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Swedish University of Agricultural Sciences Umeå (2007)

Impact of forest management regimes on ligneous regeneration in the Sudanian savanna of Burkina Faso

Zida, Didier

Titre : Impact of forest management regimes on ligneous regeneration in the Sudanian savanna of Burkina Faso

Auteur : Zida, Didier

Grade : Doctor of Philosophy (PhD) 2007

Université de soutenance : Swedish University of Agricultural Sciences Umeå

Résumé
Annual early fire, selective tree cutting and grazing exclusion are currently used to manage the State forests of the Sudanian savanna of Burkina Faso, West Africa. Such prescriptions, however, are not based on experimental evidence. The long-term effects of such management on seedlings and saplings and the germination of selected tree species are discussed. Seedling quality attributes are also assessed. Studies over a 10-year period examined the effects of the three management regimes on species richness and population density. Burkea africana Kook, f., Detarium microcarpum Guill. et Perr., Entada africana Guill. et Perr., and Pterocarpus erinaceus Poir. seed germination was tested for different temperatures, light conditions, dry heat treatments and scarification methods. The quality of Acacia macrostachya Reichenb.ex DC. and P. erinaceus planting stock was evaluated in relation to nursery production period ; field performance was assessed with and without watering. Fire, grazing, and selective tree cutting acted independently on sapling and seedling population dynamics. Early fire reduced sapling recruitment ; moderate grazing had no significant effect. Although the overall seedling population density was not affected by any of the treatments, fire and grazing had strong effects on single-stemmed seedling density. Ordination using Principal Component Analysis of the seedling population data revealed species-specific responses to treatments, in particular an increase of lianas compared to other species. D. microcarpum and E. africana seeds did not exhibit dormancy. Exposing B. africana seeds to 95-97% sulphuric acid for 15–20 minutes broke their physical dormancy. All seeds tested were neutrally photoblastic, with an optimal germination temperature of 25–35 oC. E. africana, however, germinated over a wider temperature range. P. erinaceus seeds did not tolerate heat shock ; while D. microcarpum and E. africana seeds responded positively at low intensity. Eighteen months after outplanting, survival and growth of Acacia macrostachya and Pterocarpus erinaceus seedlings were not affected by their initial size. Drought and non-drought factors affected seedling survival. Performance of P. erinaceus seedlings could be predicted from initial root collar diameter ; more data will be required to build a reliable model. This thesis recommends the use of annual early fire as a forest management tool to be continued if timing, weather conditions and other factors affecting fire intensity are given due consideration. Moderate level of grazing does not affect seedling and sapling recruitment. The current prohibition on grazing State forests may need revision to allow multiple-use management. The low seedling density of socio-economically valuable species indicates that natural regeneration could be supplemented by planting high quality seedlings.

Mots clé : forest management, germination, seedlings, quality, regeneration, controlled burning, grazing, woodlands, burkina faso

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