Mise au point d'un tarif de cubage général pour les forêts québécoises : une approche pour mieux évaluer l'incertitude associée aux prévisions

Abstract

Merchantable volume assessment is of prime importance in forest management and for the estimation of wood production in Quebec Crown forests. Currently, this assessment is undertaken at the individual stem level according to a statistical model commonly identified as the Perron general stock table. This polynomial model is based on tree diameter at breast height and tree height. However, the mathematical model form and the method used to calibrate it do not enable a correct and detailed assessment of the uncertainty associated with volume assessments. This study describes a new model which, accounts for errors associated with the use of estimated height in volume forecasts and also limits the propogation of errors to sample plot and cruise line. Random effects have been specified in the model in order to take into account spatial correlation between observations made at the sample plot and cruise line level. Results indicate sample plot and cruise line random errors constitute components of model error, which individually range from 2 % to 4 % of volume assessment. Consequently, the basic premise that errors associated with volume assessment of individual stems are compensated by volume summations at the sample plot level is not valid. Key words: mixed model, random effect, error propagation, variance