By Sara Bárrios & Colin Clubbe, 20th September 2021
The British Virgin Islands, a UK Overseas Territory in the Caribbean, comprises c. 240 mostly small and uninhabited islands and cays with four main islands supporting the territory’s c. 30,000 inhabitants. With a native flora of 874 described taxa, four are considered endemic to the archipelago. For more than 20 years, the UK Overseas Territories team at the Royal Botanic Gardens, Kew has been working with the National Parks Trust of the Virgin Islands to assess the risk of extinction of its flora and providing evidence for conservation interventions. Vachellia anegadensis, (synonym Acacia anegadensis) is a small tree that for many years we believed to only occur on the limestone island of Anegada. In 2008, during our first botanical survey on the volcanic island of Fallen Jerusalem, we found an additional population of V. anegadensis. Between 2014 and 2019 we have visited Anegada and Fallen Jerusalem regularly, collecting data to evaluate the distribution, population genetics and main threats to this species. We have also partnered with colleagues from the University of Copenhagen, who studied its pollinators. These collective data formed part of the evidence to categorize this species as Endangered using the IUCN Red List Categories and Criteria.
Inflorescence of Vachellia anegadensis. Photo: Colin Clubbe
Our study established that V. anegadensis is still threatened. On Anegada we confirmed that it is distributed across the island and is less abundant in the dunes of the north-west. On Fallen Jerusalem, it mainly occurs in the forested interior, which also coincides with the area of higher availability of freshwater and reduced salt spray. The DNA extracted and analysed from 123 leaf samples did not reveal a clear genetic distinction between the trees on Anegada and Fallen Jerusalem. This could be the result of continuing gene flow between the two islands and/or reflect historical colonization events. For example, trees on Fallen Jerusalem could have originated from a colonisation event by trees from Anegada, or vice versa.
Left: A tree of Vachellia anegadensis on Anegada. Right: Collecting leaf material for DNA extraction. Photos: Sara Bárrios
Feral animals and development appear to be the greatest threats to V. anegadensis on Anegada, in common with threats observed in other Caribbean regions. Overgrazing reduces the number of seedlings, thus limiting regeneration. Overgrazing also depletes seed banks and, through changes to soil conditions, leads to compaction and reduction of topsoil, which is essential for seed germination and establishment. During this study we also observed extensive road widening across the island, especially from The Settlement to Loblolly Bay, and unauthorised land clearance for farming on the western salt ponds, in both cases this resulted in the death of individual trees. The threat of continued infrastructure development remains and will have serious implications for the future of V. anegadensis without adequate protection measures in place. Both islands are being affected by more frequent and more prolonged droughts, and more intense hurricanes, indicative of global climate change, and may be impacted by future sea level rise.
Vachellia anegadensis is visited by a variety of pollinators, both hummingbirds and insects. However, insects, especially butterflies, are the most frequent floral visitor. We found that V. anegadensis had a low seed pod production when pollinators were excluded, indicating either that the tree may also self-pollinate or can be wind pollinated, as the nylon bags only excluded pollinators. The significantly higher production of seed pods in the absence of exclusion bags indicates the importance of pollinators, especially butterflies, for successful reproduction of this species.
Left: Feral cow roaming free on Anegada. Photo:Colin Clubbe. Right: Unauthorised land clearance on Anegada. Photo: Sara Bárrios
We recommend that a conservation strategy for V. anegadensis should aim to maintain the present levels of genetic variability, reduce the pressure from threats and help maintain suitable habitat. There is a pressing need to address the greatest threat to V. anegadensis, feral livestock that roam freely across the island. The Protection of Trees and Conservation of Soil and Water Ordinance, which prohibits grazing of livestock in protected areas, is a mechanism that could deal with this issue once proposed protected areas are approved. In addition, some areas designated as proposed protected areas, which are uninhabited, need to be temporarily fenced, to promote vegetation regeneration. Monitoring of V. anegadensis, and of the species’ pollinators and seed dispersers, is required, as well as keeping a close eye on invasive alien plants, which we observed to be spreading from The Settlement. These proposed conservation measure need to guide conservation interventions, to ensure the long-term survival of this iconic endemic plant species.
Left: Butterfly (Polygonus savigny) visiting Vachellia anegadensis inflorescence. Photo: Colin Clubbe. Right: Fieldwork to study the species’ pollinators. Photo: Maria Dufke
The article The conservation status and ecology of the British Virgin Islands endemic tree, Vachellia anegadensis available in Oryx—The International Journal of Conservation.
