In 1994, FERIC evaluated the performance of feller-bunchers, grapple skidders, roadside delimbers and slashers operating in overmature aspen stands in Central Alberta. The study aimed at providing the forest industry with information for projecting productivities and costs of harvesting overmature aspen stands. FERIC measured machine productivity in aspen stands of different characteristics, and fibre losses from excessive butt rot, upper stem defects, and conversion of tree-length stems into 2.6-m logs. The field data provided the input for determining operating cost and projected machine productivity as functions of tree size or skidding distance. This report also discusses the impact on cost of harvesting decaying stands.