Table 3 Approaches of bridging functions applied by the 21 NFIs
From: Harmonisation of stem volume estimates in European National Forest Inventories
Approach | Description |
|---|---|
Alternative model | Refers to volume models that are additionally used by NFIs to predict other than the national stem volume estimates by including or excluding the desired tree parts. Such alternative volume models are used by NFIs to satisfy different information needs about e.g. merchantable volume, volume under- or over-bark, or tree volume including branches |
Complementary model | The existing set of volume models applied by an NFI is complemented by additional models to predict the volume of the individual tree parts stump, stem top and branches, or the trees below the dbh-threshold. Empirical models like allometric equations and geometric approximations can be applied. The first are developed from field measurements, the second assume geometric bodies (e.g. cone, cylinder, neiloid, paraboloid and truncates of them) and follow the idea of describing the stem shape by generic conoids (Prodan 1965) |
Taper curve | Taper curves describe the stem shape along the stem axis from the base point up to the stem tip and allow determining the stem diameter at any specified height (e.g. stump height), or reversely the height for a specified diameter (e.g. stem top base diameter of 7 cm). Thus, taper curve models allow for deriving the volume for the whole stem, or defined stem segments which for instance correspond to the reference definition |