Résumé : Background and aims - A synchronic study has been achieved in fallows distributed in three age classes (0-2 years, 3-5 years and more than five years) in the natural forest reserve of Kigwena (Burundi). The aim was to show that differences in the proportion of plant functional groups could be used as indicators in characterizing the post-cultivation succession stages. Methods - The retained functional groups concerned biological and phytogeographic types, leaf size and diaspores dispersion. Key results - The data analysis gave five floristic associations. The functional group analysis evidences that the young successional stages are often characterized by sclerochorous herbaceous (therophyts) with often anemochorous dispersion, while the aged stages are essentially dominated by sarcochorous phanerophyts with essentially autochorous dispersion. The proportion of species with large distribution decreases with the age of the fallow contrary to species with regional distribution. A progressive increase with the age of species number with large leaves and a reduction of species with small leaves has been observed. Conclusion - The follow-up of the temporal variability of biological traits of species permits to characterize stages of post-cultivation succession.