"Non-native" plants and animals pose the second greatest threat to the environment after habitat destruction, but their menace is not widely recognised, a conference in Tralee, Co Kerry, heard at the weekend.
Known as "invasive alien species", they look normal but have rapidly colonised natural and semi-natural areas and are threatening biological diversity, Declan O'Donnell, of the National Parks and Wildlife Service, told the Natura 2000 conference on sustainable development in designated sites.
Conservation groups, local authority representatives, planning consultants, heritage groups and environmental consultants along with landowners, foresters and farmers' groups attended the conference.
Alien species also had impacts on human health as well as "huge economic impacts", he said.
Mr O'Donnell, a district conservation officer based in the southwest, listed several species including the spectacular purple flowered rhododendron ponticum from the Caspian Sea area, which has spread into wide areas of prime woodland in Killarney, Co Kerry, and Glengarriff, Co Cork. He also spoke of the zebra mussel, which is plaguing lakes on the Shannon; the Sika deer, introduced from Japan, which is cross-breeding with native red deer; and mink and the grey squirrel, which are threatening the native red squirrel.
"Alien species are reckoned to be the second greatest threat after habitat destruction. Everyone is talking about habitat destruction; it's about time we talked about alien species," Mr O'Donnell said.
His warning comes as anglers and boatmen on the Killarney lakes are urgently seeking meetings with wildlife service management after curly-leaved waterweed was recently identified at a number of locations on the lower lake. The lakes are part of a Unesco biosphere reserve and contain several unique species. The waterweed, which is extremely invasive in Irish waters, has the potential to destroy fish life as well as making boating impossible on the lakes.
Mr O'Donnell said three-quarters of the 1,200 hectares of native woodland in Killarney had been identified in the 1990s as having been infested with rhododendron. The plant blocked out undergrowth and sterilised whole areas. Removing alien species had high costs and needed management plans. Tenders for the removal of rhododendron ranged from €3,200 a hectare to €8,800 in 2005. In Glengarriff, where 200 of the 300 hectares of native woodland were infested, "we more or less have the problem solved", Mr O'Donnell said.
Sea buckthorn in Castlegregory, Co Kerry, was taking over the sensitive dunes and Japanese knotweed had run riot in Ballingeary, Co Cork.
Helen Walsh, of the Environmental Protection Agency, said funding is to be provided for a study of the impact of non-native alien species in the Clare/Galway area.