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  • Author or Editor: Oliver Dünisch x

Oliver Dünisch

The influence of low night temperatures on the kinetics of tracheid expansion of two-year-old Podocarpus latifolius (Thunb.) R.Br. ex Mirb. was studied in a growth chamber experiment. In experiment 1 the plants were exposed to an almost constant air temperature of 18 to 20°C, while in experiment 2 the air temperature was reduced from 20°C during the day to 6°C during the night. The formation of the cambium derivative cells and the kinetics of tracheid expansion were analysed by high resolution laser increment measurements in combination with microscopic methods (accuracy: ± 2 μm, spatial resolution of 9.7 to 13.1 μm, temporal resolution: 60 s). Low night temperatures had no significant influence on the rate of cambial cell divisions and the proportion of tracheids and parenchyma cells in the xylem. However, they irreversibly interrupted the expansion of differentiating tracheids causing a high proportion of flattened tracheids in the xylem of the plants grown under the conditions of experiment 2. The results indicate that large differences between day and night temperatures can be an important trigger for the variation of the wood structure in subtropical and tropical gymnosperms.

Oliver Dünisch

The influence of swelling on the roughness of rehydrated, machinery-treated wood surfaces of Millettia laurentii De Wild. (Wengé) was studied under controlled climate conditions. The surface roughness of transverse, radial, and tangential planes was quantified by high resolution laserscan measurements with an accuracy of ±2 μm and an optical resolution of 8 × 50 μm. The surface profiles were compared with the anatomical structure of the xylem in the surface layer of the samples. The surface roughness of swollen samples increased significantly compared to unswollen samples. Higher surface roughness was found on swollen radial and tangential planes compared to swollen transverse planes. The high increase in roughness of conditioned radial and tangential planes was due to the higher swelling of tissue zones dominated by fibres compared to zones dominated by axial parenchyma, ray parenchyma, and vessels. In thinner rehydrated samples the surface roughness was lower than in thicker samples. Although the increase of surface roughness of the rehydrated samples was only in the range of 10 to 60 μm in these experiments, the gloss level of rehydrated coated surfaces decreased significantly. The results are discussed with special regard to high quality surface finishing of wooden furniture.

Oliver Dünisch

ABSTRACT

The relationship between the spatial organization of different cell types, of the xylem rays, and of the tree rings and the frequencies in vibrating softwoods and hardwoods was studied under controlled conditions. In total, the frequencies in 1007 standardized vibrating plates from 16 softwoods and 74 hardwoods were analysed using high resolution laser sensors (accuracy ± 0.02 μm, sampling frequency 30 kHz) for vibration measurements. Overlapping frequencies within the frequency spectra were identified by means of Fast Fourier Transformation analysis. With regard to the number of distinct frequencies within the spectra, four different vibration types were identified: type 1–one dominant frequency within the frequency spectra; type 2-two dominant frequencies within the frequency spectra; type 3-three dominant frequencies within the frequency spectra; type 4-no dominant frequencies within the frequency spectra. The presence of distinct frequencies was correlated with a highly organized spatial arrangement of tracheids in softwoods, with a storied arrangement of the xylem rays in hardwoods, and with low variation in tree-ring width in both softwoods and hardwoods. The grid size for repetition in these xylem structures influenced the frequencies of the vibrating wood in absolute numbers. The results indicate that the analysis of the anatomical structure of the wood can contribute to the grading of timber for its vibration characteristics, which is of special interest for the selection of resonance wood for musical instruments.

Oliver Dünisch and Pieter Baas

The anatomy, frequency, and origin of intercellular canals in the xylem of ten Meliaceae species (Carapa guianensis Aubl., Carapa procera DC., Cedrela odorata L., Cedrela fissilis Vell., Entandrophragma cilindricum Sprague, Entandrophragma utile Sprague, Khaya ivorensis A. Chev., Khaya senegalensis (Desr.) A. Juss., Swietenia macrophylla King, Swietenia mahagoni (L.) Jacq.) were investigated using 327 samples from institutional wood collections, 398 plantation grown trees, and 43 pot cultivated plants. Tangential bands of intercellular canals and single canals were found in the xylem of all ten species. Staining of microtome sections indicated that the chemical composition of the secretion is similar to that of “wound-gums”. Studying the origin of the intercellular canals along the stem axis, it became obvious that the formation of the canals can be induced by wounding of the primary meristems (in particular by insect attacks of Hypsipyla spp., wounding of root tips) and by wounding of the cambium (formation of 43–100% of the intercellular canals). In fast growing trees of Carapa spp., Entandrophragma utile, and Khaya ivorensis, planted at an experimental site near Manaus, Brazil, numerous canals were found which were not induced by wounding of the meristems. In these trees an out of phase sequence of xylem cell development and high growth stresses were observed, which are hypothesised to be a further trigger for the traumatic formation of intercellular canals.

Josef Bauch and Oliver Dünisch

This study responds to the demand for recultivation of degraded land areas in Central Amazonia and the desire to add long-lived trees for high-quality timber production to polyculture plantation systems. Carapa guianensis Aubl. from two monocultures (ages 4 and 17 years) and a primary forest were studied. The growth dynamics of the 4-yearold trees revealed 11 to 15 increments marked by tangentially oriented vessel rows. By the 5th year, parenchyma bands indicate mature wood. Monthly labelling by pin-markers revealed short dormancy periods during the dry season. The early formation of mature wood is shown by the pattern of percentage composition of vessels, fibres, and parenchyma. Fibre length reaches its plateau of 1.45–1.59 mm at about four years. Fibre lengths and average density (0.63 g /cm3) of plantation-grown trees correspond to those of primary forest trees. According to this study, Carapa guianensis can be recommended for plantations in order to produce high-quality timber with a decorative heartwood.

Oliver Dünisch

The influence of cell type and cell arrangement on the vibration characteristics of 91 softwood and hardwood species was studied under controlled conditions. The vibration of standardized wood plates was measured by means of high-resolution laser sensors with an accuracy of ± 0.02 μm and a sampling frequency of 30 kHz. First and second order waves within the vibration spectra were identified by Fast Fourier Transformation analysis. The amplitudes, the frequencies, and the duration of the waves of the 91 timber species were compared by means of principal component analysis. Special attention was paid to the influence of tracheids, vessels, storied rays, growth rings, and the anatomical direction of the wood on the vibration spectra. Due to significant differences in vibration between samples on which the vibration was induced in the transverse, radial, and tangential plane, a comparison between tree species was only possible if plates with precise and identical orientation of the grain were used. In plates with exactly oriented surfaces along the radial plane, distinct vibration characteristics were found in timber species with tracheids as ground tissue (softwoods), in timbers without distinct growth rings, and in timbers with storied rays. In contrast, no relationship was found between the arrangement of the vessels, the width of the xylem rays and the vibration characteristics of hardwoods.

Oliver Dünisch, Josef Bauch and Luadir Gasparotto

The pattern of growth increment zones, the cambial growth dynamics and the structural variation in wood formation of Swietenia macrophylla King, Carapa guianensis Aubl., and Cedrela odorata L. (Meliaceae) were investigated in order to understand the relationship of site conditions and sustainable growth in Central Amazonian plantations. Trees were available from 8-, 17-, 23-, and 57-year-old plantations, and from primary forests in Manaus (Amazônia), Santarem (Pará), and Aripuanã (Mato Grosso). The wood anatomical structure and the annual increments of 61 Swietenia, 94 Carapa, and 89 Cedrela trees were studied for different tree heights. The curves of annual increments were cross-dated and tested for synchronisation. The cambial growth dynamics of up to 52 trees per species were dated by means of dendrometer measurements, monthly labelling by pinmarkers, and extracted cambium samples investigated using a microscope. The intraannual course of the growth and structural variation was compared with the water supply of the soil and insect attacks (Hypsipyla grandella (Zeller) Lep.).

In Swietenia and Carapa parenchyma and vessel bands as well as bands of resin canals were observed. Within the xylem of Cedrela, alternating bands of fibres and vessels surrounded by paratracheal parenchyma were found; bands of resin canals were only occasional. In the juvenile wood of Swietenia and Carapa no synchronization of the increment curves was possible, whereas the increment curves obtained in the juvenile wood of Cedrela showed parallel run in growth. The increment curves obtained in adult wood of Swietenia and Cedrela indicate an annual formation of increment zones, whereas the number of increment zones in the xylem of Carapa was approximately 50% higher than the tree age (years) indicating that the growth increments of Carapa also were not annual during the adult phase of growth.

The study of the intraannual growth dynamics of the trees showed that the formation of parenchyma bands in Swietenia is induced by dry periods before a cambial dormancy. The formation of parenchyma bands of Carapa was induced by extremely dry and extremely wet periods before a cambial dormancy, whereas fibre bands in Cedrela were induced by dry periods before a cambial dormancy and the formation of vessel bands embedded in paratracheal parenchyma was induced by wet periods after a cambial dormancy. In addition, insect attack (Hypsipyla grandella) induced locally restricted formation of parenchyma bands and bands of resin canals in Swietenia, Carapa and Cedrela.

Oliver Dünisch, Carlos Bruno Reissmann and Afonso Oliszeski

In this study the wood anatomy of two leaf-morphotypes (“Yellow” and “Grey”) of Ilex paraguariensis St. Hil. (Aquifoliaceae) from South Brazil was compared with special attention to vessel attributes and a possible relationship of leaf morphology and wood structure. Sampling was carried out in a 15-year-old plantation in the state of Paraná, South Brazil. The anatomy of the juvenile and mature wood of five male and five female plants of each morphotype was investigated by light microscopy. In all plants the increment and the proportion of vessels decreased from pith to cambium, while vessel element length increased. Plants of the morphotype “Grey” had shorter vessel members (157–382 μm) and a lower number of bars per perforation plate (14–15) compared to the plants of the morphotype “Yellow” (vessel member length: 304–567 μm, bars: 22–24). No significant differences were found between the wood of male and female plants.