This master thesis is a collaboration between Luleå University of Technology, Swedish University of Agricultural Sciences in Umeå and Sveaskog AB. The primary goal was to develop and verify a mechanical solution for continuous thinning in young dense forests. The combination of silviculture and biomass production shows reduced costs for pre-commercial thinning. One million hectares of forest land is covered with young dense stands in Sweden. The content of those areas consists of a large amount of biomass. The first yield corresponds to 64 TWh and after that the yearly return could be 5-10 TWh. The importance of this energy is highly valued because biomass stands for 31,7% of Sweden’s energy usage 2009.During this project a crane mounted concept for continuous thinning was developed. The harvester head is designed to be used on 15-20 ton harvesters. Within one crane cycle the harvester head should harvest an area of 1x10 meters. The aim is to use the harvester head in stands were the diameter in breast height is between 4-10 centimeters and the trees are between 5-10 meters tall. Data information about young dense stands showed that the total tree mass in the 1x10 meter corridor rarely exceeds 300 kg. The harvester head was designed to manage 350 kg within one crane cycle. The required functions for continuous thinning were set to the following sub-functions; separation, accumulation and grading. The main focus was set towards solving problems around continuous accumulation. Earlier studies on conventional harvester heads for thinning showed that felling and positioning for each tree, or groups of trees, stands for 60-70% of the crane work.Existing harvester heads on the market were reviewed. Related technology and patent documents were also investigated. The purpose was to generate alternative solutions for separation and accumulation that differs from conventional techniques. The product development was performed in cooperation with a focus group. The focus group consisted of representatives from Sveaskog and the University of Agricultural Sciences in Umeå. The final concept is equipped with two saw blades and a system for continuous accumulation. The separated trees are pushed upright into the harvesting head with a feeding roller chain. After the feeding mechanism has pushed the trees, a chain made of torus-shaped links accumulates the trees. To verify the sub-function accumulation a physical prototype was built and tested. Conclusions from the test were that the rotation speed of the roller chain should be reduced to a speed under 200 revolutions/minute. Further the feeding system should be improved with four chains instead of two. The prototype tests showed that continuous accumulation is possible.