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A-Z of farming acacia trees for Gum Arabic

Friday May 19 2017

A he goat perches on a sisal plant to reach for

A he goat perches on a sisal plant to reach for leaves of an acacia tree at Banita in Rongai, Nakuru. PHOTO|NATION FILE 

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On April 29, I highlighted the many uses of acacia trees, especially for the production of Gum Arabic, a highly sought product for industrial use, including in the making of Coca cola.

After getting several inquiries, today I will focus on the cultivation of acacia tree as a cash crop. There exists more than 500 species of the acacia trees that mainly grow in the arid and semi-arid areas of sub-Sahara Africa. Most of them produce gum, but it’s only that produced by Acacia senegal and Acacia seyal that is of commercial interest.

Acacia seyal, whose bark is characterised by a reddish-brown colour, produces an inferior quality of gum. The highest quality Gum Arabic, however, is obtained from the grey-barked Acacia senegal, which is a thorny leguminous tree.

In Kenya, Acacia Senegal variety kerensis is common. It is a small tree, growing to about 2-6m high, occasionally becoming taller under optimal climatic conditions. The plant is usually low branched with a short stem and many upright twigs that form umbrella-shaped crown.

Most of these trees grow naturally in the wild. However, cultivation is possible. In Sudan, the world’s largest exporter of Gum Arabic, cultivation is practised in what is called “gum gardens”. These “gum gardens” are areas where Acacia senegal are cultivated and tended as cash crop trees. More than 50 per cent of Gum Arabic produced in Sudan is obtained from these plantations.

Growth conditions
Acacia senegal is extremely drought-resistant as it grows well in the arid and semi-arid lands of Kenya. It grows in areas with a range of annual rainfall of between 100-800mm, which is typical of regions in North, North Eastern and Eastern Kenya where average annual rainfall of as low as 100mm is reported.

Optimal growth and performance is expected where annual rainfall falls between 280mm and 450mm. It is, therefore, very drought-resistant and tolerates dry periods of about 8-11 months as well as wide temperature variations. It is, however, sensitive to waterlogging and frost. The species prefers sandy soils, but grows also on slightly loamy sands and to a lesser extent on clay soils. In addition, its tolerance to pH variation is wide. It can survive in soil with a pH range of about 5-8.

Propagation/regeneration of Acacia senegal

Artificial regeneration is carried out either from direct seeding of seeds or via transplanting nursery-grown seedlings. In Kenya, high quality tree seeds and seedlings for cultivation can easily be obtained from the Kenya Forestry Research Institute (KEFRI) in Nairobi, Kenya or through their various branches. Nursery beds can be prepared easily using available materials. Seedlings can then be transplanted when they reach 15-20cm high. Acacia senegal also regenerates by coppicing. Thus, if these trees are cut to ground level for any other purpose, this may stimulate growth of new shoots which eventually grow into bigger ones capable of producing Gum Arabic.

Just as it has been done successfully in Sudan, irrigated gardens can be set aside for planting Acacia senegal. Moreover, the trees can be planted around water sources and water pans in the dry areas. These trees can also be planted on farms together with other crops. In this way, other crops may continue to benefit from the tree since it enhances soil stabilisation and fertility through biological nitrogen-fixation. Intensive agricultural methods, such as mechanical cultivation and continuous cropping, constantly remove nutrients from the soil, allowing no time for replenishment by natural means.

However, planting acacia trees on farms helps conserve and maintain fertility in the soil. Much deforested land in Kenya would, therefore, benefit from a return to more traditional methods of farming and acacia planting.

Suitable areas for cultivation in Kenya

In Kenya, about 80 per cent of land is dry with potential for cultivation of acacia trees and production of Gum Arabic. Eight counties namely Garissa, Isiolo, Mandera, Marsabit, Moyale, Samburu, Turkana and Wajir, have great potential for production of the gum. In these areas, cultivation of acacia trees and the resulting income from the sale of tree resources like Gum Arabic has potential to enhance livelihood for both pastoralists and agro-pastoralists.

Harvesting of Gum Arabic

Acacia senegal produces Gum Arabic two years after planting in the field. However, the quality and yield are consistent after five years. Exudation may be natural or through “tapping”. During the harsh climatic conditions, the bark of the trees break naturally allowing Gum Arabic to ooze out. Occasionally, cutting the bark of the tree before it naturally breaks under these adverse climatic conditions is called “tapping”, which is an action intended to accelerate the process of exudation.

Tapping begins when the trees are just starting to shed their leaves. After five weeks, the first collection of gum is made, with further collections from the same trees at approximately 15–day intervals.In both instances, the gum dries into rough spheres which are manually collected. Depending on the climatic conditions, the annual average gum yield per tree is reported to be in the range of 100-300 grams. In some cases, some trees have been reported to produce between 800g and 1kg per year. Nevertheless, gum harvests from wild Acacia senegal are not as dependable as those from the “gum gardens” since the latter has potential to produce more. After harvesting, collectors may sort and grade the product before it is sold to the bigger companies. This way, collectors stand to earn more from the product.

Acacias, therefore, offer great potential in arid areas of Kenya where increasing population and livestock, together with a series of droughts, have led to deforestation and severe land degradation.

Mr Mwove is based at Department of Dairy and Food Science and Technology, Egerton University [email protected]