Within and between-tree variation of wood density components in Pinus sylvestris at five sites in Portugal

Pinus sylvestris is widely distributed in Europe and Asia, and Portugal constitutes its westernmost limit. The reduction of the Portuguese forest area of resinous species has provoked strong constraints on wood industries supply. Therefore, an increase in Scots pine area might be important, namely by reforestations of higher altitude areas, where Pinus pinaster has great difficulties to vegetate and where the risk of pinewood nematode attack is smaller. However, large gaps remain in the knowledge of Pinus sylvestris wood characteristics growing in Portugal. To address this question, the radial wood density and growth were evaluated by X-ray microdensitometric technique, sampling 100 adult trees from five representative sites of P. sylvestris distribution area in Portugal. The results revealed that Portuguese Pinus sylvestris shows good radial growth and denser wood than those found in northern European regions. Among the Portuguese stands, sites at a lower altitude (Geres and Marao) exhibited denser wood. Regarding density components, it was verified that the differences among sites were more significant in latewood, while the differences between trees/sites were most expressive in earlywood. These facts induce a higher genetic control in earlywood characteristics and a greater dependence of latewood components on environmental and climatic effects. Regarding growth components, Trees and Rings effects were more noticeable than Site effect. Concerning radial patterns, Portuguese Pinus sylvestris shows a downward trend in the first years after the pith, followed by an increase in latter rings for the density traits, while the radial variation of ring width is expressed by a tendency of decrease from the pith to the cambium. Compared to other European regions, Portuguese Pinus sylvestris reveals good wood quality features, namely higher density and ring width values. However, compared to Portuguese Pinus pinaster it shows a relatively lower density and identical or relatively lower radial growth. Scots pine could be a good solution for future reforestations of Portuguese mountainous areas, less favorable to other species.