- The bicolored waterberry (Syzygium guineense subsp. barotsense) is a dominant tree along the Kafue and other major Zambian rivers, where it plays a vital structural and ecological role.
- Though capable of self-pollination, the tree’s flowers attract bees, birds and moths, creating vibrant micro-ecosystems in its canopy.
- While not currently threatened, riparian clearing poses local risks, and the trees’ value to pollinators may offer a path to conservation.
KAFUE NATIONAL PARK, Zambia — At a bend in Zambia’s Kafue River, the bicolored waterberry trees resemble an avenue planted along a city boulevard. Their evergreen crowns stretch as far as the eye can see, reflected in the still, glassy water, only broken by the surfacing of two curious hippos. These trees — Syzygium guineense subsp. barotsense — are a dominant feature of this stretch of river, yet their role in maintaining river ecology is only just beginning to be understood.
During a recent 300-kilometer (186-mile) canoe expedition through Kafue National Park, Mongabay joined The Wilderness Project (TWP) — a group of researchers and explorers gathering data on Africa’s major rivers and their basins — to document the Kafue River’s biodiversity and human impact along its course. On one island, shortly after the river crosses the northern boundary of the park, the team encountered the fantastical, deeply fluted trunks of waterberry trees, the soil at their bases threaded with the spoor of African clawless otters (Aonyx capensis). Further downstream, dozens of white-breasted cormorants (Phalacrocorax lucidus) burst from nests wedged into branches of a small copse of waterberries growing directly in the river’s current.
Known for fruits that sometimes emerge half-white, half-purple, the bicolored waterberry is one of several Southern African subspecies in a genus found as far afield as Asia and Australia that includes the famous clove tree (Syzygium aromaticum).
But this tree, found growing along riverbanks throughout the upper Zambezi River basin, including the main Zambezi, Lunga, Kabompo and Kafue rivers in Zambia, and along major rivers in Botswana, Zimbabwe and northern South Africa, is “strictly riverine,” says Zambian pollination ecologist Christine Coppinger. “There are other closely related species and subspecies that only occur in woodland habitats within the region, so not necessarily around water bodies.”
Bicolored waterberry trees’ roots cling to soft sediments and dip into the water, providing shelter for crabs and fish. The trees also appear to play a structural role along riverbanks, buffering them against floods. “Without that sort of strong protection of the riparian soils, I think you would definitely have a lot more scouring and a lot more erosion,” says Coppinger, though she says this role hasn’t been quantified.
Coppinger’s research on the Kabompo River — to the northwest of the Kafue and not linked to TWP’s work — showed that the trees can self-pollinate without help from insects or animals; cross-pollination via an assortment of floral visitors is, however, likely an important way the trees maintain genetic diversity. Her weeks spent in the canopies of trees as they flowered in August and September over two consecutive years revealed lively interaction: western honeybees (Apis mellifera adansonii), flies, beetles, butterflies, wasps, sunbirds and northern yellow white-eyes (Zosterops senegalensis) during daytime. “It just feels like you’re in a different world altogether,” she says.
At night, the trees would come alive with the buzzing wings of hawk moths. “We often heard them from our tent on the river bank when we were living in [a camp in] West Lunga National Park.”
The tree’s subspecies name, barotsense, is derived from Barotseland, a name formerly used to refer to a region in western Zambia.
While not currently under threat as a species, bicolored waterberry trees can be lost where riparian vegetation is cleared to make way for agriculture in this part of Zambia.
Encouraging farmers to protect them, Coppinger suggests, might hinge on highlighting their value as “bee trees.” Their dense, sweet-smelling and nectar-rich flowers could offer both ecological and economic incentives to keep these quiet sentinels standing.
The bicolored waterberries were just one of the species TWP’s team found prospering along the stretch of the Kafue inside the national park. It also noted the presence of potential threats, from invasive crayfish to heavy human presence in the Game Management Areas (GMAs) that are supposed to form a buffer around the park. In other parts of the Kafue River, whose 1,600-km (994- mi) length TWP surveyed last year, the team noted fewer hippos, numerous water extraction facilities, and pollution from plastic and discarded fishing nets in the densely populated upper reaches of the river.
The data the team collects during its surveys is shared with the government’s wildlife and fisheries departments as well as conservation groups to inform policies and practices that will help protect the river, its rich biodiversity and the human communities that depend on it.
Mongabay joined an expedition of The Wilderness Project traveling the length of the Kafue River, part of TWP’s wider project to gather data in Africa’s major river basins. Read Ryan Truscott’s other articles from this journey here.
Banner image: The Wilderness Project team stops to conduct research on the island, surrounded by the waterberry trees’ fluted trunks. Image by Ryan Truscott for Mongabay.
River of giants: Canoe team tracks hippos in one of Africa’s last strongholds
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