Spredningsveier for fremmede arter i Norge

Abstract

Fremmede arter er et fokusområde for naturforvaltning på internasjonalt nivå. Når først frem-mede arter har etablert seg i et nytt område er det ofte særdeles vanskelig å fjerne dem igjen, og omkostningene ved en eventuell utrydding er ofte vesentlig høyere enn forebyggingstiltak. Kunnskap om innvandringsveier og –vektorer er dermed sentralt for effektiv forebygging av inn-vandring, spredning og etablering av fremmede arter. I denne rapporten analyserer vi spred-ningsveiene til 1170 fremmede arter som reproduserer i fastlands-Norge og 1071 fremmede arter som ikke reproduserer her, samt 79 arter på Svalbard. Datamaterialet er basert på Artsda-tabankens fremmedartsdatabase. Datamaterialet opererer med fem spredningsveier: Utsatt, for-villet / rømt, blindpassasjer, sekundær spredning fra naboland og ukjent vektor, men av antro-pogen opprinnelse. For en del arter finnes ytterligere informasjon om spesifikke vektorer, f.eks. via drivhus, ballastvann o.l. Prosjektet er utført på oppdrag fra Miljødirektoratet. Det er en omfattende litteratur om fremmede arter, men først i de senere årene har man begynt å se spesifikt på ulike spredningsveier. En gjennomgang av den tilgjengelige litteraturen viser at risikoen for at nye fremmede arter etablerer seg generelt øker med antallet individer og / eller arter som introduseres. De vanligste gruppene av fremmede arter som rapporteres i litteraturen er karplanter, virvelløse dyr og marine organismer. En komplett overvåking eller registrering av fremmede arter er ikke realistisk. Analysene i denne rapporten basere seg på klassifiseringer, risikovurderinger og beskrivelser av egenskaper som er tilgjengelig i fremmedartsdatabasen. Resultatene er dermed direkte avhengige av de data som finnes i risikovurderingen, og de valgene som ligger til grunn for denne, og de representerer virkelige forhold bare i den grad risikovurderingen beskriver virkelige forhold. I analysene av data fra fremmedartsdatabasen fant vi et mønster som likner på mønsteret i andre analyser. Flest fremmede arter har etablert seg i Norge som følge av forvilling, etterfulgt av arter som har kommet til landet som blindpassasjer. Dette står i motsetning til ikke-reproduserende fremmede arter, hvor blindpassasjer er langt den viktigste spredningsveien. Begge grupper do-mineres av karplanter. De tidligst ankomne fremmede artene er kommet som blindpassasjer i 1765. Dette er også den spredningsveien, der antallet av arter tidligst (i 1908) når 50 % av det nåværende nivå. Generelt er den relative utviklingen over tid, dvs. tidspunktet for når antallet av arter fra en spredningsvei når en viss prosentdel av det nåværende nivå, ganske lik mellom spredningsveier. Kun arter som er kommet med sekundær spredning fra naboland skiller seg ut med sen ankomst (1875) og sen 50 prosentil (1975). For ikke-reproduserende fremmede arter er den relative utviklingen lik for spredningsveiene blindpassasjer, forvillet og arter med ukjent vektor, mens arter som er satt ut er litt forsinket i forhold til disse. Hovedparten av arter i fremmedartsdatabasen er knyttet til det terrestriske miljø. Forvillede arter dominerer denne gruppen, etterfulgt av blindpassasjerer. Terrestriske arter domineres av kar-planter og insekter, og utviklingen over tid svarer derfor til utviklingen for disse gruppene. For arter knyttet til det marine miljø er spredningsveiene forvilling og blindpassasjer omtrent like vik-tige. Arter som er satt ut, og i de senere årene også forvillede arter, er de dominerende blant fremmede arter i det limniske miljø. fremmede arter, spredningsveier, biologisk invasjon, alien species, distribution pathways, biological invasion

Alien species are of considerable interest to management of natural resources at an international level. Once alien species have established in new regions, it is often very difficult to completely remove them, and the costs of removal is generally much higher than preventing their establishment in the first place. Knowledge about dispersal pathways and vectors are therefore central to effective prevention of immigration, spread and establishment of alien species. In this report, we analyse the pathways of 1170 alien species that reproduce in mainland Norway and 1071 alien species that are here but without reproducing populations, as well as 79 species from Svalbard. The data is based on the alien species database form the Norwegian Biodiversity Information Centre. The data includes five dispersal pathways: Released, escaped, contaminant / stowaway, secondary spread from neighbouring countries and unknown vector, but of anthropogenic origin. For some species there is also information available about specific vectors, e.g. through green houses, ballast water etc. The project is commissioned by the Norwegian Environment Agency. There is an extensive literature on alien species, but the interest in dispersal pathways only goes back a few years. A review of the available literature shows that the risk that new alien species establish generally increases with the number of individuals and / or species introduced. The most common groups of alien species reported in the literature are vascular plants, invertebrates and marine organisms. An exhaustive monitoring or registration of alien species is not realistic. The analyses in this report are based on the classifications, risk assessments and descriptions of properties available in the alien species database. The results are thus directly dependent on the data contained in the risk assessment, and the choices that underlie this, and they represent real conditions only to the extent that the risk assessment describes real-world conditions. In the analyses of the data from the alien species database, we found a pattern that corresponds to other analyses. Most alien species have established in Norway as a result of naturalization, followed by species that have come to the country as a stowaway. This is in contrast to the nonreproductive alien species, where stowaway is by far the most important dispersal pathway. Both groups are dominated by vascular plants. The earliest arrivals of alien species have come as a stowaway in 1765. This is also the dispersal pathway, which first reach 50 % of the current number of species (in 1908). The relative development over time, i.e. the time when the number of species from a dispersal pathway reaches a certain percentage of the current level, is generally fairly similar between different dispersal pathways. Only species that have come with secondary dispersal from neighbouring stands out with late arrival (1875) and late 50th percentile (1975). For non-reproducing alien species, there is a similar temporal development between the dispersal pathways stowaway, escaped and species with unknown vector, whereas species that has been released are slightly delayed in relation to these. The majority of species in the alien species database are terrestrial. Naturalised species dominate this group, followed by stowaways. Terrestrial species dominated by vascular plants and insects, and the temporal trends therefore correspond with the development of these species groups. Marine species have primarily come by escape from captivity or as stowaway; the two dispersal pathways being approximately equally important. Species which have been deliberately releases, or in later years also species that have escaped, are predominant among alien species in the limnic environment. There is a clear positive correlation between the degree of human intervention and the proportion of species that manage to establish and reproduce in Norway. Of the species that have been released in Norway, 74 % has established, compared with 61% of the species that has escaped and 39% of species that have come as stowaways. The dispersal pathways differ with respect to how large a proportion of species that are included on the Norwegian blacklist. More species than expected by chance have been either released or arrived from neighbouring countries, whereas for stowaways and species that have come with unknown but anthropogenic vector there are fewer blacklisted species than expected if the distribution was random. Among species that have been naturalised the proportion of blacklisted species reflect the proportion in the group of alien species in general. Naturalisation is the most common dispersal pathway for species on the Norwegian blacklist from 1850 and onwards. In 2012, 46 % of the registered alien blacklisted species had come by this pathway, which corresponds with naturalisation as being the most common of the dispersal pathways. Stowaway, the second most important pathway, account for 20 % of the species. Naturalisation is also the dominant dispersal pathway for species which are not included in the blacklist, but classified as potentially high risk species, whereas species classified as low or no known risk species have come by a variety of pathways. 'Regulations relating to plants and measures against pests ' specifies a series of plants and pests for which introduction into Norway is forbidden. Of these, approximately 129 taxa are included in the alien species database. Vascular plants constitute the largest species group; about 107 species. Among these, naturalizing is the most common dispersal pathway, followed by species thats have been released. Insects have come as stowaways, while nematodes and fungi primarily have come with an unknown vector of anthropogenic origin. Thirteen species are included on the Norwegian blacklist. There is a clear positive correlation between the development in wealth, measured as gross development product, population growth and import of goods, and the number of new species arriving in Norway each year. There is sufficient data available for the large species groups, vascular plants and non-marine invertebrates, to perform more detailed analyses of the properties that characterize species arriving with the individual pathways. For non-marine invertebrates, we found that while there was an equal distribution of stowaways and non-stowaways among the species that originated in Europe, only few species arrived as stowaways from regions outside Europe. Of the European species many were associated with horticulture. For vascular plants, generation time was of paramount importance: species with long (> 35 years) generation time dominated the group of plants that had been actively released, whereas plants that had escaped from cultivation were characterised by species with a generation time of > 2.5 years and stowaways of species with a generation time of <2.5 years. Some attention should be given to stowaways not currently able to establish themselves. They can be important vectors of pathogens and diseases, and a warmer climate in the future may improve their opportunities to establish and reproduce. An analysis of the relationship between alien species and habitats show that areas with a high degree of modification to the surface soils (such as build up areas) are by far the most common habitat for alien species, with 19-34% probability that a species establishes itself, depending on the dispersal pathway of the species. Released plants are strongly associated wirh agricultural activities with some 86 % having arable land as their main habitat. The majority of the alien species in freshwater originated in North America, whereas species from Asia dominate the marine littoral zone. Cultivated and arable land is dominated by species from Europe, while European species are almost absent in the marine environment. In Svalbard, vascular plants constitute the dominant species group, but in recent years there has also been reports of invertebrates and fish. Most of the species are categorised as non-reproductive alien species, and registration of this group has increased considerably since the late 20th century. Only 10 species are currently classified as established, reproducing alien species, but it is likely that a warmer climate will increase the opportunities for successful establishment. Experiences from Antarctica may be useful for analysing the effects of and risks associated with the alien species in polar regions, including Svalbard.