region and broad habitat
type.
Geographical area
and habitat types
South
Central Belt
West
East
North
Outer Hebrides
Orkney, Shetland
Mammals
12
12
12
12
10
6
5
Non-semi-natural
Coasts
Grasslands
Woodlands
Wetlands
Freshwaters
Rocks, walls
Uplands
4
0
4
4
1
1
0
2
Taxonomic group
Birds Amphibia Fish
7
0
9
5
1
13
6
0
2
5
0
6
4
0
2
1
0
1
1
0
0
4
0
5
4
2
3
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
16
0
0
Invertebrates
63
61
48
50
41
23
28
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Three other species have been introduced deliberately for ‘aesthetic’ or sporting
purposes: the grey squirrel (Sciurus carolinensis), which is now implicated in the
decline of the native red squirrel (Sciurus vulgaris), Cervus nippon, which is now
introgressing with native red deer (Cervus elaphus), and fallow deer (Dama dama),
which is a pest of both agricultural and forest crops in some areas. Also, the
hedgehog (Erinaceus europaeus) has been introduced for aesthetic reasons to the
Outer Hebrides where it did not occur naturally, and has seriously damaged the
ground-nesting native avifauna on some islands. This species has been excluded
from the audit table being native over most of Scotland, but is profiled in Appendix 2
as an example of the unfortunate consequences that even local translocations can
have.
Finally, two other introductions to Scotland are either present in a single colony or
are presumed to be extinct on the mainland and of unknown abundance elsewhere.
The red-necked wallaby (Macropus rufogriseus) has lived as a ‘small’ colony on an
island in Loch Lomond since at least 1975 (Corbet & Harris, 1991). The ship/black
rat (Rattus rattus) was introduced to Britain (and presumably Scotland) by the
Romans by the 3rd century. There now (post-1983) appear to be no self-sustaining
populations on the Scottish mainland, although they may be present on Westray in
Orkney and the Shiant Islands of Skye (Corbet & Harris, 1991; Arnold, 1993).
35
Table 14. Lists of alien animal species classed as having moderate or highly
significant impacts, grouped by broad habitats and showing their regional
distribution. The codes for the regions are shown in Fig. 1.
Note:
Regional occurrence is indicated by
Uppercase – occurrence of species in more than 15 per cent of hectads for which
records were available from BRC; and
Lowercase – occurrence of species in less than 15 per cent of hectads for which records
were available from BRC.
Central
Belt
West
East
North
Outer
Hebrides
Orkney,
Shetland
Geographical occurrence
South
Habitat type and species
Non-semi-natural habitats
Brown rat
Feral cat
New Zealand flatworm
S
S
S
C
C
C
W
w
w
E
E
e
n
n
n
h
h
h
z
z
z
Grasslands (including roadsides)
Rabbit
S
C
W
E
N
H
Z
Woodlands
Common pheasant
Green spruce aphid
Grey squirrel
Sika deer
S
S
S
s
C
C
C
c
W
W
w
W
E
E
e
E
N
N
h
H
Z
Z
Freshwaters
American mink
Canada goose
Grayling
Rainbow trout
Roach
Ruddy duck
Ruffe
Signal crayfish
S
S
S
S
s
s
s
s
C
C
C
C
c
c
c
c
W
w
E
e
E
E
e
e
n
n
H
N
H
W
w
N
e
Birds
There are eight alien species considered to have self-sustaining populations in
Scotland (Table 12 and Appendix 1), although at least 41 other species occurring
recently in Scotland are alien escapes or feral birds (Thom, 1986). The selfsustaining aliens are somewhat less widely distributed than the alien mammals
(Table 13), and a greater proportion of them occur in semi-natural habitats (fresh
water, grasslands and woodlands). Their present range may reflect the quite recent
36
date of some of the introductions, e.g. little owl (Athene noctua) (1925). Also, the
mobility of birds means that most species that are fitted to the environmental
conditions in a country have long ago become established there, leaving at the
present a stock of potential aliens that are not well fitted to colonise.
The alien bird species have come from all over the northern hemisphere. Five
resulted from escapes or releases from ornamental collections (geese, ducks and
golden pheasant (Chrysolophus pictus)).
Two species, common pheasant
(Phasianus colchicus) and red-legged partridge (Alectoris rufa), were originally
introduced as gamebirds and continue to be released as sporting quarry.
With relatively few species involved, there is little pattern to the current geographic
distribution, habitats occupied, trends and impacts of the alien bird species.
Compared with elsewhere in the world, Britain has only a few problem alien bird
species, and only three species have been rated as having potentially adverse
impacts in Scotland (Table 14). These species are the Canada goose (Branta
canadensis) , the ruddy duck (Oxyura jamaicensis) and Phasianus colchicus. The
last is considered a problem only because of the management practices normally
associated with its releases. The other species are currently considered benign,
being tolerated because they have no major adverse effects on crops, other habitats
or birds.
The Canada goose has already proved a sufficient nuisance that it may ultimately
become a pest of agricultural and riparian habitats. Canada geese are still
increasing and could in time interfere with other goose populations through both
competition and introgression. The ruddy duck is of international concern, in that the
North American birds hybridise freely with the globally threatened white-headed duck
(Oxyura leucocephala), and introgression is likely if their geographical ranges are
allowed to overlap. There is little evidence of Scottish-breeding ruddy ducks
contributing directly to the problem, but by providing recruits to the English and
Welsh populations they could thwart attempts to reduce numbers there.
Amphibia
Only one alien amphibian occurs in Scotland at present. The alpine newt is a recent
introduction in the Edinburgh area resulting from surplus experimental animals being
released (Appendix 2). There seem to have been no adverse impacts apart from
confusion with native newts.
Fish
There are 16 species of alien fish found in Scotland at present. Although fish
introductions are relatively numerous, most species are restricted in range
(Table 12). Occurrences are concentrated in the South and Central Belt regions
(Table 13), reflecting their connection with the sport of fishing - 11 species are
believed to have been deliberately released as sporting quarry, and another four
species are accidental releases as bait.
Broadly, the fish introductions in Scotland can be placed into three categories:
introduced in the last two centuries for sport or aquaculture and widespread;
37
introduced in the last two centuries but with few sites; and very recent introductions.
The groups are described in turn.
 Three salmonids have been introduced since 1800 by man for sport and
aquaculture. The rainbow trout (Oncorhyncus mykiss) was first introduced in
1888 and releases have continued to the present. However, under the current
temperature regime there is very little evidence of self-sustaining (i.e. breeding)
populations in Britain (or Scotland) and populations are maintained by continual
releases/aquaculture escapes. Rainbow trout are almost ubiquitous, being found
in all parts of Scotland except the Northern Isles and Islay. The grayling
(Thymallus thymallus) was introduced by man as a sport fish in the 19th century
to Border rivers and the Forth, Clyde and Tay catchments.
There are
approximately nine populations of brook charr (Salvelinus fontinalis) in Scotland,
again the result of angler/aquaculture releases.
 Eleven species have been introduced by man either deliberately (as sport or
ornamental fish) or accidentally (as unused live bait) and are generally confined to
a few (<10 and often single) sites in Scotland. These fish are tench (Tinca tinca),
common bream (Abramis brama), chub (Leuciscus cephalus), Crucian carp
(Carassius carassius), common carp (Cyprinus carpio), goldfish (Carassius
auratus), gudgeon (Gobio gobio), rudd (Scardinius erythrophthalmus), orfe
(Leuciscus idus), dace (Leuciscus leuciscus), and bullhead (Cottus gobio).
Several of these species, mostly those in the carp family, breed in Scotland only
in ‘warmer than average summers’ but breeding may increase if water
temperatures were to increase.
 There are two very recent Scottish introductions, the ruffe (Gymnocephalus
cernua) and the barbel (Barbus barbus). The ruffe was introduced to Loch
Lomond and Loch Ken as the unused live bait of pike anglers. It has increased
dramatically in Loch Lomond where it is now one of the commonest fishes, and is
implicated in major changes in the food web of the loch and as a predator of
powan (Coregonus lavaretus) (a scarce whitefish confined to Lochs Lomond and
Eck in Scotland). The barbel was introduced to the River Clyde by coarse
fishermen during the 1990s and, from evidence gathered in 2000, is now known
to be breeding there.
Over half of the fish introductions (10 of them) were of species native in England
which had not been able to colonise Scotland after the last glaciation (Appendix 1).
So human interference has narrowed the ecological difference between fresh waters
in Britain, lakes in northern Britain having previously had few species, some of them
considered relicts from the Ice Age.
Invertebrates
Invertebrate aliens form a striking comparison to the other classes of biota. There
are comparatively few species (hundreds) which are considered or suspected of
being alien out of the large total number of British species. Only a small proportion
of these alien species occur in Scotland, the number listed in Appendix 1 being 77.
Nevertheless, alien Mollusca (slugs, snails) are quite numerous (Table 12). A
handful of invertebrate aliens have adverse impacts, five of which are profiled in
38
Appendix 2, and three are rated as having moderate or highly significant impacts
(Table 14). Most alien invertebrates have insufficient records to be classed as
widespread or ubiquitous (Table 12), but this may well reflect the few recorders,
many of the species having wide ranges (Appendix 1).
The small proportion of invertebrate species that are considered alien may be partly
due to the prevalance of obligate sexual reproduction in invertebrates. In such
species successful colonisation of a foreign country requires the simultaneous
introduction of at least one male and one female. It is conspicuous that many of the
invertebrates tabulated here have a form of asexual reproduction or self-fertilisation:
the broad-nosed weevil (Otiorhynchus porcatus), the green spruce aphid (Elatobium
abietinum) and the snail Potamopyrgus antipodarum are parthenogenic. Many, but
not all, of the hermaphrodite molluscs can self-fertilise (Wilbur & Yonge, 1964).
Thus, in these species, a single individual can potentially found a population.
The mode of introduction of many alien invertebrates is unknown, and there is rarely
conclusive evidence that a species is even an alien; many species are described as
perhaps native in the notes column of the audit table (Appendix 1). But many of the
invertebrates listed can be transported in soil and thus their mode of dispersal is
probably linked to horticultural and agricultural activities.
Introduction of alien races of native plants
The sowing of seed for the creation or re-establishment of plant communities is often
encouraged, particularly in agri-environment schemes. Much of the seed sown in
the past in such habitat restoration, conservation and amenity projects has been
non-native, or if native has been of non-local provenance.
Concern has been growing among conservationists about this use of material of
non-local provenance. Akeroyd (1994) suggested that the use of seed of alien races
of native species or of agricultural varieties could result in
 confusion of the natural distributions of plants in Britain;
 confusion of complex and ancient landscape patterns, and the creation of a
facsimile of the countryside;
 competition between native races and the perhaps more vigorous introduced
races of the same species; and
 the erosion of native genetic variation due to crossing between native and
introduced races.
As a result of worries such as these, Plantlife and the Institute of Ecology and
Environmental Management have developed Flora Locale, an initiative funded by
English Nature and the World Wide Fund for Nature UK. The main objective of
Flora Locale is to protect indigenous wild plants and communities from the effects of
introduced species and varieties, both non-indigenous strains of native species and
also native plant material of non-local provenance.
Whilst there is great concern surrounding the introduction of non-native races, there
is relatively little evidence to support these concerns, and the consequences of such
39
introductions are largely unknown. A further objective of Flora Locale is to gather
evidence about the performance and effects of these non-native introductions.
A lack of local adaptation in non-native races/agricultural varieties to ‘new’ locations
may often mean that they do not establish well or persist when introduced (and there
is certainly anecdotal evidence for this). Thus, the introduced race may die out or
could actually become adapted to the local environment as a result of introgression
with the local race. Moreover, because non-native races will not be adapted to the
receptor site, it is perhaps more likely that the local race will spread into, rather than
the non-native race spreading out from, the site of introduction.
Barratt et al. (1999) compared the performance of different races of wet grassland
plant species over a range of water-level scenarios. Material used included
commercial seed of native provenance, seed collected from native populations and
seed of forage varieties. The performance of the different races varied significantly
in terms of germination and establishment, suggesting that the races were
differentially adapted to specific environmental conditions. The implications of this
for habitat restoration schemes are that races not adapted to the particular local
environmental conditions may perform poorly.
It should also be noted that in the past many herbaceous species were widely sown
in agricultural systems throughout the UK, being present either as impurities or
ingredients in seed mixes. Many semi-natural communities containing (native) wild
populations of these species may already have been exposed to gene flow from
these varieties. It is thus quite possible that there are now ‘local’ races of many of
these widely sown species in the wild.
There are a number of potential ways in which non-native races could affect native
populations. The main concerns are focused on possible genetic interactions and
the potential of alien race introductions to alter the genetic structure of wild
populations of the native race of the species. These concerns are variously
expressed as ‘spread of unsuitable genotypes’, ‘genetic erosion’, ‘contamination of
local genetic stock’ and ‘dilution of native gene pools’ (Cairns, 1993; Akeroyd, 1994;
Millar & Libby, 1994). A non-native race could spread from the site of introduction
and either hybridise with the local race or replace it altogether. The degree to which
the local population will be affected will depend upon the existing genetic variation of
the native race and the degree of adaptation exhibited. Where populations are
locally adapted, the introduction of genetically differentiated non-native races may
result in the loss of local specialisation through the introduction of maladaptive traits
(Hodder & Bullock, 1997).
In certain circumstances it may actually be beneficial to introduce new genetic
variation into the wild. Where the native wild race exhibits inbreeding depression or
genetic bottlenecks, the introduction of individuals of non-native races may result in
an increase in genetic diversity locally and hence a decrease in inbreeding
depression.
Thus, the main concerns, mostly unsubstantiated, appear to be that the introduction
of non-native races may be detrimental to native races of the species. However, the
current evidence from habitat restoration schemes (both experimental and
40
anecdotal) suggests that the main concern should perhaps be the failure of such
schemes due to the selection of unsuitable material for (re-)introduction.
It would seem sensible, despite lack of evidence, to exercise the precautionary
principle, i.e. only introduce native or local races of species, particularly in areas of
high conservation value. However, the use of material of local provenance will not
necessarily avoid the problems outlined above. Since geographic separation often
results in the genetic differentiation of populations, even adjacent populations can
vary greatly in genetic structure and variation (Billington et al., 1988). Thus, even
the (re-)introduction of local races from nearby areas could result in the introduction
of maladaptive traits to local populations.
41
42
DISCUSSION
The information presented in the Audit Findings section for the several individual
classes of biota is drawn together here. An attempt is made to evaluate the
pressures from aliens of different types and to pick out the main pathways of their
entry. Differentiation between regions and habitat types in the pressure from, and
success of, aliens is examined. Judgements are then made about the overall
impacts of aliens, giving recognition to the benefits they sometimes bestow besides
their damaging effects, and the criteria for making such judgements are considered.
Finally, possible broad measures for dealing with alien species in Scotland are
outlined.
The current entry, status and impact of aliens in Scotland
In terms of the number of species reaching the ‘wild’ in Scotland, and being available
to colonise semi-natural habitats, it seems that vascular plants far exceed all other
groups (Table 15). Over half of these vascular plants are garden escapes or
outcasts (Table 7). It is clear that the several thousand plant species currently being
cultivated in gardens in Britain constitute a very large source of alien plants that
could potentially enter semi-natural habitats. There are also in Scotland collections
of mammals and birds, especially wildfowl and some species have escaped, so
entering our lists, e.g. red-necked wallaby and Canada goose profiled in Appendix 2.
The numbers of these species are very small, reflecting the impracticality of keeping
animals in collections, as opposed to plants in gardens. Also, the total numbers of
species belonging to these groups are much smaller than to vascular plants.
Table 15. Numbers of alien species belonging to different classes of biota that occur
in Scotland, that are considered naturalised, and for which specific control
programmes are undertaken.
Vascular plants
Bryophytes
Fungi
Mammals
Birds
Amphibia
Fish
Insects
Molluscs
Other Invertebrates
Total
T
Number of species
recently recorded in
Scotland
824
6
>2
13
49T
1
16
22
50
>5
>988
Number of species
considered
naturalised
77
2
1
11
8
0
9
12
32Q
3
155
Number of species
having targeted
control programmes
7
0
0
8
2 (+2SPO)
0
1 (+11SPO)
0
0
2
20
Species classified as escapes or feral breeding birds by Thom (1986)
SPO
Species regularly culled for sport
Q
Qualification: present in more than ten 10 km grid squares
43
Vagrant birds potentially add to the pressure of foreign species becoming
established in Scotland, with about 120 species being recorded (Thom, 1986). The
small numbers of individuals, and their scattered occurrence across the country,
much impedes their chances of breeding, and also they are free to fly away again to
seek their accustomed and more favourable environments. In contrast, fishes, most
mammals and most invertebrates, are totally dependent on human agency to bring
them to Scotland and place them in a suitable habitat, and once in the country they
have little chance of moving away again. From Table 15 it appears that a relatively
high proportion of the introduced species become naturalised in these groups. For
the fish this might be expected, because many of the species have moved only from
England (p. 38), and have been placed in types of fresh water to which they are well
adapted. For the mammals, the total of 13 species recently recorded in Scotland is
probably an under-estimate of the actual number that have reached the wild here in
the past decade, e.g. there are reports of porcupines, pumas and several other
elusive species escaping from zoos. The relatively high proportion of mammals
naturalised is a real measure of the frequently observed success of a very few
individuals in establishing large colonies, for example in muntjac deer elsewhere in
Britain, and in sika deer in Scotland (Appendix 2). Many mammals are able to move
to join in pairs and breed, and with most species having low mortality rates, they can
establish naturalised populations from very small initial numbers of individuals.
The invertebrates that appear most successful at becoming naturalised are the
molluscs (Table 15), although possibly the large number of 10 km grid squares
occupied by these species (Appendix 1) result from regular further introductions
rather than breeding. However, as pointed out in the Audit Findings section, many
snails and slugs are hermaphrodite and can self fertilise, so a single entrant can
found a population.
Pathways of entry
The pathway by which the greatest number of species are introduced to the wild in
Scotland is from gardens, either as escapes or outcasts. This is because alien
vascular plants so much exceed other groups in the number of species. Passive
carriage of plant fruits and seeds in imported products especially grain and wool is
also important (Table 7). The proportion of deliberate direct introductions is small in
vascular plants. In the vertebrate groups direct introduction is more important, and
especially so in the fish (Appendix 1). But these comparisons are beset with
semantic conventions and the innate differences between living groups: the
freshwater bodies into which fishermen put fish to multiply could be viewed as being
equivalent to gardens, into which owners put plants to thrive. The difference which
makes the one pathway be described as deliberate, and the other as an accidental
escape, is that the freshwater bodies are considered as being in the wild and the
flower gardens are not. In reality, the pathway of each type of these introductions
has at least two steps, one deliberate and one accidental; neither the fishermen nor
the garden owners intend their objects of interest to escape into the countryside.
Those managing birds and mammals desire a large free environment in which they
behave naturally, this being especially true for predatory birds, wildfowl and quarry
species. Hence, many people are not content to have aviaries or bird gardens, but
instead release birds on water bodies (wildfowl) or into open countryside, e.g. the
44
little owl and goshawk (an extinct native species recently reintroduced), which may
explain the greater proportions of deliberate releases in these groups.
Differences between regions and habitats
Alien plants occur in greater numbers in the South and Central Belt regions of
Scotland than elsewhere (Table 4), and many naturalised ones occur in these
regions (Table 10). This could partly be due to the greater human population in
these regions, with the South region including Lanarkshire (vice county 77), which
contains about a third of the Greater Glasgow conurbation. The extent of tipping of
garden refuse, the use of herbicides and climatic factors may have influenced the
differences in spread of alien species in different parts of Scotland.
A further reason for the abundance of alien plants in the South and Central Belt
regions might be the chance distribution of botanists keen on their identification and
study. Olga Stewart (Edinburgh, but recorder for Dumfriesshire), Peter MacPherson
(Glasgow, and recorder for Lanarkshire), and Alan Stirling (Helensburgh, and
recorder for Dunbartonshire) all have contributed many recent records to the BRC
database, and made them available to Clement & Foster (1994). Mary McCallum
Webster also hunted for alien plants in Moray, many of these records being
published in her flora (1978), but the records have only been included in the present
database if recently confirmed.
The habitats into which most vascular plants have become established are manmade ones (arable land, waste ground), grasslands and woodlands (Table 5).
Almost certainly this reflects the greater pressure, in terms of numbers of alien plant
species, being imposed on these habitats. In contrast there are only 15 aliens
occurring in upland habitats.
Differences between regions in the occurrence of alien animals are modest, being
most apparent for fishes (Table 13 and Appendix 1). Deliberate releases of bait and
quarry fish in the interests of recreational fishing have taken place mostly in the
South and Central Belt regions, whereas deliberate releases for sport, have been in
less populated regions and in more semi-natural habitats.
Historical perspective
Knowing whether the numbers of alien species are increasing or decreasing
compared with 50 or a 100 years ago would be very useful for conservationists trying
to decide whether the pressures aliens currently exert on the countryside require
strong preventative measures. For various reasons it is difficult to answer this
question, and for most groups assessments of trend are inevitably imprecise. At first
sight, the current number of alien vascular plants is much increased compared to the
19th century. Reliable floras such as Dickie’s (1860) Botanist’s Guide to the
Counties of Aberdeenshire, Banff and Kincardine list far fewer aliens (88 species)
than are now known to occur. British botanists in the 19th century were much less
interested in aliens, which they termed exogenous plants, than they are nowadays,
and only a few individuals recorded them and wrote up their findings. In Scotland,
Trail, Professor of Botany at Aberdeen University from 1877, was a pioneer of such
activity, publishing a paper on the introduced plants of the north-east (Trail, 1885).
45
The first flora in Britain devoted to alien species did not appear until the early 20th
century (Dunn, 1905). About 1,000 aliens were then known, many having been
brought to Britain in ships’ ballast or as adulterants in grain imports. Garden
outcasts were comparatively unimportant, but then gardens were a far less common
adjunct to houses, and the range of plants grown in them was probably relatively
restricted.
For the vertebrate groups there are similar problems of recording intensity. The
current large number of vagrant birds almost certainly reflects the large numbers of
ornithologists seeking to add extra species to their ‘twitch’ lists, rather than that wind
patterns have changed and brought more species than in the past. Nevertheless,
the number of fish introductions has almost certainly increased in recent years as a
result of deliberate releases, fishing having become a more popular sport; such
activities in the past would have been recorded due to the considerable literature.
Reasons for the success of aliens
Possible causes for alien species being successful are quite numerous, but the
species that have become widespread generally have four basic attributes, i.e.
 they originate from areas with closely similar climate to the regions they colonise
in Scotland;
 they reproduce effectively and have good dispersion;
 they are competitors able to do well in widespread habitat types; and
 they have good defences against herbivory and carnivory.
These will now be considered in turn.
For vascular plants, the greater majority of aliens come from Europe, and some from
North America and Asia, but hardly any from Tropical Africa (Table 6). For
mammals, seven of the 11 aliens considered naturalised are from Europe
(Appendix 1), the remainder being the brown rat from Russia, the mink and grey
squirrel from North America, and the sika deer from Japan. The red-necked wallaby
from Australia is said to suffer heavy mortality in snowstorms (Appendix 2), and
seems unlikely to be able to spread from its present colony at Loch Lomond. The
alien birds established here are all from the Northern Hemisphere, with three from
North America and three from Asia (Appendix 1), and the fish are mostly from
England (Appendix 1).
The most successful alien plants have particularly good seed output and dispersal,
e.g. American willowherb (Epilobium ciliatum) (Appendix 2), giant hogweed
(Heracleum mantegazzianum) (with up to 100,000 seeds per plant (Appendix 2)),
and Rhododendron ponticum (Appendix 2). Similarly, the rabbit, brown rat and
house mouse in the mammals are known to be highly prolific, producing several
families per year. The two successful bryophytes have very effective vegetative
reproduction (Campylopus introflexus and Orthodontium lineare) (Appendix 2). Alien
birds have been less successful than plants or mammals in Scotland, and the
commonest species, the pheasant, owes its present large numbers to continual
artificial inputs to its population.
46
The competitive nature of the successful alien species in the vascular plants is
illustrated by the tall rapid growth of Heracleum mantegazzianum, Himalayan balsam
(Impatiens glandulifera), Sitka spruce (Picea sitchensis) and rhododendron
(Rhododendron ponticum) (Appendix 2). Similarly, the ruffe in Loch Lomond is
considered to be highly competitive to the native fish species present in the loch
(Appendix 2). Among the mammals and birds, competitive ability is a less important
criterion, perhaps because there are relatively few same-niche species to compete
against, and colonisation may more often be of vacant niches.
The last attribute of successful alien species, their defence capability, or avoidance
of danger, is well shown by Rhododendron ponticum (poisonous, Appendix 2),
Heracleum mantegazzianum (injurious sap, Appendix 2), rabbits (burrows), brown
rats (secretive, nocturnal) and sika deer (secretive, lives in thickets).
The literature on successful aliens is extensive and has been discussed in Bullock
et al. (1997). For several groups of biota, lists of characteristics associated with
invasive potential have been made, e.g. for weeds (Baker, 1965), birds (O’Connor,
1987), and vertebrates (Ehrlich, 1986), but these lists have been found to have little
predictive value in picking out successful invaders (Bullock et al., 1997; Drake et al.,
1989). Thus, successful alien plants in Britain were found to have only a few
significant differences to native species (Williamson & Fitter, 1996b), and Gray
(1986) considered that British invading plants did not have special genetic
characteristics. However, Forcella (1985) found that the rate of spread of alien
weeds in North-West America was positively correlated with range size, and
suggested that reproductive potential could be used for identifying future
troublesome species.
Evaluation of the costs and benefits of aliens
A recent policy review (Bullock et al., 1997) gave the following list of problems posed
by introductions







competition with native species;
predation on native animals;
grazing on native plants;
providing alternative prey, and so disrupting ecosystems;
alteration of habitats;
spread of diseases; and
genetic impacts due to hybridisation.
All of these problems have occurred in Scotland as a result of alien introductions,
with the most serious impacts probably being competition with native species,
alteration of habitats and hybridisation. However, Bullock et al. (1997) state that "the
impacts of alien species upon the British flora and fauna have not been as great as
found on other land masses", and they regard impacts on remote islands as often
being severe. The worst impacts suffered in Scotland (from mink, rabbits and
rhododendrons) are not as serious as some of the disasters recorded elsewhere, for
example on Macquarie Island, New Zealand, where an endemic parakeet became
extinct following the liberation of rabbits and consequent great increase of feral cats
47
(Taylor, 1979). Also, on other New Zealand islands the arrival of rats (Rattus
exulans) is believed to have caused the extinction of tuatara lizards (Sphenodon
punctatus) (Crook, 1973), and King (1984) states that approximately 150 populations
of native birds on New Zealand islands have been drastically reduced or totally lost
due to the arrival of carnivores.
Other North Temperate countries have experienced problems from introductions that
are at least equal to those in Britain if not worse. Several of the plant species
spreading invasively here, have been just as successful on the continent of Europe,
e.g. Impatiens glandulifera, which has colonised many riverbanks (Pysvek, 1995)
and Heracleum mantegazzianum (Tiley et al., 1996). Compared to continental
European countries, Britain receives some protection from landward dispersion of
plants by being an island. On the other hand, Britain has fewer native species, so
any increase of aliens is disproportionately greater here.
This applies more so to Scotland, because the number of species per unit area of
land is less, e.g. for vascular plants the 10 km grid squares in Scotland have
approximately 60 per cent of the number of species found in Southern England
(Perring & Walters, 1962). As an example, we consider lowland deciduous woods:
many in Scotland have around 30 alien vascular plants which, out of a normal
species list of 120 plants, is 25 per cent of the total. A woodland of approximately
10 ha near Banchory in the East region has 23 aliens out of a total of 105 species
(22 per cent). In comparison, Hadleigh Great Wood in Essex has 54 aliens out of
374 total plants (14 per cent) (Bullock et al., 1997). Many of the aliens in the
Banchory wood strongly affect its character, e.g. beech (Fagus sylvatica), sycamore
(Acer pseudoplatanus), Spanish bluebell (Hyacinthoides hispanica) and leopard’sbane (Doronicum pardalianches), and may well exclude less competitive native
herbs, e.g. three-nerved sandwort (Moehringia trinervia), besides changing the
whole ambience of the woodland.
Although the cost of aliens in Scotland is presently considerable, producing an
estimate of the financial loss caused is far beyond the scope of this audit. There are
estimates of the costs of aliens in the literature for foreign countries, but almost all
are for situations where a commercial activity has suffered, such as a fishery in a
lake. Attaching ‘value’ to conservation losses is very difficult.
The benefits accruing from the introduction of alien species are less obvious and
more debatable, including




increased biodiversity;
creation of novel habitats;
adding to the national stock of objects of beauty or interest; and
adding extra objects of resource.
Biodiversity is only crudely measured by the number of species present per unit
area, and other useful measures could be assessed such as the number of typical
species of the ecosystem or habitats (Bullock et al., 1997). For some Scottish
habitats, the latter measure has certainly been increased by introductions, e.g. of
fishes, several species not having been able to reach Scottish river systems
48
because of the chance timing of cut-offs from freshwater bodies after the last Ice
Age.
New habitats provided by aliens include conifer plantations and rhododendron scrub,
as well as patches of dwarf shrubs different in character to native heath, e.g. stands
of shallon (Gaultheria shallon). Conifer plantations and rhododendron scrub are
certainly less rich in plant species than are the vegetation types they replace, but
being different they give extra niches which biota can occupy now or in the future, as
they become better adapted to them. It has also been argued, particularly with
regard to gardens, that the extra plant species, resulting from the presence of aliens,
allow greater assemblages of insects to exist (Owen, 1986).
The items of beauty range from the generally accepted, e.g. beech and cedar trees,
to some popular with the general public but not to conservationists, e.g. the palepink massed stands of pink purslane (Claytonia sibirica) in north-east Scottish
woods, to the controversial, e.g. the statuesque but eerie stands of Heracleum
mantegazzianum along some rivers. As many of the plant species are deliberately
cultivated in gardens for their perceived beauty, it is not surprising that some people
think of them in the same way when they grow elsewhere; this must be balanced
against the likely problems many cause.
Finally, the objects of resource are mostly relics of the past such as medicinal plants,
e.g. henbane (Hyoscyamus niger) and monk’s rhubarb (Rumex pseudoalpinus).
They resulted from past introductions near dwellings, and now constitute a very
minor part of the stock of aliens.
Ethical consideration about aliens
The simple view that all aliens should be actively discouraged because some have
proved damaging is neither logical nor practical. To set up policies for dealing with
aliens, their impacts need to be ranked in severity, extent and likelihood, and
balanced against the costs of prevention and any benefits arising from their
presence. Out of this, three categories of aliens will emerge, those to be strongly
resisted, those to be resisted if possible, and those not to be resisted. It would be
expected that this last group would be considerably more numerous than the former
two groups, most alien animals and plants being considered neither to be
competitors nor habitat damaging (Appendix 1 and Table 9).
The number of aliens considered naturalised in Scotland is roughly a tenth of the
total identified in the audit (Table 15), in line with Williamson & Fitter’s (1996a) ‘tens
rule’. This in itself is a strong argument for a selective approach in combating aliens.
In fact of the approximately 160 identified naturalised aliens, it appears that only 20
have been targeted with control programmes (Table 15).
Strategies for combating aliens will be considered in the next section, but it must be
said that putting likely management into effect may conflict with conservationists’
desires for wildness and lack of human interference. To some, having a visible
herbicide treatment is not much different to having an alien present, and to others
killing any sort of wildlife in order to protect other species will be strongly criticised.
49
There are also problems in compelling landowners to ensure that their ground does
not carry aliens, or blaming them for natural processes occurring that they can only
prevent with much effort. For all of these reasons, a selective approach to tackling
alien introductions seems desirable.
Possible measures for dealing with unwanted introductions
After the necessary first steps of gathering key information about alien species and
the habitat being impacted, the measures for responding to the problem may involve










guidelines to conservation managers;
guidelines to landowners, farmers and foresters;
guidelines to the general public;
financial inducements funded by conservation bodies, etc.;
programmes of management and control;
cross compliance (i.e. financial reward for an output or management being given
only if landowners/farmers keep their ground free of an unwanted alien);
import disincentives, e.g. tax or quarantine;
import restrictions;
local bye-laws; and
state legislation.
All of these actions against aliens are to a degree being done at present in Scotland,
with the possible exception of cross compliance. For example, there are leaflets
giving guidance for the control of invasive plants near watercourses, and some
management programmes have received substantial finance, particularly work to
clear rhododendron thickets within the EC LIFE 97 Atlantic Oakwoods Project.
Viewed as a whole the actions being taken seem patchy and retrospective, but only
once a problem has become major is thought given to appropriate and effective
methods of control. Of the profiled vascular plants (Appendix 2), 14 were judged to
be naturalised and having adverse impacts but only for four of these are targeted
control programmes taking place. Moreover, the alien plant species covered by
legislation are quite few, e.g. listed in Schedule 9 of the Wildlife and Countryside Act
(not to be released or allowed to escape), and some additions proposed for this list,
but recently turned down, do not seem very damaging, e.g. few-flowered garlic
(Allium paradoxum). However, for mammals and birds the legislative lists are longer
and more wide-ranging, and a considerable system for licensing or prohibiting the
keeping of potentially damaging animal species is now in place (reviewed by Ward
(1998)).
Some ingredients which could be considered in a more comprehensive programme
for tackling undesirable introductions are
 measures to reduce the dumping of garden refuse, particularly making the
gardening public aware of the likely long-term consequences of outcasts
becoming naturalised;
 measures to make those responsible for animal collections and animal culture
take greater precautions against escapes;
50
 measures to compel those selling seed mixes, either for sowing or for animal or
bird food (e.g. pheasant rearing), to have them adequately tested for the
presence of unsuitable species;
 an appraisal of existing aliens, particularly the vascular plants now naturalised in
Scotland, for species likely to increase greatly in the next few years (this would
entail gathering information about their reproductive capacity and dispersion);
 an attempt to get agreement among conservationists and conservation bodies
about which habitats should be kept clear of aliens, and those where aliens are
now so numerous that removal is impractical (uplands and coasts would seem
good candidates for the former, and lowland woodland for the latter);
 an attempt to get agreement among conservationists about policies on alien tree
species - presently some conservationists are trying to remove Acer
pseudoplatanus by herbicides and ring-barking, while others are content to
observe its spread as a wild species (and many consider any woodland a benefit
whatever the origin of its component trees);
 Scottish legislation equivalent to the Wildlife and Countryside Act with a rational
set of species for Scotland for which it would be an offence to allow their spread,
or which could only be planted in the wild, or released to the wild, under licence;
and
 the promotion and application of a consistent set of criteria and definitions such
as those adopted by SNH (Usher, 1999, 2000). This would help to establish
clearer perspectives on what is native or non-native (Table 16).
Table 16. Categories of species status (native or non-native)
Status
Description
Native
Species presumed to be present in Scotland through their own
volition. Most of these will have migrated into Scotland after the last
Ice Age, without assistance from humans.
Formerly native
Species that no longer occur naturally, but which are known (or
presumed) to have occurred naturally at some time in the past.
Non-native
Species that have been introduced deliberately or accidentally, by
humans.
Locally non-native
Species that have been introduced beyond their natural geographical
range.
Long-established
Species that might have been introduced by humans a long time
ago, but which have now become part of the ‘natural’ food chain.
Recently arrived
Species whose recent occurrence has been associated with human
activity, for example through changes in agricultural practices, or
through climate change caused by human activities.
51
52
ACKNOWLEDGEMENTS
We are grateful to many CEH colleagues and several non-CEH experts for
responding readily to our requests for information and for helpful discussions. We
particularly thank Peter Macpherson, David Mardon (vascular plants), Ren
Hathaway, Francis Hicks, Rosemary Parslow (fungi), Digger Jackson, David Scott
(mammals), Mike Harris, Sarah Wanless (birds), Jim Foster (amphibia), Peter
Maitland (fish), Brian Boag, Jenny Cowling, Nick Greatorex-Davies, Graham
Hopkins, Margaret Palmer, Sankurie Pye, Matthew Shardlow and Allan Watt
(invertebrates).
We are grateful for the further helpful comments and advice which we received from
Scottish Natural Heritage staff, in particular Michael B. Usher (Chief Scientist),
Stephen Ward, Chris Sydes (plants), David Phillips (invertebrates), Mairi Cole
(mammals and amphibia), Andy Douse (birds), Willie Duncan (freshwater fish) and
Vin Fleming* (fungi).
We thank the British Trust for Ornithology and the British Mycological Society for
permission to use distribution data. Denise Wright and Suki Finney gave good
practical advice in developing the databases.
We are much indebted to Julian Holbrook, the SNH nominated officer, for helpfully
and wisely guiding us through the audit.
*
Now with the Joint Nature Conservation Committee, Peterborough.
53
54
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Webster, M.Mc. (1978). Flora of Moray, Nairn & East Inverness.
University Press, Aberdeen.
Aberdeen
Wilbur, K.M. & Yonge, C.M. (1964). Physiology of Mollusca. Academic Press, New
York.
Williamson, M. & Fitter, A. (1996a). The varying success of invaders. Ecology, 77,
1661-1666.
Williamson, M. & Fitter, A. (1996b). The characters of successful invaders.
Biological Conservation, 78, 163-170.
58
APPENDIX 1: LISTS OF ALIENS AND KEY DESCRIPTIVE INFORMATION
Summary of column headings, abbreviations and conventions
Explanations are given in column order from left to right. An asterisk next to the
column heading shows the column is not presented in the report tables but included
in the SNH database; the asterisk is bracketed if columns are presented only in the
tables for some groups.
(*) CHECK-LIST NUMBERS for FAMILY, GENUS and SPECIES (FAM, GEN, SP)
The numbers are given to place the plant species in a systematic order familiar to
botanists. They come from the lists of Kent (1992) and Corley & Hill (1981). For
extra species not listed by Kent but included in Stace (1991) or Clement & Foster
(1994), further numbers or letter groups have been allocated which place the plants
sensibly. For families, Kent’s numbering is continuous, so in order to assist
searching the digital database held by SNH and to allow use of the EXCEL SORT
facility, we have added a suffix to the number of the most closely similar family to
provide numbers for unlisted families, viz.: 20.1, 21.1, 26.1, 60.1 and 103.1.
For bryophytes the FAM column carries a class abbreviation (LIV = liverwort, M =
moss).
For the animal groups, the FAM column has abbreviations MAM for mammal, BIRD
for bird, AMPH for amphibian, FISH for fish and INV for invertebrate.
SCIENTIFIC NAME and ENGLISH NAME
These come from the most recent lists. For invertebrates we have given English
names only when they are widely known, and otherwise use the column to give the
species group, e.g. a snail, a carabid beetle.
PLACE of ORIGIN
The following abbreviations are used for main continents. Further detail on native
range is often given in brackets after the continent abbreviation.
Am
As
Aus
Caf
Eur
Nz
Saf
S.Am
Unk
North America (Am4 = Western N. America; Am6 = Eastern N. America)
Asia E of 60ºE, (As1 = Asia 60-120º, As2 = Asia E of 120º)
Australia
Central and North Africa
Europe
New Zealand
South Africa
South America
Unknown (used for some long-cultivated species)
59
Three other abbreviations appear in this column for vascular plants:
BritIs
GO
HYB
For species considered alien in Scotland but native elsewhere in the British
Isles
Garden origin, for taxa that have arisen in cultivation
Hybrid origin, for spontaneous hybridisation, with at least one parent being
an alien species
* MODES of INTRODUCTION
For plants, 17 categories for mode of entry have been given separate columns,
based on information in Clement & Foster (1994), with a further column for Unknown
mode and a final column which gives a total of the separate entry modes for the
species; these columns have been used to calculate the data presented in Table 7,
with some amalgamation e.g. the Deliberate Planting (Other) category includes
planting for fisheries, game preservation, domestic uses, windbreaks, etc.. The
information on entry is summarised in the ‘Manner of Introduction’ column (see
below). For animals, the Mode of Introduction columns are left blank.
PLACE of INTRODUCTION
Individual places are named only if the number of entries was very few; otherwise
‘multiple’ has been used. For molluscs the column has been left blank; even though
first records for some species could have been localised, there has been too little
recording to make the exercise of tracking down records worthwhile.
DATE of INTRODUCTION
This is the date of introduction to Scotland. For invertebrates, single-year dates are
of the earliest Scottish record, but for many species there have probably been
further unrecorded introductions. Similarly for fish, only a date based on the first
record is given for most species although further introductions perhaps occurred,
e.g. accidental escapes of unused bait. Note that C = century.
MANNER of INTRODUCTION
For plants, this column gives a brief summary of the information in the Modes of
Introduction columns (not shown in the report tables). For animals, descriptive terms
such as escapes and releases (for bait, sporting quarry, etc) are used. The ‘+’
symbol is added for species of both groups considered to be reproducing and
spreading by their own powers, i.e. that are naturalised.
The Deliberate Planting category, which comprises several of the Modes of
Introduction columns, has been divided up into 9 sub-categories, thus
(A)
(C)
(D)
(F)
Agricultural - in fields
Conservation purposes
Domestic cultivation outside gardens e.g. Rumex pseudoalpinus
Fishery - for improving waters or providing food plants for fish, etc.
60
(G)
(H)
(M)
(V)
(W)
Game - for feeding game or giving cover e.g. Gaultheria shallon
Horticultural - for flowers outside gardens e.g. Alchemilla conjuncta
Medicinal e.g. Aristolochia, Hyoscyamus
Vegetable, fruit
Windbreak
Garden Escapes include outcasts and relics; if these species are not cultivated for
flowers the descriptors (M) (V) are used with meanings as above.
REGIONAL OCCURRENCE
The columns show presence in seven regions of Scotland defined by vice-counties.
The regions are mapped in Fig. 1 and comprise the following vice-counties (Stace
(1991) gives names for the numbers).
S
C
W
E
N
H
Z
South
Central Belt
West
East
North
Outer Hebrides
Orkney, Shetland
Vice counties 72-75, 77-81
Vice counties 76, 82-87, 99
Vice counties 97-98, 100-104
Vice counties 88-96
Vice counties 105-109
Vice county 110
Vice counties111,112
For vascular plants, only records made after 1986 are used, upper case showing
occurrence in more than 15 per cent of the hectads for which records had reached
BRC (Biological Records Centre) by late 1998, and lower case occurrence in less
than 15 per cent of these hectads.
x
shows the species is known to occur in the region from local floras e.g.
Rothero & Thompson (1994), Smith et al. (1992) and Stewart (1988), despite
BRC having no records for it in the region.
For bryophytes, mammals, birds, amphibia and fish, occurrence is based on records
made from 1950 onwards, with an arbitrary split into two levels of abundance
approximating to the threshold levels used for plants. For most groups of
invertebrates there has been so little recording that all known occurrences have
been used with no date cut-off. For these species the column entries are numbers
of 10 km grid squares having any records in the region; for four invertebrate
species, 1950s onwards records are coded as for vertebrates.
SCOTTISH DISTRIBUTION
The following four levels of abundance have been employed:
Pres
Local
present in 1-4 regions, with frequency of occurrence never over 15 per cent
present in 1-4 regions, with frequency of occurrence at least 15 per cent in
one or more regions (shown by upper-case letters)
61
Wdsp
Ubiq
widespread, being present in 5-7 regions; if in 7 regions with less than 15 per
cent frequency in 1-3 regions
ubiquitous, being present in 7 regions, with frequency at least 15 per cent in
4-7 regions
CURRENT TREND in STATUS
For plants, this was decided systematically using a statistical test (see Methodology:
Vascular plants). For other groups arbitrary division into equivalent categories has
been made. The five categories are
O
<
<<
>
>>
no trend or minor change
small increase
significant increase (Sign Test on number of occurrences)
small decrease
significant decrease (Sign Test)
MODE of IMPACT
For plants, three categories have been employed for impact from: competition,
habitat damage, or mere presence. Also, two species are considered to have
genetic impact (yellow vetch (Vicia lutea) and common bird’s-foot trefoil (Lotus
corniculatus var sativus)), but they have been counted in the Impact by Presence
column of Table 9.
For animals, other descriptive terms are used, e.g. herbivores, predators.
* HABITATS occupied
Eight columns are employed, using the following heading codes for habitat
groupings
MM
CO
GR
WO
MA
FW
RO
UP
Man-made, including arable land, gardens, parks and waste ground
Coastal, including cliffs, dunes and salt marsh
Grassland, including semi-natural grasslands, roadsides and railways
Woodland, policies and scrub
Wetlands, including marsh, flushes, riversides and streamsides
Fresh water, including lochs, ponds and rivers
Rocks, walls and scree
Upland and montane habitats
Species can be assigned to more than one habitat.
HABITAT Impacted
This column gives a verbal description, providing more detail than the classification
given by the foregoing columns contained in the SNH database. The following
abbreviations have been used to compress the information:
62
dstbd grd
grsld
mrld
rdsds
rvrsds
strmsds
wdld
disturbed ground
grassland
moorland
roadsides
riversides
streamsides
woodland
VALUE of IMPACT
These are based on arbitrary judgements using three categories.
X
0
$
adverse
benign
beneficial
For most invertebrates too little is known for these judgements to be made.
IMPACT SIGNIFICANCE (SIG), PRESENT & FUTURE
Again arbitrary judgements have been made, for now (present) and about 20 years
from now (future). Three categories are used
L
M
H
low significance
moderate significance
high significance
NOTES
This column is used to provide more detail about the alien species, their localities, or
modes of entry, etc. Sources of information are given for certain species; other
general sources used that are not cited elsewhere in the text are Holmes & Simons
(1996) (birds), Johnson (1993), Majerus & Kearns (1989) and Morris (1997)
(invertebrates) and Scott & Palmer (1987) (vascular plants).
Abbreviations
employed are
Clem. & Fost.
Pankhurst et al.
Stace
P. McPherson
for Clement & Foster (1994),
for Pankhurst & Mullin (1991),
for Stace (1991), and
for information given by Peter McPherson, Glasgow (pers.
comm.).
63
Vascular plants
64
Bryophytes (Liverworts)
107
Bryophytes (Mosses)
108
Mammals
109
Amphibia
112
Fish
113
114
Invertebrates
115
APPENDIX 2: PROFILES
Scientific name
English name
Page
Pirri-pirri-bur
Corncockle
Oilseed rape, rape, cole
Butterfly bush
Small-leaved cotoneaster
New Zealand pigmyweed
New Zealand willowherb
American willowherb
Shallon
Giant hogweed
Himalayan balsam
Common bird’s-foot-trefoil (alien race)
Welsh poppy
Fringed water-lily
Rhododendron
Magellan ragwort
Alpine campion
Eastern rocket
Few-flowered garlic
Wild oat
Nuttall’s waterweed
Spanish bluebell and hybrid bluebell
122
124
126
128
130
132
134
136
138
140
142
144
146
148
150
152
154
156
158
160
162
164
European larch
Sitka spruce
Western hemlock-spruce
Water fern
166
168
170
172
Bryophytes
Campylopus introflexus
Orthodontium lineare
A moss
A moss
174
176
Fungi
Clathrus ruber
Suillus grevillei
Red cage fungus
Larch bolete
178
180
Vascular plants
Acaena novae-zealandiae
Agrostemma githago
Brassica napus
Buddleja davidii
Cotoneaster integrifolius
Crassula helmsii
Epilobium brunnescens
Epilobium ciliatum
Gaultheria shallon
Heracleum mantegazzianum
Impatiens glandulifera
Lotus corniculatus var sativus
Meconopsis cambrica
Nymphoides peltata
Rhododendron ponticum
Senecio smithii
Silene quadrifida (=alpestris)
Sisymbrium orientale
Allium paradoxum
Avena fatua
Elodea nuttallii
Hyacinthoides hispanica and
Hyacinthoides hispanica x
non-scripta
Larix decidua
Picea sitchensis
Tsuga heterophylla
Azolla filiculoides
120
Mammals
Cervus nippon
Erinaceus europaeus
Macropus rufodriseus
Mustela furo
Mustela vison
Rattus norvegicus
Sciurus carolinensis
Sika deer
Hedgehog
Red-necked wallaby
Feral ferret
American mink
Common/brown rat
Grey squirrel
182
184
186
188
190
192
194
Birds
Branta canadensis
Nycticorax nycticorax hoactli
Oxyura jamaicensis
Phasianus colchicus
Canada goose
North American black-crowned night heron
Ruddy duck
Common pheasant
196
198
200
202
Amphibian
Triturus alpestris
Alpine newt
204
Fish
Oncorhynchus mykiss
Gymnocephalus cernua
Rainbow trout
Ruffe
206
208
Invertebrates
Artioposthia triangulata
Australoplana sanguinea
Elatobium abietinum
Pacifastacus leniusculus
Tetropium castaneum
New Zealand flatworm
Australian flatworm
Green spruce aphid
Signal crayfish
A longhorn beetle
210
212
214
216
218
121
220
APPENDIX 3: SCIENTIFIC NAMES OF SPECIES APPEARING IN THIS REPORT
Scientific Name
English name
Abies alba
Abramis brama
Acaena novae-zelandiae
Accipiter gentilis
Acer campestre
European silver-fir
Common bream
Pirri-pirri-bur
Northern goshawk
Field maple
Acer pseudoplatanus
Aconitum napellus
Aconitum napellus x variegatum (A. x cammarum)
Aesculus hippocastanum
Agrostemma githago
Agrostis castellana
Sycamore
Monk's-hood
Garden monk’s-hood
Horse chestnut
Corncockle
Highland bent
Alchemilla conjuncta
Alectoris rufa
Allium paradoxum
Silver lady's mantle
Red-legged partridge
Few-flowered garlic
Alnus incana
Anas strepera
Anser albifrons
Anser anser
Anser brachyrhynchus
Anser caerulescens
Athene noctua
Avena fatua
Avena sativa
Grey alder
Gadwall
White-fronted goose
Greylag goose
Pink-footed goose
Snow goose
Little owl
Wild oat
Oat
Azolla filiculoides
Barbarea intermedia
Berberis darwinii
Berberis darwinii x empetrifolia (B. x stenophylla)
Berberis vulgaris
Branta canadensis
Branta leucopsis
Brassica napus
Bubo bubo
Water fern
Medium-flowered winter-cress
Darwin's barberry
Hedge barberry
Barberry
Canada goose
Barnacle goose
Rape
Eagle owl
Buddleja davidii
Cairina moschata
Campylopus introflexus
Butterfly bush
Muscovy duck
A moss
221
Scientific Name
English name
Capra hircus
Carassius auratus
Carassius carassius
Cerastium tomentosum
Cervus elaphus
Cervus nippon
Chenopodium rubrum
Chrysolophus pictus
Feral goat
Goldfish
Crucian carp
Snow-in-summer
Red deer
Sika deer
Red goosefoot
Golden pheasant
Cicerbita macrophylla
Ciconia ciconia
Clathrus ruber
Claytonia sibirica
Columba livia
Common blue-sow-thistle
White stork
Red cage fungus
Pink purslane
Rock Pigeon
Coregonus lavaretus
Coronopus didymus
Cottus gobio
Crassula helmsii
Powan
Lesser swine-cress
Bullhead
New Zealand pigmyweed
Crocosmia x crocosmiiflora (C. aurea x pottsii)
Crocus biflorus
Cymbalaria muralis subsp. muralis
Cyprinus carpio
Dama dama
Doronicum pardalianches
Elatobium abietinum
Elodea canadensis
Montbretia
Silvery crocus
Ivy-leaved toadflax
Common carp
Fallow deer
Leopard's bane
Green spruce aphid
Canadian waterweed
Elodea nuttallii
Epilobium brunnescens
Epilobium ciliatum
Equus caballus
Erinaceus europaeus
Eriocaulon septangulare
Esox lucius
Fagus sylvatica
Fallopia japonica
Nuttall's waterweed
New Zealand willowherb
American willowherb
Horse
Hedgehog
Pipewort
Northern pike
Beech
Japanese knotweed
Felis catus
Felis silvestris
Galanthus nivalis
Domestic/feral cat
European wildcat
Snowdrop
222
Scientific Name
English name
Gaultheria shallon
Gobio gobio
Gymnocephalus cernua
Haliaeetus albicilla
Helleborus viridis
Hennediella stanfordensis
Heracleum mantegazzianum
Hesperis matronalis
Shallon
Gudgeon
Ruffe
White-tailed eagle
Green hellebore
A moss
Giant hogweed
Dame's violet
Homogyne alpina
Hyacinthoides hispanica
Hyoscyamus niger
Ilex aquifolium x perado (I. x altaclerensis)
Impatiens glandulifera
Purple colt's-foot
Spanish bluebell
Henbane
Highclere holly
Himalayan balsam
Laburnum anagyroides
Lamiastrum galeobdolon subsp. argentatum
Larix decidua
Larix decidua x kaempferi (L. x marschlinsii)
Laburnum
Yellow archangel
European larch
Hybrid larch
Larix kaempferi
Lepus europaeus
Leuciscus cephalus
Leuciscus idus
Leuciscus leuciscus
Leycesteria formosa
Ligustrum ovalifolium
Linaria purpurea
Japanese larch
Brown hare
Chub
Orfe
Dace
Himalayan honeysuckle
Garden privet
Purple toadflax
Lonicera involucrata
Lophocolea bispinosa
Lotus corniculatus var sativus
Lunularia cruciata
Lysichiton americanus
Lysimachia punctata
Macropus rufogriseus
Matricaria discoidea
Meconopsis cambrica
Californian honeysuckle
A liverwort
Common bird`s-foot trefoil
A bryophyte
American skunk-cabbage
Dotted loosestrife
Red-necked wallaby
Pineappleweed
Welsh poppy
Microtus arvalis
Milvus milvus
Mimulus guttatus
Orkney/Guernsey vole
Red kite
Monkeyflower
223
Scientific Name
English name
Moehringia trinervia
Mus domesticus
Mustela erminia
Mustela furo
Mustela vison
Myrrhis odorata
Noemacheilus barbatulus
Nycticorax nycticorax hoactli
Three-nerved sandwort
House mouse
Stoat
Feral ferret
American mink
Sweet cicely
Stone loach
Black-crowned night heron
Oncorhynchus mykiss
Orthodontium lineare
Oryctolagus cuniculus
Otiorhynchus porcatus
Ovis aries
Rainbow trout
A moss
Rabbit
A broad-nosed weevil
Feral sheep
Oxyura jamaicensis
Oxyura leucocephala
Pentaglottis sempervirens
Perca fluviatilis
Ruddy duck
White-headed duck
Green alkanet
Perch
Persicaria wallichii
Petasites albus
Phasianus colchicus
Phoxinus phoxinus
Picea abies
Picea sitchensis
Pilosella aurantiaca subsp.carpathicola
Pinus contorta
Himalayan knotweed
White butterbur
Common pheasant
Minnow
Norway spruce
Sitka spruce
Fox-and-cubs
Lodgepole pine
Poa palustris
Potamopyrgus antipodarum
Pseudotsuga menziesii
Rangifer tarandus
Ranunculus reptans
Rattus norvegicus
Rattus rattus
Rhododendron luteum
Rhododendron ponticum
Swamp meadow-grass
A snail
Douglas fir
Reindeer
Creeping spearwort
Common/brown rat
Ship/black rat
Yellow azalea
Rhododendron
Ribes rubrum
Ribes sanguineum
Rosa rugosa
Red currant
Flowering currant
Japanese rose
224
Scientific Name
English name
Rumex pseudoalpinus
Rutilus rutilus
Salvelinus fontinalis
Sambucus racemosa
Saxifraga spathularis x umbrosa (S. x urbium)
Scardinius erythrophthalmus
Sciurus carolinensis
Sciurus vulgaris
Monk's rhubarb
Roach
Brook charr
Red-berried elder
London pride
Rudd
Grey squirrel
Red squirrel
Sedum album
Senecio smithii
Senecio squalidus
Silene quadrifida
Sisymbrium orientale
White stonecrop
Magellan ragwort
Oxford ragwort
Alpine campion
Eastern rocket
Solidago gigantea
Sorex minutus
Sphenodon punctatus
Spiraea douglasii
Early goldenrod
Pygmy shrew
Tuatara lizards
Steeple-bush
Streptopelia decaocto
Suillus grevillei
Symphoricarpos albus
Tetrao urogallus
Tetropium castaneum
Thuja plicata
Thymallus thymallus
Tinca tinca
Collared dove
Larch bolete
Snowberry
Capercaillie
A longhorn beetle
Western red-cedar
Grayling
Tench
Tolmiea menziesii
Triturus alpestris
Tsuga heterophylla
Turdus pilaris
Veronica filiformis
Veronica peregrina
Veronica persica
Vicia lutea subsp vestita
Vinca minor
Pick-a-back-plant
Alpine newt
Western hemlock-spruce
Fieldfare
Slender speedwell
American speedwell
Common field-speedwell
Yellow vetch
Lesser periwinkle
225