- Scientists have recently described six new species of millipedes found in Tanzania’s Udzungwa Mountains.
- The six were among thousands of specimens collected by researchers studying forest ecology there and in the nearby Magombera Nature Reserve.
- Magombera was damaged by commercial logging in the 1970s-80s, and affected areas have been overrun by woody vines known as lianas.
- But teams working on the ground think that millipede diversity and abundance in liana thickets is equal to that of undisturbed forests, suggesting they may be dynamic places poised for forest regeneration with minimal human intervention.
Scientists have recently described six new species of millipedes, including one from an entirely new genus, in Tanzania’s Eastern Arc Mountains. This brings the number of new species found in the Udzungwa Mountiains since 2014 to 81 — further confirming the rich biodiversity of these isolated mountain blocks. The newly-described millipedes are helping researchers to assess ecosystem recovery.
One of the newly-described millipedes, Udzungwastreptus marianae, grows to around 3 centimeters in length, and lives in forests above 1,000 meters. Henrik Enghoff, a professor of zoological systematics and zoogeography at the Natural History Museum of Denmark, who has described 69 of the 81 new species found in these mountains, says the genus was given the name Udzungwastrepus to celebrate the Udzungwas’ astonishing biological richness.
U. marianae and other millipedes trundle along the forest floor like miniature locomotives, feeding on dead plant matter and organic debris. “Some of the millipedes had unique features, such as colorful legs or shiny exoskeletons,” says Alain Ngute, a tropical forest ecologist who was part of the team working in the Udzungwa Mountains that collected the millipedes.
Ngute explains that millipedes help to recycle nutrients and maintain soil fertility, and contribute to soil aeration and water retention — all essential for plant growth and forest regeneration.
In areas of degraded forest that have been taken over by thick layers of woody vines known as lianas, the millipedes can indicate that the ecosystem is actually recovering.
“Millipedes can help restore these areas by breaking down the detritus and facilitating the growth of [tree] seedlings and saplings,” says Ngute.
Millipedes weren’t Ngute’s first choice of research subject. He grew up in the western highlands of Cameroon, an experience that he says helped him to forge a strong connection with tropical forests. He was initially interested in researching the impact of forest degradation on bird communities in his home region.
It was only later, while conducting research for a PhD in the Udzungwas that Ngute’s focus shifted from birds to millipedes.
“I was initially reluctant to work with these creatures, as I had some childhood taboos and fears about them,” says Ngute. “However, as I learned more about their ecology and roles in the forest, I gradually became fascinated and intrigued by them.” When Ngute’s PhD supervisor, conservation scientist Andrew Marshall, first started working in Tanzania in the late 1990s, he was shown large areas of damaged forest in another part of the Eastern Arc.
“There were just vines growing over the whole thing,” Marshall recalls. “I hadn’t got a clue what was going on, but was told by people there that they were the disturbed parts of the forest where trees had been cut down [and] the vines had just taken over.”
Lianas, rooted in the ground, resemble large snakes as they coil up tree trunks in rainforests. Beyond that aesthetic appeal, however, they are also parasites that can damage or kill trees. In mid-2007, Marshall set up small vegetation study plots within the Magombera Forest to analyze the recovery rates of areas disturbed by commercial logging decades earlier.
His initial findings suggested that lianas, such as the ubiquitous species known to science as Ucaria africana, and to the local Hehe community as mtonasimba, or “lion’s grasp”, due to its hooked spines, smothered recovering forest patches. This undermined the forest’s ability to regenerate. Half of the plots in the study were managed by cutting lianas with secateurs, and saw a marked improvement in tree growth over five years.
But after years of further research in the Udzungwas, Marshall and international colleagues working under the banner of the Forest Restoration and Climate Experiment (FoRCE) have developed a more nuanced view of lianas.
Invertebrates, including millipedes, are helping them to see this bigger picture.
Communities of millipedes, and those of other invertebrates like termites and ants, appear to be just as rich in liana thickets as they are in primary, undisturbed rainforest. This could indicate that liana thickets are in fact dynamic places poised to regenerate into forest with the right environmental or management triggers, says Marshall.
“These places that appear on the surface to be very damaged and look very messy and tangled and don’t look like what you think of as forest – are actually teeming with all sorts of things that are helping it tick over,” he says.
Marshall and his team think that lianas can act as “bandages”, sheltering tree seedlings in damaged areas from external threats.
“If you remove them entirely, you’re removing that protective layer and we see in our [study sites] that areas that are opened up [are] impacted by things like elephants, or drought or even people coming in and cutting the trees,” he says. “It’s not quite as simple as: take the lianas away and the trees will grow back.”
While the question of whether lianas hinder or help tropical forest recovery remains unresolved, the battle to develop the “bandage hypothesis” has been hard won. The Tanzanian vegetation survey plots have never been easy places in which to work.
“When we survey them, we have to crawl underneath the vines, and they’re hot, humid, sweaty areas covered in thorns, and lots of bugs – so we get bitten a lot, and scratched a lot,” says Marshall.
Thankfully though, millipedes are easier to study than the termites or ants that live in large colonies and are “fiddly” to survey. Some ants, like those from the genus Dorylus and known by their Swahili name siafu, will inflict painful bites on humans that get in their way.
Finding new millipede species is a fun part of the ecological survey work, says Marshall, and Tanzania’s Eastern Arc Mountains appear to be particularly well-endowed. This can’t be said of the other places where the FoRCE teams work.
“Across the world, different invertebrate groups tend to dominate, so there is not really any consensus on the best groups to focus on,” he explains. In the tropical forests in the north of Australia’s state of Queensland, where Marshall has students studying the “bandage hypothesis”, only “a handful” of millipedes is ever collected compared to thousands of other forest-floor detritivores, beetles and flies.
“We rarely see [millipedes] at all,” he says
As the research progresses in Tanzania, the scientists expect to find new millipedes, and, intriguingly, new species of fungi too. Although it remains a mystery as to why it happens, tiny species of fungi – many less than half a millimeter long – grow on millipedes and other soil arthropods, says Enghoff, the Danish zoologist in Copenhagen studying the samples sent to him from the Udzungwas.
The fungi often grow on those parts of the male and female millipedes that will come into contact during courtship or copulation. That way, the fungi ensure their own fertilization is successful.
One species of fungi, found growing on the sides of U. marianae, the new millipede genus and species described by Engoff and colleagues, was actually described back in 2016, well before its millipede host was.
The zoologist is currently working on another paper – the 12th in a series known as “Mountain of Millipedes” – that will describe yet another seven new species from the Udzungwas.
“With the material I have, I have more than enough to last for the rest of my life,” says Enghoff, who has worked in his field for more than 50 years.
“I’m not going to sit idle.”
Conflict in the canopy as human and climate factors drive liana dominance over trees
Citations
Enghoff, H., Ngute, A. S., Kwezaura, R. L., Laizzer, R. L., Lyatuu, H. M., Mhagawale, W., … Marshall, A. R. (2024). A mountain of millipedes XI. The trachystreptoform spirostreptids of the Udzungwa mountains, Tanzania (Diplopoda, Spirostreptida, Spirostreptidae). European Journal of Taxonomy, 918, 1-50. doi:10.5852/ejt.2024.918.2405
Marshall, A. R., Coates, M. A., Archer, J., Kivambe, E., Mnendendo, H., Mtoka, S., … Njilima, F. M. (2016). Liana cutting for restoring tropical forests: A rare palaeotropical trial. African Journal of Ecology, 55(3), 282-297. doi:10.1111/aje.12349
Marshall, A. R., Platts, P. J., Chazdon, R. L., Seki, H., Campbell, M. J., Phillips, O. L., … Pfeifer, M. (2020). Conceptualising the global forest response to Liana proliferation. Frontiers in Forests and Global Change, 3. doi:10.3389/ffgc.2020.00035
Banner image: Researcher Alain Senghor K. Ngute processing a millipede specimen. Image by Hamidu Mnendendo.
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