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Alien Ferns in Hawai'i
Human activity has led to the naturalization of 30 species of pteridophytes in the Hawaiian flora. The first record of naturalized ferns in Hawai'i is in collections made in 1887. By 1950,21 species had become established. Many of these species have spread into the native forests and are now found on all the main Islands. Since then, nine additional alien species of ferns and fern allies have been found growing in the wild. The naturalized ferns represent fewer than 16% of the pteridophyte species in Hawai'i. Although some of these species do not appear to be serious problems in the local ecosystem, others are known to be having a pronounced impact. Some naturalized ferns are displacing native species; others are hybridizing with native ferns; and still others are invading native forests, crowding out the local vegetation, and posing a serious threat to the Hawaiian ecosystem. Continued disturbance of the native habitat and introduction of new alien plants contribute to successful invasion of alien plants into the Hawaiian Islands. More than 260 species of alien pteridophytes are in cultivation on the Islands, mostly in botanical gardens and arboretums. These provide a reservoir of species for new additions to the local flora. Programs need to be established to restrict the invasion of alien species into the Hawaiian ecosystem.