Agroforestry parklands are widespread …
|Agroforestry parklands, broadly defined as areas where scattered multipurpose trees occur on farmlands as a result of farmer selection and protection, are widespread throughout the world. On a land area basis, they may represent one of the most extensive farming systems in the tropics. They are the dominant farming systems in semi-arid West Africa and cover the vast majority of cultivated area in Sahelian countries. This is reflected in the fact that most of the literature on agroforestry parklands deals with West African systems. In contrast with exclusively silvipastoral systems, these parklands include a long-term cultivation (and fallow) component, and have been described at length since they were first discovered by explorers in the early 1800s.|
… and important for rural food security,
Agricultural production in this region, which is mainly subsistence-oriented, mostly occurs under the discontinuous cover of parkland trees, so that these agroforestry systems contribute to the sustenance of millions of livelihoods in Africa alone. They also represent a major source, both in number and volume, of timber and non-timber forest products, which contribute to the food security of local communities and individuals. Current trends of growing pressure on limited natural forest resources coupled with a rising demand for forest products suggest that reliance on on-farm forest resources is likely to increase in the future. Certain parkland products, including gums, oils, proteins, fruit and drinks, are among the main and most frequently consumed items in their respective food categories by a majority of people, especially in rural areas. Some very popular products such as Vitellaria paradoxa butter and Parkia biglobosa spice are consumed throughout their distributional range, while patterns of consumption for others are more limited geographically. Edible parkland products are not only critical in supplementing the nutritional value of basic staple foods in lipids, proteins and micronutrients, but they also diversify diets and enhance people's seasonal food balance since they become available at different times of the year.
… for income generation,
NTFP production in agroforestry parklands generates significant income for a variety of local economic actors. A wide range of parkland products are intensively commercialized. Although a coordinated evaluation of the importance of individual commodity markets has not been carried out, available figures point to income-earning opportunities which are far from insignificant for individual households, communities and local economies. Income from parkland products can amount to 25 percent or more of the total income of non-specialized individual producers. A few products such as gum arabic and Vitellaria nuts are internationally traded and represent primary export earnings for a number of Sahelian economies.
… and are particularly relied on by vulnerable social groups.
Parkland production also plays a fundamental role in ensuring social equality and cultural stability. Specific social groups including women, the poor, immigrants and young adults, are particularly involved in the gathering and sometimes the processing of parkland products, because these activities require no cash investment. Marketing of these products is also predominantly a woman's activity. Parkland products tend to represent a higher proportion of women's than men's income, and can have an impact on women's economic level and the nutritional status of children. Production and commercialization activities of parkland products promote interactions between gender, age and ethnic groups and encourage transfer of indigenous technical knowledge, economic exchanges and social integration. Parkland trees also contribute to the reproduction of cultural and spiritual values in traditional rural societies.
A rich pool of forest genetic diversity has been actively maintained by farmers in these systems.
Although frequently dominated by just one or a few species, parklands include a large number of woody species, often up to 40–50 in the cultivation cycle alone. Most parkland species have a wide distribution range, occurring either in very localized or continuous patterns. They are, therefore, a very biodiverse agro-ecosystem with a high potential for biodiversity conservation across the region. Far from being residual tree populations from a one-time land clearing process, agroforestry parklands represent an elaborate manipulation of nature to meet farmer needs which reflects hundreds of years of accumulated knowledge and experience of relatively complex ecosystems. Even though additional studies on the topic are desirable, there is little doubt that parkland management has been crucial in promoting and maintaining the distribution and intra-specific genetic variation of tree species composing these systems. Agroforestry parklands should therefore be considered a reservoir of forest genetic diversity conserved by a dynamic and sustainable land-use system.
Because their positive ecological effect is only tangible in the long term, current preservation efforts are critical.
Parkland trees play a significant role in maintaining the ecological sustainability of farming systems in the long term, i.e. over one or more generations. They contribute to improving the physical, biological and chemical fertility characteristics of surrounding soils through a variety of processes. Data on the buildup of soil fertility and microclimate properties over the life of trees demonstrate that benefits are only realized over a long period. Thus efforts to conserve and enrich existing parklands and to establish new ones are particularly critical.
Parklands may have expanded in area but tree density and regeneration rates have declined, …
In Sahelian countries, the expansion of cultivation over the last few decades into frontier areas, river basins freed from onchocerciasis, and the northern (sometimes marginal) lands, suggests that parklands may have expanded on a land area basis. However, qualitative assessments, farmer perceptions, and a few quantitative studies indicate that parkland tree densities have significantly declined in past decades and that they are characterized by a predominance of old trees and a lack of regeneration. This may have been accompanied by a decline or disappearance of forest species at the local level.
…but the ways in which parkland dynamics are analysed depend on the spatial and temporal scales used.
In order to prescribe appropriate management and conservation measures, parkland dynamics need to be assessed at a variety of different time scales. Rather than being a sign of parkland degradation, for example, a decline in tree density may be inherent to farmers' long-term strategies for developing parklands with appropriate tree-crop combinations and high fruit production. This is particularly true for parklands sustained through the alternation of cultivation and fallow cycles.
Their capacity to support continuous cultivation is the key to their sustainability.
Parkland systems differ in the amount of land they require to be sustained and in their capacity to support increased human pressure. Thus high population densities, and the ensuing land-use intensification, can have a positive effect on the density and regeneration of Faidherbia albida parklands, which are suited to permanent cultivation. In contrast, Vitellaria paradoxa and Parkia biglobosa parklands, which rely on fallow periods for soil fertility restoration and renewal of tree cover, are particularly at risk of degradation and impoverishment with increasing population density and fallow reduction. Nevertheless, even these relatively extensive systems can absorb high levels of population growth, provided more intensive soil and tree management techniques are applied to permit longer cropping intervals, reduce risks, and sustain a diversity of tree products and services.
Parkland systems do not evolve unilinearly, but respond to a wide range of opportunities.
The decline of parkland cover in semi-arid West Africa is by no means uniform and conceals existing islands of active parkland regeneration, many of which have probably not been recorded. Far from being fated to deteriorate, these systems display a high degree of resilience. Farmers responsible for their creation and maintenance respond dynamically to a variety of natural, economic, socio-cultural, technical, demographic and political parameters. This implies that there is probably no single recipe to ensure the long-term survival of agroforestry parklands. Rather, a variety of factors can, if used wisely in correctly defined geographical settings, offer farmers positive conditions for preserving these systems.
A recent field of study characterized by methodological challenges …
The definition of agroforestry parklands is an inclusive concept with sometimes unclear boundaries and distinctions between subsystems. Because of their mixed human and natural origins, and their crop and forestry components, parklands have in the past received variable recognition in vegetation studies and have not been associated with any single traditional discipline. This may have diluted the attention given to these systems by the research and development community and policy-makers. Thus parklands have only recently moved on to the agroforestry research agenda as an integral object of study, but this remains beset by practical challenges of how to cope with their diverse nature and overall complexity.
… with a need to refine and operationalize classification methods to better exploit local development potential of the systems …
Several classification methods based on intensity of tree management, tree uses, spatial variation linked to soil management type, and ethnic identity, have been used to distinguish parkland types. However, they are often described in a very static way in the literature and are difficult to operationalize in the field. These typologies need to be tested, adapted and refined to reflect farmers' changing parkland management practices, and to enable them to be used as tools for the assessment and promotion of improved management potential. A closer link might be established, for example, between the intensity of parkland management (particularly planting practices) and the potential to domesticate several promising species. Characterization efforts and assessments of parkland management strategies also need to be carried out at increasingly finer units from the ethnic group to the village, household and subhousehold levels within the wider economic and institutional context.
… using multidisciplinary approaches.
This has methodological implications. Characterization techniques need to cover a range of different scales from the region, terroir and parkland unit down to the field, plot and individual tree level. Parkland studies also demand a strong multi-disciplinary approach and wide collaboration between various sciences including morphogeology, soil science, agronomy, forestry, geography, history, socio-economics, animal science, remote sensing and GIS technology.
The development of sound conservation and improvement strategies requires collection of longitudinal data…
In sharp contrast to their importance in semi-arid West Africa, there is a deplorable lack of longitudinal data comparing tree cover (density, age composition, etc.) and management at distinct time intervals which could help to assess the past and recent evolution of parklands and assist the R&D community in setting priorities to support their sustainability. Historical data will also be needed on the changes in social, political and economic context which may have accompanied resource management in communities. This implies a need to refine historical research methodologies for the collection of oral and documentary evidence.
… and coordinated regional assessments.
Characterization studies and information on West African parklands are relatively abundant and reflect the high diversity of floristic composition, density and age structure in these systems. But these often in-depth studies remain spatially and temporally fragmented and of relatively limited geographical scope. Their use of a variety of field and remote sensing techniques makes comparisons and synthesis difficult. This results in an incomplete picture of the condition of parklands at the scale of the Sahel and Sudan zones. Regionally-based quantitative data on the actual geographical extent of parklands, relative frequency and importance of parkland species, parkland stocking rates, and age structure, are necessary to guide appropriate research and development efforts, particularly given the transnational character of parkland biodiversity and intra-specific diversity.
A comprehensive regional assessment based on common classification procedures would provide the scientific basis needed to evaluate the condition of agroforestry parklands and develop conservation and improvement strategies. Such an assessment could be undertaken by individual countries in a regionally coordinated fashion through remote sensing and field studies in representative agroecological and socio-ethnic zones. Countries would be in a better position to evaluate the national area falling under this land management system, assess priorities, and renew their commitment to sustaining and enhancing it. The data could also help to make agricultural and economic policies target parkland systems more specifically and take into account their particular needs. Finally, a regional assessment would strengthen global recognition of parklands, and support regional or international frameworks for collaboration on parkland-related research and development.
Economic incentives are a powerful driving force for the reproduction of agroforestry parklands …
There is ample evidence to show that farmers invest actively in the protection and reproduction of parklands whenever they perceive that trees and their products become more valuable whether because of increased demand or declining availability. They also strengthen or construct institutional arrangements and maintain the necessary knowledge base for the management of these systems. In contrast, farmers tend to neglect their forest resources and favour alternative agricultural practices, items of consumption and income-earning activities, when these yield higher benefits than parkland-related activities. Factors of particular importance in their decision-making are lower costs, higher revenues, lower labour expenditure, better product availability, greater subsistence priority, preferred taste, etc. External parameters such as markets, external pressure on village resources, migration and relations with urban centres, also strongly influence the relative value of parkland trees.
…which should be actively promoted through a domestic political will to use and commercialize parkland products.
The direct relationship between market demand and economic incentives associated with parkland products suggests this as an important way of influencing the conservation and regeneration of parkland resources. This relationship is not new. More detailed historical research on these tree crop economies could contribute to an understanding of how various forms of parklands were born out of traditional mercantilist production and marketing structures and routes within Sub-Saharan Africa, and sometimes beyond. Economic sectors or systems for parkland crops (gums, oils, fruit, proteins, drinks, fodder, medicines, etc.) have been unevenly studied and monitored. Some occupy relatively small but significant, resilient niches in the international economy. Others may not have much impact on national economies, but represent a very important source of subsistence and income for local communities and individual households. With the opening up of village economies to the wider society, both regional and international, the commercial development potential of parkland tree crops appears to be under-exploited in national Sahelian economies.
National, bilateral, regional and international institutions should move vigorously towards supporting the development and commercialization of parkland products. In addition, countries ought to promote policies and practical actions to increase the local production, diversity, quality and use of parkland products.
Labour and quality constraints in storage and processing technologies must be alleviated,
Market development for parkland products calls for reliable chains of production which can guarantee product quality and consistent supplies. Collection, processing, and pre- and post-processing storage technologies for parkland products are often time-consuming, labour-intensive, require large amounts of fuel and water, and result in low efficiency, low profitability and sometimes poor price competitiveness. More support should go towards the identification of production and quality constraints, the further development and improvement of appropriate, cost-effective technologies with higher extraction yields, lower investment and labour demands, and durable equipment, as well as the design of appropriate institutional and financial arrangements for the development of village-level production units.
…the various product markets characterized,
Because of their traditional importance, parkland products are generally in popular demand. However, little is known about the constraints and opportunities for their further market development. This requires information on both the products concerned and commercial possibilities. Additional scientific data on the chemical composition of raw and processed materials and their nutritional, pharmacological and cosmetic characteristics would help to pinpoint their commercial potential and establish product quality requirements. An in-depth national characterization of parkland commodity systems (product flow, market participants, prices, seasons, information systems, product grading systems, processing and transport infrastructure, patterns of consumption and demand, substitution products and processes, etc.) would support an assessment of the potential for improvement of each commodity sector. It may then be possible to identify specific research and policy interventions and to monitor and evaluate their capacity to stimulate these systems. Results need to be communicated to all concerned to update the research, policy and extension agenda and enrich the decision-making process.
…and possibilities for development explored.
With the support of pilot research and commercial operations, market developments could be pursued in the form of diversification of end products, enhanced quality, packaging and image of traditional products to meet expanding urban demand, and the promotion of products through local awareness campaigns. Strengthening producer groups and maintaining a high proportion of profits at the producer level would be essential to encourage farmer participation. Catalysing the development of such initiatives by promoting partnerships with local non-governmental organizations, rural groups and local entrepreneurs, could be an important role for national researchers, particularly in the fields of agroforestry systems, technology and marketing.
Domestication of parkland species may proceed most actively in localized niches of relatively high management intensity.
Trees improved through modern domestication methods may increase farmers' interest in maintaining and expanding their investment in parkland agroforestry. This requires tree planting, however, which is a growing but not strongly rooted practice in the Sahel. Because practices are unlikely to change overnight in these risk-averse systems, researchers could focus on localized niches of increasing management intensity, where demand for germplasm is active. A number of these niches displaying favourable characteristics for parameters such as soil management units, farm type, degree of resource scarcity, access to markets, favourable land and tree tenure, and enabling forest regulations could be identified for promising species. The attributes and functions of trees desired by target groups in these specified environments would then gradually form the basis of specific, adapted domestication strategies. These would need to be preceded or accompanied by the optimization of production, processing and commercialization systems in order to stimulate further demand for improved germplasm. A more precise knowledge of the patterns and impact of indigenous forms of domestication, which have been little studied in agroforestry parklands, would help to set a realistic agenda and clarify the potential of ‘modern’ domestication.
Where there is a demand for tree planting, government and decentralized seed centres and nurseries need to support it by developing flexibility and responsiveness to the (food, fuelwood, etc.) needs of farmers, and drawing on indigenous knowledge for the propagation of desired parkland species.
Agroforestry parklands will survive and reproduce best where they are sustained by sound institutional frameworks such as the indigenous management systems established by communities.
The management of parkland resources has been upheld by indigenous arrangements concerning access to natural resources both at the community and individual levels. These arrangements are adapted to local conditions, possess a strong degree of flexibility, and reflect local institutional capacities. They are a major cause for optimism about the future of agroforestry parklands, and should be increasingly recognized and respected. To support these indigenous institutions in their sustainable parkland management, a better understanding is needed of the conditions enabling them to operate and adapt successfully.
Field professionals can assist these flexible systems to move towards more intense levels of tree management…
An increase in the management intensity of land use, which may be linked to intense population pressure or high resource value, has generally been accompanied by clearly articulated regulation of rights of access to resources, and often a more individualized control. Similarly, where arrangements are secure and unambiguous, parklands have the greatest chance of reproduction, while ambiguous and insecure tenure relations are a disincentive to their maintenance and emergence. Forestry extension and development personnel thus need to acquire a detailed understanding of local land and tree tenure dynamics surrounding parkland resources in order to identify constraints and opportunities for the adoption or enhancement of parkland agroforestry practices.
…by helping multiple actors craft clearly articulated agreements regarding land and tree rights.
In the African context, caution is needed not to equate the individualization of land and tree rights with ‘private property’ as defined by formal administrative and legal frameworks. Experience shows that individual control, nested in the bundle of overlapping rights to tree crops which have been created by inheritance, labour investment and migration, remains subject to renegotiation and redefinition. These control patterns are guided by economic and social objectives, rather than being sustained by formal laws. Supporting the clarification of tree rights while respecting their possible multiplicity and socio-economic rationale will probably be more fruitful than land and tree privatization programmes, which may sometimes support expropriation by one social group against another.
The apparent paradox of ‘complex’ indigenous regimes with multiple tenurial niches is their unique flexibility. While farmers borrowing land appear less likely to plant trees in parklands than owners of inherited land, these systems provide a wide range of possibilities for designing mutually appropriate agreements. Forestry practitioners can make a significant contribution in helping individuals and communities negotiate arrangements allowing tree planting and use by these and other secondary rights-holders.
A more difficult and long-term task will be the revision of national forest laws and institutions…
National forest policies and the way they have been implemented in the Sahel are often greater obstacles to the improved management of agroforestry parklands than indigenous tenure systems. Ambiguous policies have been interpreted as applying to on-farm trees resulting in, often repressive, enforcement of access restrictions and centralized control over parkland resources. Such policies have led farmers to believe that they have limited rights to trees on their own farms and kept them from carrying out basic management activities such as pruning, thinning and coppicing, which are crucial in optimizing their land use systems. As a result, farmers often choose not to plant trees or protect their regeneration.
…to allow improved, decentralized parkland management.
True advances in parkland management cannot take place unless farmers can apply tree management techniques - as dictated by the requirements of crop and tree health and production, as well as underlying goals of subsistence and economic welfare - on agricultural land they traditionally own and control. Despite several breakthroughs in recent policy revisions, a major turnaround in the attitudinal, legislative and institutional features of forest administrations is still necessary. Governments should consider minimizing the degree of intervention in parkland areas where individual landholding rights are recognized, and even find practical legal and administrative means to reward people for developing land through the maintenance and expansion of such agroforestry systems.
A new advisory role for the state…
Local management institutions provide a strong basis for the establishment of comanagement schemes between government and local communities to promote decentralized management of forest lands under communal tenure. Devolving management rights to communities often promotes a higher efficiency of local resource management, but it would be unrealistic to assume that communities are automatically capable of more sustainable and equitable management than currently achieved by the state. Governments should be ready to continue to provide inputs as they assess the limits to local authority, administrative and technical competence, and arbitration capacities. The shift in the role of the state from centralized decision-making to advising and negotiating will also require fundamental changes in attitudes and skills of state officials.
…can only be achieved with adequate training and financial resources.
The process of revising forest policies will inevitably have considerable economic implications at local and national levels which have to be closely examined. The removal of permit requirements from some forest resources may decrease state revenues, while the transfer of resource management and regulation responsibilities to local groups may increase their financial burden. New forms of state assistance for communities will have financial implications, as will the need to improve forestry training, extension and information dissemination. Assessments of the economic impacts of such changes, as well as commitment and financial support from national, regional and international administrations, will thus be necessary.
Parklands are not incompatible with modern cropping techniques. Extension services have a major role to play in the promotion of parkland agroforestry.
There is no inherent incompatibility between trees scattered in fields at appropriate densities and the use of cash crops, modern cropping techniques such as animal traction, or chemical fertilizers. While fertilized cash crop production may displace staple crops, shorten or eliminate fallows, and encourage shorter-term tenure, all of which can be detrimental to parkland sustainability, these technologies can also be applied less negatively with more attention paid to trees and their improved management. A greater effort by extension services and agricultural commodity agencies to include the agroforestry agenda in their promotion of modern agricultural practices is desirable. Results of research on the effect of trees on soil fertility, soil water, crops and microclimate, as well as the importance of indigenous parkland management institutions, should be translated into practical recommendations and communicated to national and parastatal extension services and field agents.
Agricultural fertilizer policies emphasizing the removal of input subsidies and price controls have had a positive impact on the expansion of Faidherbia albida parklands in western Senegal. Although too location-specific to be easily generalizable, the conditions under which similar policies might have positive effects in other parkland types should be investigated.
More research is needed into traditional management techniques, which focus on rejuvenating parklands through natural regeneration…
Technologies which increase tree and crop productivity will create additional incentives for farmers to invest in parkland agroforestry. Their efficiency and adoptability are likely to be greatest if technology development recognizes and builds upon indigenous management systems. In order to ensure the reproduction of parklands in which rates of tree attrition are higher than recruitment, applied research, development and extension activities should emphasize tree enrichment. This can be achieved either through the planting of species desired by farmers or through the easier, cheaper and more widely applicable technique of protecting natural regeneration. The impact that projects promoting this simple but effective traditional technique have had in communities should convince donors that funding of such projects is key to poverty alleviation, environmental protection, and biodiversity conservation. The conditions under which these projects are successful need to be identified and widely communicated. Research into the kinds of local incentives (prizes, training, tax reduction, etc.) needed to enhance planting and regeneration rates, and into ways in which local groups and administrations can sustain them with minimal outside support, would also be worthwhile.
…and improving the cropping environment through pruning.
In the low soil fertility environment faced by most farmers in the Sahel, tree pruning appears to be an attractive option for improving crop production around tree canopies. Repressive forest policies have probably prevented farmers from practising and experimenting with this and other tree management techniques to realize their full potential. Before it can be widely recommended, research will need to assess the effect of repeated pruning on long-term subcanopy soil fertility and crop performance, as well as on fruit, leaf and wood production.
Intercropping crops and parkland trees is biologically and economically profitable. But more information on production levels could lead to improved management and greater benefits.
Parkland agroforestry is increasingly acknowledged to be a rational production system, practised and improved by Sahelian farmers over many centuries. In spite of methodological difficulties, experiments comparing crop production with and without parkland trees show that increases are experienced with several tree species. A small number of studies indicate that where trees have a negative effect on crop yields, this is more than compensated for by revenues derived from major tree products. Systematic recognition of the importance of such NTFPs is rather recent, however, and more work is needed to quantify levels of production and to identify the factors responsible for its variation in key parkland species.
To make appropriate recommendations on species choice and management, scientists need a better understanding of tree-crop interactions. These are based on complex biophysical processes …
Tree-soil interactions usually include the redistribution of nutrients available in the system as well as an overall nutrient enrichment. While the underlying processes are conceptually well established, methodological constraints mean that there is little first-hand experimental evidence to indicate which process predominates. Thus, in areas where spatial redistribution is the primary process of improved soil nutrient content, maximum tree densities may be limited by the overall nutrient pool size, whereas the latter will be less of a constraint in poorly stocked, degraded parklands.
… which have often only been studied in isolation.
Experiments so far have highlighted the individual biophysical mechanisms involved in tree-soil-crop interactions. But they do not yet indicate which mechanisms are likely to have the greatest impact on crop performance and how they interact under different conditions. Several mechanisms can take place simultaneously, either in harmony or in opposition. Thus subcanopy crops may benefit from microclimatic effects of temperature and evapotranspiration reduction, at the same time as being negatively affected by a decrease in incoming solar radiation and more substantial attacks of pathogens caused by higher humidity. In the case of Faidherbia albida parklands, experiments indicate that crop production generally improves, whereas the evidence is more controversial for parkland tree species with typical leaf fall phenology. While the importance of microclimatic factors in influencing the outcome of tree-crop associations is acknowledged, a greater understanding is needed of the specific causal relationships which can explain how crop physiology is enhanced in each particular case.
Tree-crop interactions need to be studied over a range of latitudes and a time-span of several years.
In spite of the methodological complexities involved, additional, comprehensive tree-crop interaction experiments are called for. These should measure an increasing number of the biophysical processes involved, including soil fertility, sunlight intensity, temperature, soil and air moisture, and evapotranspiration. Experiments using combinations of artificial shade and fertilizers under and away from parkland trees could further clarify the specific contribution of nutrient enrichment, solar irradiance, and microclimate on crop yields. In order to better understand the conditions which contribute to the improvement, depression, or variability of cereal production under canopies, studies should simultaneously focus on various latitudes, and monitor and compare crop productivity over several years of variable rainfall conditions. The same applies to economic assessments of tree-crop systems, which should reflect the fact that farmers invest in parkland agroforestry as a long-term strategy to provide a buffer against extreme natural events (droughts, pest attacks, etc.) and socio-economic changes. The contribution of trees in the cropping environment, in both biological and economic terms, can be properly evaluated only over the span of several years.
Important factors affecting crop yields include underground competition …
The extent of competition between tree roots and crops for soil nutrients and water is a question that researchers have hardly started to tackle in parkland situations. This question is probably more relevant to tree species which are biologically active at the same time as crops. However, the fact that Faidherbia trees are often pruned, resulting in the extension of their foliation and growth phase into the agricultural season, also makes such investigations necessary for this species. Information on the spatial patterns of root distribution is desirable for various parkland densities and rainfall regimes, and can be generated through trenching experiments in the distinct zones of interactions (sub-canopy, outside edge of canopy, open field).
… and tree size.
Many tree-crop interactions appear to vary depending on the size of the tree involved. Not enough is understood about the relative importance of different interactions under trees of varying sizes. Are there given tree sizes when interactions lead to a positive outcome for intercrops? We already know that islands of high soil fertility under adult trees constitute a significant asset for crop production. But while these may develop naturally under Faidherbia albida, in the case of other species they may require crown reduction practices in order to reduce light interception, excessive moisture, or even rainfall interception and evaporation. A more precise investigation of nutrient, water and light dynamics for different tree sizes is needed in parkland conditions to permit more precise management prescriptions (e.g. on fertilizing, pruning, thinning and harvesting) for the various cases of parkland density and tree size.
More work is needed on a wide range of useful species …
While there has been a relative abundance of studies on F. albida, only a handful of studies have been carried out on other equally or more widespread and important parkland species, such as V. paradoxa, P. biglobosa, Cordyla pinnata and Hyphaene thebaica. More biophysical research is needed to improve the management of these and other important parkland species with promising socio-economic potential, such as Borassus aethiopum, Balanites aegyptiaca, Tamarindus indica, and Lannea microcarpa.
… and on scaling up from individual trees to the ‘parkland effect’.
Determining the biophysically-optimal densities for different parklands is complex. While further work on the processes involved in fertility amelioration, microclimate and tree-crop interactions at the level of individual trees is essential, it should be accompanied by analyses at the scale of whole parkland systems. The use of GIS and modelling instruments should facilitate the scaling up from the individual tree to the field level. Despite the larger sample size and number of sites required, research into interaction processes and performance should be carried out along a continuum of parkland densities. The need for this scale of analysis is particularly obvious in the study of wind reduction and associated ‘parkland effects’, which researchers have so far only begun to examine in woodlands. This scale of investigation may reveal another dimension of these systems' efficiency. The verification of these effects in parkland conditions and the assessment of their impact on crop production will greatly contribute to justifying initiatives for the conservation and improvement of these systems.
As shown in this review, agroforestry parklands are a rational land-use system developed by farmers over many generations to provide them with subsistence and income-generating products. The many different types of parklands existing in Sub-Saharan Africa today reflect the dynamic nature of these systems and the ability of farmers to adapt them to changes in the natural and socio-economic environment. Their importance as a livelihood buffer, particularly for vulnerable groups in society, and their significance as a rich pool of forest genetic diversity, have increasingly brought them to the attention of the policy-making and research community in recent years. There is a growing interest in promoting the conservation of parklands and in further improving their management to increase the benefits they provide to farmers. To achieve this, changes in legislation may be necessary to allow for the devolution of management to local levels and to turn state forestry services from repressive into essentially advisory bodies. Research into the biophysical interactions underlying parkland productivity can build on indigenous knowledge to provide management prescriptions more precisely attuned to the needs of different environments. And the promotion of markets and improved processing for parkland products will encourage farmers to invest in the further development of their parkland systems. Together these initiatives will enable an already resilient and productive system to play an even greater role in the future livelihoods of rural populations in semi-arid West Africa.