The St Helena Olive Tree (Nesiota elliptica), endemic to the remote South Atlantic island of St Helena, represents a significant case in conservation. Its story, marked by a dramatic decline and dedicated conservation efforts, highlights the fragility of island ecosystems and serves as a powerful symbol for biodiversity preservation.
Discovery and Original Habitat
The St Helena Olive Tree was first formally described in 1871 by Joseph D. Hooker, with earlier records from the 1850s noting 12 to 15 trees. This species was the sole member of its genus, Nesiota, and belongs to the buckthorn family (Rhamnaceae), not the common olive tree family. Its natural home was the cloud forest in the upland regions of St Helena, above 750 meters, with sightings around Diana’s Peak, the island’s highest point.
The tree was small and low-spreading, reaching about 5 meters in height, with dark brown to black bark. Its oblong leaves were dark green on top, with pale, hairy undersides that curled outwards. Pink flowers, approximately 10 mm in diameter, appeared in clusters, primarily between June and July. These flowers were likely pollinated by the endemic St Helena hoverfly species, Sphaerophoria beattiei.
The Path to Extinction
The decline of the St Helena Olive Tree began shortly after European contact with the island in the early 1500s. Human settlement led to widespread habitat destruction, as land was cleared for timber, plantations, and agriculture. This deforestation severely impacted the tree’s native cloud forest environment.
The introduction of non-native species further exacerbated the situation. Feral goats, brought to the island, grazed on young tree shoots, preventing regeneration. Invasive plants, such as New Zealand flax (Phormium tenax) and Whiteweed (Austroeupatorium inulifolium), outcompeted native flora. These pressures drastically reduced the St Helena Olive Tree’s population, leading to its disappearance from the wild. The last known wild specimen was found dead on October 11, 1994, officially marking the species as extinct in the wild.
A Second Chance
Despite its declaration as extinct in the wild, the St Helena Olive Tree’s story continued. A single wild plant, discovered in August 1977 by naturalist George Benjamin, provided hope. Conservationists made efforts to propagate this last individual through cuttings, though few were successful due to the tree’s self-incompatibility. This self-incompatibility means pollen from the same tree or close relatives often fails to produce viable seeds, making reproduction challenging when only a few individuals remain.
One successful cutting was transported to a greenhouse in Scotland in 1988, growing to two meters before succumbing to fungal infections in 1996. Three seedlings were raised from this cutting, with one transplanted back to St Helena. The last known living individual, a seedling from this cultivated line, died in December 2003 due to fungal and termite infestations, leading to its classification as totally extinct by some sources. Genetic material from the St Helena Olive is preserved in the DNA and Tissue Bank at Kew Gardens, offering potential for future research.
Lessons from a Resilient Species
The journey of the St Helena Olive Tree serves as a reminder of the delicate balance within island ecosystems. Its rapid decline underscores the impact that human activities and introduced species can have on biodiversity. The species’ self-incompatibility highlights the unique vulnerabilities of small, isolated populations to extinction.
Efforts to save the St Helena Olive Tree, even after its disappearance from the wild, exemplify the dedication of conservationists. This ongoing work, despite setbacks, shows a commitment to preventing further ecological loss. The St Helena Olive Tree illustrates the consequences of habitat destruction and the role scientific intervention and dedicated conservation can play in recovery.