Sofia Leal

Radial variation of wood density components and ring width in cork oak trees

The radial variation of ring width and wood density was studied in cork oaks (Quercus suber) using microdensitometry. The observations were made in young never debarked cork oaks (30–40 years of age) and in mature trees under cork production (37–60 years of age). The cork oak wood is very dense (mean ring density 0.86 g.cm−3, between 0.79 g.cm−3 and 0.97 g.cm−3) with a small intra-ring variability (mean earlywood density 0.80 g.cm−3 and latewood density 0.90 g.cm−3). The density components decreased from pith to bark more rapidly until the 15th ring, and then only slightly. There were no significant differences in the mean density components between never debarked trees and trees under cork production but their outwards decrease was accentuated in the never debarked trees. The annual growth was high, with a ring width mean of 3.9 mm (4.2 mm in the first 30 years) and the latewood represented 57% of the annual growth.RésuméLa variation radiale de la largeur des cernes et de la densité du bois a été étudiée dans le chêne-liège (Quercus suber) par microdensitométrie. Les observations ont été réalisées dans des arbres jeunes jamais écorcés (âge 30–40 ans) et des arbres en phase de production de liège (37–60 ans). Le bois de chêne-liège est très dense (densité moyenne 0,86 g.cm−3, variant entre 0,79 g.cm−3 et 0,97 g.cm−3) avec une variabilité dans le cerne faible (densité moyenne du bois initial 0,80 g.cm−3 et du bois final 0,97 g.cm−3). Les composantes de la densité diminuent du cœur à la périphérie rapidement jusqu’au 15e cerne, puis plus lentement. Les différences entre valeurs moyennes des composantes de la densité du bois des arbres non écorcés et écorcés ne sont pas statistiquement significatives, quoique la diminution radiale soit plus accentuée dans les arbres non écorcés. La croissance annuelle était élevée avec une largeur moyenne de cerne de 3,9 mm (4,2 mm dans les premiers 30 ans) avec le bois final correspondant à 57 % de la croissance annuelle.

CLONAL AND SITE VARIATION OF VESSELS IN 7-YEAR-OLD EUCALYPTUS GLOBULUS

Pith to bark variation of vessel anatomy was studied in 17 clones of 7-year-old Eucalyptus globulus trees grown on two sites in Portugal. Vessels were measured by image analysis on transverse microsections cut from radial strips sampled at 25% tree height. The mean vessel area increased gradually from pith to bark, whereas the vessel frequency (number of vessels per unit area) decreased outwards from the innermost ring on and levelled off towards the bark. The proportion of vessels relative to other tissues remained constant across the radius. The vessel variables showed cyclic variations defined by minima (vessel area and proportion) or maxima (number of vessels). The effect of site and clone on vessel variability was significant. Clonal variation accounted for 30% and site explained 67% of the total variance of vessel proportion. At the least water stressed site, vessels appeared to be generally larger and occupied a greater proportion of total cross-sectional area.

Characterization of cork oak (Quercus suber) wood anatomy.

The cork oak (Quercus suber L.) is important for ecological and socioeconomic sustainability and nature conservation in the Mediterranean area. Anatomical and structural features of cork oak wood were characterized at two sites in Portugal, including never-debarked trees and trees under cork production. Cork oak wood showed semi-ring porosity, solitary vessels with simple perforation plates, and large rays. Vessels were arranged in a diagonal to radial pattern, larger and more abundant in earlywood, and gradually decreasing in intermediate and latewood. In trees under cork production vessel distribution and frequency were altered, with more frequent and smaller pores, and a less distinct porosity pattern. Vessel diameter, element length and frequency were 133 ± 49 μm, 433 ± 103 μm and 2.9 ± 0.5 vessels/mm2 for never-debarked trees and 139 ± 50 μm, 341 ± 100 μm and 5.1 ± 1.5 vessels/mm2 for debarked trees. Multiseriate ray width ranged 0.15–1.04 mm, and uniseriate ray height 9.1–791.3 μm. Fibres had a mean length of 1.15 ± 0.20 mm. Vasicentric tracheids were frequent. Tyloses and crystals were commonly present. The anatomical features of cork oak wood favour water conduction and mechanisms of drought adaptation to the Mediterranean climate. The wood can also adapt to cork removal.

Tree-ring structure and climatic effects in young Eucalyptus globulus Labill. grown at two Portuguese sites: preliminary results

Summary Dendrochronological analyses of Eucalyptus are generally rare and mostly restricted to Australia. This work reports an attempt to identify annual ring patterns in young blue gum trees ( Eucalyptus globulus Labil) grown in Europe through studying the radial variation of vessel characteristics. Common radial trends were seen such as increasing vessel areas, decreasing vessel abundances and a cyclic variability of vessel characteristics associated to the seasons. Low water availability was related to reduced ring widths in combination with more and smaller vessels. Even with the given juvenility of the investigated eucalypt trees the pith to bark trends of vessel parameters might be useful in dendroecological studies, particularly with respect to drought scenarios. The employed method of using vessel parameters to identify rings seem to be the only accurate way of identifying annual rings in E. globulus .