Teresa Quilhó

WITHIN AND BETWEEN-TREE VARIATION OF BARK CONTENT AND WOOD DENSITY OF EUCALYPTUS GLOBULUS IN COMMERCIAL PLANTATIONS

Eucalyptus globulus trees, 15 years old, were sampled at different heights from commercial pulpwood plantations in two sites in Portugal. Bark thickness was higher in the site with better growth and always decreased from the tree base to the top. Bark content was site independent and on average 11% of stem dry weight, higher at the base and top, and lower at 35% height level.Tree mean wood basic density averaged 600 kg /m3 and 568 kg /m3 for best and worst site, respectively, and was not correlated with tree growth. Wood density increased from base to top of the tree. Between-tree variation was low with coefficients of variation of site mean below 10%. Bark density (374 kg /m3 and 454 kg /m3 for best and worst site, respectively) did not show significant within tree variation. Average tree wood density could not be predicted with reasonable accuracy using a breast height sampling and better results were obtained using a sampling as a percentage of total height (e.g. 15%).

Within-tree variation in phloem cell dimensions and proportions in Eucalyptus globulus.

The axial variation of bark thickness and quantitative anatomical features of Eucalyptus globulus bark were analysed for one site based on individual measurements of ten 15-year-old trees at six height levels (DBH, 5%, 15%, 35%, 55% and 75% of total tree height). The parameters studied were: length, tangential diameter and percentage of sieve tubes; length, width, cell wall thickness and percentage of fibres; height and percentage of rays; percentage of sclereids in the secondary phloem. Bark thickness decreases from base to top of the tree. Fibre width and wall thickness decrease from base upwards. No distinct axial patterns of variation were observed for the other biometric variables studied. Parenchyma is the main cell type of the bark (50%) followed by fibres (27.9%), rays (12.1%), sieve tubes (2.7%), and sclereids (7.3%). The cell type proportions vary significantly within the tree, i.e., parenchyma, ray and sclereid proportions decrease, fibre and sieve tube proportions increase towards the top of the tree.

Variability of fibre length in wood and bark in Eucalyptus globulus.

Ten trees of Eucalyptus globulus Labill. from three different sites within Portugal were felled at 12–15 years, to study fibre length variation in bark and wood. The fibres of E. globulus were morphologically similar in bark and wood, but generally longer in the bark (on average, 0.97 mm in wood and 1.11 mm in bark). The axial variation was small and opposite in wood and bark; fibre lengths decreased in the wood and increased in the bark from the base to the top. Fibre length in wood increased significantly from pith to bark at all height levels. The measurement of fibre length at 1.3 m height level was representative for the tree average for both wood and bark.

Within-Tree Variation in Wood Fibre Biometry And Basic Density of the Urograndis Eucalypt Hybrid (Eucalyptus Grandis × E. Urophylla)

Within-tree variations in fibre length, width, wall thickness and wood basic density of Eucalyptus grandis × E. urophylla (urograndis) were studied in five 6.8-yr-old seedling trees and five 5.6-yr-old trees from one clone from Brazil. Samples were taken at 5%, 25%, 35%, 55%, 65% and 90% of stem height and five radial positions (10%, 30%, 50%, 70% and 90% of radius). The tree average fibre length, width and wall thickness were in seed and clone trees: 0.955 mm and 1.064 mm, 18 μm and 20 μm, 3.6 μm and 4.4 μm respectively. The axial variation of fibre dimensions was very low, while there was a consistent but small increasing trend from pith to periphery. The basic density ranged from 397–464 kg/m3 to 486–495 kg/m3 respectively in seedling and clone trees with a low variation along the stem. In comparison with other eucalypt pulpwood, e.g. E. globulus, the urograndis hybrid showed similar fibre dimensions and lower basic density. Overall the within-tree variation of these wood properties was low and age had a small impact on the variation of density and fibre dimensions.

Variability of Bark Structure in Plantation-Grown Eucalyptus Globulus

The bark structure of Eucalyptus globulus Labill. grown in plantations in Central Portugal is described, based on specimens extracted at six height levels from ten 15-year-old trees. No significant variation of qualitative features between trees was observed. The non-collapsed phloem is characterised by multiseriate tangential rows of phloem parenchyma alternating with rows of phloem fibres, interspersed with large sieve tubes and their respective companion cells, and uniseriate rays . With the onset of sieve tube collapse (collapsed phloem ), some parenchyma cells expand and sclerify, the course of rays becomes irregular, and ray dilatation is initiated. The periderm is composed of a phellem of lignified cells with horseshoe thickening (phelloids), followed by a layer of cells with suberised tangential walls, and a phelloderm with a variable number of layers of thin-walled cells. Age-related secondary changes give rise to a specific within-tree pattern of axial variation. Both the intensity of sclerification of phloem parenchyma cells and the degree of ray dilatation increase with tree age.

Anatomy and Chemical Composition of Pinus Pinaster Bark

The secondary phloem of Pinus pinaster Aiton bark has sieve cells and axial and radial parenchyma, but no fibres. Resin ducts are present in fusiform rays . Stiloid crystals, starch granules and tannins occur inside sieve and parenchyma cells. The rhytidome of P. pinaster bark has a variable number of periderms forming scale-type discontinuous layers over expanded parenchyma cells. Phellem comprises 4-6 layers of thickwaIled and little suberized cells and phelloderm a layer of 2 or 3 thickened lignified ceIls and a layer of expanded cells.

THE EFFECT OF TREE SHELTER ON THE STEM ANATOMY OF CORK OAK (QUERCUS SUBER) PLANTS

The effect of tree shelter on the growth and anatomy of bark and wood of cork oak (Quercus suber L.) seedlings was evaluated one year after planting. Stem cross sections were examined and percentage of tissues (vessels, axial parenchyma, rays and fibres) and diameter of vessels analysed. The cork oaks responded to the effect of shelter tubes with a 22% increase in apical growth and a 35% decrease in radial enlargement resulting into highly significant differences in the diameter-to-height ratio (0.099 and 0.193 respectively for sheltered and unsheltered plants). The stem anatomy showed adaptations to the protected environment of the shelter: the sheltered plants had a significantly higher percentage of parenchyma (30% vs. 19%, P < 0.001) and lower percentage of wood fibres (40% vs. 47%) compared with unsheltered plants. Annual rings were less clearly visible in the sheltered plants. These observations suggest that trees grown in protective shelters are less able to withstand the environment than those directly subjected to it.

ANATOMICAL CHARACTERISATION AND VARIABILITY OF THE THISTLE CYNARA CARDUNCULUS IN VIEW OF PULPING POTENTIAL

The thistle Cynara cardunculus L. is an herbaceous perennial with high productivity that is harvested annually and is a potential fibre crop for paper pulp production. The anatomical variation within stalks was studied (base, middle and top) and compared in C. cardunculus plants at different development phases. The stalk of C. cardunculus includes an epidermis, cortex and a central cylinder with fibro-vascular bundles with phloem, xylem and a fibrous sheath that is variable in arrangement and size within and between plants.At harvest, the pith represents 37% of the stalk transectional area and 7% of the total weight. There was a slight variation in quantitative features of, respectively, the three development groups studied; mean fibre length was 1.04 mm, 0.95 mm and 1.05 mm; mean fibre width was 15 μm, 16 μm and 21 μm; mean fibre wall thickness was 3.2 μm, 3.4 μm and 4.9 μm. Fibre length and width decreased within the stem from base to top, while fibre wall thickness increased. Mean vessel diameter was 22 μm and mean vessel element length 220–483 μm. In mature plants, parenchyma represents 39% of the total transectional area and fibres 25%. The proportion of fibres increases during plant development and in mature plants is highest at the stalk base.As regards anatomical features, Cynara stalks compare favourably to other annual plants and fibre biometry indicates good potential for paper sheet forming and strength properties.

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.

Characterization of Betula pendula Outer Bark Regarding Cork and Phloem Components at Chemical and Structural Levels in View of Biorefinery Integration

Betula pendula outer bark includes a cork-rich periderm and a rhytidome, including periderm and phloem layers. Cork and phloem from the outer bark were chemically analyzed after fractioning into different particle sizes; coarser fractions were obtained in higher yields. Cork and phloem chemical composition were different: the coarse and medium fractions of cork were enriched in suberin (37.7–38.4%) and lipophilic extractives (31.1%); phloem fractions were enriched in lignin (32.2%) and polysaccharides (43.0%). Lipophilic and suberin extracts were analyzed by GC-MS. Triterpenes constitute the most abundant identified compounds (90.1–97.1% in cork, 76.1–90.2% in phloem), and betulin is the most representative (64.6–70.7%). The majority of the suberin monomers are ω-hydroxyacids, (55.2–83.9%); namely, 9,10-epoxy-18-hydroxyoctadecanoic, 9,10,18-trihydroxyoctadecanoic, and 22-hydroxydocosanoic acids. A chemical valorization of the cork component from B. pendula outer bark as an industrial residue is proposed based on the fractionated production of triterpenoids, suberinic acids, oligo/monosaccharides, and lignin.