Invasive non-native and alien garden escape plant species on the southern cliffs of Howth Head, Co. Dublin (H21).
A survey of non-native invasive and alien plant species was carried out along the coastal cliffs of Howth, Co. Dublin. Many such species have established themselves on the tracks and cliffs in this location as a result of dumping of garden waste over the past few decades. These cliffs are within the Howth Head Special Area of Conservation (SAC000202). Thirty-one non-native invasive and alien species were recorded and one vigorous native species (Carex pendula), which is also considered to be introduced in some vice-counties in Ireland. Three of the non-native species had a 'high risk' invasive species category; seven were categorised as 'medium risk' and six were 'low risk'. Fifteen of the recorded species have not been nationally assessed, two of which were considered by the surveyors to be invasive in this location (Veronica × franciscana and Echium pininana). Echium pininana, a Canary Islands endemic, has been noticeably spreading on the southern cliffs of Howth Head. The presence of invasive alien species negatively affects the native flora in this location due to the vigorous and often dense growth habit of many of these species which can impede growth of native species in these locations, i.e. Carpobrotus edulis, Reynoutria japonica, Gaultheria shallon, V. × franciscana, and in the case of E. pininana, the copious numbers of seeds produced per flower spike results in many seedlings germinating. C. edulis in particular is a known aggressive invader of coastal habitats and forms vast mats to the exclusion of all other plants. The native species Inula crithmoides was recorded in a location where C. edulis had been successfully chemically treated. A localised non-native invasive species control and/or eradication program could prevent the spread of both invasive and potentially invasive species while the population sizes are metres instead of miles in diameter and currently manageable. For well-established species such as C. edulis and V. × franciscana, complete eradication would be difficult, therefore, a control program is imperative to reduce the continued spread of such species in this location, with the aim of eradication of these species over time.