In Scandinavia a widely adopted biodiversity maintenance measure in managed forests is to leave retention trees to the clearcutting areas. A certain number of retention trees are left to the cutting area permanently as residual trees, which distinguishes them from shelterwood and seed trees. The aim is to increase the amount of large-diameter decayed wood in managed forest stands throughout their different development stages. However, there is evidence that some forest owners have removed the retention trees. The attitudes of forest owners in Finland towards biodiversity issues in managed forests and their knowledge and behavior concerning retention tree management were studied based on two surveys conducted in 2001 and 2006. In general, forest owners' attitudes were positive but their level of knowledge on biodiversity issues was moderately low. There were no significant change in forest owners´ attitudes and the level of knowledge between the two succeeding surveys. A sample of clearcutting areas was measured in order to find out if retention trees had been removed during a decade after the clear-cut. According the results some retention trees had been removed from every third of the inspected cutting areas. All the retention trees were harvested only from four percent of the areas. Received forestry extension and better knowledge on biodiversity issues decreased the likelihood to remove the retention trees.