African tulip tree (Spathodea campanulata)
African tulip tree (Spathodea campanulata) is considered one of the 30 worst terrestrial invaders. This large, fast-growing tree is native to tropical Africa. It has been introduced to many countries, including parts of Asia, the Pacific, and the Americas, and has become a widespread pest. African tulip tree produces large quantities of seeds that are easily dispersed by wind, water, or animals, allowing it to spread rapidly. This tree also reproduces by suckering, forming dense thickets. Up to 12,000 plants per ha have been recorded in Fiji.
Impacts
African tulip tree has many harmful impacts. Native forests are at risk as this invasive tree outcompetes native vegetation and disrupts natural successional processes. Biodiversity is therefore reduced and ecological processes such as nutrient cycling and soil chemistry are affected. African tulip tree can also rapidly colonise disturbed areas, such as roadsides, riverbanks, and land cleared for growing food. Its dense canopy can shade crops and reduce yields.
In addition, the resilience and well-being of communities is also at risk from African tulip tree. The tree's shallow root system can cause soil erosion and destabilize slopes, leading to landslides and other hazards. The branches are weak and can break in high winds, potentially harming people and damaging infrastructure.
The impacts of the African tulip tree are expected to increase in the future, as it continues to spread and colonize new areas. A recent study found that wind-dispersed seeds could likely disperse as far as 1364 km*. African tulip tree’s ability to thrive in a variety of soil types and climatic conditions makes it particularly well-suited to take advantage of changing environmental conditions, including those caused by climate change.
Control methods
African tulip tree is difficult and expensive to control. Hand-pulling small saplings, cutting down large trees and treating the stumps with herbicides, or drilling holes into standing trees to introduce herbicide, are all labour intensive and impractical for large infestations.
A new approach involving natural enemies now offers some hope for controlling African tulip tree. A gall-forming mite (Colomerus spathodeae), and a leaf-mining flea-beetle (Paradibolia coerulea), are being deployed in the Pacific. Both are African tulip tree specialists and will not attack any other plants. It is expected that the combined impact of both natural enemies will be needed to reduce the invasiveness of African tulip tree.
African Tulip Mite [Colomerus spathodeae]
A gall mite from Ghana was introduced into Rarotonga, in the Cook Islands, in 2016 to control African tulip tree ([Spathodea campanulata]). This was the first time this mite has been used for this purpose anywhere in the world. The gall mite is now well established in the Cook Islands. In 2022 the gall mite was successfully released and established in Vanuatu, and in 2023 it was released in Tonga. Work is underway to introduce it to other places in the Pacific where African tulip tree is a problem.
How would I recognise it and what is its lifecycle?
The mite is too small to be seen with the naked eye. Look instead for the galls (erinea) they make and live in – they look like hairy deformations on the new leaves and shoots of the tree. The affected leaves will appear discolored and distorted. Damage is visible all year.
Eriophyid mites have four life-stages they develop through: eggs, protonymphs, deutonymphs, and then adults which takes about a fortnight. There can therefore be up to 26 generations a year and numbers can build up very rapidly.
How can I get the most out of it?
The mites disperse by ‘ballooning’ on silk threads carried by the wind. In the Cook Islands the mites became widespread within a few years without any human assistance. However, if redistribution to new sites or islands is required this can be achieved by placing galled leaves next to the growing tips of uninfested African tulip trees.
Are there other natural enemies for this weed?
A second natural enemy of African tulip tree was released in Rarotonga in 2021, a leaf-mining flea-beetle (Paradibolia coerulea). The combined impact of both natural enemies is likely to be needed to reduce the invasiveness of African tulip tree. Natural enemies that could reduce seeding are currently being sought.
