Miombo is the vernacular (plural) name for Brachystegia boehmii and similar trees found across Southern Africa (Coates Palgrave et al. 2002). However the name miombo is widely used to describe the savanna woodlands of Southern Africa that are dominated by trees of the subfamily Detarioideae of the Leguminosae, mainly of the genera Brachystegia, Julbernardia and Isoberlinia.

The area dominated by these trees is coincident with White’s (1983) Zambezian Phytochorion, the largest of his regional centres of endemism in Africa (Chidumayo 1997). Miombo woodland covers about 2.7 million km² in Southern Africa (Frost 1996).

White’s (1983) map of African vegetation. Miombo woodlands are shown in dark green.

As well as a diverse tree community, miombo is rich in other plants (Coates Palgrave et al. 2007). Common grasses include the genera Hyparrhenia, Andropogon, Loudetia and Digitaria (Frost 1996). For a given rainfall, miombo has only around 20% of the grazer biomass expected on more fertile savanna (2.2 Mg dry matter ha^-2) and the grazing community is dominated by elephant and buffalo, with some large antelope (including Lichtenstein’s hartebeest and Sable) (Frost 1996). The nutrient-poor soils in miombo mean that the grass has very low nutrient content and this, combined with the presence of the Tstse fly in much of the region, means that miombo is not widely used for grazing cattle.

Miombo woodland in Nhambita, Mozambique

Miombo occurs on well drained soils that are derived from the African and post-African planation surfaces that form the Central African plateau (Cole 1986). They are nutrient poor and acidic (Frost 1996), with very low organic content. The dominant trees utilise ectomycorrhizae to obtain phosphorus (Hogberg 1986; Hogberg et al. 1986). Several non-dominant species have nitrogen-fixing nodules.

The dominant trees are described as fire-tender (Trapnell 1959), although this is disputed (Chidumayo 1988). What is clear however is that fire is a major determinant of miombo woody biomass. Several long term fire experiments in Zimbabwe (Furley et al. 2008) and Zambia (Trapnell 1959) have show that fire exclusion leads to the formation of closed canopies and a succession towards forest. Annual fires have been shown to destroy all woody vegetation.

Miombo trees are variously described as semi deciduous, semi evergreen, drought deciduous or simply deciduous. The seasonal cycle of leaf display is broadly in sync with the rainfall seasonality (Chidumayo 2001), but pre-rain leaf flush is often reported (Frost 1996). In many areas, the new leaves of miombo trees are coloured red, brown and yellow, due to the presence of anthocyanins (Tuohy et al. 1990; Choinski et al. 1993; Frost 1996). Evergreen trees are found in the wetter miombo areas, and along river lines (Chidumayo 1997). Other phenological strategies are also observed among co-occurring species, including the reverse phenology of Faidherbia albida(Barnes et al. 2003) which drops its leaves during the wet months and displays them through the dry season, making it useful in agroforestry systems.

The root system of a typical miombo tree, Brachystegia spiciformis Benth. from a site in Chati, Zimbabwe on deep sandy soils. The tree was 26 m high. Source: (Timberlake et al. 1993).

Miombo is often divided into wet and dry miombo based on the 1000 mm isohyet. In dry miombo aboveground woody biomass averages around 55 t dry matter ha^-1, whilst in wet miombo 90 t dry matter ha^-1 is typical (Frost 1996). There is a significant correlation between rainfall and woody biomass. These biomass values are slightly lower than dry forests under similar conditions in other continents (Frost 1996). Root biomass can comprise between 32% of total woody biomass (in Zambia, Chidumayo 1997) and 20% (in Tanzania, Malimbwi et al. 1994). However there are very few studies of root biomass, partly because taproots can exceed 5 m in depth (Timberlake et al. 1993). Grass biomass decreases with increasing tree biomass, but in a non-linear and complex way (Robertson 1984; Frost 1996).

The effect of fire in miombo at Marondera, Zimbabwe. The photo on the top shows a plot that was burned annually for 50 years. The plot on the bottom has been protected from fire for the same period. See Furley et al (2008) for further details.

References

Barbosa, P. M., D. Stroppiana, J. M. Gregoire and J. M. C. Pereira (1999). “An assessment of vegetation fire in Africa (1981-1991): Burned areas, burned biomass, and atmospheric emissions.” Global Biogeochemical Cycles 13(4): 933-950.

Barnes, R. D. and C. W. Fagg (2003). Faidherbia albida : monograph and annotated bibliography. Oxford, Oxford Forestry Institute.

Bond, W. J., G. F. Midgley and F. I. Woodward (2003). “What controls South African vegetation – climate or fire?” South African Journal of Botany 69(1): 79-91.

Bond, W. J., F. I. Woodward and G. F. Midgley (2005). “The global distribution of ecosystems in a world without fire.” New Phytologist 165(2): 525-537.

Chidumayo, E. N. (1988). “A Re-Assessment of Effects of Fire on Miombo Regeneration in the Zambian Copperbelt.” Journal of Tropical Ecology 4(4): 361-372.

Chidumayo, E. N. (1997). Miombo ecology and management : an introduction. London, IT Publications in association with the Stockholm Environment Institute.

Chidumayo, E. N. (2001). “Climate and phenology of savanna vegetation in southern Africa.” Journal of Vegetation Science 12(3): 347-354.

Choinski, J. S. and J. M. Johnson (1993). “Changes in Photosynthesis and Water Status of Developing Leaves of Brachystegia-Spiciformis Benth.” Tree Physiology 13(1): 17-27.

Coates Palgrave, K., R. B. Drummond, E. J. Moll and M. Coates Palgrave (2002). Trees of southern Africa. Cape Town, Struik Publishers.

Coates Palgrave, M., A. E. van Wyk, M. Jordaan, J. A. White and P. Sweet (2007). “A reconnaissance survey of the woody flora and vegetation of the Catapú logging concession, Cheringoma District, Mozambique.” Bothalia 37(1): 57-73.

Eriksen, C. (2007). “Why do they burn the ‘bush’? Fire, rural livelihoods, and conservation in Zambia.” Geographical Journal 173: 242-256.

Frost, P. (1996). The ecology of Miombo woodlands. The Miombo in transition : woodlands and welfare in Africa. B. M. Campbell. Bogor, Indonesia, Center for International Forestry Research: 11-55.

Furley, P. A., R. M. Rees, C. M. Ryan and G. Saiz (2008). “Savanna burning and the assessment of long-term fire experiments with particular reference to Zimbabwe.” Progress in Physical Geography 32(6): 611-634.

Hogberg, P. (1986). “Soil Nutrient Availability, Root Symbioses and Tree Species Composition in Tropical Africa: A Review.” Journal of Tropical Ecology 2(4): 359-372.

Hogberg, P. and G. D. Piearce (1986). “Mycorrhizas in Zambian Trees in Relation to Host Taxonomy, Vegetation Type and Successional Patterns.” Journal of Ecology 74(3): 775-785.

Laris, P. S. (2005). “Spatiotemporal problems with detecting and mapping mosaic fire regimes with coarse-resolution satellite data in savanna environments.” Remote Sensing of Environment 99(4): 412-424.

Malimbwi, R. E., B. Solberg and E. Luoga (1994). “Estimation of biomass and volume in miombo woodland at Kitulangalo Forest Reserve, Tanzania.” Journal of Tropical Forest Science 7(2): 230-242.

Mouillot, F. and C. B. Field (2005). “Fire history and the global carbon budget: a 1° fire history reconstruction for the 20th century.” Global Change Biology 11(3): 398-420.

Robertson, E. F. (1984). Regrowth of two African woodland types after shifting cultivation. Aberdeen, University of Aberdeen.

Sa, A. C. L., J. M. C. Pereira and R. H. Gardner (2007). “Analysis of the relationship between spatial pattern and spectral detectability of areas burned in southern Africa using satellite data.” International Journal of Remote Sensing 29(16): 3583-3601.

Sankaran, M., N. P. Hanan, R. J. Scholes, J. Ratnam, D. J. Augustine, B. S. Cade, J. Gignoux, S. I. Higgins, X. Le Roux, F. Ludwig, J. Ardo, F. Banyikwa, A. Bronn, G. Bucini, K. K. Caylor, M. B. Coughenour, A. Diouf, W. Ekaya, C. J. Feral, E. C. February, P. G. H. Frost, P. Hiernaux, H. Hrabar, K. L. Metzger, H. H. T. Prins, S. Ringrose, W. Sea, J. Tews, J. Worden and N. Zambatis (2005). “Determinants of woody cover in African savannas.” Nature 438(7069): 846-849.

Scholes, R. J. (1990). “The Influence of Soil Fertility on the Ecology of Southern African Dry Savannas.” Journal of Biogeography 17(4/5): 415-419.

Scholes, R. J., J. Kendall and C. O. Justice (1996). “The quantity of biomass burned in southern Africa.” Journal of Geophysical Research-Atmospheres 101(D19): 23667-23676.

Stronach, N. (2009). A review of the impact of fire on the carbon content, dynamics and biodiversity value of miombo woodlands A report prepared for Fauna & Flora International.

Timberlake, J. R. and G. M. Calvert (1993). Preliminary Root Atlas for Zimbabwe and Zambia. Zimbabwe Bulletin of Forestry Research: 96.

Trapnell, C. G. (1959). “Ecological Results of Woodland Burning Experiments in Northern Rhodesia.” Journal of Ecology 47(1): 129.

Tuohy, J. M. and J. S. Choinski (1990). “Comparative Photosynthesis in Developing Leaves of Brachystegia-Spiciformis Benth.” Journal of Experimental Botany 41(229): 919-923.

van Wilgen, B. W. (1997). Fire in southern African savannas : ecological and atmospheric perspectives. Johannesburg, South Africa, Witwatersrand University Press : Thorold’s Africana Books [distributor].

White, F. (1983). The vegetation of Africa : a descriptive memoir to accompany the Unesco/AETFAT/UNSO vegetation map of Africa. Paris, Unesco.

The miombo: a very short introduction / Miombo matters by blogadmin is licensed under a Creative Commons Attribution CC BY 3.0

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