The performance of a radio-controlled hammer knife mower and a hand-held brush-cutter fitted with a shredder blade for shrub removal was evaluated to effectively restore shrub-encroached abandoned farmlands. To determine the shrub removal rates (effective field capacities) of these machines, two sets of three experimental plots, each measuring 1.5 m×20 m for the hammer knife mower and 1.0 m×10 m for the brush-cutter, were established in a field dominated by multiflora rose (Rosa multiflora Thunb.). The vegetation height and slope gradient of experimental plots was 124±15 cm and 4.4±1.7° for the hammer knife mower and 118±21 cm and 3.4±1.5° for the brush-cutter, respectively. The shrub removal rate of the hammer knife mower was 1,894 m2/h, which is higher than that of the brush-cutter with circular saw blade (conventional method). The removal rate of the brush-cutter with shredder blade (131 m2/h) was tended to be higher than that of the conventional method. These results demonstrate that both machines can improve the efficiency of shrub removal operations in abandoned farmlands.
