Miombo is one of the most important forest ecosystems in southern Africa, covering large areas of Angola, Mozambique, Tanzania, Zimbabwe, Zambia, and the Democratic Republic of Congo, covering between 2.5 to 3.6 million square kilometres.
This ecosystem includes mosaics of dry forests and wooded savannahs, with a high diversity of flora and fauna, with medium productivity and high social value in terms of woody fuel, building materials, pasture, food, and medicinal plants.
Miombo usually has a multistrata structure: an upper stratum with adult trees between 15 and 18 m tall and a density around 65 trees per ha; an intermediate stratum with trees between eight and 12 m tall and a density of 80 trees per ha; and the lower stratum with saplings, shrubs, and grassland with a height lower than eight m and a density range between 375 and 500 trees per ha. The volume varies between 14 and 59 cubic metres per ha in dry Miombo and between 41 and 100 cubic metres per ha in wet Miombo, with higher productivity in wet Miombo forests.
More than 55 percent of Angola’s land area is forested, amounting to about 69 Mha, of which 58.6 Mha is Miombo lands, 3.6 Mha correspond to other native forest and plantation forest, and 2.1 Mha of other lands with scattered trees.
Angolan Miombo is characterised by species of the genus Brachystegia, Julbernardia, and Isoberlinia. This ecosystem provides many ecosystem services to the rural population, including timber and nontimber products biomass for household energy production (firewood and charcoal), fodder for livestock, medicinal plants, and wild fruits.
Water cycle regulation, the reduction of erosion, and the diversity of habitats favouring a high biodiversity are also important ecosystem services of Miombo lands. Estimated data confirm that Miombo forest in Angola has an annual harvest capacity of 326,000 cubic metres and an average annual commercial timber productivity of 0.3 cubic metres per ha per year.
In addition, Miombo forests play an important role in atmospheric CO2 sequestration with fixation rates of up to 39.6 MgC per ha in above-ground biomass.
Thus, under sustainable management criteria, the Miombo could be an important source of economic income and employment, especially in rural areas. However, at present, this ecosystem is under great pressure from the local population, which puts its sustainability at risk, mainly due to some specific deforestation drivers.
Causes Of Deforestation
There is a differentiation between proximate causes (or drivers) and driving forces (or indirect drivers). Proximate causes are human activities that have a direct influence on the deforestation while driving forces are complex interactions of key social, economic, political, cultural, and technological processes.
Several works have assessed deforestation drivers as a tool for decision-making to reduce emissions from deforestation.
The main drivers identified in tropical forests are the agriculture expansion, urban expansion, infrastructural development, mining activity, and commercial timber exploitation or as fuel (firewood and charcoal), grazing, and forest fires.
Studies carried out in sub-Saharan Africa have concluded that the subsistence agriculture is the main driver in the poorest rural populations, often associated with deforestation for charcoal production and/or forest fires.
Thus, some authors link deforestation to food security, with the most frequent causes being agriculture and exploitation of biomass as fuel. In Angola, the main proximate drivers are the overextraction of timber resources, clearing for agricultural purposes, unregulated burning, and overgrazing. This has led to an increase in deforestation rate from 0.2 percent in 2000 to 0.8 percent in the period 2000–2019, compromising the current and future ecosystem services of the Miombo.
Charcoal production is a very important activity in Miombo and is increasingly becoming a lucrative business.
Charcoal production in rural areas causes large environmental impact, especially in comparison with that generated by fuelwood, mainly in periurban areas. This activity, which is continuously growing in Africa, is one of the main causes of deforestaton and forest degradation both in Africa and Angola.
One of the main problems related to charcoal production in the Angolan Miombo is the lack of data about the potential productive capacity of this ecosystem. This leads to a lack of tools for assessing admissible annual cut values and, thus, for sustainable management.
Some of the tools often used for assessing productive capacity, such as dendrochronology, have not often been used in such studies in tropical forests due to the great diversity of species and the difficulty in assessing annual growth.
Previous works have assessed annual growth in Miombo species to determine the annual allowable cutting volume.
Therefore, study of the productivity of the Miombo ecosystem is an important tool to increase knowledge about the charcoal production capacity and the annual allowable cutting volume, including the variables in forest management plans to increase the sustainability of this activity.
The aim of this study was to assess the productivity of Miombo ecosystem in Huambo (Angola) to estimate carbon sequestration and charcoal production capacity. The specific objectives were (i) to assess deforestation in miombo forest in Huambo province (Angola) during the last 20 years, (ii) to evaluate carbon storage capacity of miombo, and (iii) to calculate the charcoal productive capacity of those forests and compare them with the carbon storage capacity.
The results obtained will provide information about the charcoal production for the management of miombo woodland resources in Huambo province, ensuring the sustainability of the activity and ecosystem services and improving forest management in a context of vulnerability of the local population.
This information could also open up new funding opportunities, facilitating the engagement of rural communities with initiatives for reducing emissions from deforestation, forest degradation, and forest management (REDD+) or Clean Development Mechanisms (CDM).
Deforestation Circumstances From The Survey
In our work, deforestation rate, carbon accumulated, and productive capacity of miombo forest on Huambo province were evaluated in order to provide information about the current situation and the future potentiality. This information will be provided to the authorities and local population to improve forest management, ensuring not only forest-based benefits but also their sustainability.
However, the study of the structure, composition, and forest dynamic is a starting point for designing strategies for the conservation and sustainable management of forest resources in the tropical forests of southern Africa. Further research on related issues is also necessary.
According to the National Forest Inventory of Angola, there is an increase in forest area in the country, but no data are provided by year, nor by provinces, and a comparison is made between current data and data from the 1980s obtained with different methodologies and sources; so, the level of confidence is very low.
However, our results showed that in the last 19 years, the deforestation of miombo forests on Huambo province (Angola) was 359,130 ha, which represents an annual rate of 0.68 percent.
These results were particularly worrying in some municipalities such as Caála, Bailundo, Longonjo, and Tchinjenje.
The differences in deforestation between the municipalities are conditioned by their proximity to the main roads that carry charcoal to the country’s capital, Luanda, and to the port, Benguela. The municipalities with the least deforestation are those furthest away from the main road (Ecunha and Mungo) and Huambo, the provincial headquarters municipality, with little forestry activity.
These data are similar with FAO (Food and Agriculture Organization of the United Nations) data (2020), which place Angola among the 10 countries with the highest rate of net forest area change, losing 0.8 percent annually, similar to other dry forests in regions such as DRC (The Democratic Republic of the Congo) (0.83 percent), Tanzania (0.88 percent), Zambia (0.63 percent), or Mozambique (0.59 percent).
Despite the decrease in the deforestation rate in the last five years, Africa remains the continent with the highest deforestation level. Several studies have identified the main drivers of deforestation.
In Angola, the main causes are associated with the activity of local populations, clearing for agricultural purposes, overextraction of wood with commercial and energy purposes, and unregulated burning, identified as the main drivers of this deforestation.
In Huambo province, deforestation is associated with the demand for charcoal and firewood production for cooking and heating.
In fact, charcoal demand is having a particularly adverse impact on the natural Miombo woodlands of Huambo Province, leading to losses in forest stock, biodiversity, and opportunities for rural livelihoods.
Due to this high dependence between the economic activities of the local population and deforestation, there is a need to improve forest governance for the sustainable management of the Miombo.
Composition & Structure Of Miombo Forests
Forty species were identified in miombo forests, with a higher frequency of species from the Fabaceae family (45.71 percent). These data coincide with previous results for Miombo forest.
The species with the higher frequencies were Albizia anthunesiana, Brachystegia spiciformis, Julbernardia paniculata, Monote spp., Brachystegia boemii, Isoberlinea angolensis, Anisophyllea boehmii, Syzygium guineense, and Erythrophleum africanum, coinciding with previous studies conducted in the Central Plateau of Angola.
The mean density in the forests studied was very high (3616.38 trees per ha), with values higher than Miombo from other countries in the region.
Some municipalities show a high density due the plots coincided in private properties, in which forest management plans exist and, therefore, there has been no suppression of adult trees in recent years. These data should be used for the implementation of miombo management zoning according to density, as proposed by other authors.
Biomass Accumulation & CO2 Equivalent Values
The biomass and volume values found in Huambo province were similar to those found in other miombo forests in Angola. The high biomass accumulation in this forest type implies a high carbon sequestration capacity, with values similar to those found by other authors in the region, though higher than values obtained in other degraded Miombo formations of Mozambique, Zambia and Zimbabwe, and Tanzania.
Further, the accumulated carbon from the survey in the most-degraded miombo forest of Huambo is higher than other Miombo forests in the central and southern region of Africa. CO2 equivalent values were similar to miombo forest in Zambia, although higher than other studies in the region.
Other works have shown that when miombo is properly managed (conservation, e.g., in reserves), these values can increase, reaching up to 845 Mg per ha in areas with little human intervention.
Potential Productivity Sourced From Forest
Determining the amount of wood that an ecosystem can sustainably provide is very important for a country’s economy. This applies to both commercial wood and wood used as biofuel (fuelwood and charcoal).
In the case of charcoal, production is conditioned by several factors, including the potential charcoal productivity and the annual allowable cut to be considered a sustainable activity, which—in this work—was translated into annual allowable cut volume and annual allowable potential charcoal productivity.
Internationally, there are not many works of this type on Miombo forests, although there are some studies carried out in other African savanna ecosystems. In the study area, the potential charcoal productivity in the Miombo forest was similar to that found in other works in the Huambo province, although below that reported in other works carried out on Miombo in other areas.
When comparing the biomass, the accumulated carbon, and the CO2 equivalent values with the potential charcoal productivity and allowable cutting values, there is correlation at the extreme values, which suggests that a greater conservation of tree cover would allow a greater use of resources for energy purposes.
The most common assumption for the Miombo in Angola is an ideal rotation length of 40 years. With this assumption, the Annual Allowable Cutting (AAC) (19.6 ± 7.72 trees per ha per year) and Annual Allowable Cutting Volume (AACV) (14.13 ± 7.96 cubic metres per ha per year) shows very low values, coinciding with previous works in Angola.
Besides, the result of our survey shows a greater degradation of Miombo in Huambo in relation to other provinces of the country. Within Huambo, even though average values were presented in this work, there was a great variability according to the municipality.
In fact, the Potential Annual Allowable Charcoal Productivity (PAACP) ranged from 761.84 kg per ha to 11,063.62 kg per ha, the average being 2762.96 kg per ha, far above that of the municipality of Caála.
Reducing the cutting shift to the minimum (15 years) presented the highest value of harvestable trees per hectare and year. Even in this case, the volume of sustainably explored wood was 9.29 cubic metres per ha per year, with just 32 trees per ha per year and a potential annual allowable charcoal productivity of 6422.55 kg per ha per year.
For all hypotheses evaluated, results are far below those of cuttings currently carried out by the rural communities of the municipalities studied. Therefore, the activity of cutting wood for charcoal and firewood production is currently unsustainable.
Strategies For Forest Conservation & Deforestation Reduction
Deforestation and forest degradation account for 17.4 percent of the world’s greenhouse gas emissions.
Despite the lack of official data, Angola’s contribution to global emissions is not very high, being ranked 88th out of 211 countries assessed with a contribution of the LULUCF (Land Use, Land Use Change and Forestry) sector of 37.4 percent.
For this reason, it is important to develop works to know the capacity of the country’s forest systems to sequester and store carbon. Although progress is currently being made in this regard, there are not too many works carried out in Angola, so this work has relevance for the development of conservation strategies.
An appropriate conservation strategy is including Miombo areas in carbon credit projects—REDD+, CDM, etc.—which could generate economic incentives for forest conservation, promoting the need to conserve miombo forests to ensure the regulation ecosystem service.
However, for the development of these projects, information about forest stock and CO2 sequestration is needed.
This work can contribute to the baseline (FRL) that Angola must establish to its Intended Nationally Determined Contribution (INDC). Carbon sequestered and CO2eq in the miombo forest of Huambo province is higher than other degraded Miombo ecosystems in the sub-Saharan region.
These values could be exploited to develop projects to generate carbon credits—REDD+, CDM, etc.—which could generate economic incentives for forest conservation, especially in municipalities with higher C sequestered and CO2eq, such as Bailundo, Ukuma, and Ekunha.
However, the high rate of deforestation in the last 19 years and the consequent low productive capacity could compromise this ecosystem service of the miombo in the short term.
It is, therefore, necessary to develop forest management plans to reduce deforestation, especially in Bailundo, Caála, and Longonjo municipalities, where the highest deforestation rates are found.
Furthermore, we could also look at the Potential Charcoal Productivity (PCP), the Allowable Cutting Value (ACV), and the Potential Annual Allowable Charcoal Productivity (PAACP) in each municipality, regardless of the rotation lengths, as it is necessary to establish protection and conservation figures in all municipalities because the charcoal production activity is currently not sustainable.
