Influence of 20 years of anthropogenic disturbance, grazing, early fire, and selective cutting on aboveground biomass in savannah woodland of Burkina Faso, West Africa

Abstract

Savanna ecosystems support low biomass per unit area, but they are more widespread than humid forests and could contributesubstantially to carbon storage. The objective of this study was to measure biomass accumulation in savannah woodland subjectedto disturbances such as grazing, early fire, and selective logging. Biomass was estimated indirectly using allometric equations.To this end, dendrometric variables measured sequentially since 1992 were used. For each measurement period, biomass wascalculated for each individual tree. Then, the individual biomass was added together to find the total biomass for each 2,500 m²(50 x 50 m) subplot for each 5-year period. A repeated measures analysis of variance was applied to the data, and a two-tailed testwas used to compare the means of the different treatments. Aboveground biomass increased from 50 to 67 t ha-1, representing35% increase over 20 years. This corresponds to an average annual increase of 0.8 t ha-1 year-1. The impact of early burning onroot biomass varied by location: while it had no significant effect in one area, it led to a marked reduction in fine root biomass inthe other. Aboveground, early burning consistently reduced wood density across both sites, though a negative impact on annualincrement was localized to only one. Selective cutting negatively affected coarse roots in the more sensitive area and reducedaboveground biomass across both study sites. Similarly, grazing impacted both fine and coarse roots in only one location butshowed no significant effect on aboveground biomass in either. Notably, the simultaneous application of early burning, grazing,and selective cutting resulted in a cumulative negative impact on aboveground biomass. The difference in the effects of disturbancesbetween sites suggests that the biophysical conditions of the sites must be considered when using them as management tools.