José Tomé

Modeling dominant height growth of maritime pine in Portugal using GADA methodology with parameters depending on soil and climate variables

Abstract• BackgroundMaritime pine (Pinus pinaster Ait.) is a common conifer species in Portugal that contributes significantly to the national economy. Accurate classification of forest productivity based on site index and height growth dynamics is the main basis for sustainable forest management of this species.• ObjectivesThe main objective of this study was to develop a new dynamic site-dependent height–age model for the maritime pine in Portugal, using the generalized algebraic difference approach (GADA) methodology, and to explore possible improvements of the model´s performance by expanding its parameters as sub-functions of soil and climate variables.• MethodsWe tested for this purpose several dynamic equations, including anamorphic, polymorphic with common asymptote, and polymorphic with multiple asymptotes equations. The candidate models were fitted to a large set of stem analysis data, and tested on independent data from permanent sample plots.• ResultsThe two best models with multiple asymptotes, one anamorphic and one polymorphic, showed similar performance; however, upon expanding the parameters as sub-functions of the climate and soil variables, the polymorphic model outperformed the anamorphic model, as well as other models previously used for the management of this species in Portugal. The results of this study also demonstrated that the maritime pine model, developed with stem analysis data, can accurately predict the dominant height growth measured on permanent sample plot data.

A system for compatible prediction of total and merchantable volumes allowing for different definitions of tree volume

A system of equations for compatible prediction of total and merchantable volumes that allows for different definitions of tree volume was developed in this study. The use of the developed system will allow the conversion and subsequent comparison of results from forest inventories using different definitions of tree volume (e.g., including or not the top material of the tree and (or) the stump, inside or outside bark). The compatibility between taper, total volume, and volume ratio equations is ensured by properly integrating the taper equation. The diameter under the bark at any height is modeled with the Demaerschalk taper equation, and the corresponding diameter over the bark is obtained by assuming that bark thickness is also modeled with Demaerschalk’s function. The set of equations that has contemporaneous cross-equation error correlation (known as nonlinear seemingly unrelated regression equations) was fit using nonlinear joint generalized least squares regression. The predictive ability was evalu...