Madagascar's vanishing trees

Madagascar has a documented 2,900 endemic species of trees, but a new report shows that almost two-thirds of them are in danger of disappearing.
Of the 3,118 species covered, more than 90% had never been systematically evaluated before, and one in 10 fell in the IUCN’s critically endangered category, a step away from going extinct in the wild.
Though the island nation’s protected area network has expanded to more than 7 million hectares (17 million acres), a tenth of the tree species are found outside this safety net.
Scientists are racing against the extinction clock to document this mind-boggling biodiversity and determine just how imperiled individual species are.

Aina Randriarisoa found a perch for Labramia ambondrombeensis on the taxonomical tree of life. She helped identify the tree from its genetic signature, the arrangement of its leaves, the shape of its flowers. Yet Randriarisoa, a 28-year-old Malagasy botanist, has never set eyes on the tree, and she fears she never will.

A 400-hectare (988-acre) forest fragment in northeast Madagascar, slightly bigger than Central Park, is the tree’s only known habitat, and it is shrinking. In Madagascar, a bottle-gourd-shaped island off Africa’s eastern coast, it is easy to miss the trees for the woods. Its fabled forests are retreating rapidly; 1-2% are wiped out each year.

Millions of years of isolation have given birth to a breathtaking variety of life-forms on the island, including 2,900 endemic tree species. Today, only a few thousand years since humans appeared here, two-thirds of these unique tree species are at risk of disappearing.

Scientists are racing against the extinction clock to document this mind-boggling biodiversity and determine just how imperiled individual species are. The effort sprinted forward this year with the completion of more than 2,400 assessments by a team of Malagasy and foreign researchers.

It was spearheaded by the Missouri Botanical Garden (MBG), Kew Madagascar Conservation Centre, the University of Antananarivo, and the IUCN. It is part of Botanic Gardens Conservation International’s Global Tree Assessment initiative. Madagascar is a top priority; it has 5% of the world’s tree species, high endemicity, but also one of the highest deforestation rates.

Of the 3,118 species covered in a recent report, more than 90% had never been systematically evaluated before. One in 10 of these trees falls in the IUCN’s critically endangered category, a step away from extinction in the wild. It’s analogous to Madagascar’s iconic lemurs; almost all of the 108 lemur species are threatened.

The incredible array of fauna the country has to offer often overshadows its vegetal diversity. Some experts estimate that only about half of Madagascar’s tree diversity is known to us.

A Dalbergia hirticalyx, a tree species endemic to Madagascar. Image Courtesy of Roger Bernard.

Even when it does attract attention, the focus tends to be on high-value species like rosewood, palisander and ebony. Madagascar is rich in precious wood, home to more than a third of Dalbergia (including rosewood) and Diospyros (ebony) species. The illicit export of their timber has decimated large swaths of Malagasy forests. Randriarisoa and colleague Laurent Gautier from the Conservatory and Botanical Garden of the City of Geneva hope to save the Sapotaceae, a family of 90 species of hardwoods, including L. ambondrombeensis, from a similar fate.

These towering trees are in high demand locally, if not in the international market. Gautier described them as “old aristocrats.” They are well-adapted to their environs and do not take kindly to change. They grow and reproduce slowly, reaching sexual maturity in about 20 years. A Sapotaceae tree is confirmation that the forest has stood the test of time. “They are a symbol of a healthy forest,” Randriarisoa said.

But such undisturbed old-growth forests are dwindling. Slash-and-burn cultivation has eaten into woodland, and uncontrolled fires sear through forested areas every year. Even within the vestiges that remain, people single out these massive trees for logging.

L. ambondrombeensis is found in a coast-hugging evergreen littoral forest, which grows on sandy soils. It sits next to the Makirovana-Tsihomanaomby protected area, a block of moist, humid forests further inland in the Sava region of Madagascar. These rainforests lining the island’s eastern escarpment are bursting at the seams with endemic plant life.

Aina Randriarisoa in the field in southeastern Madagascar observing a tree belonging to the Labourdonnaisia genus.

At higher altitudes, the montane forests take over, which host the third-highest number of documented endemic species. Though bereft of its natural vegetation, the central high plateau still retains islands of high diversity, says Pete Lowry, director of MBG’s Madagascar program.

The western flank of the island sports dry forests dotted by majestic boababs, a ubiquitous Malagasy motif. The harsh dry clime is not suitable for all life, but these stout giants flourish by storing water in their bulbous trunks. They are bearers of precious water and innumerable tales. The Alley of the Baobabs and Baobab Amoureux in the west, the 1,600-year-old Grandmother’s Baobab in Tsimanampetsotse National Park in the south, and Mahajanga’s gigantic baobab in the northwest are landmarks on Madagascar’s landscape, must-sees on a tourist’s itinerary.

Of the nine baobab species on Earth, six are found only in Madagascar. Three of those are currently endangered, none more so than Adansonia perrieri, of which fewer than 250 mature trees remain today. Its cousin, A. grandidieri, as its name suggests, counts among its ranks some of the grandest baobabs. It is also faltering in the face of human-made threats. Lonely giants remain scattered around the famous Alley of Baobabs that cuts through a landscape ravaged by fire.

These trees are built to last; they are no stranger to fire, but even they cannot survive repeated burning. New seedlings also perish in fires because they lack the thick, protective bark of older trees. Their only shield is the vegetation around the parent tree. Isolated in a singed terrain, they are unable to regenerate.

The Boabab Amoureux. Image by Rhett A. Butler/ Mongabay.

Like baobabs, Sapotaceae trees, too, are difficult to replace.

Madagascar’s protected area network has expanded rapidly in the past decade, and today spans 7 million hectares (17 million acres). Yet 307 endemic tree species like L. ambondrombeensis lie outside this safety net. “Before establishing a protected area, we must know what we are protecting, and that is why these assessments are important,” said David Rabehevitra, a botanist at the Kew Madagascar Conservation Centre. “It helps in prioritizing conservation.”

Until 2017, only about 12% of the island’s tree species had been assessed. More species joined Madagascar’s ever-growing catalog of trees between the time the research took place and the report’s publication this year. Samples collected over many decades are still waiting to be disentangled, new species waiting to be described.

“We find new species every year. Even for species that have been discovered, we have a lot of work to do in gathering data,” Rabehevitra said. “It requires money and knowledge.”

These records allow researchers and conservationists to seek greater protection and funds not just for individual species but plots that could harbor other endemic species, known and unknown.

The Schizolaena tampoketsana. Image courtesy of George E. Schatz.

The approach has worked in some places. The Ankafobe protected area, co-managed by MBG, was set up, in part, after the discovery of the critically endangered Schizolaena tampoketsana in the tiny forest spread across 33 hectares (82 acres). Forest fires menace even this shard of forest. Community members have taken an active role in recent years to protect the forest with modest funding from MBG. They have put in place fire breaks and carry out patrols to prevent illegal logging.

In the case of L. ambondrombeensis, Laurent said they would like to see the existing protected area extended to the adjacent forest, where the tree is found. With biological riches hidden in every nook and cranny of Madagascar, deciding what to safeguard and what to leave out is devilishly difficult. “Population geneticists would say everything should be protected,” Laurent said. “but from the point of view of someone who has been in the field [and] seen the people trying to grow rice for their daily needs, we have to be reasonable in the trade-off between what is needed and what is possible.”

But protected area designation itself can only go so far if the dependence of people on forests and forestland is not reduced. With existing protected areas, deforestation pressure is often deflected to surrounding areas, Randriarisoa said. The L. ambondrombeensis trees standing at the edge of a protected forest also bear this brunt.

The COVID-19 pandemic has put Randriarisoa’s planned visit home and to the refuge of L. ambondrombeensis on hold. It is an unnerving wait as satellite imagery shows the green isles spangled across Madagascar steadily withering away.

Citations:

Randriarisoa, A., Naciri, Y., & Gautier, L. (2020). Labramia ambondrombeensis (Sapotaceae), a critically endangered new species from Madagascar. Candollea, 75(1), 83-87. doi:10.15553/c2020v751a8

Patrut, A., Von Reden, K. F., Danthu, P., Leong Pock-Tsy, J.-M., Patrut, R. T., & Lowy, D. A. (2015). Searching for the oldest baobab of Madagascar: Radiocarbon investigation of large Adansonia rubrostipa trees. PLOS ONE, 10(3). doi:10.1371/journal.pone.0121170

(Banner image of baobabs at sunset by Rhett A. Butler/Mongabay.)

Malavika Vyawahare is a staff writer for Mongabay. Find her on Twitter: @MalavikaVy

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Article published by Malavikavyawahare