Notes on the Status of an Invasive Australian Tree Fern (Cyathea cooperi) in Hawaiian Rain Forests

Abstract

Tree ferns are a characteristic growth form of tropical cloud and wet montane forests. In the Hawaiian Islands, native species of tree ferns are important components of rain forest ecosystems. Hawaiian rain forests and other native ecosystems are vulnerable to invasion by introduced plant species, especially with disturbance (Stone & Scott, 1985: Loope & Mueller-Dombois, 1989). Although 26 species of alien pteridophytes have become naturalized in Hawai'i (Hobdy, 1991; Wagner, 1950), not one was listed among the 86 most aggressive plant invaders of native Hawaiian ecosystems (Smith, 1985). This paper documents the distribution and ecology of the tree Cyathea cooperi, native to northeastern Australia, that has escaped from cultivation and is now naturalized in rain forests of several Hawaiian islands. It also provides some details on one invasive population on eastern Haleakala volcano on Maui island. Tree ferns occur predominantly in two families, Cyatheaceae (700 spp.) and Dicksoniaceae (30 spp.), and less commonly in other families, e.g. Blechnaceae, Dryopteridaceae, and Thelypteridaceae. In the Hawaiian Islands, native tree ferns occur in the families Dicksoniaceae with 5-6 endemic species in the genus Cibotium, Blechnaceae with 4-6 endemic species in the genus Sadleria, and several small tree species in the family Dryopteridaceae (Wagner, 1981, 1990; Lamoureux, 1984). Tree ferns in the large cosmopolitan genus Cyathea, known in Hawai'i as tree fern, have been in cultivation in the Hawaiian Islands at least since the 1960s (Neal, 1965) as ornamentals at homes and botanical gardens. Cyathea is widely planted locally since it is a hardy, attractive species, evocative of tropical settings, and is faster growing and more tolerant of warmer, drier conditions than native Hawaiian tree ferns (Cibotium spp.) Hawai'i's Australian tree fern has long been identified in Hawaiian botanical literature and the horticultural trade as Cyathea australis (R.Br.) Copel. (Neal, 1965).