Miconia is one of the most destructive invaders in insular tropical rain forest habitats. It is a serious threat to ecosystems in the Pacific because of its ability to invade intact native forests. Miconia has earned itself the descriptions such as the “green cancer” of Tahiti and the “purple plague” of Hawaii. Once miconia is established at a certain place it drastically changes the ecosystem and biodiversity of that environment.
Physical disturbance: Invasion by miconia has eliminated native forest understorey vegetation, increasing rapid runoff and potential for soil erosion and landslides on steep slopes.
Modification to Hydrology: Dense stands of miconia may damage watershed functions; there may be a significant change in the water balance, with an increase in runoff and a potential reduction in groundwater recharge, but this plausible result has yet to be fully investigated and documented (Burnett et al. 2006).
Economic/Livelihoods: Potential (as yet hypothetical) losses from an invasion of miconia on Oahu to groundwater recharge may conceivably be as high as $137 million per year (Kaiser and Roumasset 2002, in Burnett et al. 2006). Increased sedimentation could likely incur surface water quality damages; potential costs for Oahu have been estimated to be almost $5 million per year (Kaiser and Roumasset 2000, in Burnett et al. 2006). Comparable damage is possible on other Hawaiian islands, though the greatest economic impact is likely to be on Oahu, where 85% of Hawaii’s population is located.
Agricultural: Control programs underway since about 1995 have prevented significant agricultural impacts in the Hawaiian Islands. Invading miconia in ranchland near Hana, Maui in 1995-2000 was successfully removed. Theoretically, runoff from miconia stands could trigger erosion and loss of agricultural soil fertility (Chan-Halbrendt et al. 2007), but this has not yet happened or at least has not been documented.
Competition: When compared with a large group of native species M. calvescens appears to be better suited to capture and use light, which is consistent with its rapid spread in Hawaiian environments (Baruch Pattison & Goldstein 2000). Invasive characteristics of the species include rapid growth, fairly early maturity (after four years or more), production of large quantities of fruits and seeds, and effective seed dispersal by birds.
Threat to Endangered Species: In Tahiti, 70-100 native plant species, including 35-45 species endemic to French Polynesia, are directly threatened with extirpation by invasion of miconia into native forests (Meyer and Florence 1996).
Hawaii is home to a great number of rare and endemic plant, bird and invertebrate species at risk of global extinction, including over 350 federally endangered species. Upper Kipahulu Valley of Haleakala National Park on Maui, Hawaii, is a prime stronghold of Hawaiian biodiversity, containing stands of ohia (Metrosideros polymorpha) and koa (Acacia koa) that provide the primary habitat for rare native Hawaiian plants, birds and insects. Proactive response of Haleakala National Park personnel originally triggered a community-wide response to the miconia invasion in Hawaii about 30 years after M. calvescens had first been introduced to the State.
