Abstract

This paper follows the transition from ethnobotany to a deeper scientific understanding of the food and medicinal properties of African agroforestry tree products as inputs into the start of domestication activities. It progresses on to the integration of these indigenous trees as new crops within diversified farming systems for multiple social, economic and environmental benefits. From its advent in the 1990s, the domestication of indigenous food and non-food tree species has become a global programme with a strong African focus. This review of progress in the third decade is restricted to progress in Africa, where multi-disciplinary research on over 59 species has been reported in 759 research papers in 318 science publications by scientists from over 833 research teams in 70 countries around the world (532 in Africa). The review spans 23 research topics presenting the recent research literature for tree species of high priority across the continent, as well as that in each of the four main ecological regions: the humid zone of West and Central Africa; the Sahel and North Africa; the East African highlands and drylands; and the woody savannas of Southern Africa. The main areas of growth have been the nutritional/medicinal value of non-timber forest products; the evaluation of the state of natural resources and their importance to local people; and the characterization of useful traits. However, the testing of putative cultivars; the implementation of participatory principles; the protection of traditional knowledge and intellectual property rights; and the selection of elite trees and ideotypes remain under-researched. To the probable detriment of the upscaling and impact in tropical agriculture, there has been, at the international level, a move away from decentralized, community-based tree domestication towards a laboratory-based, centralized approach. However, the rapid uptake of research by university departments and national agricultural research centres in Africa indicates a recognition of the importance of the indigenous crops for both the livelihoods of rural communities and the revitalization and enhanced outputs from agriculture in Africa, especially in West Africa. Thus, on a continental scale, there has been an uptake of research with policy relevance for the integration of indigenous trees in agroecosystems and their importance for the attainment of the UN Sustainable Development Goals. To progress this in the fourth decade, there will need to be a dedicated Centre in Africa to test and develop cultivars of indigenous crops. Finally, this review underpins a holistic approach to mitigating climate change, as well as other big global issues such as hunger, poverty and loss of wildlife habitat by reaping the benefits, or ‘profits’, from investment in the five forms of Capital, described as ‘land maxing’. However, policy and decision makers are not yet recognizing the potential for holistic and transformational adoption of these new indigenous food crop opportunities for African agriculture. Is ‘political will’ the missing sixth capital for sustainable development?

Highlights

  • The idea of domesticating traditionally important indigenous trees as new crops in the tropics for their useful and marketable food and non-food products originated in the 1980s [1]

  • When the 759 publications were divided by research topic, those from most topics had greatly increased in number, with some new topics being very well represented, especially: (i) the nutritional/medicinal value of non-timber forest products (NTFPs); (ii) the evaluation of the state of natural resources and their genetic diversity, governance and management; (iii) the ethnobotany of candidate species; and (iv) the characterization of useful traits (Figure 2)

  • Local use and socioeconomic importance were documented, as well as the pressure on natural stands due to overexploitation and unsustainable management of food, medicine and other services from Baillonella toxisperma, a multipurpose food, medicinal and timber species in Cameroon [247]; Garcinia lucida, a medicinal species in Cameroon [248]; Xylopia aethiopica, a tree species used as food, spice and medicine in Benin and other Central and West African countries [249]; Gnidia glauca, a medicinal tree species in Cameroon [198]; Cola spp., a group of food, medicinal and ritual species in Benin [250,251]; and Canarium schweinfurthii, a multipurpose tree species used for food, ritual and medicinal purposes [252,253,254,255]

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Summary

Introduction

The idea of domesticating traditionally important indigenous trees as new crops in the tropics for their useful and marketable food and non-food products originated in the 1980s [1] This idea, which includes both cultivation and genetic improvement, was taken up by the World Agroforestry Centre (ICRAF) in 1993, following a conference in Edinburgh in 1992 aimed at ‘Rebuilding Tropical Forest Resources’ and the advent of Woody Plant or Really Green Revolution [2]. It was morphological variation that was investigated, but this was later expanded into nutritional and other biochemical traits; The start of the evaluation of genetic variation using molecular technologies; The examination of communal, socio-economic, legal and political issues affecting both the adoption and impact of domesticating indigenous food and non-food tree species and the marketing of their Agroforestry Tree Products (AFTPs). This is more than double (125%) the total number of African papers published over the first two decades combined (Figure 1)

Research Topics
Species
Advances in Domestication Technologies and Their Application
Pan-African Priority Species
Commercialization of Products
Genetic Variation and Domestication
Post-Harvest Storage
Impacts and Multiple Benefits
Governance Issues
Management Issues
Ethnobotany of Food and Medicinal Species for Cultivation
Commercial Value of Non-Timber Forest Products in Local Markets
Characterization of Useful Traits
Molecular Studies
Nutritional Value of Non-Timber Forest Products
Medicinal Value of Wild Non-Timber Forest Products
Selection of Elite Trees and Ideotypes
5.10. Nursery Development and Improved Planting Stock
5.11. Vegetative Propagation
5.12. Post-Harvest Issues
5.13. Enterprise Development
5.14. Upscaling and Capacity Building—The Role of Rural Resource Centres
Ethnobotany of Food and Medicinal Species Candidates for Cultivation
Assessment of Genetic Variation and Its Characterization
Provenance Studies
Medicinal of Non-Timber Forest Products
6.10. Nursery Developments and Improved Planting Stock
6.11. Vegetative Propagation
6.12. Post-Harvest Issues
6.13. Upscaling and Capacity Building
State of Natural Resources and Their Governance and Management
Characterization of Trees
Assessment of Genetic Variation
Medicinal Value of Non-Timber Forest Products
Nursery Development and Improved Planting Stock
7.10. Vegetative Propagation
7.11. Trade and Law
7.12. Local Impacts of Cultivation and Marketing of Tree Products
Commercial Value of NTFPs in Local Markets
8.10. Nursery Developments and Improved Planting Stock
8.11. Vegetative Propagation
8.12. Community Action
8.13. Post-Harvest Issues
8.14. Enterprise Development
8.15. Trade and the Law
8.16. Local Impacts of Cultivation and Marketing
10. Policy Relevance
11. Towards the Fourth Decade
Findings
12. Conclusions
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