Charles Darwin Foundation, Galapagos, Ecuador, and Department of Ecology, Technische Universität Berlin, Germany
Biodiversity hotspots, defined as having high plant endemism and major habitat loss, encompass 35 geographic regions. Together they only cover 15.9% of the global land surface but contain 152,000 plant species (over 50% of the world’s total). Oceanic islands comprise one third of global biodiversity hotspots and provide particularly suitable habitats for invasive species. Hundreds of invasive plant species have invaded island ecosystems and threaten native biodiversity worldwide. Although an effective biosecurity system provides the best way to prevent new plant invasions, few oceanic island governments have implemented them to date. Once a non-native species is established, a swift action to eradicate it would be best – but often the establishment goes unseen and subsequently, only control measures can curb the impacts of the species. Control of invasive plant species is carried out on most oceanic islands now with varying success. Invasive species control is all the more important on islands that house many endemic plant species. The unique flora of the Galapagos Islands, with 43% of the plant species being endemic, provides a good example of this situation. Many of these are threatened by invasive species, transported to the islands by multiple vectors. The exceptionally high levels of endemism led to the recognition of the Galapagos Islands as a UNESCO World Heritage site, a Priority Ecoregion for Global Conservation, a ‘flagship’ area for conservation and one of the 137 ‘most irreplaceable protected areas in the world’. As such, conservation management in Galapagos is challenged by the dual needs of sustaining native biodiversity while controlling invasive species. Currently, there are 810 introduced plant species in Galapagos (about 60% of the Galapagos flora), with about 6% of these having become invasive. The most infamous are blackberry (Rubus niveus), common guava (Psidium guajava), Cuban cedar (Cedrela odorata) and quinine (Cinchona pubescens). While there have been successful eradications of some of the plant species with a limited distribution, manual and chemical control methods are being used by the Galapagos National Park Directorate (GNPD) to tackle the most invasive ones. Our recent study of the efficiency and impacts of blackberry control in a forest of the endemic, threatened tree species Scalesia pedunculata, shows that without control, this unique forest will be lost within the next generation. High resolution vegetation mapping using drones indicates that the restoration actions carried out by the GNPD are highly effective. However, this mapping effort also suggests an indirect effect of goat eradication, as blackberry has now become rampant, 10 years after goat removal. While the breeding success of Darwin’s finches and the abundance of some invertebrates have been negatively affected by the blackberry control, results also indicate that these effects may be transient. Efforts to find a biological control agent for blackberry are underway and have produced promising results to date. For other invasive species, conservation efforts in Galapagos seem to be getting unforeseen help. For example, our 21-year long monitoring study of the highly invasive quinine tree C. pubescens indicates that it is dying off, which has enabled the native vegetation to recover without additional restoration actions. While the reason for this seemingly natural die-off of quinine trees is still under investigation, it is likely caused by a root pathogen. In summary, conservation of the Galapagos biodiversity has been advanced by science-based technical assistance to the GNPD on invasive species control, which advocates a more holistic, management approach.