The tree fern Dicksonia antarctica invades two habitats of European conservation priority in São Miguel Island, Azores

Abstract

Sixty fern species are considered problematic worldwide because of their invasiveness, but only two of them are tree ferns. This paper reports the invasion by the Australian tree fern Dicksonia antarctica to the eastern part of Sao Miguel Island (Azores archipelago—Portugal). It probably escaped from cultivation in the nineteenth century and has spread to an area of over 48 km2, mainly at high altitude (>500 m a.s.l.). The invaded area is characterized by high precipitation (mean = 2,857 mm/year), high relative humidity (mean = 96.4%), and mild temperatures (mean = 12.1°C). The species has invaded forest plantations, exotic forests and two habitats of European conservation priority: native laurel forests and blanket bogs. Dicksonia antarctica plantlets (individuals with no trunk) were predominant in exotic forests,D. antarctica shrubs (trunk height 1 m) in gardens. Blanket bogs had the maximum percentage (90%) of fertile individuals (i.e. with sporangia). The large size and poor access of invaded area makes full eradication from the island impossible. We recommend complete elimination in blanket bogs and to take control measures in native laurel forests as these are priority conservation habitats.