Portugal has a vast experience in developing empirical models for even-aged eucalyptus stands for which the planting date is known. Stand age is an important variable for modeling the growth of these stands, however in the course of national or regional forest inventories age is often unknown or difficult to access. Therefore, an age independent growth model, GYMMA, was developed for even-aged stands of unknown age (Barreiro et al. 2004). This model has been used to predict the growth of uneven-aged stands.

The methodology used for developing the model is based on the use of age independent difference equations (Tome et al. 2006). GYMMA is composed of an initialization module and a prediction module, responsible for predicting basal area and dominant height growth, and a calculus module integrating the estimation of total and merchantable under- and over-bark volumes, total biomass as well as of biomass by tree component.


Barreiro S, Tomé M, Tomé J, 2004. Modeling Growth of Unknown Age Even-aged Eucalyptus Stands. In: Hasenauer H, Makela A, Proceedings of the International Conference on Modeling forest production. Scientific tools – data needs and sources. Validation and application. Vienna, Austria.

Tomé J, Tomé M, Barreiro S, Paulo JA, 2006. Modelling tree and stand growth with growth functions formulated as age independent difference equations. Can. J.  For. Res. 36, 7, pp 1621

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