Abstract: A method for determining sap flow velocity, constituted of: providing a heat source and a thermal sensor on a single needle: at a no-flow condition, providing first heat energy to produce a steady state first pre-determined temperature rise: determining a total amount of first heat energy provided to produce the first pre-determined temperature rise: at a flow condition: providing second heat energy to produce a steady state second pre-determined temperature rise: determining a total amount of second heat energy provided to produce the second pre-determined temperature rise: and determining a sap flow rate responsive to the determined total amount of first heat energy and the determined total amount of second heat energy.