This study is a contribution to the knowledge of the floristic diversity of Burundi in general and fallow land in particular. The data processed come from a sampling in 4 stations representative of the phytogeographical districts of Burundi. Based on a floristic inventory, the species collected were classified in higher taxa. An analysis of the spectra of biological traits was carried out. Finally, a comparison between the sites made it possible to highlight the most decisive factor in the variability of the flora of the fallow areas studied.