This dataset contains monthly sap flux density measurements from 44 trees growing in monocultures, two-species mixtures, and four-species mixtures in the IDENT experiment located in Sainte-Anne-de-Bellevue, Québec, Canada. Data were collected during the 2022, 2023, and 2024 growing seasons from four temperate broadleaved tree species (Acer rubrum, Betula alleghaniensis, Betula papyrifera, and Quercus rubra). These data were used to evaluate how tree diversity influences transpiration at the tree and community levels, given its central role in forest water balance.