Compatible volume and taper equation systems for roble and hualo second-growth forests in Chile

Abstract

Estimates of merchantable volume in second-growth forests are made in an environment of high uncertainty. Therefore, there is a need to develop more flexible predictive models for estimating volume at multi-product level. This research developed compatible volume and taper equation systems for the native tree species roble (Nothofagus obliqua) and hualo (Nothofagus glauca). Data were obtained from a destructive sampling of 144 individuals of roble and 196 individuals of hualo. For each tree species, 70 % of the sample trees were randomly selected for parameter estimates, and the remaining 30 % for model validation. Two compatible volume and taper equation systems were derived from a segmented and a high-degree polynomial taper model. Error autocorrelation was accounted incorporating a second-order continuous autoregressive error structure CAR(2). A comparison between the two compatible systems was made based on the stem diameter and total tree volume predictive capabilities. The inclusion of CAR(2) in the model error structure allowed to reduce the effect of the autocorrelation generated by the diameter measurements taken along the stem. For both tree species, the segmented taper model presented the best performance for stem diameter predictions in comparison to the polynomial taper model. However, both compatible systems showed similar predictive capabilities for total volume. Based on the results obtained we recommend the use of the compatible volume and taper equation system derived from the segmented taper model.