Modeling bark thickness and probability of trunk cavity occurrence relative to tree size in Araucaria angustifolia trees

Models of bark thickness and trunk cavity occurrence improve allometry assessments and provide good indicators of the probability of tree decay or vitality—knowledge useful for old-growth tree conservation and management. This study aimed to model the attributes of Araucaria angustifolia that influence allometry assessments and its biomechanics. We used samples collected during dendrochronological studies to measure bark thickness and data from old-growth attribute surveys to assess the occurrence of trunk cavities (or hollows) associated with heartwood decay. First, nonlinear mixed-effects models were calibrated to predict bark thickness. Then the probability of hollow occurrence was evaluated with binomial regression using generalized linear models. Bark thickness increased with tree size, attaining an asymptote of 11.9 cm. This finding suggests that thickness above the asymptote may not offer additional protection to trees. Because bark has an influence on allometry assessments, we provide an accurate model to improve wood volume estimates. Hollows are associated with tree size and affect mechanical stability, and due to their empty space, it can cause bias in allometry assessment of biomass and wood volume. Suitable predictors of the probability of tree decay or vitality are provided. The predictors evaluated can also be used as a tree-level indicator of quality in selection systems. Our results highlight the importance of accounting for bark thickness and trunk hollows in carbon, conservation, and management surveys of Araucaria forests.