Stem Profile and Volume Models for Scots Pine and Norway Spruce Trees in Lithuania

The National Forest Inventory in Lithuania has collected Scots pine and Norway spruce trees measurement data across the country. Investigations to determine the suitability of these data for updating stem profile and volume models are required. Work associated with the National Forest Inventory has derived very accurate Scots pine and Norway spruce trees stem profile equations that have an application not only in deriving total tree volume estimates, but as a cost-effective mensuration tool to estimate stem volume at any part of the trunk. Three previously constructed models and a new q-exponential model for stem profile and stem volume were employed to compare predicted values with empirical values of diameter outside bark and stem volume. Performance statistics for the stem volume and stem profile equations included four statistical indices: mean percentage of absolute bias, precision, Acaike's Information Criteria, and an adjusted coefficient of determination.