Survival Strategies and Ecological Performances of Plants in Regularly Burning Savanna Woodlands and Grasslands of Western Ethiopia, Gambella

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Addis Ababa Universty


The survival mechanisms of plants in response to fire were investigated to understand the ecological freqances of plants in frequently burning plots of savanna woodlands and grasslands. These studies included: strategies of post-fire regeneration and resistance of tree-bark to fire; plant cover, leaf nutrient and condensed tannin concentrations following experimental burning treatments and relationships between fire and seasonal variations in leaf condensed tannin; soil seed bank dynamics; influence of heat on seed germination. Regeneration mechanisms of vegetation were studied along a transect line by quantifying foliar cover and fi'equency of individual plant species regenerating by resprouting, by seedlings or both, during the dry season and the early wet season. Resprouting plants (both facultative and obligate) significantly contributed to post-fire recovery, comprising 98.S % of total vegetation cover. The contribution of seedlings to cover and abundance immediately following fire was negligible, but seedling density increased in the early rainy season, 4 to S months after fire. The vigour of resprouting and seeding among species in different plant growth forms was discussed in relation to fire regimes. The role of tree bark thickness to sUlvival was studied. Results indicated that tree bark resistance to fire varied interspecifically related to bark thickness, other characteristics and age ofthe plant. The effects ofthree treatments: fire, biomass additions and ash fertilisation on plant cover, leaf nutrient (N, P, K) and condensed tannin concentrations were examined prior to experimental burning and after 90 and 210 days. There was a strong effect of fire on the cover of grasses and tree seedlings (P<O.OS), whereas the effect of fire and other treatments was not significant on the cover of broadleaved plants and shrubs/trees. There was a significant effect of fire on the plant species richness after 90 days. The concentrations of N, P, and K and leaf condensed tannins were higher in broadleaved plants than in grasses. The effect ofthe different treatments on the level ofN, P and K and condensed tannins are discussed. The changes in vegetation composition and herbage quality with fire, biomass and ash treatments are small compared to the changes between seasons. Therefore, the current fire regime (i.e. a regime with early annual burning of relatively low intensity) appears to maintain the present balance between the various plant fOlms



Woodlands and Grasslands