Plants associated with Myrica faya and two other pioneer trees on a recent volcanic surface in Hawaii Volcanoes National Park
Mueller-Dombois, D.; Whiteaker, L.D.
During the past two decades, Myrica faya, a nitrogen-fixing tree native to the Macaronesian Islands, has become one of the most aggressive alien invaders in volcanically disturbed Metrosideros polymorpha ecosystems of Hawaii Volcanoes National Park. Because of their high annual rate of N-fixation, contributing 18 kg/ha of fixed nitrogen to the 5.5 kg estimated as natural background rate, isolated Myrica trees that became established about ten years ago on an ash blanket deposit were suspected to promote weed invasion in their immediate surroundings. Twenty-five sets of three non-overlapping but juxtaposed circular releves were established around isolated pioneer trees of Metrosideros polymorpha, Myrica faya and Buddleja asiatica, the only tree species growing in scattered formation in this young volcanic habitat. No preferential association of weeds with Myrica could be documented. A growth period of one decade may be insufficient for such a reaction to occur, or the herbaceous and shrubby colonizers currently in the area may be there because they are tolerant to low levels of soil nitrogen. An unexpected trend emerged, with Myrica being preferentially associated with Buddleja. This indicates that Myrica, in spite of its N-fixing ability, is not an independent pioneer but rather a secondary colonizer as are most of the other currently invading species.