Dominant Height Model for Site Classification of Eucalyptus grandis Incorporating Climatic Variables

This study tested the effects of inserting climatic variables in Eucalyptus grandis as covariables of a dominant height model, which for site index classification is usually related to age alone. Dominant height values ranging from 1 to 12 years of age located in the Southeast region of Brazil were used, as well as data from 19 automatic meteorological stations from the area. The Chapman-Richards model was chosen to represent dominant height as a function of age. To include the environmental variables a modifier was included in the asymptote of the model. The asymptote was chosen since this parameter is responsible for the maximum value which the dominant height can reach. Of the four environmental variables most responsible for database variation, the two with the highest correlation to the mean annual increment in dominant height (mean monthly precipitation and temperature) were selected to compose the asymptote modifier. Model validation showed a gain in precision of 33% (reduction of the standard error of estimate) when climatic variables were inserted in the model. Possible applications of the method include the estimation of site capacity in regions lacking any planting history, as well as updating forest inventory data based on past climate regimes. 1. Introduction In its wider scope, forest management involves the choices of strategies that ensure the sustainability of the enterprise as a whole. The optimum management regime, under certain conditions of demand, productivity, distances, and silvicultural and harvests costs, is the higher objective procured. Thus, the choice of the ideal management practice for each forest site greatly contributes to the success of the activity. According to Louw and Scholes [1], the classification of forest site productivity requires the knowledge of the geology, topography, climate, soils, and biotic factors that occur in the local. These authors sustain that the classification of forest sites should have ecological bases and not aligned specifically with productivity (even if a covariance occurs). Although the use of site factors that influence forest growth (e.g., soil characteristics, climatic conditions) for the classification of site quality is reliable to differentiate broad regions of growth, in forestry the use of more direct stand characteristics (e.g., volume, height) is more common due to practical reasons. The use of height growth for assessing site quality in forest stands seems to have been first proposed by Remy de Perthuis de Laillevault, in the second half of the 18th century, working with