initiated to feed wheels 40 the hydraulic flow will cause a hydraulic motor that drives feed wheels 40 to rotate thereby moving the stem of a tree through harvester head 26 to move the stem there is a need for sufficient energy to overcome the inertia of the tree the drag of limbs on the ground as well as limbs encountering delimbing blades controller 34 directs the flow of hydraulic fluid to feed wheels 40 from hydraulic pump 28 and accumulator 30 in a coordinated manner the fluid flow can be substantially simultaneously supplied from these two sources or the flow from one of the sources can be delayed relative to the other as directed by controller 34 the fluid flow requirement to move wheels 40 can be assumed to be greatest when movement is initiated additionally since measuring device 46 provides positional information and controller 34 would include timing information the movement of the stem of the tree can be monitored and controller 34 can selectively couple accumulator 30 to the motors of wheels 40 if the stem slows below a predicted or predetermined speed since accumulator 30 stores pressurized fluid the flow from accumulator 30 will dissipate over time as it flows to an element of harvester head 26 and the valve.