The volume functions used in the first Swiss National Forest Inventory (NFI) were developed from stem  analysis data of cut sample trees on growth and yield research plots. Analysis, in which the data from NFI-plots and data from the growth and yield plots were compared showed, that stem forms of NFI sample trees have a greater variability than the available stem analysis data. Therefore, additional measurements have been taken and new volume functions are now being constructed.
Bole volume functions, the form of the tariff function and the method chosen to describe taper curves for the species spruce are presented. Robustness and precision of the different types of functions are compared.
All trees on the circular NFI sample plots are calipered. A subsample of trees in each plot is measured for an upper stem diameter and tree height. Alternative sample tree selection procedures for the second NFI have been studied. Volumes per plot are calculated using the predictions of both volume functions and tariff functions in a way, that the error component arising from the tariff regression function is included in the sampling error and volume estimates are unbiased even in small strata.