Detecting trends in introductions is fundamental for assessing the threat from invasive species.

Trends in introductions can indicate if we have an increasing or decreasing flow of invasive [or alien] species into Ireland; what general habitat types are most at risk; what are the main pathways of introductions (if known); where are the native source areas for these species and detect possible future scenarios.

These indicators can then help inform policy and target action, education and awareness.



In 2014, a report titled ‘Ireland’s invasive and non-native species – trends in
’ provides, for the first time in Ireland, an overview of the apparent trends in the introduction of invasive alien species.

Some of the key findings are:

  • 13% of the alien species recorded and assessed in Ireland are high impact invasive species. This figure is comparable to other European countries
  • 4 times as many species were recorded in the 20th Century as in the previous one
  • The trend increased dramatically from 2001 to 2010 for high impact invasive species
  • While the majority of species are found in the terrestrial environment the rate of increase in introductions is increasing for all environments with the greatest increase for the freshwater environment since 1980

    View the 12 invasive species with alerts issued for their detection in Ireland between 2000 and 2010
  • Freshwater non-native species are more likely to be high impact invaders when they are introducedView the 12 invasive species with alerts issued for their detection in Ireland between 2000 and 2010
  • To date, the majority of invasive species in Ireland are plants, but the future trend may be towards invertebrate and vertebrate species comprising a greater percentage of all new arrivals
  • Most species are native to North America and Asia but future invasions of species native to mainland Europe is likely.

Limitations to the analysis are highlighted and 10 recommendations made for future work to fill key knowledge gaps.

Download report:

Selection of figures on the trends of non-native species from the Trends Report

Figure 1. Number and percentage of species in each of the risk impact categories. Of the 377 non-native species that were assessed, 250 (66%) are risk of low impact, 79 (21%) are risk of medium impact, and 48 (13%) are risk of high impact.



Figure 4. Cumulative trend in the number of high and medium risk species per decade from 1901 to 2010. The rate of introduction for both high and medium impact species has increased steadily since the 1950s, with a rapid increase since 2000


Figure 5. Percent of species in each broad environment category. 67% of invasive species occur in the terrestrial environment, 21% in freshwater and 12% in the marine environment.
Figure 9. Percent of species per taxon group. 48% of the high and medium impact species are plants, 24% are vertebrates and another 24% are invertebrates (Figure 7). The remaining 4% represent just five species, comprising two fungi and three algae.


Figure 18. Percent of species per native region. Most of the high and medium impact species in Ireland originate from Asia (22%) and North America (20%). The third highest contributor of species is Europe (16%) including Great Britain, Eurasia (15%) and Australasia (8%), followed by Eurasia (15%) and Australasia (8%).

Selection of figures on potential future of introductions of non-native species to Ireland

From a horizon scanning exercise, a further 342 species were identified as potential invaders to Ireland.

Figure 22. Number and percent of species in each impact category – potential invaders. 15% of the potential invaders are ranked in the high impact species category (n=51), 28% as medium impact (n=96), and 57% as low impact species (n=195).
Figure 23. Percent of species in each broad environment category – potential invaders. 55% of the species in the high and medium impact categories are terrestrial species, 29% are freshwater and 16% are marine species.
Figure 25. Percent of species per taxon group – potential invaders. 45% of the high and medium impact potential invaders are invertebrates, 31% are vertebrates and 19% are plants.









Figure 28. Percent of species per geographic region – potential invaders. As with the recorded species, most of the potential invaders are native to Asia (24%) and North America (23%). 14% are native to Europe, 8% to Eurasia and 8% to South America (Figure 28). Australasia, Africa and North and South America contribute 6% each. 5% of the species are listed as unknown native origin.