Variations in phenology and growth of European white birch (Betula pendula) clones

Phenology can have a profound effect on growth and climatic adaptability of northern tree species. Although the large interannual variations in dates of bud burst and growth termination have been widely discussed, little is known about the genotypic and spatial variations in phenology and how these sources of variation are related to temporal variation. We measured bud burst of eight white birch (Betula pendula Roth) clones in two field experiments daily over 6 years, and determined the termination of growth for the same clones over 2 years. We also measured yearly height growth. We found considerable genetic variation in phenological characteristics among the birch clones. There was large interannual variation in the date of bud burst and especially in the termination of growth, indicating that, in addition to genetic effects, environmental factors have a strong influence on both bud burst and growth termination. Height growth was correlated with timing of growth termination, length of growth period and bud burst, but the relationships were weak and varied among years. We accurately predicted the date of bud burst from the temperature accumulation after January 1, and base temperatures between +2 and -1 degrees C. There was large clonal variation in the duration of bud burst. Interannual variation in bud burst may have important consequences for insect herbivory of birches.     

Gluability of thermally modified beech (Fagus silvatica L.) and birch (Betula pubescens Ehrh.) wood

Abstract

One of the main disadvantages of wood is hygroscopicity resulting from its polar character. The sorption–desorption of water causes unwanted swelling and shrinkage in wood. Thermal modification substantially reduces this inconvenient feature. Unfortunately, the same chemical changes that reduce water sorption alter the polar character of the material and result in poorer wetting of thermally treated wood by waterborne adhesives. Gluability of thermally modified beech (Fagus silvatica L.) and birch (Betula pubescens Ehrh.) wood with two commercial amino resins, melamine–urea–formaldehyde (MUF) and melamine–formaldehyde (MF), and a two-component polyurethane (PUR) adhesive was investigated. Both wood species were modified according to two temperature regimes: 160°C and 190°C. Shear strengths of the joints were then determined according to EN 205:2003 standard. The results showed that thermally modified beech and birch wood can be effectively glued not only with commercially available PUR adhesives, but also with aqueous MF and MUF resins. The resultant shear strengths of the joints were limited by the strength of the thermally modified substrate.     

Origin of the acetylated structures present in white birch (Betula pendula Roth) milled wood lignin

The occurrence and nature of acetate groups in the milled wood lignin (MWL) isolated from birch (Betula pendula Roth) has been addressed by spectroscopic (2D-NMR) and chemical degradative (derivatization followed by reductive cleavage, DFRC) methods. Considerable amounts of acetate groups were present in the MWL preparation. However, 2D-NMR analysis indicated that the lignin polymer is not extensively acetylated and that the major part of the acetate groups is attached to the xylan moieties present in the MWL preparation. Nevertheless, evidence of the presence of minor acetylation of the γ-carbon of the lignin side chain (<3% of both syringyl and guaiacyl lignin units) was provided by DFRC analysis.     

Properties of white birch (Betula papyrifera) outer bark particleboards with reinforcement of coarse wood particles in the core layer

? This study proposes substituting traditional raw materials in the surface layers of wood particle-boards with the water resistant white birch (Betula papyrifera) outer bark particles, which can help improve the dimensional stability of manufactured mixed particleboards, thereby alleviating shortages of raw material in a cost-efficient manner.

? Mixed particleboards were fabricated in the laboratory using untreated or alkali treated white birch outer bark particles as substitute material. These particles were resinated successively with three percentages of phenol-formaldehyde resin. Overall, the results of this study clearly demonstrate that the panels could be manufactured using up to 45% of the proposed substitute material and still maintain the required mechanical and physical properties.

? Alkali treatment was used to remove natural wax from bark particles surface which hinders resin adhesion. This treatment negatively affected mechanical and physical properties of finished panels and the variation of phenol-formaldehyde resin percentage in the bark particles significantly affected only their hardness.

? Panel with untreated bark particles in the surface layers, resinated with 5% phenol-formaldehyde resin was selected as the best with the help of a statistical analysis carried out in a factorial complete block design, especially from the dimensional stability criterion.

     

Seasonal and within-stem variations of neutral lipids in silver birch (Betula pendula) wood

Neutral lipids were analyzed in stem wood of a 7-year-old clone and in five 35-70-year-old mature trees of silver birch (Betula pendula Roth). In young trees and in mature wood of old trees, the free fatty acid fraction comprised less than 5% of the concentration of triacylglycerols (TG). The concentration of free linoleic acid was lowest in March when the young trees were dormant and highest during midsummer and September. In mature trees, the TG concentration increased toward the pith, indicating that living parenchyma cells close to the pith have a large TG storage capacity. The TG concentration (mean 0.51 +/- 0.02% of wood dry mass) remained constant throughout the year in young trees, whereas the concentration of beta-sitosterol, the dominant free sterol (mean 82.5 +/- 0.4% of total free sterols), decreased during spring and early summer when the temperature gradually increased, and increased during autumn when the trees became dormant. In young trees, we detected a seasonal interconversion between the free and esterified forms of beta-sitosterol and campesterol, and within the steryl ester fraction between squalene and betulaprenol-7. The concentration of esterified sterols/isoprenoids was exceptionally high, especially in the inner regions of mature stem wood (mean 0.6 +/- 0.03% of wood dry mass). No heartwood formation was detected.     

Early developmental responses of mountain birch (Betula pubescens subsp. czerepanovii) seedlings to different concentrations of phosphorus

Phenolic compounds, identified by high performance liquid chromatography (HPLC), and growth were investigated in the first true leaves, cotyledons, stems and roots of 2.5-week-old seedlings of mountain birch (Betula pubescens subsp. czerepanovii (Orlova) H?metahti) grown with 1.5, 15 and 50 ppm phosphorus (P). Phenolic compounds in seeds and unfertilized 6-day-old seedlings were also studied. Seeds contained few phenolics, but had an abundance of condensed tannins. There were fewer HPLC phenolic compounds in 6-day-old seedlings than in 2.5-week-old seedlings. In 2.5-week-old seedlings, growth of the first true leaves, but not of other plant parts, was affected by P regime. In the first true leaves and stems, the concentration of condensed tannins was significantly affected by P, being higher at 1.5 ppm than at higher concentrations. The concentration of total HPLC phenolics was significantly affected by P only in stems.     

Temperature sum accumulation effects on within-population variation and long-term trends in date of bud burst of European white birch (Betula pendula)

Within-population variation in phenology of boreal trees indicates their adaptability to climatic variations. Although interannual variations in date of bud burst have been widely discussed, little is known about within-population variation, the key determinants for this variation and the effects of this variation on estimates of trends in bud burst date. Over a period of nine years, we monitored timing of bud burst daily in 30 mature white birch (Betula pendula Roth) trees in a naturally regenerated stand. Our results revealed not only large interannual variation but also considerable intraannual variation among individual trees in date of bud burst, the maximum within-population variation being four weeks. Bud burst can be accurately predicted by the date when a threshold value of temperature sum in spring is reached (base temperature +5 degrees C). Based on this temperature sum and past temperature records, we estimated the trend in date of bud burst. The linear trend estimate based on the years 1926-2005 is an advancement of 1.2 days per decade (95% confidence interval, +/- 0.7 days), which is much less than that predicted by time series based on coarser time intervals. We conclude that, because of large interannual differences, and large annual within-population variations in bud burst, estimates of bud burst date based on measurements made over a period of only a few decades are unreliable.     

Current growth differences of Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and birch (Betula pendula and Betula pubescens) in different regions in Sweden

Abstract

The choice of species in forestry is important, and a real issue as large areas of wind-damaged forest land in southern Sweden need to be regenerated. To compare the growth potential between the most common tree species in Sweden, ratios between site quality derived from site index values determined with site properties were used. A regression function to determine site index for birch from site properties was used to complement the known relationships between site properties and site index for spruce and pine. In large regions of Sweden the distribution of site quality classes was calculated to compare the special characteristics and demands of the three species. On average, the growth difference for pine compared to spruce was about 60% in southern Sweden and 95% in northern Sweden. Corresponding figures between birch and spruce were 40% and 60%. Birch was expected to produce around 60% of pine in northern Sweden and about 70% in southern Sweden. However, it must be stressed that the comparison is based on survey data encompassing mainly naturally regenerated birch, whereas spruce and pine are mainly planted.     

Characteristics of normal and discoloured wood of Ilomba (Pycnanthus angolensis Exell)

Summary In the West African Ilomba wood (Pycnanthus angolensis Exell) discolourations frequently develop after felling, which lead to serious degradation with regard to utilization. Therefore, structure and chemical composition of normal and discoloured wood were investigated in order to characterize the original wood and give a detailed account of the reactions which lead to discolourations. According to the results Ilomba, in normal condition, is all sapwood, which explains its high reactivity. The species does not have the ability to develop heartwood; only false heartwood is formed, initiated by exogenous influences. Discolourations arising in the wood after felling are reddish-brown, due to the deposition of extraneous compounds in the lumina of the ray cells. Soluble sugars disappear and the permeability decreases as a result of tyloses development. From discoloured wood only 60% of extraneous compounds could be extracted as compared to the normal sapwood, thus indicating that polymerisation of extraneous compounds takes place. Discoloured wood appears even more susceptible to decay than the bright sapwood. The pH-value increases from about 5.5 to 7.5 during discolouration, and bacteria present within the reddish-brown zones are involved in that process.We are indebted to Mrs. R. Endeward for assistance in the experimental work, to Prof. N. Parameswaran for support in the REM work, to Fa. Bernhard, Wangen and to Mr. K.-G. Dahms, Hamburg, for the supply of Ilomba wood. Acknowledgement is given to Deutsche Forschungsgemeinschaft for financial support     

Effects of winter temperatures on two birch (Betula) species

In Massachusetts, low winter temperatures delay the onset of flowering in black birch (Betula lenta L.), but not in gray birch (B. populifolia Marsh.). During the winter of 2006, male inflorescences and twigs of black birch had higher water contents than those of gray birch, and the inflorescences of black birch experienced greater frost kill than those of gray birch. Vessels diameters were greater in black than in gray birch, a difference associated with a higher incidence of winter xylem embolism, as indicated by reduced xylem hydraulic conductance. In both species, recovery of hydraulic conductance in twigs that survived the winter coincided with the development of root pressure. Frost kill to male inflorescences or associated damage to plant tissues may account for the difference between species in the effect of winter temperature on the time of first flowering. In a comparison of 24 birch species, sensitivity of the first flowering date to temperature was also correlated with water content in male inflorescences.     

Genetic transformation of silver birch (Betula pendula) by particle bombardment

We used in vitro callus and shoot cultures as target material for genetic transformation of silver birch (Betula pendula Roth) by particle bombardment. Cultivation of in vitro shoot cultures before particle bombardment and a long selection period, combined with a high concentration of selective agent after bombardment, led to the production of transformed plantlets that were stable, and no escapes were found among the tree lines produced. Clonal variation in transformation efficiency was found in transient expression of the beta-glucuronidase gene in callus cultures and in plantlets transformed by stable integration of the ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit (RbcS) and neomycin phosphotransferase (npt2) genes.     

Influences of anthropogenic disturbances on the dynamics of white birch (Betula platyphylla) forests at the southern boundary of the Mongolian forest-steppe

We investigated the effects of disturbances on the dynamics of white birch-dominated forests at the southern boundary of the Mongolian forest-steppe. Dendroecological techniques were used to assess regeneration patterns and recent mortality trends in three stands with no evidence of recent anthropogenic disturbance (undisturbed) and four stands with evidence of cutting or fire (disturbed). In the undisturbed stands, only one distinct stem establishment was observed in the period between 1910 and 1950, and no establishment has been observed since then. In the disturbed stands, however, high establishment mainly by sprouting was observed in the period between 1960 and 1980. Percentages of standing dead stems were higher in the undisturbed stands than in the disturbed stands. Mean ages at death in the undisturbed stands were ≥70 years old. The high mortality was likely induced by the death of smaller stems due to light competition, whereas the mortality of larger stems was likely the result of tree senescence. In summary, the undisturbed stands seem to be in danger of decline due to a lack of regeneration during the last half of the previous century and recent high mortality rates of older stems, while the disturbed stands may be maintained for the next several decades by the younger cohort established between 1960 and 1980. White birch-dominated forests at the southern boundary of Mongolian forest-steppe have probably relied on relatively short disturbance intervals in the past because of the disturbance-dependent regeneration trait and relatively short longevity of Betula species.     

Twilight far-red treatment advances leaf bud burst of silver birch (Betula pendula)

Bud development of boreal trees in spring, once initiated, is driven by ambient air temperature, but the mechanism triggering bud development remains unclear. We determined if some aspect of the diurnal or seasonal light regime influences initiation of bud burst once the chilling requirement is met. We grew 3-year-old birch plantlets cloned from a mature tree of boreal origin in light conditions realistically simulating the lengthening days of spring at 60 degrees N. To emulate the reduction in red to far-red light (R:FR) ratio between daylight and twilight, one group of plantlets was subjected to reduced R:FR ratio in the morning and evening in addition to progressively lengthening days, whereas the other group was subjected to the same R:FR ratio throughout the day. The reduced R:FR ratio of twilight advanced bud burst by 4 days compared with the reference group (P = 0.04). To assess the interplay between the fulfillment of the chilling requirement and the subsequent response to warming, we fitted a thermal time model to the data with separate parameterizations for the starting dates of heat sum accumulation in each treatment. Least-squares fitting suggested that bud development started in light regimes corresponding to late March, almost two months after the chilling requirement for dormancy release was satisfied. Therefore, shortening night length or increasing day length, or both, appears to be the cue enabling bud development in spring, with twilight quality having an effect on the photoperiodic response. If twilight alone were the cue, the difference in bud burst dates between the experimental groups would have been greater than 4 days. The result gives experimental support for the use of thermal-time models in phenological modeling.     

Effect of high temperature treatment on the mechanical properties of birch (Betula papyrifera)

The thermal treatment of wood is an alternative to the chemical treatment for preservation purposes. The heat treatment process improves wood’s resistance to decay and its dimensional stability. However, mechanical strength decreases as a result of heat treatment. Therefore, the treatment parameters have to be optimized to keep this loss at a minimum while improving other properties. Thermal treatment is new in North America, and its parameters are not yet adjusted for the Canadian species. Carrying out the parameter adjustment in an industrial furnace requires many trials which are costly in terms of material and man-power. A laboratory study was carried out to determine the effect of different parameters of the heat treatment on the mechanical properties of birch in order to optimize this process. A thermogravimetric analyzer was built to carry out the laboratory tests. The impact of the process parameters–such as maximum treatment temperature, holding time at this temperature, heating rate, and gas humidity–on the mechanical properties of birch was investigated. Temperature distributions in wood and in gas as well as the weight loss of wood were measured during the experiments. Afterwards, hardness, modulus of elasticity, modulus of rupture, and resistance to screw withdrawal of the samples were measured. The relation between the process parameters and the resulting mechanical properties was examined.     

Isolation of genes up-regulated by copper in a copper-tolerant birch (Betula pendula) clone

Suppression subtractive hybridization (SSH) was used to isolate genes differentially expressed following exposure to copper (Cu) in a naturally selected Cu-tolerant birch (Betula pendula Roth.) clone originating from a disused lead/zinc smelter. Of the 352 cDNA fragments initially isolated, 108 were up-regulated by Cu, of which 55 showed over twofold induction by macroarray analysis. Searches against protein databases (Blastx) and sequence analysis provided the tentative identity of 21 genes. Three fragments lacked homology to any sequences in the databases. Most of the identified genes are involved in cellular transport, regulation or cell rescue and defense. Several genes have not previously been reported to be up-regulated by Cu, e.g., plasma intrinsic protein 2, glutamine synthetase and multi-drug resistance-associated protein (MRP4). The expression of MRP4, a vacuolar sorting receptor-like protein and an unidentified gene was studied in more detail by quantitative real-time PCR. These genes showed stronger up-regulation by Cu in the roots and shoots of the Cu-tolerant birch clone compared with a less tolerant clone. Clear clonal differences in gene expression were observed, e.g., for the regulator of chromosome condensation family protein, DnaJ protein homolog, vacuolar sorting receptor-like protein and MRP4. These findings contribute to our understanding of Cu tolerance in birch, a pioneer plant in metal-contaminated soils.     

Photosynthesis and canopy characteristics in genetically defined families of silver birch (Betula pendula)

Net photosynthetic rates (A) of leaves in upper and lower crown layers (A(upper) and A(lower)), leaf area index (LAI), mean tilt angle (MTA), several leaf characteristics, and volume growth were observed in fast- and slow-growing families of a 14-year-old full-sib and half-sib family progeny test of Betula pendula Roth. Each measure of net photosynthetic rate was calculated after correcting measured net photosynthesis for the effects of environmental variables. The differences in A(upper) and LAI among families were significant. The proportions of the total variance assigned to family for A(upper), A(lower) and LAI were 33.64, 28.93 and 54.99%, respectively. The mean A(upper) and LAI of the fast-growing families were significantly higher than those of the slow-growing families, whereas the mean A(lower) of the fast-growing families was significantly lower than that of the slow-growing families. There were also significant differences among families in leaf size, leaf shape, and the ratios leaf fresh weight/area and leaf dry weight/area. Between 27.55 and 54.55% of the total variance in these characteristics could be assigned to the family effect. Volume growth was positively correlated with A(upper) and LAI, but it was most strongly correlated with A(upper) x LAI.     

Differential responses of silver birch (Betula pendula) ecotypes to short-day photoperiod and low temperature

We investigated interrelations of dormancy and freezing tolerance and the role of endogenous abscisic acid (ABA) in the development of silver birch (Betula pendula Roth) ecotypes in controlled environments. Short-day treatment induced growth cessation, bud set and dormancy development, as well as initiation of cold acclimation and an increase in freezing tolerance. Subsequent low temperature and short days (12-h photoperiod) resulted in a significant increase in freezing tolerance, whereas bud dormancy was gradually released. The concentration of ABA increased in response to short days and then remained high, but ABA concentrations fluctuated irregularly when the dormant plants were subsequently exposed to low temperature during short days. Although there was a parallel development of freezing tolerance and bud dormancy in response to short days, subsequent exposure to low temperature had opposite effects on these processes, enhancing freezing tolerance and releasing dormancy. Compared with the southern ecotype, the northern ecotype was more responsive to short days and low temperature, exhibiting earlier initiation of cold acclimation, growth cessation and an increase in ABA concentrations in short days, and higher freezing tolerance, faster dormancy release and greater alteration in ABA concentrations when subsequently exposed to low temperature during short days. The rates and extent of the increases in ABA concentration may be related to increases in freezing tolerance and dormancy development during short days, whereas the extent of the fluctuations in ABA concentration may play an important role in enhancing freezing tolerance and releasing dormancy during a subsequent exposure to low temperature during short days.