From 1881 to 2000, a National Forest Census was carried out roughly every 10 years based on questionnaires sent to forest owners. Since the data was based on questionnaires and not field observations, the actual forest definition may have varied, although it was specified that the tree covered area should be minimum 0.5 ha. In 2002, a sample-based national forest (NFI) inventory similar to inventories used in other countries was initiated. This year, the Danish NFI has completed its third five-year rotation.