Walk in the forests of Tanzania’s East Usumbara Mountains and you may be lucky enough to hear the metallic call – peedoo peedoo – of one of the world’s rarest birds, the Long-billed forest warbler (Artisornis moreaui). This species lives nowhere else on Earth and, according the International Union for the Conservation of Nature, there are fewer than 250 mature individuals.
Conservationists fear the bird will be silenced forever by the steady march into its territory of invasive umbrella trees. These trees also threaten other local species of endangered birds, reptiles, insects and plants. But now there are glimmers of hope, thanks to a project that has supported local villagers to remove umbrella trees and replace them with indigenous species.
The project was implemented by Nature Tanzania in collaboration with the Tanzania Forest Conservation Group and the village authorities in Mbomole and Shebomeza villages in Muheza district, Tanga region. Its activities took place in the buffer zone around Amani Nature Reserve, Mbomole village forest reserve and community forests. While the project officially ended in September 2019, activities continue thanks to the villagers’ commitment and ongoing support from a local organisation called Amani Friends of Nature.
A spreading problem
The umbrella tree (Maesopsis eminii) arrived in Tanzania in the 1930s, when colonial foresters introduced it in plantations as a timber tree. It became particularly widespread in the East Usambara Mountains after the Amani Forest was harvested in the 1980s. But large-scale planting created a huge source of seeds and, since then, the tree has become one of the area’s dominant species, helped on its way by hornbills and fruit bats that disperse its seeds.
This is a problem for the East Usambara Mountains because they are part of what scientists call a biodiversity hotspot, meaning they have large numbers of species including many that are found nowhere else in the world. The invasive umbrella trees pose a threat there as they grow fast, outcompete native plants, and reproduce within just a few years.
The umbrella tree is especially abundant in the village forest reserves and community forests in the buffer zone around Amani Nature Reserve, as well as on farmland. It most favours forest edges and open gaps in the forest that result from tree cutting. But by growing in these places, the tree threatens local species that prefer those habitats to life under the forest canopy. This includes chameleons, insects such as butterflies and the critically-endangered Amani flatwing damselfly, African violets and several endangered bird species.
A 2008 study stated, for example, that the abundance and diversity of bird species were both higher in natural forest than in areas where the umbrella tree was common. The study said the tree threatened the critically-endangered Long-billed forest warbler in particular, as the bird favours gaps in the forest that the tree’s fast growth rapidly closes.
Other local bird species affected by umbrella trees include the Amani sunbird and Usambara hyliota, both of which are endangered, and the Uluguru violet-backed sunbird. But there are still many questions about how the umbrella trees affect other species and how best to reduce the risk these trees pose.
“We don’t have enough funds to conduct research on this invasive tree that drives away some endangered species,” says Fikiri Maiba, the Chief Conservator of Amani Nature Reserve. “We are looking for international donors involved in nature conservation, critically endangered species or endemic species that can support us with funds so that we can carry out research.”
Maiba says a research budget of at least USD 1 million is needed because, apart from the umbrella tree, another 13 other exotic and invasive species are affecting the ecological balance of the Amani Nature Forest Reserve.
Taking umbrellas down
In August 2018, Nature Tanzania and partners began working with local communities in a project that aimed to improve the Long-billed forest warbler’s prospects of survival by removing umbrella trees. Victor Mkongewa, one of the authors of the 2008 study on local birds, was hired to manage the project, which was funded by Critical Ecosystem Partnership Fund.
The project established experimental plots in the Shebomeza village community forest, Mbomole village forest reserve and at Emau, a suburb of Shebomeza. Nature Tanzania and the Tanzania Forest Conservation Group started training villagers on forest conservation and highlighting the importance of Long-billed forest warblers to local incomes.
Mkongewa points out that Long-billed forest warblers and other rare species attract birdwatchers from around the world who spend money in local communities. “Ninety percent of Amani residents benefit from bird tourism,” he says.
As well as raising awareness, the project also set out to increase the warbler’s habitat. It incentivised farmers to participate by training them in agroforestry. The project also provided thousands of seedlings of cinnamon, clove and black pepper plants for farmers to grow.
“Men were involved in cutting down invasive trees and removing logs, while women planted indigenous trees and uprooted umbrella tree seedlings in those plots,” says Subira Amiri was one of the women who worked on the plots in Mbomole village forest reserve.
In just over a year, the participants removed umbrella trees from 2.1 hectares of forests and replanted some 3,874 seedlings of 24 indigenous tree species. The planted trees are growing well and other species are returning. “We are very happy with what we have achieved by planting trees, because right now chameleons and bird species are coming back into the forest,” says Amiri.
Wildlife bouncing back
After the project ended in September 2019, Victor Mkongewa and other local people established a non-governmental organisation called Amani Friends of Nature to continue the work of battling the invasive trees. Under Mkongewa’s leadership, the group planted another 700 indigenous trees last year.
Amani Friends of Nature is also doing censuses of birds and chameleons in the experimental plots, as well as monitoring bird nests in those areas, says Martin Joho, an ornithologist with the organisation. Joho says this will allow them to assess the impacts of removing umbrella trees and gain a better understanding of the ecology and breeding habits of different species in disturbed and undisturbed habitats.
So far, the results are promising. According to Mkongewa, the number of chameleon species in all of the experimental plots has increased from three in 2019 to 24 in 2020. This includes the East Usambara pygmy chameleon, the Usambara three-horned chameleon and the Giant East Usambara blade-horned chameleon, all of which are endangered species.
The number of bird nests has also increased, from just 2 in 2018 to 14 in 2020. Species nesting in the plots include White tailed crested flycatcher, Collared sunbird, Mouse-coloured sunbird, Olive sunbird, Little greenbul, Red-capped forest warbler and Sharpe’s akalat.
Mkongewa says it is still too early to assess the impact on the critically-endangered Long-billed forest warbler, as the indigenous tree seedlings planted after removal of umbrella trees had not grown mature enough to provide suitable habitat for the bird. But he says the presence of its close relative, the Red-capped forest warbler, suggests the rarer bird will also recolonise.
“Our efforts over three years to restore natural habitat for critically endangered species and other endemic species have started paying off,” says Thomas Peter, one of the farmers from Mbomole village who has been removing umbrella trees. “Natural vegetation and biodiversity have improved and we have managed to see new species, like the four-horned chameleon.”
There is still much work to do. Mkongewa warns that if the umbrella trees continue to spread, the Long-billed forest warbler and other rare and endangered species in the East Usambara Mountains will continue to be affected and will ultimately disappear. But if the Amani Friends of Nature and local communities can sustain their progress, future generations may also hear that metallic peedoo peedoo call and may even catch a glimpse of the elusive bird that makes the call.
Beatrice Philemon produced this story with a grant from EJN’s Biodiversity Media Initiative. It was first published on 12 May 2021 by Tanzania’s The Guardian newspaper and has been lightly edited for length and clarity. The Biodiversity Media Initiative is supported by Arcadia — a charitable fund of Peter Baldwin and Lisbet Rausing.
Banner image: The critically endangered long-billed forest warbler (Artisornis moreaui) / Credit: Norbert Cordeiro.