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Monodominant woody species are frequent in the Pantanal. Monodominant forests of Erythrina fusca(Fabaceae) occur in Northern Pantanal, but little is known about the environmental factors that influence this dominance. This work investigated the relationship between flooding and soil characteristics and the E. fuscamonodominance. We hypothesized that the dominance of E. fuscais mainly associated with extended flooding periods and lower soil fertility, factors frequently related to monodominance. We sampled 16 sites within the study area of 115 km2. We sampled three 50 × 5 m vegetation plots in each site, for species composition and abundance in multispecies forests and E. fuscamonodominant forests. Soil samples were taken in each plot, and the duration of flooding was determined. We performed Canonical Correspondence Analysis and Regression Trees to verify the variation of species composition along environmental gradients and to identify which environmental factors influence this monodominance. We observed that flooding is the main factor driving E. fuscadominance, where higher flooding duration led to higher dominance. Further, the dominance of E. fuscais related to low soil fertility and higher concentration of sulfur and organic matter, than multispecies forests. Our findings confirm the hypothesis that dominance of E. fuscais associated with high flooding regimes with low soil fertility, which together act as a strong filter for other riparian forest species, thus favoring the dominance of E. fusca.