By guest author Dr. Heinke Jäger, Restoration Ecologist at the Charles Darwin Foundation.
An invasive plant species introduced to Galapagos in the 1940s completely changed a highland ecosystem on Santa Cruz Island before experiencing a mysterious decline. We are trying to find out why.
Cinchona (quinine), a genus in the family Rubiaceae (coffee family), is second only to the genus Coffea (coffee) in terms of commercial importance, due to its quinine-containing bark. Cinchona is comprised of 23 species of tropical evergreen trees and shrubs, distributed from Costa Rica to Bolivia, 16 of which are found Ecuador. In the early 1940s, C. pubescens, one of the species found in the mainland, became the only Cinchona species ever introduced to Galapagos. Unfortunately, in time, it became one of the most invasive woody plants on Santa Cruz Island…until recently, that is. But that is the second part of this story.
The first part begins with its introduction to the Islands. You might wonder why anyone would bring a tree species to Galapagos. At the time, the species was quite valuable. Quinine, extracted from its bark, was used as a remedy for malaria worldwide. Various Cinchona species were cultivated in the tropics (America and Asia) for their high economic value. During World War II, the price of quinine rose drastically as many of the plantations in Asia were occupied by the Japanese and quinine trees in Latin America were over-exploited. In fact, exploitation in mainland Ecuador nearly caused the extinction of C. pubescens.
In 1944, quinine was artificially synthesized, resulting in a rapid decline in the economic value of Cinchona plantations. Unfortunately, before the news reached Ecuador, the species had been introduced to Galapagos, where it found perfect growing conditions. Due to its light, wind-borne seeds and vigorous vegetative reproduction, it spread from its original plantations in the agricultural zone of Santa Cruz to the top of the island — becoming very abundant throughout the highlands, and converting much of the formerly fern- and shrub-dominated landscape into an open woodland. Ironically, the species brought to Santa Cruz, C. pubescens, doesn’t even contain significant levels of quinine. Instead of being a boon to the local economy, the tree became a threat to the local ecosystems. Our studies have shown that quinine shaded out native plant species, changed the microclimate of the area, and altered nutrient cycling in the soil.
About 10 years ago, scientists, farmers and others began to notice that the quinine trees, both within the national park and in the agricultural zone, were losing their leaves and appeared much less vigorous than previously. We wanted to understand why. Perhaps whatever was causing the decline could be exploited as a natural biological control of quinine.
In 2014, our research group at the Charles Darwin Foundation (CDF) and the Galapagos National Park Directorate (GNPD), with support from Galapagos Conservancy, teamed up with international experts from the Centre for Agricultural Bioscience International (CABI), UK, to investigate possible reasons for the quinine decline. Unfortunately, no culprit of the mysterious quinine die-off has yet been found.
During the EMAPI (Ecology and Management of Alien Plant Invasions) conference in Hawaii in 2015, for which GC sponsored my participation, I learned of other cases in the world where a once widespread invader species began to decline in abundance, in some cases due to a pathogen. Dr. Luke Flory from the University of Florida, a leading scientist in this field, was interested in searching for the cause of the dying quinine trees in Galapagos. He encouraged me to revive some old monitoring plots that might provide crucial data.
In 2016, in response to Dr. Flory’s suggestion, we relocated 14 vegetation monitoring plots, originally established in 1998, to assess the impacts of quinine on the native vegetation. These plots had not been monitored since 2005. Quinine in these plots had never been manually or chemically controlled by the GNPD, and thus might be vital to finding answers to the natural decline of the population.
With ongoing support from GC, preliminary results from this study — a collaboration between CDF, GNPD, University of Florida, and the Technische Universität Berlin — were presented at the 14th EMAPI meeting in Portugal in September 2017. These results showed a drastic decline in the quinine population, as well as substantial regeneration of native plant species. In January 2018, Dr. Luke Flory and PhD candidate Catherine Fahey from the University of Florida visited Galapagos to collaborate with me on a paper covering the results of this study, and to plan a more vigorous sampling of affected quinine trees. Together, we hope to soon shed light on the causes of this mysterious die-off, and to be able to use the results for the long-term conservation benefits of the Galapagos Islands.
For further reading, visit the author’s Research Gate profile.
Heinke Jäger has been working at the Charles Darwin Research Station (CDRS) since 1998 on several research projects involving introduced species, such as quinine and blackberry, and also on many rare and endangered plant species. After receiving her PhD from Technische Universität Berlin, Germany, she carried out her postdoctoral research on invasive species at Brown University, USA. She is now a Restoration Ecologist at CDRS; her research focuses on terrestrial plant and animal species in Galapagos, including distribution, impacts, and control of invasive species, as well as the restoration of invaded ecosystems. All photos © Surya Castillo except final photo of researchers in the field © Anna Walentowitz.
Galapagos Conservancy has been supporting the Charles Darwin Foundation’s Invasive Species project since 2011. Read more about controlling invasive plants in Galapagos.