Origin of the miconia in Tahiti

More than two-thirds of Tahiti is currently under the control of a single species, Miconia calvescens, a tree with large leaves whose underside turns violet. The tree was planted in 1937 as a simple ornamental plant in a private garden in Papeari by Harrison Willard Smith, an American former physics professor and botany enthusiast who arrived in Tahiti in 1919.

Miconia's spread and impact

The species comes from the humid forests of Central and South America, where it is not common and never forms pure stands. It generally requires more than 2,000 mm of rain per year, whereas in Tahiti, it adapts to 800 mm. Its planting may have come from Ceylon, the current Sri Lanka, a theory that should be treated with caution.

Spread from a private garden

The miconia was also planted at the agricultural station on the Taravao plateau by Jean-Marie Boubée, an agricultural engineer, friend and collaborator of Smith. Boubée later inherited the Papeari garden. In about fifty years, the miconia has established itself on approximately 70% of Tahiti.

Miconia's growth characteristics

In the 1930s, an American horticulture book already listed it among the most beautiful foliage for greenhouses. As an adult, it is a tree 12 to 16 meters tall, not a shrub, with leaves 20 to 80 cm long, the largest approaching the width of an interior door. It begins its life as a shrub, with a violet-blue underside of the leaves.

Extent of the invasion

In about fifty years, the miconia has established itself on approximately 70% of Tahiti. A 1996 study signed by Meyer estimates the invasion to more than 65% of the forests, or about 70,000 hectares, more than six times the area of Paris. In more than 25% of these areas, it grows alone.

Miconia's reproductive capacity

From the initial domain of 137 hectares to the 70,000 hectares of forest colonized, the affected area has been multiplied by more than 500. Since then, the species has spread to other islands, including Moorea and Raiatea. Germination reaches up to 90% of the seeds, even under 2% of full light, and it also succeeds on rocks or the bark of trees.

Biological control efforts

A fungus introduced in 2000 has slowed its expansion but has not eradicated it. The fungus was therefore first tested in the laboratory. After two years of testing, 10% of the plants were dead and 50% seriously affected. In 2000, 63 years after Smith's planting, the fungus Colletotrichum gloeosporioides f. sp. miconiae was introduced to Tahiti, which attacks the miconia.

Broader ecological impact

Tahiti is not an isolated case. In Hawaii, the first miconia was a single tree in the Wahiawa botanical garden on Oahu, planted in 1961. In the north of Queensland, Australia, wild populations seem to follow a similar propagation pattern. Harrison Smith died on January 3, 1947, in Papeari. He never saw the invasion: the cyclones that revealed it occurred 35 years after his death.

Current management and prevention

The miconia is now among the species monitored by the French Office for Biodiversity. Before buying an exotic plant for your garden, consulting these invasive species fact sheets is the missing reflex from 1937.