DOI: 10.5061/dryad.8sf7m0cjc
title: Data from: Ecological impact assessments of alien species in Norway

description: Due to globalisation, trade and transport, the spread of alien species is
 increasing dramatically. Some alien species become ecologically harmful by
 threatening native biota. This can lead to irreversible changes in local
 biodiversity and ecosystem functioning, and, ultimately, to biotic
 homogenisation. We risk-assessed all alien plants, animals, fungi and
 algae, within certain delimitations, that are known to reproduce in
 Norway. Mainland Norway and the Arctic archipelago of Svalbard plus Jan
 Mayen were treated as separate assessment areas. Assessments followed the
 Generic Ecological Impact Assessment of Alien Species (GEIAA) protocol,
 which uses a fully quantitative set of criteria. A total of 1519 species
 were risk-assessed, of which 1183 were species reproducing in mainland
 Norway. Among these, 9% were assessed to have a severe impact, 7% high
 impact, 7% potentially high impact, and 49% low impact, whereas 29% had no
 known impact. In Svalbard, 16 alien species were reproducing, one of which
 with a severe impact. The impact assessments also covered 319 so-called
 door-knockers, i.e. species that are likely to establish in Norway within
 50 years, and 12 regionally alien species. Of the door-knockers, 8% and
 10% were assessed to have a severe and high impact, respectively. The
 impact category of most species was driven by negative interactions with
 native species, transformation of threatened ecosystems, or genetic
 contamination. The proportion of alien species with high or severe impact
 varied significantly across the different pathways of introduction,
 taxonomic groups, time of introduction and the environments colonised, but
 not across continents of origin. Given the large number of alien species
 reproducing in Norway and the preponderance of species with low impact, it
 is neither realistic nor necessary to eradicate all of them. Our results
 can guide management authorities in two ways. First, the use of
 quantitative assessment criteria facilitates the prioritisation of
 management resources across species. Second, the background information
 collected for each species, such as introduction pathways, area of
 occupancy and ecosystems affected, helps designing appropriate management
 measures.
description: The species assessed were a subset of the inventory of alien
 species in Norway (described by Sandvik et al.,
 <i>Biological Invasions</i> <em>21:</em>2997, 2019).
 The assessments followed the Generic Ecological Impact Assessment
 of Alien Species (GEIAA, described by Sandvik et al.,
 <i>Biological Invasions</i> <em>21:</em>2803, 2019).
description: The dataset contains three files: (1)
 Data.xlsx (microsoft excel spreadsheet workbook)<br> (2) assess.txt
 (data file as semicolon-delimited plain text)<br> (3) Info.pdf
 (explanations of the data file) The workbook
 "Data.xlsx" contains the same information as the two latter
 files:<br> - The data are provided both in "assess.txt"
 and in the "Assessments" sheet of
 "Data.xlsx".<br> - The information needed to interpret the
 data is provided both in "Info.pdf" and in
 "Data.xlsx". For questions on these files,
 please contact the first author (hanno.sandvik@nina.no) or the Norwegian
 Biodiversity Information Centre
 (fremmedearter@artsdatabanken.no).