Miombo woodlands
Miombo woodlands represent the most extensive tropical seasonal woodland type in Africa, characterized by a rich diversity of plant species, particularly from the legume family, with notable genera including Brachystegia, Julbernardia, and Isoberlinia. This biome predominantly spans tropical Africa, thriving on geologically old and less fertile soils, receiving an average annual rainfall of about 28 inches. The woodlands have a closed deciduous structure with mature trees reaching heights of 33 to 66 feet and a unique understory that supports various plant species, including endemic ones. Fire plays a significant role in the ecosystem dynamics of miombo woodlands.
These woodlands not only provide essential ecological services, such as climate regulation and erosion control, but also offer material products that contribute to local livelihoods, including food, medicine, and construction materials. However, the miombo woodlands face significant threats from climate change, deforestation due to agriculture and ranching, and increased wildfire occurrences. Recent studies have highlighted the potential of these woodlands to sequester high levels of carbon, underscoring their importance in global climate discussions. As such, there is an urgent need for sustainable management and restoration efforts to preserve this vital ecological resource amid changing environmental and socio-economic conditions.
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Miombo woodlands
- Category: Forest Biomes.
- Geographic Location: Tropical Africa.
- Summary: Africa’s most common vegetation type is experiencing the effects of climate change.
The most widely distributed vegetation type in Africa is the savanna, which is also the most extensive vegetation stratum in Africa south of the Equator. The most common of these savannas is the miombo woodlands, which predominantly comprise closely related genera from the legume family (Fabaceae, subfamily Caesalpinioideae) in particular Brachystegia, Julbernardia, and Isoberlinia. There are reportedly twenty-one species of Brachystegia in the Miombo Woodlands biome, and three species of each from Julbernardia and Isoberlinia.
Vegetation types associated with the miombo woodlands are the Acacia savannah, Mopane woodland, and other dry savanna woodlands. The ecology of the miombo woodlands make it the most extensive tropical seasonal woodland type and the most extensive dry forest type in Africa, perhaps even globally.
When undisturbed, the miombo woodlands are composed of a closed deciduous non-spinescent woodland type that occurs on geologically old, rather infertile soils at an average annual rainfall around 28 inches (700 millimeters). Mature stands boast trees ranging to 33–66 feet (10–20 meters) high. Small trees and shrubs in the scrub layer vary in density and composition, while the understory ranges from dense, coarse grass to scattered herbs or forbs, small sedges, and short grasses. Fires are a typical feature of the miombo woodlands ecosystem.
Miombo woodlands are relatively homogenous in community composition internally, yet extremely rich in plant species. Consequently, the Miombo Woodlands ecosystem has an estimated 8,500 species of higher plants; out of this, 334 are tree species. More than half of these are thought to be unique to this biome, in other words, endemic. Across the biome, it is in Zambia where the highest species diversity for trees is found, with, for instance, seventeen species of Brachystegia that are endemic. Comparatively, there is one such species in Kenya, six in southeastern Tanzania, and eleven in western Tanzania.
However, generic endemism is found in less than 15 percent of the genera; such species are linked to the Sudanian and coastal formations. In many herbaceous plant genera, like Crotalaria and Indigofera, there is high species diversity and some localized endemism. In Zimbabwe, where there are serpentine soils, there are additional localized sites of speciation and endemism.
Plant Life Cycle Stages
There are basically five main phenological, or plant life cycle, seasons for the miombo woodlands. These include: the warm, dry pre-rain season (September to October), the early rainy season (November to December), the mid-rainy season (January to February), the late rainy season (March to April), and the cool and dry season (May to August). Phenology of miombo plants is also determined by seasonal variations in soil moisture. Leaf fall and flush occurs during the dry season in most trees and shrubs, while flowering takes place during the warm, dry pre-rains season (September–October).
However, fruit production varies from year to year. Sometimes, fruiting failure may occur due to lack of flowering and/or flower abortion, which may be caused by bud infestation by the Curculionid beetle larvae and imagoes. Fruits normally take six months to mature in the miombo, with a few exceptions that take under six months. Fruit dispersal occurs in the late dry season; in rare cases, it overlaps into the early rainy season. There is huge diversity in fruit types and dispersal modes in the miombo.
Seed germination of most trees and shrubs takes place soon after dispersal, as long as optimum germination conditions exist. In terms of regeneration, miombo regrows naturally from stumps, suckers, shoots, old stunted seedlings or wildlings, and from coppices. A more significant number of seedlings and wildlings may be concentrated under tree canopies than in the open. Stem height increments in regrowth miombo woodlands are accelerated within the first and second years, and later on decline. Success of seedling establishment is low, due to various factors including moisture and heat stress.
Ecological System
Miombo woodlands are involved directly and indirectly in global change, in terms of land-use, atmospheric composition, and climate. Conversion of miombo woodlands to short-duration croplands has resulted in accelerated carbon emissions, as well as disturbances in the rainfall formation processes. Deforestation is considered a major threat to the woodlands and has been occurring due to agriculture, ranching, and charcoal production. Climate change has increased the number of droughts, which has increased the number of wildfires. This all accelerates global warming.
Ecosystem services provided by the miombo woodlands fall into two broad categories: material products, which include fertilizer, foods, fiber, medicines, energy, browse fodder, construction and craft material; and ecological services, comprising climate regulation, erosion control, and hydrological control, as well as cultural and spiritual values. The greatest concern regarding this suite of products and services revolves around the dramatic recent, current, and projected future change in the Miombo Woodlands biome. These must be interpreted in view of the changing demands of various African communities, the large portions of miombo woodlands that are cleared each year for different reasons, and the looming effects of climate change.
Alterations in the coverage and quality of miombo woodlands have been rising gradually in response to several underlying causes, such as the pre-colonial, long-distance caravan trade; the Ngoni penetration; the rinderpest epidemic; colonial intervention; crafting of ploughs as animal drought implements; the market economy; growing rural populations; and post-independence political, economic, and land-use restructuring. However, a study published in 2024 found that the biome potentially holds much higher carbon reserves than previously estimated, heightening the importance of these woodlands for climate change throughout the region and beyond. To address these findings and aforementioned concerns, it is perhaps best that the Miombo Woodlands biome be examined and analyzed multi-dimensionally as a complex, interactive ecological-social-economic system and restoration efforts be emphasized in order to better protect and preserve the woodlands.
Bibliography
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Demol, Miro, et al. "Multi-Scale Lidar Measurements Suggest Miombo Woodlands Contain Substantially More Carbon Than Thought." Communications Earth & Environment, vol. 5, no. 1, 2024, pp. 1-11. doi.org/10.1038/s43247-024-01448-x. Accessed 1 Nov. 2024.
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Martin, Emma, and Neil Burgess. “Dry Miombo Woodlands.” One Earth, www.oneearth.org/ecoregions/dry-miombo-woodlands/. Accessed 1 Nov. 2024.
Nhantumbo, Isilda and Godwin Kowero. Modeling Method for Policy Analysis of Miombo Woodlands. Center for International Forestry Research, 2001.
Rodgers, W. A. “The Miombo Woodlands.” In T. Mclanahan and T. Young, eds., The Habitats of East Africa. Longmans Harare, 1996.
Sumaila, U. R., A. Angelsen, and G. Kowero. A System Dynamics Model for Management of Miombo Woodlands. Center for International Forestry Research, 2001.