PREDICTIONG OF EUCALYPTUS WOOD BY COKRIGING, KRIGING AND REGRESSION

Abstract

In the Gypsum Pole of Araripe, semiarid zone of Pernambuco, where is produces 97% of the plaster consumed in Brazil, a forest experiment with 1875 eucalyptus was cut off and all the trees were rigorously cubed by the Smalian method. The location of each tree was marked on a Cartesian plane, and a sample of 200 trees was removed by entirely random process. In the 200 sample trees, three estimation methods for variable volume timber, regression analysis, kriging and cokriging were used. To cokriging method, the secondary variable was the DBH (Diameter at Breast Height), and for the regression model of Spurr or the combined variable, it uses two explanatory variables: total height of the tree (H) and the DBH. The variables volume and DBH showed spatial dependency. To compare de methods it was used the coefficient of determination (R2) and the residual distribution of the errors (real x estimated data). The best results were achieved with the Spurr equation R2 = 0.82 and total volume estimated 166.25 m3. The cokriging provided and R2 = 0.72 with total volume estimated of 164.14 m3 and kriging had R2 = 0.32 and the total volume estimated of 163.21 m3. The real volume of the experiment was 166.14 m3.