Biology and impacts of Pacific Island invasive species. 11. Cinchona pubescens (red quinine tree) (Rubiaceae).
Cinchona pubescens Vahl (red quinine) is an evergreen tree ranging in height from 10 to 25 m with broad leaves and white or pink fragrant flowers arranged in clusters. Growing at altitudes between 130 and 3,300 m, it is one of 23 species in the genus Cinchona and has a natural distribution from Costa Rica to Bolivia. Cinchona pubescens has been cultivated in tropical regions (e.g., in South America, Africa, China, India, and Indonesia) for its quinine-containing bark and has become invasive in some regions. This is especially the case in the Pacific region, where C. pubescens has invaded humid highland areas of Galápagos, Hawai'i, and Tahiti. It shades out and reduces cover of native plant species and adversely affects endemic birds. In addition, it changes microclimate and nutrient cycling in the soil, especially phosphorus, in Galápagos. Characteristics that make it such a successful invader include production of numerous, windborne seeds and vigorous vegetative reproduction by resprouting from underground stems and fallen trees. In Galápagos, C. pubescens is currently being manually controlled by uprooting the trees and by applying herbicides to cuts in the bark. However, this method requires continuous hand pulling of seedlings to be successful. Disturbance by control actions appears to facilitate establishment and invasion by other nonnative plant species, especially blackberry (Rubus niveus). Quinine and other alkaloids extracted from Cinchona bark are still being used for medicinal purposes today and the wood is increasingly used as construction material in Galápagos. Ironically, C. pubescens is now considered rare and endangered in its native range in Ecuador.