Evidence for anthropic selection of the Sheanut tree (Vitellaria paradoxa) |
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Authors: | P N Lovett N Haq |
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Institution: | (1) The Shea Project, COVOL Uganda, P.O. Box 833, Lira, Uganda;(2) Environmental Research Group, International Centre for Underutilised Crops, The University of Southampton, Highfield, Southampton, SO17 1BJ, UK |
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Abstract: | The Sheanut tree (Vitellaria paradoxa Gaertn.), a multi-purpose species highly valued for the oil obtained from its seeds, is commonly maintained in the semi-arid
parklands of sub-Saharan West Africa. An inventory in the West Gonja District, Northern Region, Ghana, revealed that on intensively
farmed land this species constituted 79.7 ± 7.2% (Basal area = 2.19 ± 0.64 m2 ha−1) of the woody biomass, on low intensity farmland 84.2 ± 10.0% (2.16 ± 0.57 m2 ha−1) and only 10.2 ± 3.3% (0.92 ± 0.23 m2 ha−1) in unmanaged woodland, with similar environmental characteristics. No significant differences were found between total Sheanut
tree densities on different land use intensities, although as a proportion of all trees surveyed, large trees were more common
on farmed land. Participatory surveys revealed that these populations are a direct result of anthropic selection as local
farmers eliminate unwanted woody species on farmland, leaving only those Sheanut trees that meet criteria based on spacing,
size, growth, health, age and yield. Characteristics that could affect population dynamics during traditional management and
harvesting including short viability seeds and cryptogeal germination are also discussed with reference to unconscious selection.
Tree improvement is currently constrained, as true to type varieties are difficult to propagate. It is proposed that Sheanut
trees on farmland are semi-domesticated having been subject to long-term anthropic selection during cycles of traditional
fallow and crop cultivation.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | tree domestication unconscious selection Vitellaria paradoxa Gaertn |
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