VARIATION OF FORM FACTOR AND TAPER IN PROVENANCES OF SPANISH CEDAR (Cedrela odorata L.)

Abstract

Knowledge of tree stem geometry is relevant for progeny studies aiming to obtain germplasm since the best individuals should have adequate growth and the best characteristics of stem formation. Thus, it is necessary to evaluate stem form with analytical methods. The objective of this study was to identify the progeny with the highest milling yield, considering form factor, taper variation and commercial volume of seven provenances of Cedrela odorata L. established in Tezonapa, Veracruz, Mexico. To this end, destructive sampling of 211 trees was carried out. Two linear regression and two non-linear regression models were fit and complemented with tests of additionality in the parameters form and taper. The results showed that the form parameters of the progenies from Tuxtepec, Tierra Blanca and Tezonapa adopted a paraboloid shape, and those from María Lombardo, San Andrés Tuxtla, Costa del Golfo and Comala tended to be conical. All the progenies were statistically different in taper parameters, which is attributed to the interaction genotype-environment and to infestation by the borer Hypsipyla grandella Zeller. Moreover, form parameters were evaluated in three compatible form and taper systems fitted with SUR (Seemingly Unrelated Regressions) estimation. The geographical source of Tuxtepec was less conical because the stems were geometrically closer to a paraboloid (form factor, ff=0.45). Therefore, Tuxtepec could be the main line of germplasm collection for local production.