Transpiration of 22 individual trees in a mature plantation of spruce in Drahanska Vrchovina uplands, Moravia (Querci-fageta abietis forest-type group) was studied through the measurement of sap flow by the stem section heat balance method over six years. Relative transpiration of trees was calculated as the ratio of daily totals of their actual transpiration and potential evapotranspiration (standard crop evapotranspiration, E 1). This was expressed in % of the canopy projected area unit and in m 2 per tree as the effective crown area when a ratio of whole tree transpiration to E 1 was considered. Significant relationships were found between the sap flux density (expressed per stem section 1 cm wide) measured at breast height and tree size. Relative transpiration of canopy area unit (T rcl) reached in average about 1/3 of potential cvapotranspiration, it was very variable between individual trees as well as between different periods of time during growing seasons. Highest values occurred in medium size trees, while in small and large trees they were mostly smaller and less variable. Higher T rcl occurred in medium and big trees with relatively narrow crowns. T rcl had two limits, gradually appearing outside of a rather wide range of soil water storage values between 100 to 135 mm per 40 cm layer. Canopy water storage capacity reached in average 0.6 mm - within the wide range of 0.1 to 1.7 mm, which was dependent on social positions of trees.