Within- and between-tree variation of wood density components in Pinus nigra at six sites in Portugal

Key message In Europe , P. nigra wood presents a density pattern of longitudinal variation with an increase from east to west. However, no latitudinal tendencies were detected. Compared to other Portuguese resinous species, P. nigra revealed higher density, identical radial growth and intra-ring heterogeneity, which presents advantages for industry purposes. The environmental factors (Sites effect) manifest more strongly in the latewood components while the Trees/Sites effect is more strongly expressed in the earlywood components. Context Although P. nigra Arnold is one of the most important conifers in Europe, little is known about the wood’s characteristics in the southwest European region. Aims Our aims are to outline a first approach to study the growth and wood quality in P. nigra in Portugal comparing to other European natural stands and other resinous species. Methods Inter- and intra-wood density variation of P. nigra from six Portuguese sites was studied using microdensitometry. Analysis of variance (ANOVA) was performed in three subsets: 50 common rings, core (juvenile wood) and peripheral analysis (mature wood). Results The average ring density was 0.588 g cm −3 , with maximum values in the north and low altitudes. Regarding growth traits, no latitudinal and altitudinal tendencies were detected. Compared to the main timber species in Portugal ( P. pinaster Aiton), P. nigra showed similar radial growth, higher density but lower intra-ring density homogeneity. The Sites effect mainly influenced latewood density components, while the Trees/Sites effect primarily influenced earlywood components. The Rings effect was found to be relatively low, with a density decrease in the tree’s first years followed by an increase in the periphery. Growth traits showed a reduction from pith to bark. Conclusion Considering the quality (density) and growth features of the Black pine, this species could be useful for the reforestation of mountainous Southern Europe areas that are not favourable for other species.