Zambezian Cryptosepalum dry forests
Zambezian Cryptosepalum dry forests are distinctive ecosystems primarily located in the western regions of Zambia, eastern Angola, and southern Democratic Republic of the Congo. Characterized by the evergreen mukwe tree (Cryptosepalum exfoliatum pseudotaxus), these forests feature a dense understory of shrubs and lianas, creating a rich habitat despite being relatively species-poor overall. The landscape is shaped by sandy, infertile Kalahari soils and a distinct dry season that can last up to eight months, with groundwater likely supporting the trees during these dry periods.
Biodiversity in this biome is notable, particularly among bird species, with over 380 identified, including several unique subspecies. While human settlement is limited, the forests do provide valuable resources such as honey from mukwe flowers and materials for beehives. Conservation efforts focus on managing the West Lunga National Park, which aims to restore and protect this ecosystem. However, challenges such as logging, small-scale farming, and the potential impacts of climate change continue to threaten its integrity. Overall, these forests represent a unique blend of ecological and cultural significance within their geographic context.
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Zambezian Cryptosepalum dry forests
Category: Forest Biomes.
Geographic Location: Africa.
Summary: On deep and infertile Kalahari soils and with a dry season comparable to savanna regions, the Zambezian Cryptosepalum Dry Forests form the largest area of tropical evergreen forest outside the equatorial zone.
This unique forest, largely in the western parts of Zambia, eastern Angola, and southern Democratic Republic of the Congo, is dominated by mukwe trees, or Cryptosepalum exfoliatum pseudotaxus. This evergreen tree, actually a tree legume, is usually less than 98 feet (30 meters) in height, with a dense and flat crown. The lower areas of vegetation characteristic of this forest, consisting of a very dense evergreen shrub or thicket matrix, remain about 13 feet (4 meters) in height. This tangled understory contains liana species including Combretum microphyllum, Uvaria angolensis, Artabotrys monteiroae, and Landolphia. These dry forests are found on hills of sandy soil drained by the Kabompo River.
Within Zambia, this forest is called the Mavunda and includes parts of West Lunga National Park. Although not densely settled by people, it has some valuable resources. The fragrant white flowers of the mukwe tree are a valued source for honey, and the bark is used for constructing beehives. Other trees in the Zambezian Cryptosepalum Dry Forests biome include rosewood and Guibourtia coleosperma.
Further south, the character of the forests gradually changes, and they become dominated by Zambezi teak trees (Baikiaea plurijuga). Logging is potentially a serious threat to these species. However, the lack of surface water and relatively infertile Kalahari soils mean that this ecoregion is less attractive for human settlement and agrarian activities. Disturbance by natural fire is not significant, but small-scale farming on the edges can change Cryptosepalum forest to a more open and fire-prone vegetation type known as chipya.
The Kalahari soils are deep, infertile, and well drained. The apparent lack of surface water should be a limitation on the evergreen trees. The mean annual rainfall of 31–47 inches (80–120 centimeters) becomes higher to the north away from the Kalahari Desert; nevertheless, there is a distinct dry season lasting up to eight months. The evidence gathered suggests that trees have access to groundwater during the dry season, thus providing the natural conditions for a higher biomass.
There is a question as to how the evergreen trees have access to this subsurface water. The water table in this part of Africa is more than 328 feet (100 meters) below the surface; therefore, the suggestion is that there must be “perched” water up to and around 66 feet (20 meters) below the surface. This also helps to explain the mosaic quality of this vegetation.
Biodiversity
This biome is distinctive in terms of its biota, but is not especially species-rich, nor does it support many endemic (found only here) or near-endemic populations. The only species that is virtually endemic to the ecoregion is a striped African grass mouse (Lemniscomys roseveari).
Among the mammals found are the elephant (Loxodonta africana), bush pig (Potamochoerus porcus), warthog (Phacochoerus africanus), blue and yellow-backed duiker (Cephalophus monticola and C. sylvicultor), kudu (Tragelaphus strepsiceros), and buffalo (Syncerus caffer).
Cryptosepalum forests are exceptionally rich in bird fauna, with more than 380 known species. Some of these include the Guttera edouardi kathleenae subspecies of the crested guinea fowl, the olive long-tailed cuckoo, Cabanis’s greenbul, purple-throated cuckoo-shrike, African crested flycatcher, olive sunbird, forest weaver, and black-tailed waxbill. Interestingly, the highest levels of species richness are found where local habitat disturbance has resulted in a patchwork of tree savanna, thicket, savanna woodland, and forest habitats.
The tree Cryptosepalum exfoliatum is not an economically important timber species, and the arable potential of the ecoregion is very low. The soils are nutrient-poor Kalahari sands, cultivation of rain-fed crops is limited to one or two seasons, and the dense vegetation is difficult to clear. These factors, combined with this ecoregion’s remoteness from roads and modern urban settlement, and consequent low population density, have prevented its destruction or stark transformation.
West Lunga National Park falls within this ecoregion. Hunting restrictions form the main conservation management strategies of the area. This park covers an area of 650 square miles (1,700 square kilometers) in Mwinilunga District. The park occupies an area between two major rivers: West Lunga to the west and Kabompo to the east and south. It was declared a national park in 1972. In the following years, it fell into some decline; however, in 2002, several local stakeholders formed the West Lunga Development Trust. A new initiative called the West Lunga Conservation Project was formed in 2014 with the purpose of managing the national park and restoring it to a functional ecosystem. The project was working in coordination with several other groups, including the Worldwide Fund for Nature and the Nature Conservancy.
Local chiefs have helped mobilize communities into village action groups, helping patrol and monitor ecological conditions of the area. Community resource boards control the natural resources in the surrounding areas and derive a financial benefit from any operations there. Community-based natural resource management has been adopted as a strategy for sustainable wildlife management in many places. It aims to contribute to poverty alleviation and help improve household food security.
Small-scale farming, logging, and poaching are challenges this ecoregion still faces. However, impact continues to be low because of the inaccessibility of the region. Another concern is how climate change will ultimately affect this area in terms of water resources, because the arable potential of the ecoregion is already minimal and projected rainfall will fall, while temperatures are slated to rise.
Bibliography
Aregheore, Martin Eroarome. “Country Pasture/Forage Resource Profiles: Zambia.” United Nations Food and Agriculture Organization. http://www.fao.org/ag/AGP/AGPC/doc/Counprof/zambia/zambia.htm.
Coates Palgrave, Keith. Trees of Southern Africa. Cape Town, South Africa: Struik Publishers (Pty.), 1996.
"Our Work." West Lunga Conservation Project, 2021, www.westlunga.org/ourwork. Accessed 8 Aug. 2022.
Scholes, Richard J., P. R. Dowty, K. Caylor, D. A. B. Parsons, P. G. H. Frost, and H. H. Shugart. “Trends in Savanna Structure and Composition Along an Aridity Gradient in the Kalahari.” Journal of Vegetation Science 13, no. 3 (2002).