A method and a system for forestry, in particular harvesting by means of a harvesting machine comprising a vehicle and a harvesting arrangement mounted thereon, is based on the fact that at least one position determining device (5), capable of determining the positioning of the harvesting machine by means of external wirelessly receivable signals, is arranged on the harvesting machine (1). A marking device adapted to apply a marking on pieces of timber obtained from trees is arranged on the harvesting machine. A control unit (8), suitably a computer, is arranged on the harvesting machine to control the marking device to mark the piece of timber with position information or a code corresponding thereto by means of position information received from the position determining device (5).