Transforming Kenya’s invasive ‘mathenge’ bushes into charcoal farms

Widely considered a nuisance, the shrub is now a sustainable bioenergy option
A pot sits on charcoal embers
Cooking with Prosopis charcoal in Kibera, Nairo (one of the largest informal settlements in Africa). CIFOR/Axel Fassio

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This initiative will be discussed in the session Sustainable wood-fuel value chains for food security in Sub-Saharan Africa at the upcoming Global Landscapes Forum.

Kenya’s population is rapidly growing and urbanizing, which is driving a soaring demand for charcoal in the country’s main cities. Studies show that charcoal production increased between 1.6 to 2.5 tons a year between 2004 to 2012, while revenues grew from $0.3 to $1.6 billion in the same period.

Most wood used for charcoal production is sourced from trees on farms. It is estimated that around 40 percent of wood fuel, which includes both charcoal and firewood, is unsustainably harvested, causing negative impacts on Kenya’s biodiverse forests.

This situation is aggravated by poor governance that is more prohibiting than enabling.

But a solution is cooking in Baringo County, one of the Kenya’s charcoal production hotspots, located about 200 km northwest of Nairobi.

Mathenge (Prosopis juliflora), a shrub that has long caused nightmares for local communities, is providing an alternative source of wood to produce sustainable charcoal while supporting the livelihoods of rural households in drylands, which happen to be hurt more by the vagaries of climate change.

More than good intentions

Prosopis juliflora, also known as mesquite, was first introduced to Kenya in the mid-1970s with the objective of countering rangeland degradation and providing a source of firewood for rural families. At first, the alien species made life better for dryland communities because it grew on barren landscapes, reduced soil erosion and dust storms, providing shade and pods for livestock.

But it soon started spreading incredibly fast — between 500 to 1,300 hectares per year. Its tough thorns caused physical injuries, its sweet pods caused goats to lose their teeth – leading livestock owners to sue the government of Kenya — mosquito invasions increased and human settlements were displaced.

In a 2011 report, scientists estimated that mathenge now grows on 2 percent of Kenya’s land area (citation below), causing countless losses of grasslands, woodlands, cropland and settlements.

By using this species elsewhere throughout the country for charcoal production as an option to manage the uncontained spread of mathenge, the existing Prosopis juliflora could provide a biomass of 37 million tons suitable for charcoal use.

This could improve the living conditions of over half a million people directly employed in charcoal production and trade – a potential game-changer to sustainably meet Kenya’s thriving demand, with potential surplus for export.

Passing knowledge

In 2018, World Agroforestry (ICRAF) conducted a household survey across Baringo county, finding prevalent unsustainable practices in charcoal production – one of the main economic activities in the region.

First, the survey revealed that the majority of landowners who source wood for charcoal did not carry out any kind of tree management. For example, they did not thin or cut down some stems or branches to promote growth, reduce formation of thickets (in the case of Prosopis) or replant when they cut native species.

Second, it showed that all charcoal producers used traditional earth mound kilns (TEK) which produce low yields, result in wood waste and result in cutting more trees down than necessary.

Taking into consideration Baringo’s pressing need to manage the spread of mathenge, ICRAF set off to promote ‘Prosopis charcoal’ to support farmers and charcoal producers.

Part of the Governing Multifunctional Landscapes in Sub-Saharan Africa (GML) project financed by the European Union, ICRAF’s intervention for capacity development, focuses on “training the trainers” for going to scale. This means that local representatives received a course, which they will in turn deliver to other people in their communities.

The first training of trainers took place in October 2019 and included members of local charcoal producer associations, representatives of the Ministry of Agriculture, a teacher and local artisans.

Participants learned about sustainable wood management and harvesting, and discussed benefits and challenges of managing the invasive Prosopis juliflora.

They also gained hands-on experience on more efficient carbonization processes, recovering the charcoal waste to produce charcoal briquettes or biochar for soil improvement, and clean cooking using wood fuel. Finally, they were trained on effective wood fuel trade, marketing, and how to meet local and national regulations.

They said they were thrilled to learn that managing the Prosopis thickets into a good forest with big stems could make charcoal production easier and increase local incomes.

   Demonstrations in Baringo on Prosopis management to open thickets and accelerate growth of few stems. Photo: Mary Njenga/ICRAF
   Improved earth mound kiln (IEK) showing halfway progress in carbonization. Photo by Mary Njenga/ICRAF

Lessons from the GML project in Baringo 

Although the training occurred just a few months ago, there are already important lessons that we can draw to guide further interventions and policies to make charcoal production more sustainable.

For instance, an enormous potential to improve carbonization methods exist. Following our training, local TEK practices were enhanced by drying wood to below 20 percent moisture content, arranging the wood tightly to reduce air spaces and enhance heat transfer, using six breathers and two chimneys at a cost of 5,500 Kenyan shillings ($55), and closely monitoring the kilns.

With assistance of trainers, charcoal producers ran improved earth mound kilns (IEK) and compared them to TEK, finding an incremental increase in charcoal yield of 50 percent.

There are also attractive opportunities to integrate circularity in charcoal production by recovering charcoal dust otherwise considered waste, as well as carbonizing such tree residues as small branches and stems to increase charcoal yield while providing low materials for charcoal briquettes and biochar for soil improvement.

A charcoal producer who participated in the training set up two comparison plots to measure the efficiency of biochar to increase agricultural outputs. In the first plot she added biochar into the soil, while the other one was left as the control sample.

She was very pleased to find that in the plot with biochar kale vegetable seedlings germinated at a faster pace and were healthier, she said.

Use of biochar should be promoted elsewhere as it improves yields and buries carbon in the soil.

Finally, national and local charcoal regulations should support Prosopis charcoal farming to provide rural households with a source of income. Promoting the use of Mathenge to produce charcoal can support bush encroachment control, while ensuring the presence of a tree cover.

For more information on this topic, please contact Mary Njenga at
This research was supported by European Union
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