Itigi-Sumbu thicket
The Itigi-Sumbu thicket is a unique and threatened ecosystem located in small patches in central Africa, primarily in Zambia and Tanzania. Characterized by dense, mostly drought-deciduous, spineless shrubs, this thicket forms a low canopy that supports a high level of endemism, meaning many plant species found here are not present elsewhere. The ecosystem is influenced by its distinctive duricrust soils, which contribute to its physical structure and species composition, setting it apart from the surrounding woodlands and savannas. Covering approximately 3,000 square miles (7,800 square kilometers), it includes a notable area near Itigi in Tanzania and a larger patch in Zambia's Kaputa District.
The climate features a seasonal wet-dry pattern, with significant variations in annual rainfall between the two regions. While the thicket supports diverse flora, including over 100 woody plant species, the vertebrate fauna is less pronounced, with large mammals being uncommon due to the dense vegetation. However, it is home to a rich avian population and some endemic reptiles and butterflies. Despite its ecological significance, the Itigi-Sumbu thicket faces serious threats from agricultural expansion, charcoal production, and human encroachment, leading to substantial habitat loss in recent years. Conservation efforts are limited, especially in Tanzania, where there is no designated protection for these vital ecosystems.
Itigi-Sumbu thicket
- Category: Forest Biomes.
- Geographic Location: Central Africa.
- Summary: This poorly known, highly threatened thicket ecosystem, with a high level of endemism, occurs in small blocks in Zambia and Tanzania.
The Itigi-Sumbu thicket is a poorly known, distinctive ecosystem characterized by dense vegetation and high levels of endemism (species found nowhere else). A wide variety of mostly drought-deciduous, spineless shrubs form a low, intertwined canopy. This ecosystem type occurs mainly in two small isolated patches in Zambia and Tanzania, often in mosaics with other woodlands and savannas. The thicket differs markedly in physical structure and species composition from these adjacent ecosystems. These distinct attributes are thought to be the product of the underlying duricrust or hardpan soil (hardened, mineral products of weathering).
The small extent of the Itigi-Sumbu thicket has been further reduced and degraded by ongoing threats, especially clearing for agricultural expansion. Unlike in Tanzania, blocks of the ecoregion in Zambia are protected, although this protection has failed to limit encroachment.
The thicket covers approximately 3,000 square miles (7,800 square kilometers) in two distinct locations. One part is located near the town of Itigi, Singida Region, in central Tanzania. The second, and larger, occurrence is in northeastern Zambia, in the Kaputa District of Northern Province, between the southern tip of Lake Tanganyika and Lake Mweru Wantipa, approximately 370 miles (600 kilometers) southwest of the Tanzanian location. The Zambian stand extends slightly northward into the Democratic Republic of the Congo.
Elevations in the ecoregion range from 3,100 to 4,300 feet (950 to 1,300 meters) above sea level. The climate is characterized by a seasonal wet-dry pattern typical of this part of Africa. Alternating wet and dry seasons result from the presence of the rain-bearing Intertropical Convergence Zone from November to April, and the dry-season subtropical high-pressure cell from May through October. Annual precipitation in the Zambian portion averages about 55 inches (140 centimeters), with considerable year-to-year variability; the Tanzanian section is drier with average annual rainfall of approximately 20 to 28 inches (50 to 70 centimeters).
A distinctive characteristic of the thicket is its duricrust or hardpan soils. These are well-aerated, sandy-textured, acidic soils at depths of 2 to 10 feet (0.6 to 3 meters) that desiccate in the dry season. A close spatial correlation exists between thicket vegetation and duricrust soils, suggesting that this factor may explain the distinct geographical pattern of the ecoregion as distinguished from surrounding woodlands.
Flora
The Itigi-Sumbu Thicket biome is characterized by dense, almost impenetrable, vegetation, mainly of spineless, multi-branched shrubs that form a main canopy 10 to 16 feet (3 to 5 meters) high, with some woody plants reaching as high as 20 to 40 feet (6 to 12 meters). The canopy is dominated by deciduous species that shed their leaves during the dry season. At least 100 woody plant species occur, including Albizia petersiana, Baphia burttii, B. massaiensis, Bussea massaiensis, Combretum celastroides orientale, Grewia burttii, and Pseudoprosopis fischeri.
The thicket is often spatially interspersed with xeric (dry-adapted) woodlands, especially of the miombo type. Although these mosaics are all part of the broader Zambezi River regional ecosystem that drives endemism, the Itigi-Sumbu thicket is distinct in terms of species composition, its dense physical structure, and the minor role of fire. The thicket also tends to occur in discrete patches with abrupt boundaries, rather than grading into surrounding ecosystems.
Fauna
Compared with the flora, the vertebrate fauna is relatively indistinct, and large mammals in the country, such as elephants, are uncommon, owing in part to the difficulty of movement in the dense thicket. However, these thickets were once a habitat for the black rhinoceros—though poachers have eradicated the rhinoceros in this ecoregion. On the other hand, in this relatively small area, 365 bird species have been recorded; termites are abundant, and endemism has been documented for some reptiles and butterflies.
Environmental Threats
The Itigi-Sumbu Thicket biome is considered a zone of regionally important ecological distinctiveness. Because relatively little research has been carried out here, some uncertainty remains concerning its physical integrity and conservation status. One evaluation described the thicket as relatively stable, with potential for successful conservation intervention. However, most research indicates that it remains under significant stress and is severely threatened.
A fifty-year remote sensing analysis conducted in the Zambian portion of the thicket near Lake Mweru Wantipa in 2016 indicated that its surface area had decreased by 64 percent. It is presumed that the Tanzanian portion has experienced similar deterioration; one early twenty-first-century study suggested that half of its original area had been cleared. The largest portion of the remaining thicket is in the Mweru Wantipa National Park.
Major threats to the thicket stem from increased demand for land and resources associated with agricultural exploitation, charcoal production, and human settlement. With dense and growing populations in Zambia and Tanzania, this demand remains high. Although the Zambian portion of the thicket is located in officially protected areas—including Mweru Wantipa National Park, Tabwa Nature Reserve, and Nsumbu National Park (Sumbu)—protected status has done little to control encroachment into the area. In Tanzania, no part of the thicket is protected. While portions of the biome are somewhat well-adapted to semiarid conditions, its habitats will certainly be under greater stress as global warming imparts higher annual temperature averages and, potentially, lower overall precipitation.
Bibliography
Almond, S. Itigi Thicket Monitoring Using Landsat TM Imagery. University College, 2000.
Baena, Susana, et al. “Earth Observation Archives for Plant Conservation: 50 Years Monitoring of Itigi-Sumbu Thicket.” Remote Sensing in Ecology and Conservation, vol. 2, no. 2, 2016, pp. 95–106, doi.org/10.1002/rse2.18. Accessed 1 Dec. 2024.
Chidumayo, Emmanuel, and Davison Gumbo, editors. The Dry Forests and Woodlands of Africa: Managing for Products and Services. Routledge, 2010.
Kideghesho, J. R. “The Status of Wildlife Habitats in Tanzania and Its Implications to Biodiversity.” Tanzania Wildlife, vol. 21, no. 1, 2001.
"Itigi-Sumbu Thicket." Digital Observatory for Protected Areas (DOPA) Explorer, dopa-explorer.jrc.ec.europa.eu/ecoregion/30708. Accessed 1 Dec. 2024.
"Itigi-Sumbu Thicket." One Earth, www.oneearth.org/ecoregions/itigi-sumbu-thicket. Accessed 1 Dec. 2024.
"Itigi-Sumbu Thicket." World Species, worldspecies.org/ecoregions/display/AT0708. Accessed 1 Dec. 2024.