The invention concerns a method and an arrangement to reduce interruptions in operation of linear control means (6) such as a hydraulic cylinder with a cylinder housing (6a) and a piston rod (6b) that is used for the setting displaceable machine elements (2a, 2b) in a tree harvester (1), where the interruptions in operation are caused by splashes of fluid from trees that are being processed in the tree harvester. According to the method, the piston rod (6b) is shielded from the tree (3) that has been taken up into the tree harvester (1) by means of a protective sheath (10) that surrounds the piston rod, where the protective sheath is arranged to accompany the piston rod in its motion in such a manner that the protective sheath surrounds at least partially the cylinder housing (6a) when the control means is located in its compressed condition.
