Spatial Characterization of Maritime Pine Productivity in Portugal

Abstract

This study maps maritime pine (Pinus pinaster Ait.) productivity in Portugal based on the data provided by the fifth National Forest Inventory (2005–2006). In Portugal, the usual procedure for measuring productivity uses the height and age data measured from dominant trees (the three trees with the largest diameter at breast height) in several sample areas (plots). To be able to compare measurements of different trees with different ages, empirical functions are fitted to the tree data, which enables the distribution of tree heights at a base-age of 50 years to be calculated. These reference heights are usually presented in five classes, which correspond to productivity classes. In a first step, a preliminary statistical analysis was conducted to evaluate possible relationships of the tree variables with measured contextual variables of the plots such as altitude, terrain slope, and terrain aspect. No unequivocal relationships were found for the studied variables. Secondly, maps of maritime pine productivity at unsampled plots were produced by Direct Sequential Simulation (DSS) of the height distribution of trees at a base-age of 50 years; a map of average 50-year-old tree height was then computed and transformed into classes. The set of simulated images also quantifies the local uncertainty, which identifies locations at which field sampling/survey should be performed in future forest inventory campaigns. The map image of productivity classes shows the best and worst areas in Portugal for maritime pine forestry and constitutes an effective, fundamental tool for the planning and management of maritime pine forests.