The allometric model in the stand density management of Pinus pinaster Ait. in Portugal

The allometric model is very suitable for practical applications, as it gives an approximately correct expression of a number of relations, such as plant density (N) and average plant size (dg), very useful in forest management. Density management diagrams, based on the allometric model, are simple and effective procedures to display the complex dimensional stand development relationships and to translate general management objectives into stand-specific thinning prescriptions. This study presents a comprehensive approach, based on the allometric model, to manage the development of Pinus pinaster even-aged stands in Portugal, using National Forest Inventory data of 1998. The self-thinning allometric model is a linear limiting relationship, between N and dg. It requires upper boundary plot selection and corresponds to the use of the upper confidence interval limit for the intercept coefficient (13.634), with a slope coefficient of - 1.897. The upper and lower limits for the optimum growth-density interval also requires attention. In this study, trees square spacing and a 10 cm reference diameter were selected to calculate limits that are, respectively, 63% and 32%. Two associated relationships ( dominant height and total volume isolines) were developed to allow evaluation of thinning regimes in terms of age, height and volume. Three alternative management regimes (unthinned, commercial and precommercial), aiming a 30 cm target diameter, were discussed and compared. Mortality was only predicted in the unthinned regime, accounting for 46% total yield loss. The 30 cm target diameter was reached considerably earlier in the precommercial ( 38 years) and commercial ( 45 years) regimes, compared with the unthinned regime ( 54 years), but at the expense of a much lower residual trees . ha(-1) 350, 544 and 789, yielding a total volume of 278, 600 and 992 m(3) . ha(-1) and corresponding to 7.3, 13.3 and 18.4 m(3) . ha(-1) . yr(-1) MAI, respectively.