Acotanc: Diversification of Tree Crops: Domestication of Companion Crops For Poverty Reduction And Environmental Services

Diversification of Tree Crops: Domestication of Companion Crops For Poverty Reduction And Evironmental Services

Author: Roger Leakey
E-mail: [email protected]


Agroforestry and Novel Crops Unit, School of Tropical Biology, James Cook University
PO Box 6811, Cairns, QLD 4870, Australia
Tel: (61)-7-4042-1573, Fax: (61)-7-4042-1284

Author: Z. Tchoundjeu
E-mail: [email protected]


ICRAF – International Centre for Research in Agroforestry
PO Box 2067, Yaounde,

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New initiatives in agroforestry are seeking to integrate indigenous trees whose products have traditionally been gathered from natural forests into tropical farming systems, such as cocoa farms. This is being done in order to provide marketable timber and non-timber forest products from farms that will enhance rural livelihoods by generating cash for resource-poor rural and peri-urban households. There are many potential candidate species for domestication that have commercial potential in local, regional or even international markets. Little or no formal research has been carried out on many of these hitherto wild species to assess their potential for genetic improvement, reproductive biology or suitability for cultivation. However, a number of projects are in progress to bring candidate species into cultivation. This paper describes some tree domestication activities in progress in southern Cameroon, especially with Irvingia gabonensis and Dacryodes edulis. In addition, some information about the nutritional value of these fruits is presented.

This poverty-reducing agroforestry strategy is at the same time linked to one in which perennial, biologically diverse and complex mature-stage agroecosystems are developed as sustainable alternatives to slash-and-burn agriculture. To meet the objective of poverty reduction, however, it is crucial that market expansion and creation are possible, hence for example it is important to determine which marketable traits are amenable to genetic improvement. While some traits that benefit the farmer are relatively easy to identify, there are undoubtedly others that are important to the food, pharmaceutical or other industries that require more sophisticated evaluation. Hence there is a need for better linkages between agroforesters and the private sector. The domestication activities described are relevant to the enrichment of small-holder cocoa farms and agroforests. This diversification is seen as being important for the support of the cocoa industry.


According to the World Commission on Forests and Sustainable Development (WCFSD) about 14 million hectares of tropical forests have been lost each year since 1980 as a result of changes in landuse from forest to agriculture (WCFSD, 1999). One of the five ‘radical and urgent actions’ recommended by the WCFSD to address this problem was to provide ‘more extensive support to community-based agroforestry in order to reduce the pressure on primary forests for supplying subsistence products’. Community based agroforestry also has the potential, which is being increasingly achieved, to provide on-farm sources of cultivated timber and non-timber forest products for domestic use and for marketing, in ways that also provide some important environmental services, such as biological diversity and carbon sequestration (Leakey, in press). However, there are complex tradeoffs between global environmental concerns and the objectives of poverty reduction and national development, which if not acted upon could lead to further deforestation (Tomich et al., in press). This is an area of active research by the International Centre for Research in Agroforestry (ICRAF) and its partners in the Alternatives to Slash-and-Burn Programme.

Agroforestry practices come in many forms (Nair, 1993), but it has recently been suggested that agroforestry practices should be seen more as stages in the development of an agroecosystem (Leakey, 1996). This concept sees the increasing integration of trees, or agroforestry practices, into land-use systems over time, as a parallel to natural succession. In this way, diversifying an agroecosystem, whether a maize field or a cocoa farm, moves it towards a mature agroforest of increasing ecological integrity (Leakey, 1996). Similarly, with increasing scale the integration of various agroforestry practices into the landscape creates a complex landuse mosaic that enhances biological diversity and ecological stability (Leakey, 1999). In the tropics this could lead to the development of viable alternatives to slash-and-burn agriculture. The large-scale adoption of such an approach should be especially beneficial, since the ecological and economic benefits of diversity on a landscape-scale are considerably greater than the sum of the individual farm-scale benefits.

This more ecological concept of agroforestry has been accepted by the International Centre for Research in Agroforestry (ICRAF, 1997), which now defines agroforestry as 'a dynamic, ecologically based, natural resources management system that, through the integration of trees in farms and in the landscape, diversifies and sustains production for increased social, economic and environmental benefits for land users at all levels'.

Filling some of these niches with indigenous species that provide economically valuable timber and non-timber products traditionally obtained from natural forest, and important environmental services should result in land use that is both sustainable and productive. The domestication of these trees to increase the quality, number and diversity of these products should enhance agroforestry's capacity to fulfil its ultimate potential as a way to reduce poverty and to mitigate deforestation and land depletion.

This paper reviews current activities towards the domestication of indigenous trees producing non-timber forest products, especially Irvingia gabonensis and Dacryodes edulis. It then examines the current and potential markets for these products, reviews the scope for enhancing farmer livelihoods by, firstly, establishing them within cocoa agroforests and, secondly, further enhancing them by the development of improved cultivars.


Domestication of the so-called 'Cinderella trees'(Leakey and Newton, 1994) the traditionally-important indigenous trees throughout the tropics that have been overlooked by science, has recently become a major programme in international agroforestry research (Simons, 1996a; Sanchez and Leakey, 1997; Leakey and Simons, 1998). In genetic terms, domestication is accelerated and human-induced evolution. Domestication, however, is not only about selection as it integrates the four key processes of identification, production, management and adoption of agroforestry tree genetic resources. ICRAF has started domestication programmes with a number of tree species in each of the six eco-regions in which it operates (Leakey and Simons, 1998). One of these programmes is based in Yaoundè in partnership with Institut de la Recherche Agricole pour le Dèveloppement (IRAD) and with the collaboration of the UK Institute of Terrestrial Ecology (ITE). This west and central African programme is targeted at the area in which cocoa is an important export crop and thus is the focus of this paper.

The first step in the domestication process (Simons, 1996 a) has been the identification of priority species for domestication. This first step of priority setting has already been widely reported (Leakey and Jaenicke 1995; Jaenicke et al., 1995; Franzel et al., 1996; Simons, 1996 b). It involves household interviews to determine farmer preferences, the assessment of market potential and finally the inputs of researchers on technical points relating to genetic variability, etc. From this process a shortlist of priority species for a region can be assembled (Table 1). It is interesting that farmers in humid West and Central Africa identified indigenous fruit tree species as their top priorities. In addition, as a result of wider consultation, two commercially important medicinal species, Prunus africana and Pausinystalia johimbe,have been added to the priority list. This arose from industrial fears about the future of the resource, as well as the need perceived by researchers for conservation of the species and their habitats. This illustrates the principle that while the domestication process should be driven by a farmer-led approach, consideration has also to be given to market needs, and thus not overlook a market-led approach (Leakey and Simons, 1998).

Table 1: Priority tree species selected for domestication*
Humid lowlands of west and central Africa, Priority order:
1. Irvingia gabonenis/ I.wombolu
2. Dacryodes edulis/D. klaineana
3. Ricinodendron heudelottii
4. Chrysophyllum albidum
5. Garcinia kola/G. afzelii
*by implementation of farmer preference surveys and priority setting guidelines (Franzel et al., 1996) by ICRAF and partners

After priority setting, the second step in the domestication process is that of rangewide germplasm collections of the chosen species. These activities tend to be species specific, either because of past history or because of constraints imposed by funding. To date the majority of work in humid West Africa has been restricted to the two top priority species, Irvingia gabonensis and Dacroydes edulis. Some work not reported here is also in progress on Ricinodendron heudelottii, Garcinia kola and Cola nitida.

I. gabonensis (Bush mango or Dika nut)

Germplasm collections of I. gabonensis have been made by ICRAF and partners from a wide range of sites in Ghana, Nigeria, Cameroon and Gabon, with some additional material of I. wombolu, and I. robur.The collection strategy used for Irvingia species was to involve farmers in targeting superior trees. In each village visited, farmers selected 20-30 trees with desirable fruit and kernel traits. Further selection by the collection team (NARS, NGOs and ICRAF) narrowed these down to two trees per village. During this period of exploration and collection, studies were made of the phenotypic variation in tree form, phenology and fruit characteristics such as shape, colour and sweetness (Ladipo et al., 1996). Genebanks were subsequently established at Onne and Ibadan in Nigeria, and at Mbalmayo in Cameroon, but the Cameroon collection has not thrived. Each genebank contained approximately 60 accessions (single-tree progenies).

The living genebanks provide several functions, such as genetic conservation and the provision of a source of variability for research and future breeding and selection. In this respect they are very important, although they impose a long-term cost in maintenance and management. So far, one study done on this material has characterized genetic variation captured by the germplasm collection exercise, using Polymerase Chain Reaction-based molecular techniques. Aspects of genetic structure, amount of variation, ecogeographic partitioning and hybridization have been examined in I. gabonensis and I. wombolu. Lowe et al. (in press) report that significant genetic integrity was found in these two morphologically similar species, with no evidence of hybridisation. Significant genetic differentiation was also found between geographically separated samples, with genetic similarity decreasing with geographic distance. 'Hot spots' of genetic diversity were clustered in southern Nigeria and southern Cameroon for I. wombolu, and in southern Nigeria, southern Cameroon and central Gabon for I. gabonensis. This level of understanding about within-species genetic diversity is important for the development of wise species conservation and domestication strategies.

The third phase of work is to identify superior trees within the wild population and to multiply them vegetatively as putative cultivars. This involves standard horticultural techniques of grafting, air-layering and rooted cuttings, that allow the capture of the additive and non-additive genetic variation between individual plants (Leakey and Jaenicke, 1995). There are several components to this phase. Firstly, vegetative propagation methods are required that are simple, inexpensive and robust enough for use in rural communities. Secondly, methods are required for the identification of the superior trees, based on a wide range of superior attributes affecting flavour, size, yield, quality, etc. Thirdly, farmers willing to cooperate with researchers use these methods to identify large numbers of trees with desirable attributes in their own farms and communities. This is done in accordance with the requirements of the Convention on Biological Diversity, with regard to the rights of sovereign states and of the farmers to both their indigenous knowledge and the germplasm itself.

Fourthly, the cooperating farmers have to be helped to establish village nurseries, to propagate their own trees and so form putative cultivars. Finally, the trees are established on the farms of participating farmers to test and confirm the genetic quality of the material. This last step is crucial to the long-term success of the concept and to provide the incentive to continue the domestication process. Within all of this there is also a need to ensure that the nurserymen/women understand the need for genetic diversity among cultivars and that a strategy to ensure this is built into the overall operation (Leakey, 1991). If all of this is successful, then it can be hoped that the farmers will benefit not only from having higher quality and more productive companion tree crops, but also that the nurseries will also develop a spirit of entrepreneurism so that some members of the community can benefit from selling cultivars to neighbouring villages. It is also hoped that the skills learnt on one tree species can be transferred to the domestication of other local species.

Progress down this path to implementation has been made. Simple low-technology techniques for propagating seedling/coppice shoots of I. gabonensis have been developed (Leakey et al., 1990; Shiembo et al., 1996) and are being practiced within the project and are now being transferred to the village nurseries (Tchoundjeu et al., 1998). As in all trees, propagation of mature material capable of flowering and fruiting at an early age is more difficult, but methods of air layering (marcotting) are being successfully used, albeit with only low rates of success, and grafting trials are in progress. The second component is well underway, and farmers are willingly collaborating with researchers in the identification of superior trees for propagation and an active programme of air layering is in progress in many villages in southern Cameroon. Over 2000 trees had been identified and marcotted by 1998 (Tchoundjeu et al., 1998). As part of this, village nurseries are emerging and farmers are gaining experience in what for them is a very new experience. In parallel with the farmer identification of superior trees a study is also in progress to determine the range of variability in fruit traits within the species. Thus fruits have been collected from up to one hundred trees in each of three villages in Cameroon and one in Nigeria. These are being assessed for eleven traits that influence fruit and kernel size, quality, etc. in order that a good understanding of the biological opportunity for genetic improvement can be obtained (Atangana, 1999). This will then be compared with farmer and market perceptions of the opportunities and options open for a domestication strategy, as well as helping the researchers to explain to farmers what traits, or combinations of traits (ideotypes) are available for selection (Leakey et al., in press). Additionally this work will indicate what level of improvement is possible, without recourse to tree breeding and biotechnology.

Another important form of variation relates to the ease of kernel extraction, which tends to be a very labour-demanding process that potentially reduces market appeal. Hope here arises from the discovery that in I. wombolu in Gabon there is a variety with a self-cracking nut. Recent evidence suggests that easily cracked nuts also occur at low frequency in I. gabonensis and that this trait may be the result of the formation of a thin- shelled nut (Leakey et al., in press). Assuming that this is genetically determined variation, these trees are strong candidates for selection to become cultivars through cloning (Leakey and Jaenicke, 1995).

It is generally recognised that many non-timber forest products, that have been traditionally used by local people in Cameroon, are nutritionally important as sources of vitamins, minerals, proteins, oils, carbohydrates, etc. There is published information about the chemical composition of the fruits and kernels of Irvingia species. For example, the extraction rate of juice from I. gabonensis fruit pulp was 75% and the sugar concentration of this juice is comparable with pineapples and oranges (Akubor, 1996), but with a higher ascorbic acid (vitamin A) content (67mg/100 ml). The most important product from these species (especially I. wombolu) is, however, the kernel of the nut, which is extracted, dried and can be stored for long periods. The composition of I. wombolu kernels at 88.1% dry matter has been reported by Ejiofor et al. (1987) to be 51.3% fat, 26.0% total carbohydrate, 2.5% ash, 7.4% crude protein, 0.9% crude fibre, 9.2 mg/100g vitamin C and 0.6 mg/100g vitamin A. Other reports (e.g. Oke and Umoh, 1978) have quoted values of 54-67%, and even 72%, for fat content and 38.8% for carbohydrate (Ejiofor, in press). Okolo (in press) reports that the fat has an absence of volatile oils, a melting point at 37-42oC, saponification value of 233-250 and an iodine value of 2-9. He also quotes reports from 1929-39, that the myristic acid and lauric acid content of Irvingia kernels vary depending on the source of the fruits (Nigeria: 50.6% and 38.8%; Sierra Leone: 33.5% and 58.6% respectively). Hellyer (unpublished data) has given myristic acid and lauric acid values of 39.2% and 51.1% from I. wombolu kernels from Cameroon. The amino acid composition of kernels has been reported by Amubode and Fetuga (1984).

A comparison of kernel composition between I. gabonensis and I. wombolu has shown that I. wombolu has less fat, more crude protein, less crude fibre and less vitamin C than I. gabonensis (Ejiofor et al., 1987). The fat from I. wombolu has lower iodine and saponification values (Joseph, 1995). Kernels are processed by grinding and separating the residue from the fat. The residue is used as a food additive to thicken soups and stews, as it produces a viscous consistency when added a few minutes before serving. A rheological study of the polysaccharides in dika nut found that the variation of'zero-shear' specific viscosity was broadly similar to the general form of disordered polysaccharides, although with some specific attributes consistent with it having a compact molecular geometry rather than a 'random coil' conformation (Ndjouenkeu et al., 1996). Joseph (1995) reports that the viscosity of mucilaginous solutions is lower at high temperatures and at high shear rates, making it appropriate as a thickening agent. Calculated on crude protein basis, Dika nut meal shows comparatively better water and fat absorption properties than raw soy meal and hence it may have useful applications in processed foods, such as bakery products and minced meat formations (Giami et al., 1994).

It is possible that the nutritional value of bush mango fruits and dika nuts can, in future, be increased through genetic selection within the domestication programme.

Dacryodes edulis (African plum or Safou)

In the case of D. edulis, provenance collections have been made by IRAD and these have been assessed for over 12 years for their phenology, growth and yield (Kengue and Singa, in press). They have also served as a stock of material for propagation. This has led to the establishment of the first series of clonal variety trials on station and on farms (Kengue et al., in press). As in I. gabonensis, vegetative propagation techniques have been developed for D. edulis, both for juvenile cuttings (Avana and Tchoundjeu, unpublished) and for mature marcots (Kengue et al., in press). These propagation techniques are starting to be implemented in village nurseries. Again, as in I. gabonensis, the genetic variability of fruit characteristics is under investigation (Waruhiu, 1999) to provide a knowledge base against which domestication opportunities can be based and ideotypes identified. This builds on an earlier, and much less extensive study, which found that there was at least 5-fold variation in fruit weight (Leakey and Ladipo, 1996).

Regarding the chemical composition of D. edulis fruits, the flesh has good nutritional value and has been reported by Umoro Umoti and Okiy (1987) to contain, as a percentage of dry matter, 31.9% oil, 25.9% protein, 17.9% fibre. The main fatty acids in the lipid fraction are palmitic acid (36.5%), oleic acid (33.9%) and linoleic acid (24%); giving a profile similar to palm oil (Elaeis guineensis). The main essential amino acids are leucine (9.57%) and lysine (6.3%), while others are glutamic (17.0%) and aspartic (15.1%) acids and alanine (7.7%) acids. The ascorbic acid content of the flesh is 24.5%, but this is lost by some forms of cooking (Achinewhu, 1983). Many of the nutrients are however in the skin of the fruit, which is usually discarded. Youmbi et al. (1989) have reported different fruit types vary in their chemical composition, with the large fruits characterized by a higher lipid content in the mesocarp than in the seed, and the converse in small fruits. Fatty acid content was however not significantly different in two contrasting fruit types (Kapseu and Tchiegang, 1996). Non-structural carbohydrates are higher in the seed than in the mesocarp of both types. There is also much variation in taste and some variation in protein content (Kapseu and Tchiegang, 1996). The further characterization of these differences is important in the domestication of the species and their orientation to different markets.


There is growing international interest in the commercial use of genetic resources, especially those from the tropics and consequently there are important issues (reviewed by ten Kate and Laird, 1999) regarding access to these resources and the means of ensuring the sharing of benefits. Discussion of the role of tree domestication can not, however, be divorced from that of product commercialization, since without expanded or new markets, the incentives to domesticate are insufficient. Conversely, if the market explodes, the incentive for large-scale producers to establish monocultural plantations may sweep away the benefits that agroforestry could deliver to small-scale, resource-poor farmers around the tropics (Leakey and Izac, 1996). As has been pointed out by Dewees and Scherr (1996), policies that promote the linkages between the domestication and commercialization of non-timber forest products (NTFPs) are one of the important areas for policy. In this regard, there is also a need for better integration of the needs of the food and other industries from non-timber forest products with those of the subsistence farmer, with regard to the process of tree domestication for smallholder agroforestry.

It is clear from the above descriptions of work and knowledge about the two priority species for West and Central Africa, that considerable progress towards their domestication has been made in a short period of time. It is also evident that most of the methods needed to domesticate indigenous fruits are known and that they are being disseminated to subsistence farmers. However, for substantial impact on poverty alleviation this work needs to be widely implemented. Two crucial factors in this process are: i) the development of markets and processing and marketing infrastructure and ii) the adoption of agroforestry practices that utilize these tree species. These important steps towards enhancing the livelihoods of small-scale farmers and developing sustainable approaches to agriculture based on tree crops are discussed below.

In West Africa, as in other parts of the tropics, the products of indigenous trees are marketed locally on a small-scale, as a means of generating cash to supplement a subsistence lifestyle (Falconer, 1990; Arnold, 1996). Frequently these products are collected in natural forest or from wild trees retained on farmland. Some of these products also enter regional trade (Ndoye, 1995). Irvingia gabonensis kernels are traded on both a local and a regional scale in West Africa at prices between US$0.7-4 kg-1, depending on season. Uzo (1980) considered that the fruits from a single tree could generate income of US$300 per annum. An extrapolation from market surveys in Cameroon suggests that the trade of four indigenous fruits (Ricinodendron heudelottii, Irvingia gabonensis, Dacryodes edulis and Cola acuminata) from the humid forest zone over the 6 month period January-July 1995 was valued at $1.3 million (Table 2). A proportion of this trade was to neighbouring countries of Gabon, Nigeria, Equatorial Guinea and Central African Republic (Ndoye, 1995); 30% of this trade goes to Gabon and Equatorial Guinea. In this case, the reason given by individual farmers for selling non-timber forest products was to acquire cash for basic needs of their household (74%), to pay for school fees (9%), and for other needs (17%).

Table 2. Market details of four non-timber forest products in Cameroon over a period of 6 months (after: Ndoye, 1995)

US $
Wt traded
Value of trade
US $
R. heudelottii2.7172460200
I. gabonensis2.2140301590
D. edulis0.4587244480
C. acuminata1.0212211970
others 401122580
Total for non-timber forest products 15121,340,820

Increasingly, a small quantity of these products is being marketed in the USA and Europe. To encourage the expansion of regional and perhaps international trade, local level processing is needed. For I. gabonensis kernels, for example, oil can be extracted and the residue can be made into cubes/pellets with enhanced storage life (Ejiofor et al., 1987). Okolo (in press) has calculated that a pilot plant, with a capacity of 100kg per hour, would require 256 tonnes of kernels per year. It has been recognized that expanded markets for these products would increase the value of natural forests and benefit forest dwellers (Peters et al., 1989). Similarly, markets for non-timber forest products produced on areas already deforested could improve the income of subsistence farmers, and provide an alternative to slash-and-burn agriculture, one of the major causes of deforestation. The relatively small-scale market of these NTFPs is both a problem and an asset. It is a problem in that the wild, unimproved product may not have enough market appeal to encourage greater commercial interest. This raises the question of which comes first, the demand or the supply? This is a 'chicken and egg' problem, one made more complex by the price elasticity caused by variable supply and demand. By contrast, in the current early stage of the development of domestication activities, the relatively small market for these products can be seen as an asset. If demand for the products of improved cultivars was too big, large-scale company interests might swamp the production before small-scale farmers practising agroforestry had developed marketing infrastructures. Ideally for the purpose of poverty reduction, and incidentally environmental benefits through agroforestry, small-scale operations are preferable. It's clear that such developments require two things: an appropriate policy environment (Leakey and Izac, 1996) and commercial interests sympathetic to small-scale production, like those associated with organic farming. What characteristics of fruits and other products need to be improved to make a better food-thickening agent? Here there is a need for dialogue between the food industry and the field scientists - a dialogue that doesn't exist at present. Similar problems relate to the pharmaceutical and cosmetic industries, where again appropriate domestication could lead to higher quality natural products if the desired pharmaceutical traits were known to agroforestry scientists. Furthermore, there are regulations affecting the food, pharmaceutical and cosmetic industries that determine the toxicological acceptability of products. Scientists involved in the domestication of species producing potential new products need to be aware of the limits and opportunities imposed by these regulations and by the needs of industry (Leakey, 1999).

A commercial problem arises from the seasonality of production of many NTFPs, especially for perishable products such as fresh fruits. Domestication can almost certainly have considerable impact on the seasonality of production. For example, in the fruit tree I. gabonensis, there is considerable within-species variation in phenology with some trees flowering and fruiting outside the main season or fruiting several times per year instead of the normal once per year. An alternative is to have a year-round supply of products from a number of different species coming in and out of production sequentially. Seasonality is not a problem in the case of dika nuts as kernel storage allows a year-round market.

A literature review of the chemical constituents of the priority agroforestry trees for humid West and Central Africa (Leakey, 1999), has demonstrated that, in general, there is information at the species level regarding proximate analysis of fruits and kernels. However, it was clear that there is inadequate information about the levels of within species variation in chemical composition of fruits, etc., especially at the genotypic level relevant for tree domestication by the means described above. This gap in knowledge enhances the need for the food industry to collaborate in tree domestication programmes aimed at providing products for wider scale markets.


By using the combined approach of diversification and domestication, agroforestry becomes an integrated landuse that, through the capture of intra-specific diversity and the diversification of species on farm, combines increases in productivity and income generation with environmental rehabilitation and the creation of biodiverse agroecosystems (Leakey, 1999). Progress will however be dependent on the formulation and application of appropriate development strategies, and the demonstration of environmental advantages of this more ecological approach to land husbandry.

Cocoa (Theobroma cacao), which was previously a plantation-grown export crop, is now predominantly a small-holder crop, especially in Africa. It was introduced into Cameroon in the 1880s and by 1913 there were 58 different plantations in the area around what is now Limbe (Gockowski and Dury, 1999), but by the mid-1920s cocoa production had shifted to smallholder systems. The cocoa growing area has also changed and covers most of Southwest, South, Centre and East Provinces. In South and Centre Provinces approximately 75% of rural households produce cocoa and the area per household ranges from 0.1-10 ha, with a mean of 1.4ha. In the southern area, where population pressure is not great (1-20 people km-2) but concentrated along roadsides, cocoa is grown as small plots which were established early in the shifting cultivation cycle. Many of these plots are now relatively old and have an upper canopy of indigenous timber and fruit trees, forming an agroforest with a well diversified ground flora. These agroforests resemble secondary forest. In this area, staple food crops are mostly established in newly cleared areas of secondary forest or forest fallow within the farmers' control. However, further north, in the forest-savannah transition zone, north of Yaoundè, where population pressure is higher (over 50 people km-2) and forest is much more scarce or absent, farmers have developed mixed cropping systems, or agroforests, which are based on cacao. These cocoa agroforests, which are not as tall as those in the south, are more obviously man-made and contain a greater number of exotic species. For example a recent characterisation of agroforests around Obala (Gockowski and Dury, 1999) found that the average tree composition per hectare was: 495 cocoa, 35 timber trees, 22 mango, 22 avocado, 22 Dacryodes edulis (African plum), 21 Clementine mandarines, 18 other Citrus spp., 15 oil palms, 56 banana/plantains, 18 pineapples, 5

Cola spp., 3 papayas, 3 guavas, 1 soursop and one Irvingia gabonensis (Bush mango). In the area around Makenene, which is further north and west, the agroforests have a greater preponderance of Dacryodes edulis (African plum). In both the Obala and Makenene areas, staple food crops, such as maize and cassava, are integrated within the tree crops, wherever there is a gap.

It is clear from the above information, that cocoa agroforests are already a socially and economically important landuse system in Cameroon. An economic analysis by the Alternatives to Slash-and-Burn Programme in Cameroon (ASB, 1998), showed that the social profitability (ie. returns per hectare adjusted for economic distortions using the Net Present Value approach in which profitability was evaluated over a 30-year period with a discount rate of 10%) were greatest from intensive cocoa with fruits (US$1755), and lower from intensive cocoa without fruit (US$1236), extensive cocoa with fruit (US$1136), extensive cocoa without fruit (US$616) and lowest from forest crop field (US$283). Returns to labour were also high from intensive cocoa with and without fruits and extensive cocoa with fruits.


The domestication of trees for NTFPs has not yet progressed far enough to be able to determine the economic benefits. However, a small market survey of Dacryodes edulis fruits, currently the main species planted by farmers in Cameroon to diversify cocoa farms and provide alternative income, indicates that there is 5-fold variation in fruit weight (Leakey and Ladipo, 1996). In addition, there was a 5-fold variation in price per kilogram of fruit pulp, which was independent of fruit size, and probably due to flavour and other quality attributes. In this study, 3 fruits of one type sold for 250 FCFA (US$0.40), while at the other extreme 22 fruits sold for 50 FCFA (US$0.08). In other words, the price per fruit for the best fruits was 37-fold greater than that for fruits from the poor tree. This does not suggest, however, that domestication would result in a 37-fold increase in income, because a tree producing 1000 small fruits could not necessarily be replaced by a tree producing 1000 large fruits. This is because the dry matter allocated to fruit production by fruit trees is usually a proportion of overall dry matter produced per year. A harvest index of 0.3-0.6 would be typical (Cannell, 1989). Experience from the herbaceous and other tree crops indicates that ‘harvest index’ can usually be increased by only about 100% by domestication (i.e. 0.4 to 0.75 for coffee). However, as a hypothetical example, the crop of a tree producing 1500 fruits, selling for US 8 cents each, would sell for a total of US$120. If this tree was replaced by a tree producing 600 larger and better tasting fruits, selling for US 40 cents each, the total income would rise to US$240; a doubling of the farmer’s income.

Another way of looking at what could be possible by domestication is illustrated by a farmer (Mr. Womeni) near Makenene. He had 3400 cocoa trees with 117 D. edulis (African plum) trees in the upper canopy. In 1998, he sold the fruits from his nine best D. edulis trees for about US$150 per tree. The fruits from the other trees were inferior (the worst sold for US$20 per tree), but if he had vegetatively propagated his best trees, so creating cultivars, he could have replaced the inferior ones with the cultivars. His D. edulis trees would then have made a lot more money (US$ 10 000-15 000), providing that the market demand was not saturated. The enhancement of smallholder income, and thus livelihood, in this way therefore depends on the availability of the techniques and the development of the market. The livelihoods of these cocoa-producing farmers are very important for the cocoa and chocolate industry, which in turn is dependent on their continued production.

Evidence of similar variation is emerging for Irvingia gabonensis fruits and kernels (Leakey et al, in press). This suggests that through the selection of trees that combine fruit size and these quality attributes it should be possible to develop cultivars that are very attractive to farmers. Together these variations in size and quality of products from companion trees add up to great opportunities to improve the products from these trees. These improvements from tree domestication could greatly increase the income of smallholder cocoa farmers producing cocoa in enriched/diversified cocoa agroforests.

A clear conclusion from the Alternatives to Slash-and-Burn economic study was that the most profitable system was an agroforest that combined intensive cocoa production with the production of a range of fruits and other non-timber forest products. Based on this scenario and the information on NTFP markets, it would appear that improving the quality and yield of products from companion crops through their domestication and commercialization would increase income and provide a buffer against falling cocoa prices and the risks of lower returns due to pests or disease. Greater improvements to economic returns could perhaps also be made by further enriching these agroforests with a number of other high-value species (Table 3). Studies are however, needed to test these hypotheses.

Table 3. A sample of the west African tree/shrub/liane species appropriate for inclusion in multi-strata agroforests and for domestication (after Leakey, 1998)

SpeciesCommon names
Anthocleista schweinfurthiiAyinda
Antrocaryon micrasterAprokuma/onzabili
Baillonella toxispermaMoabi
Calamus sppRattan
Canarium schweinfurthiiAiele/African canarium/Incense tree
Chrysophyllum albidumStar apple
Cola acuminataKola nut
Cola lepidotaMonkey Kola
Cola nitidaKola nut
Coula edulisCoula nut/African walnut
Dacryodes edulisAfrican plum/Safoutier
Entandrophragma sppSapele/Tiama/Utile/Sipo
Garcinia kolaBitter Kola
Gnetum africanumEru
Irvingia gabonensisBush mango/Andok
Khaya sppAfrican mahogany
Lovoa trichloidesBibolo/African walnut
Milicia excelsaIroko/Mvule/Odum
Nauclea diderichiiOpepe/Kusia/Bilinga
Pausinystalia johimbeYohimbe
Pentaclethra macrophyllaOil bean tree/Mubala/Ebe
Prunus africanaPygeum
Raphia hookeri and other sppRaphia palm
Ricinodendron heudelotiiGroundnut tree/Nyangsang/Essessang
Terminalia ivorensisFramirè/Idigbo
Terminalia superbaFrakè/afra/Limba
Tetrapleura tetrapteraPrekese/Akpa
Treculia africanaAfrican breadfruit/Etoup
Trichoscypha arboreaAnaku
Triplochiton scleroxylonAyous/Obeche/Wawa
Vernonia amygdalinaBitter leaf
Xylopia aethiopicaSpice tree

As Leakey (in press) has indicated, there are also environmental benefits from these complex agroforests, which suggest that they are win:win landuses, that marry economic benefits with environmental benefits. However, are there trade-offs between the objectives of raising farmers' incomes and the global environmental benefits (biodiversity and carbon sequestration)? Again the Alternatives to Slash-and-Burn team in Cameroon have examined this (ASB 1998). They concluded that the intensive cocoa systems were both profitable and good carbon sinks (time averaged carbon stocks increase from 4.5 to 61 tonnes ha-1 an-1), with greater biodiversity than crop fallows. By contrast with intensive cocoa, extensive cocoa had lower global environmental benefits in terms of carbon storage. However, the team raised concerns about the high incidence of pest attack, pesticide use and soil structure (bulk density) in intensive systems. They indicated that the fruit component of cocoa agroforests adds greatly to the profitability of the system, but this is negatively impacted by transportation costs due to poor road infrastructure in rural areas. Furthermore, there is a lack of data on the biodiversity or ecosystem function benefits of diversifying cocoa farms with fruit trees; for example in terms of susceptibility to pests and diseases.

In the light of the Kyoto Protocol and international concerns about global climate change, there is discussion about trading in carbon storage. Calculations by ASB in Cameroon suggest that permanent conversion of short fallow to cocoa agroforest would remove about 70 tonnes of carbon from the atmosphere (Gockowski and Dury, 1999). At current prices of US$10 tonne-1, farmers could potentially receive a lump sum payment of US$700 ha-1 as a planting subsidy for conversion of degraded forest/fallows to cocoa agroforests. This could be even greater if other larger trees were integrated into cocoa agroforests as a result of the diversification of tree crops. Somehow, the cocoa industry should help its farmers to take advantage of this opportunity.


The concepts, strategies and policies associated with agroforestry are rapidly evolving towards the creation of sustainable landuses that enhance farmers livelihoods, provide commodities for global markets and mitigate global concerns about environmental degradation. In parallel with this, the techniques for the domestication of indigenous trees for the agroforestry production of NTFPs are also evolving rapidly and should produce further benefits in terms of income generation for agricultural inputs and household welfare. The diversification of tree crops with trees to produce other traditional NTFPs appears to have a number of benefits both to the farmer and the environment. This diversification may increase as farmers develop and apply domestication strategies to a wider range of species. The economic and social values of diversification are illustrated by evidence coming from cocoa agroforests in Cameroon, but to date there is a lack of data to indicate whether or not there are ecological benefits that might confer greater sustainability.

The potential financial and environmental benefits from the domestication of companion crops and diversification of cocoa farms are important for the livelihoods of smallholder cocoa producers, and thus for a thriving industry. Finding ways for farmers to achieve these benefits will be a challenge for the cocoa industry.


We wish to acknowledge the influence of many colleagues on our thinking, especially the farmers in Cameroon who have been so interested in our work. This paper was prepared for and presented at USDA-CABI-ACRI Collaborative Cocoa Research Review Meeting, London, 7-8 December 1999.