Fire, plant-derived smoke and grazing effects on regeneration, productivity and diversity of the Sudanian savanna-woodland ecosystem

The establishment and subsequent dynamics and productivity of many plants is affected by diverse environmental factors, some of the most important in savanna ecosystems being herbivory, fire and its related cues. This thesis assessed the effects of these factors on the woody and herbaceous regeneration, productivity and diversity of Sudanian savanna-woodlands. The time (season) of fires and soil depth were found to affect both fire temperature and temperature residence time, which in turn affected the germination of seeds buried in the soil. Fairly good germination of unburied or superficially buried seeds could be obtained after early burning which is not the case of mid-season and late-season fires. Analysis of seeds’ germination responses to smoke generated by burning revealed that smoke responsiveness is a species-specific attribute that transcends plant species’ ecological characteristics, notably their fire response categories. In addition, the type and dose of smoke strongly affect germination parameters of responsive species, and for some species an appropriate combination of smoke and heat is required for maximal germination responses. Further, certain levels of heat induce temporary physiological dormancy in some species, which, in field conditions, might be beneficial in synchronizing the start of germination with the onset of rainy season. The effects of grazing and fire on the biomass dynamics of resprouts from cut stumps of selected tree species were also examined. The responses to the treatments were found to be species-specific, fire being deleterious in some cases and grazing generally having no significant effect. Finally, the time (season) of fires was found to have no significant effects on the richness, diversity, biomass or abundance of the herbaceous layer. In conclusion, grazing could be integrated in management prescriptions to promote multi-purpose uses of the forests. In addition, more attention should be paid to burning conditions to reduce fire severity as complete fire exclusion is utopian in this savanna ecosystem. Further, assuming optimal dosage levels are identified, fire-related cues (smoke and heat) could have potential uses in reforestation with native species