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In the semi-arid and sub-humid zones of West Africa, farmers have for many generations maintained a traditional land-use system, known as the ‘agroforestry parklands’ system (Pullan, 1974; Raison, 1988), which is characterized by the deliberate retention of trees on cultivated or recently fallowed land. Trees are an integral part of the system, providing food, fuel, fodder, medicinal products, building materials and saleable commodities, as well as contributing to the maintenance of soil fertility, water conservation and environmental protection.

Demographic, economic, environmental and social developments in the past 30 to 40 years have put pressure on traditional land-use systems and led to various forms of degradation. The severe droughts of the 1970s drew attention to the loss of tree cover and led the research and development community to devote a great deal of effort to trying to involve farmers in various types of tree-planting schemes. However, local participation was often short-lived and management not successful because little consideration was given to the reasons why farmers may protect or grow trees. Gradually, there was a growing awareness that trees needed to be regarded as an integral component of an overall farming system and a complex decision-making environment with interdisciplinary interactions. Dealing with many age-old practices, the new science of agroforestry was seen to provide promising solutions to the problem of degraded land-use systems and became the focus of strong research and development interest.

As part of this trend, the agroforestry parklands of the Sahel and Sudan zones of West Africa have aroused particular interest in recent years. At a time when human pressures on resources are high in natural forest ecosystems, and when more tree-related needs are being or will need to be met on-farm (Holmgren et al., 1994; Falconer, 1990; FAO, 1995), parkland agroforestry has a vital and increasingly important role to play.

Since the first descriptions of these systems in the late 1800s, followed by the seminal characterization work of geographers (Sautter, 1968, cited in Raison, 1988; Pélissier, 1964, 1966) and early agronomic research in the 1960s, the knowledge base on agroforestry parklands has been greatly advanced in the last 20 years. It has branched out to encompass research on tree-soil-crop biophysical interactions, system characterization, tree production, indigenous knowledge, genetic diversity, domestication, processing technologies, marketing systems, nutrition, social aspects, traditional tenure arrangements and policy analysis, all of which have contributed to a deeper understanding of the key characteristics, constraints and opportunities in these systems.

However, research results have been insufficiently disseminated as the abundant and diverse literature on these systems remains scattered and fragmented, so that knowledge gaps and new research priorities are not always easily identified. As in other areas of agroforestry research, the greatest challenge for work on parklands is perhaps the need to achieve a truly multidisciplinary approach, bringing together different areas of expertise, to provide integrated and practical solutions to farmers' problems. To be successful, this needs to involve the large variety of actors who participate in the promotion and management of agroforestry systems (Mallet and Depommier, 1997).

This review attempts to synthesize the state of knowledge on the wide diversity of inter-related factors, whether biophysical, nutritional, socio-cultural, economic or political, which underlie the practice of parkland agroforestry and govern its management and evolution. It also outlines the main avenues for sustaining and improving these systems as well as the kinds of data and experiences which would help to address unanswered questions. In doing so, it hopes to raise awareness of the local importance of parklands and the significant contribution they can make to sustainable natural resource management and enhanced livelihoods, and to promote greater commitment and coordination of efforts to maintain and improve these systems.

The study deals with agroforestry parkland systems in Sub-Saharan Africa. However, the main emphasis is on the semi-arid and sub-humid zones of West Africa, with occasional references to central, eastern and southern Africa. Agroforestry systems with scattered multipurpose trees in fields and fallows are its main target and other agroforestry configurations and technologies such as live fences, fodder banks, etc., which are also found within parkland systems, were not investigated.

The report emphasizes the central role which farmers play in establishing and maintaining parklands and suggests that, despite conditions which have led to degradation in many places in the Sahel, these systems are remarkably dynamic and resilient. They are not in uniform decline but, in several locations, are reproducing themselves very effectively through the concerted efforts of rural populations. The expectation that tree cover diminishes as pressure on land increases does not always hold true and land-use intensification in some places is accompanied by growing densities of managed trees (Arnold and Dewees, 1995). A variety of improvements in the institutional, economic, technological and biological environment in which these systems operate can effectively lead to the emergence and extension of agroforestry parklands.

The first chapter of the report provides a thorough description of agroforestry parkland systems. It reviews the various concepts and definitions of the system, emphasizes the wide geographical extent of their distribution and provides details on constituent species. Various classification systems, which have attempted to capture regional and local variations in parkland structure and composition, are presented.

Chapter two assesses dynamic trends in the extent, density and age distribution of parklands over time and highlights the need for more information in this area. It also outlines the variety of natural, socio-economic, technological, political and demographic variables to which farmers and parkland systems respond, and which have influenced adoption and decline of this agroforestry practice in the last few decades.

The third chapter analyses in detail the available qualitative and quantitative information on biological processes governing the biophysical influence of parkland trees on soils, crops and microclimate, and how they interact to have a positive or negative impact on crop yields. These processes are examined in relation to several factors including tree species, distance from tree, tree and crown size, and tree density. Experience with various improved parkland management techniques is presented in Chapter four. These technologies aim to improve parkland tree density, increase fruit, foliage and wood production, as well as enhancing crop production. Advances in domestication of parkland species and its potential impact on the adoption of parkland agroforestry are considered. This is followed by a discussion of knowledge gaps relating to the processes regulating genetic diversity in parkland species, with a view to promoting their conservation.

Chapter five focuses on the institutional factors influencing the management of land and trees in parklands. It highlights the need to understand existing indigenous arrangements at the level of whole communities or individual farmers for managing and regulating the use of parkland resources and the ways in which they have evolved in response to changes in the socio-economic and environmental context. Constraints and incentives for tree conservation and planting in indigenous tenure are analysed. The second part of the chapter looks at how the implementation of Sahelian forest laws has limited farmers' rights and prevented them from optimizing parkland management. It suggests possible areas of improvement in national forest policies and institutions which might help local communities achieve sustainable forest management.

Within the context of the increasing importance of on-farm tree production, Chapter six presents available data on fruit, foliage, wood and gum production in parklands and outlines additional data needs.

Chapter seven reviews the quantitative and qualitative use of parkland outputs and their importance in human nutrition, food diversity and seasonality, and health. It also emphasizes the diversity and size of local and international markets for parkland products and the role they play in local and national incomes. Their particular significance for specific gender, ethnic and social groups, who participate in the various stages of product collection, processing, marketing and consumption, is analysed. Lastly, the costs and benefits associated with the practice of maintaining trees in agroforestry parklands are evaluated.

The final chapter offers salient conclusions regarding the importance and characterization of agroforestry parkland systems, and the driving forces behind them, recommending several major lines of action for sustaining their conservation and reproduction.

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