felling capability of a harvester with the load-carrying capability of a forwarder, allowing a single operator and machine to fell, process and transport trees. These novel type of vehicles are only competitive in operations with short distances to the landing. Felling head A typical harvester head consists of (from bottom to top, with head in vertical position) a chain saw to cut the tree at its base, and cut it to length. The saw is hydraulically powered, rather than using the 2-stroke engine of a portable version. It has a stronger chain and a higher power output than any saw a person can carry. two or more curved delimbing knives which reach around the trunk to remove branches. two feed rollers to grasp the tree. The wheels pivot apart to allow the harvester head to grasp the tree and pivot together to hug the tree tightly. The wheels are driven in rotation to force the cut tree stem through the delimbing knives. diameter sensors to calculate the volume of timber harvested in conjunction with a measuring wheel which measures the length of the stem as it is fed through the head. One operator in the vehicle's cab can control all of these functions. A control computer can simplify mechanical movements and can keep records of the length and diameter of trees cut. Length is computed by either counting the rotations of the gripping wheels or, more commonly, using the measuring wheel. Diameter is computed from the pivot angle of the gripping wheels or delimbing knives when hugging the tree. Length measurement also can be used for automated cutting of the tree into predefined lengths. Computer software can predict the volume of each stem based on analysing stems harvested previously. This information when used in conjunction with price lists for each specific log specification enables the optimisation of log recovery from the stem. Harvesters are routinely available for cutting trees up to in diameter, built on vehicles weighing up to , with a boom reaching up to radius. Larger, heavier vehicles do more damage to the forest floor, but a longer reach helps by allowing harvesting of more trees with fewer vehicle movements. The approximate equivalent type of vehicle in full-tree logging systems are feller-bunchers. Manufacturers NEUSON Forest Rottne Logset EcoLog Kone Ketonen AFM-Forest Barko Hydraulics Caterpillar Komatsu Forest Ponsse SP Maskiner Tigercat Timberjack (owned by John Deere) Kesla Oyj Prosilva