Based on the assumption of the undamped propagation of Alfven waves between 2 and 5 RS, the possible range of Alfven wave energy flux density at the base of a polar coronal hole has been deduced. It is concluded that extended heating above 2 RS is needed to maintain the temperature maximum above 2 RS and to supply energy for the formation of high-speed wind streams. The energy contribution of extended heating to high-speed wind streams might be greater than that of Alfven waves by direct momentum addition.