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Aboveground biomass estimates in the Amazon region remain uncertain, partly due to extrapolations based mainly on samples collected in upland terrains of terra‐firme forests. Most biomass estimates were focused on dicotyledonous trees or included other plant groups as a category of trees. Palms dominate areas that represent 20% of the Brazilian Amazon. However, their contribution to biomass estimates and the variation within riparian zones remain poorly documented. We estimated the biomass of palms larger than 1–cm diameter at breast height (1.3 m aboveground) in riparian plots (n = 40); investigated the potential bias caused by the use of dicotyledonous‐ or family‐ rather than species‐level equations for biomass estimation; compared palm biomass between riparian and non‐riparian plots (n = 72); and evaluated the effects of soil, topography, and stream characteristics in riparian plots on palm biomass. Mean palm biomass in riparian zones estimated with species‐level equations (27.50 ± 12.94 Mg/ha, range: 3.32–63.27 Mg/ha) was three times greater than biomass estimated with a family‐level equation (9.04 ± 4.29 Mg/ha, range: 1.51–21.25 Mg/ha) and was greater than mean biomass estimated with a pantropical equation (20.46 ± 9.29 Mg/ha, range: 3.67–47.99 Mg/ha). Mean palm biomass in riparian zones was four times greater than in non‐riparian zones. Palm biomass was high in flatter areas with poorly drained soils, but lower around streams with higher discharge. Inclusion of palms can contribute to reducing the uncertainties in biomass estimates in Amazonian forests. Recognition of the importance of riparian zones may improve conservation policies. Abstract in Portuguese is available with online material.

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