Evidence for indigenous selection and distribution of the shea tree, Vitellaria paradoxa, and its potential significance to prevailing parkland savanna tree patterns in sub‐Saharan Africa north of the equator

Abstract

Aim Woody vegetation patterns in African savannas north of the equator are closely connected to human presence, but the distinctions between natural and anthropogenic landscapes have not been clear to many observers. Criteria for identifying savanna landscapes on a continuum of intensity of anthropic impact are explored.Methods A key savanna tree species, Vitellaria paradoxa (Sapotaceae), was used as model for evaluating anthropic impact. Fruits harvested from tree populations across the species range were analysed for variation in traits valued by indigenous peoples. A simple selection index was used to scale tree populations from a hypothetical wild state to a hypothetical domesticated state. Index values were compared with trait values along climate zone gradients and evaluated in the context of indigenous savanna management practices and historical species distribution reports.Results Trait values such as fruit size and shape, pulp sweetness, and kernel fat content show a significant influence of temperature and rainfall. At the same time, the mean values of groups of traits vary perpendicular to the general climatic zone gradient. Selection index values between Vitellaria populations vary up to sixfold, with highest values in central Burkina Faso. Comparison of present day Vitellaria distribution with historical range limits show range expansion by human migration.Main conclusions The prevalence of major economic tree species in the savannas of Africa north of the equator is a strong indicator of human involvement in tree dispersal. This conclusion is supported by paleobotanical evidence and by recent Vitellaria range expansion as a result of human migration. The presence of high mean values of several Vitellaria fruit traits in central Burkina Faso suggests that selection for desired characteristics has occurred. The impact of indigenous savanna peoples on woody species composition and spatial distribution is probably much greater than usually thought and is the result of a deliberate strategy of altering the landscape to provide needed human resources.

Genetic diversity of the shea tree (Vitellaria paradoxa C.F. Gaertn), detected by RAPD and chloroplast microsatellite markers

“…Its status of being a socially and economically important species may also explain the high RAPD variability within populations. Protection afforded to shea trees during traditional long-term management in parklands (from fire, competition, etc) would be expected to allow diversity to increase, particularly if coupled with amplified gene flow by transportation of fruits from village to village by humans or other animals such as elephants, birds, bats or primates (Lovett and Haq, 2000b;Maranz and Wiesman, 2003). Although cases of deliberate human planting are rare and seeds of the Shea tree are recalcitrant, as they do not maintain their viability during long transportation, models of population genetics have shown that a small number of seeds could be sufficient to reduce genetic differentiation.…”

“…'Unconscious selection' of superior landraces (high yields, early abscission, improved fruit palatability, etc) has been proposed during the cyclical farm-fallow system when unwanted individual shea trees are removed and intensive fruit harvesting occurs during annual crop cultivation periods (Lovett, 2000). According to Maranz and Wiesman (2003), other more active selection mechanisms are possible and they suggest that the prevalence of V. paradoxa north of the equator indicates pronounced and long-term human involvement in tree dispersal. They have compared the presentday distribution with historical range limits from 200-year-old records and demonstrate that range expansion by human migration has occurred.…”

The Evolution of Shea Butter's "Paradox of paradoxa" and the Potential Opportunity for Information and Communication Technology (ICT) to Improve Quality, Market Access and Women's Livelihoods across Rural Africa

“…People, cattle, bats, birds and other animals disseminate the seeds [5], however, the trees are not traditionally planted in a domesticated manner [4,5,8,9], but rather the decision to keep or to cut naturally regenerating saplings as a component of an agroforestry system, means the trees are selectively managed, with the result that semi-domestication is potentially occurring through the process that [9] describes as automatic or unconscious selection. Many indigenous agricultural annual and perennial crops have been domesticated, are still cultivated and continue to be traded in large volumes across West-Central Africa, a region that [10] refers to as part of a vast sub-Saharan "noncenter" of agricultural origin.…”

“…Many indigenous agricultural annual and perennial crops have been domesticated, are still cultivated and continue to be traded in large volumes across West-Central Africa, a region that [10] refers to as part of a vast sub-Saharan "noncenter" of agricultural origin. Across West Africa, it has been noted that this process has resulted in an increasing density of desirable traits in shea trees maintained in parklands as opposed to natural woodland formations, e.g., fruit yield, sweetness and fat content [7,8,11].…”

“…The fruits are harvested around May until September, coinciding with the rainy season [5]. The genetic variability of shea is noted to be high [7,8,[11][12][13][14] and there is no tradition of planting trees, as shea is highly effective in propagating itself in this environment. Recent work, however, with micro-propagation, rooting cuttings and grafting may allow opportunities to formally domesticate and enrich parklands through selection and planting of more productive shea trees [15][16][17][18].…”