S.S.H. (Honoré) Biaou: “Tree recruitment in West African Dry Woodlands”

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31 Mar 2009 16:00
Unit: Wageningen University
Location: Aula, building 362, Gen. Foulkesweg 1, Wageningen
Organisation: Wageningen University
Promotor: prof.dr.ir. G.M.J. Mohren (Forestecology and Forest Management)
Co Promotor: Dr.ir. F.J. Sterck , Dr. M. Holmgren
Pictures: S.S.H. (Honoré) Biaou

Woodlands spread as a vegetation bridge between savannas and rainforests representing 25% of the natural vegetation in Africa. They are disappearing rapidly due to the combined effects of unrestrained forest exploitation, the increasingly severe droughts, the loss of soil productivity, and the effects of fire and herbivores. To develop sustainable woodland management strategies we need to understand how these multiple factors interact and influence tree recruitment and species diversity. We studied these relations using large field experiments in Benin, a country located in the dry fringe that separates the large rain forest blocks from West and Central Africa, and where still extensive woodlands can be found. We found that the largest tree diversity is found in woodlands that are not too dry or not too wet. At these intermediate moisture conditions, large trees facilitated the establishment of the new recruiting trees while disturbances by grazing and fire reduced tree competition, thus favouring the coexistence of more tree species. However, with increasing abiotic stress due to increasing drought or soil salinity, these disturbances played a negative role, reducing tree abundance and diversity. Forest managers should thus tune woodland harvesting in such a way that trees are left to create favourable microclimatic conditions that facilitate the recruitment of new trees and the regeneration of woodlands, and be aware of the advantages and disadvantages of implementing grazing and fire as management tools, depending on the climate and soil conditions.
Title thesis: “Tree recruitment in West African Dry Woodlands. The interactive of climate, soils, fire and grazing”
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