Evolution of the hypsometric relation in Araucaria angustifolia crops in the mid-south region of Paraná State

The aim of this study was to assess and model the evolution of the hypsometric relationship in Araucaria angustifoliaplantations grown in the 1940’s and 1960’s in the Irati National Forest, in the mid-south region of Paraná state, Brazil. Using thecomplete stem analysis method, it was possible to reconstitute the past annual growth of the diameter at 1.3 m (d) and of the totalheight (h) of a sample of 30 trees, selected so as to cover diametric and age variability. Eleven discs were removed from each tree at0.1 and 1.3 m and at 15, 25, 35,..., 95% of the total height. Eleven models traditionally used in hypsometric relationships were tested,two of which were considered generic because they involved the age variable. The models were selected based on the AdjustedCoefficient of Determination (R²Adj), Standard Estimate Error (Syx), absolute (m) and relative (%), and on the graphic distribution ofresidues in percentage. In the models tested by age, no tendencies were observed and erros (Syx) remained below 14.6%, except for ages5 and 11. However, the coefficients of determination were low, ranging from 0.29 to 0.55. The Curtis generic model (1970), selectedto represent the h/d curve for all ages, also presented a satisfactory performance (R²Adj = 0.87 and Syx = 16%), with results similar tothose obtained for the models in each age. As age increases, the h/d curve shifts to the right and changes level, remaining steep at theyounger ages and more stable and flat as the population nears the end of its cycle.