The knowledge of the functioning of our forest ecosystems protected is an issue of the maintenance of the planetary balance as regards its biodiversity and its climate. Its floristic dynamic apprehended by the mortality of trees, has formed the base of this study in the site of Isekelende at the biosphere reserve of Yangambi (Tshopo, D.R. Congo). Collected in a device of 6 ha, the results arising from this study have shown that the rate of tree mortality is more than 4 times higher than the tropical average. The causes differ according to the type of mortality. For the mortality on foot, the aging and the Fungal pathologies are the causes mainly observed while for the Chablis, we cannot say with statistical certainty that the frequencies and the wind speeds which are the main causes. A spatial distribution of dead trees identified highlights a relief of specific gaps. This mosaic is positively correlated to the direction of the prevailing wind of Yangambi.