PROVISIONAL EQUATIONS FOR ESTIMATING TOTAL AND MERCHANTABLE VOLUME OF<i>TECTONA GRANDIS</i>TREES IN COSTA RICA

ABSTRACT Although management practices for Tectona grandis in Central America have improved during the last decade, accurate volume equations are not yet available. The aim of this study was to develop equations which best predict individual-tree total volume and merchantable volume for T. grandis in Costa Rica. A total of 112 trees with ages between 2 and 47 years and breast height diameter (dbh) between 2.4 and 58.7 cm were felled for stem analysis. Linear and non-linear regression analyses were used to model the relationship of total volume with dbh, with dbh and total height, and with age. The study also included merchantable volume equations that estimate merchantable volume to any minimum top diameter or bole length. The equations tested in this study fitted the observed data well. Other models, developed elsewhere, tended to overestimate the stem volume, especially at dbh ≥ 30 cm. General geometric cylinder volume equations combined with a Stem Form Factor of 0.45 (widely used for T. grandis) were less precise than regression models when applied to this data set. Model validation with an independent data set suggested that the models should be calibrated with local data when great accuracy is required (error less than 10%). Key words: regression analysisstem form factorvariable-top diametervariable-top height

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