Basal sweep and compression wood in young Scots pine trees

This study demonstrates the correlation between stem form and compression wood content in 36 sampled trees from a 6-yr-old container grown Scots pine ( Pinus sylvestris L.) plantation in central Sweden. Root analyses were carried out to examine causes for the high incidences of basal sweep. On the sampled trees basal sweep, stem sweep and maximum bow-height were measured. Discs were cut at different heights and the compression wood content was analysed using digital image analysis. Pith eccentricity and out-of-roundness were calculated for each disc as well as per stem. Compression wood and pith eccentricity was most pronounced near the stem base, where sweep tends to be high. In general, pith eccentricity increased with degree of basal sweep. As a conclusion, expression of basal sweep can be used to predict compression wood content in young Scots pine trees. This study also shows the importance of anchoring of a tree to prevent basal sweep formation due to instability.     

Righting response of artificially inclined maritime pine (Pinus pinaster) saplings to wind loading

To determine if trees respond to dynamic and static loading in the same manner, 2-year-old maritime pine (Pinus pinaster Ait.) trees were subjected to different types of mechanical loading in the field. One block of trees (the control) were kept in pots and planted in the field at an angle of 0 or 45 degrees to the vertical. A similar block of leaning potted trees was planted nearby and subjected to frequent, unilateral wind loading for a period of 1 s every 2 min. Half the leaning trees were oriented toward the direction of wind loading and half were oriented along the axis of wind loading. The stem profile was measured three times during the growing season to quantify the rate of stem straightening. Compression wood formation and stem shape were measured in all plants. No differences in mean height or diameter were observed between blocks and all leaning trees straightened, but not at the same rate. Although no difference in the rate of apical straightening occurred between control and wind-treated trees, the righting response of the basal part of the stem of leaning trees subjected to wind was four times greater than that of leaning trees without wind. No differences in the righting response were observed between leaning trees growing toward and trees growing away from the source of wind. No significant differences in compression wood formation were found between control trees and wind-treated trees, indicating that other factors must determine the reorientation rate of leaning trees. Results are discussed with reference to the quality of compression wood in conifers and the mechanotransductive pathway in plants.     

Gravimorphism in current-year shoots of Abies balsamea: involvement of compensatory growth, indole-3-acetic acid transport and compression wood formation

We investigated the cause of gravimorphic growth inhibition in current-year shoots of balsam fir (Abies balsamea (L.) Mill.) seedlings displaced from their normal orientation in the gravitational field. Tilting the main stem of seedlings decreased shoot elongation, cambial growth as measured by tracheid production, and leaf dry weight of the terminal shoot and the lateral shoots on the lower side of the tilted stem. Removing either the terminal shoot or all lateral shoots induced compensatory growth in the remaining shoots, but did not reduce the inhibitory effect of tilting on shoot growth. Bending the apical part of a tilted main stem to restore it to the vertical did not fully reverse the inhibition of terminal shoot growth caused by stem tilting. Stem tilting inhibited cambial activity at the base of decapitated terminal shoots treated apically with indole-3-acetic acid (IAA) and decreased the basipetal transport of a [1-(14)C]-IAA pulse. Stem tilting also induced compression wood formation on the lower side of the tilted stem. Compression wood formation was associated with increases in cambial activity and stem respiration. Stem tilting did not affect either the net photosynthetic rate in 1-year-old leaves or the xylem water potential in current-year lateral shoots. These results support the hypothesis that gravimorphic growth inhibition in a current-year shoot on a tilted stem involves reductions in (1) the shoot's capacity to export IAA, and hence to mobilize photoassimilates, and (2) the supply of photoassimilates available for import by the shoot, as a result of increased cambial sink activity associated with compression wood formation outside that shoot.     

Stem deformation in young plantations of black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.) in the boreal forest of Quebec,Canada

Stem deformation has often been observed in young black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.) plantations. Whenever important stem deformations are observed at the time of harvesting, timber value is negatively affected especially during the wood transformation process. The present work was undertaken to quantify and qualify the importance of stem deformation of black spruce and jack pine in the boreal forest of central Quebec at the stand and tree levels. In 30 black spruce and jack pine plantations, approximately 22% of spruce trees and 27% of pine trees exhibited stem deformation. The proportion of deformed trees was higher in the youngest plantations and decreased with the age of the plantations. Stem deformation caused the formation of compression wood which is another factor that can reduce the value of wood products. Thirty-nine black spruces and 34 jack pines were analysed at the tree level. On average, compression wood represented 14% and 20% of stem volume in 7- and 10-year old black spruce plantations, respectively. These proportions ranged from 18% in the youngest jack pine plantation to 26% in the oldest one. Stems of both species classified as normal contained a lower volume of compression wood than stems classified as deformed or very deformed. Annual percentages of compression wood and annual shoot length increased significantly with tree age (p < 0.0001 for both variables). Statistically significant correlations were also found between the range of displacement of the stem and the percentage of compression wood. The fewer number of trees with deformed stems in older plantations combined with high compression wood formation suggests that, over time, a deformed tree can become normal and straight in appearance.     

Differential expression of genes encoding cell wall proteins in vascular tissues from vertical and bent loblolly pine trees

Differential expression of cell wall proteins during plant development and in response to biotic or abiotic stress suggests that these proteins may contribute in different ways to plant cell wall architecture. Because the wood of loblolly pine (Pinus taeda L.) is highly specialized in the formation of secondary cell walls, it is an ideal tissue for studying these proteins. The cDNAs coding for six novel cell wall associated proteins, as well as a homologue for a phytocyanin, were identified and characterized from differentiating xylem of loblolly pine. Three of these cDNAs encoded new putative loblolly pine arabinogalactan proteins, based on their structural similarity to classical arabinogalactan proteins (AGPs). In addition, one clone was related to the proline-rich protein group and the other two to the glycine-rich protein group and the mussel adhesive protein. Relative expression of these genes was examined in different tissues and organs from normal trees (needles, phloem and vertical wood), the underside of bent trees (compression wood) and the lateral sides of the bent stems (side wood). All clones, except one, were highly expressed in vascular tissues with noticeable differences among the three types of wood. Their relationships and diversity provide the first insights into concerted expression and related function for this important group of proteins in cell wall formation of wood.     

A. Study of Compression Wood in Scots Pine (Pinus silvestris L.): With I Plate

The incidence of compression wood was studied in 24–40-year-oldScots pine plantations. It was found that compression wood distributionin trees depended on type of stem curvature and was associatedwith their attempts to correct stem inclination. Compressionwood volume percentage was not closely related to extent ofstem curvature but was highly correlated with compression woodpercentage in the tree at breast height or 10 feet. There wassignificantly less compression wood near the butt than at higherlevels. In stands examined, compression wood formed 20–40per cent, of the standing volume. The prevailing wind appearedlargely responsible for the initial development of stem inclinationand consequent compression wood formation. Provision of shelterduring establishment should reduce compression wood developmentin second rotation crops.     

Effects of phloem girdling in conifers on apical control of branches, growth allocation and air in wood

We investigated effects of stem phloem girdles on apical control of branch angle, stem and branch growth and stem air content in six conifer species. A stem girdle 2 cm above a branch caused the branch to bend upward in all six species. Upward bending was associated with increased formation and action of compression wood (CW) in the lower portion of the branch. Compression wood also formed in the main stem below the branch, suggesting increased auxin production in the branch. A stem girdle 2 cm below a branch (the branch remained directly connected to the apex and distal branches) released the branch from apical control in Tsuga canadensis (L.) Carr., Pinus contorta Dougl. ex Loud. and Pseudotsuga menziesii (Mirb.) Franco. The branch bent up, but there was no CW formation in the stem. In Pinus rigida Mill., the branch exhibited increased cambial activity but did not bend up. A stem girdle > 20 cm below a branch did not release the branch from apical control in any of the species. These results support the hypothesis that branches compete with the subjacent stem for branch-produced photosynthate and that when the branch lacks this competitive sink it is released from apical control. A stem girdle 2 cm below a branch did not cause release of apical control in either Juniperus virginiana L. or Picea abies (L.) Karst. In these species, decreased shoot elongation and cambial activity above the girdle probably prevented release. A stem girdle 2 cm below a branch increased air content in the stem below the girdle in four of five species, whereas the other girdle treatments had no significant effect on stem air content. Although growth was inhibited above the girdle in the two species with the largest increase in air content, growth was not inhibited in the other species. High air content in stem segments isolated from distal auxin and carbohydrate sources is consistent with the hypothesis that a carbohydrate supply is required to refill embolized cells.     

Photoperiodic control of seasonal development and dormancy in tropical stem-succulent trees

Tropical stem-succulent trees store large quantities of water in their trunks yet remain leafless during the early and mid dry season. In contrast to most other tropical trees, bud break of vegetative buds is not induced in fully hydrated stem succulents between the winter solstice and the spring equinox by leaf abscission, abnormal rain showers or irrigation. Vegetative buds of leafless trees are therefore in a state of endo-dormancy similar to that of temperate perennial plants during early winter. Highly synchronous bud break regularly occurs soon after the spring equinox, often weeks before the first rainfalls of the wet season. These observations suggested that endo-dormancy and bud break might be induced by declining and increasing photoperiods after the autumn and spring equinoxes, respectively. In phenological field observations, we confirmed highly synchronous bud break after the spring equinox in many trees of five stem-succulent species in the northern and southern hemispheres. Shoot growth of potted saplings of Plumeria rubra L. was arrested by a decline in day length below 12 h after the autumn equinox, but continued in saplings maintained in a 13-h photoperiod. Conversely, exposure to a 13-h photoperiod induced bud break of dormant apical buds in saplings and cuttings in January, whereas plants maintained in the natural day length of < 11.7 h remained dormant. Photoperiodic control of endo-dormancy of vegetative buds in stem succulents is thus supported by field observations and experimental variation of the photoperiod. At low latitudes, where annual variation of day length is less than 1 h, bud dormancy is induced and broken by variations in photoperiod of less than 30 min.     

Effect of thinning on the development of compression wood in stems of Corsican pine

This study considered the effects of thinning on the development of compression wood in stems of 35-year-old stand of Corsican pine (Pinus nigra L.). Part of the stand had been thinned at 5-yearly intervals and part left unthinned. Twenty trees each from the thinned and unthinned stands were randomly selected and felled. Measurements were made on tree height, stem diameter, stem slenderness and canopy depth. Wood samples were removed from the central part of the main log and cross-sectional measurements made on ring width, basic density and compression wood content. Cross-sectional area of compression wood was found to be three time higher in stems from the unthinned trees in comparison with those from the thinned trees. No significant differences in mean radial ring width or basic density were found between treatments. Correlations indicated that, with increasing in stem diameter, compression wood content increased in the unthinned trees, while a decline in compression was observed in the thinned trees. Tree height was also positively correlated with compression wood content in unthinned trees, while no equivalent relationship was observed in thinned trees. Observations from this study, while not conclusive, suggest that phototropic stimulus may be producing stem inclinations in the unthinned stand as trees compete for space in the canopy, whereas crown competition has been largely eliminated in the thinned stand; and that this is responsible for compression wood levels recorded in this study.     

Formation and structure of reaction wood in Buxus microphylla var. insularis Nakai

Summary Anatomical differences in xylem between the upper and lower sides formed in the inclined stems of Buxus microphylla with different angular displacement from the vertical were examined microscopically. B. microphylla exhibited a pronounced growth promotion on the lower side of the inclined stems. Formation of tension wood (gelatinous fibers) was not observed. Xylem formed on the lower side showed some interesting features resembling the compression wood formed in gymnosperms. The reaction wood tracheids and vessels showed an excessive lignification in their secondary walls but lacked both helical cavities and an S₃ layer, features that were almost the same as those of primitive gymnosperms. These results indicate that B. microphylla has an ability to form compression wood, suggesting that in the genus Buxus a different mechanism in the conducting elements was developed in the phylogenetic evolution.The first author would like to express his sincere thanks to Dr. T. E. Timell, College of Environmental Science and Forestry, State University of New York, Syracuse, New York, for his invaluable suggestions in connection with this research     

Patterns of tree growth in a single tree selection silver fir–European beech forest

The basal area and height growth of trees and saplings in silver fir–European beech single stem selection forest were studied with regard to their social status and crown parameters of size, coverage, shading and vitality. On 24 permanent research plots (20 m × 20 m each) all trees [diameter at breast height (dbh) ≥10 cm] and saplings (≥1.3 m tall and dbh <10 cm) were surveyed. Repeated measurements of dbh (N = 1,608) and height (N = 1,135) 10 years apart enabled the calculation of annual basal area increment (BAI) of trees and saplings, and annual height (HI) increment of saplings. To obtain the growth characteristics for individual trees and saplings, their social status and crown parameters were assessed by rank. In the multivariate general linear model for BAI, social status, crown size and crown coverage of individuals as the predictors, and dbh² as the covariate, explained 70% of total variability. Similarly, social status, crown size, crown coverage and crown shading had a significant impact on the HI of saplings, explaining 70% of total variability. Among the observed variables, social status determined according to the individual’s position in vertical stand structure was, in addition to dbh, the most important predictor for both BAI and HI. Significant differences were observed between the BAI and HI models for the main tree species (European beech and silver fir), indicating their different growth characteristics. The applied method could be used as a supplement to the more widely used approaches for studying basal area and height growth of individual trees in selection forest stands.     

An investigation of the influence of selected factors on the properties of spruce wood

Thirty Norway spruce trees (Picea abies (L.) Karst.) from the forest district of the ETH Zurich were tested for bending MOR, static MOE of bending and dynamic MOE (calculated from eigenfrequency and sound velocity). The specimens were clear and were sampled from the whole of the stem. Their correlations to density, annual ring width, height in the tree, distribution over the stem diameter and the percentage of compression wood were statistically analysed. All three elasticity modules and the maximal stress can be very well predicted from a linear function of the sample density with a common gradient across the compression wood values but with different intercepts that decrease with increasing compression wood content. The other variables have highly significant impacts on the response variables too, however, this is largely irrelevant for the goodness of fit. Further, a clear increase of density, of MOE and of bending MOR was measured from pith to bark and similarly with decreasing annual ring width. Concerning the height of the stem, no distinct trend for the mechanical properties could be found.     

Growth strain in the trunk and branches of Chamaecyparis formosensis and its influence on tree form

Distributions of growth strains in branches, straight trunks and basal sweeping trunks of Chamaecyparis formosensis Matsum. trees were measured with strain gauges. Microfibril angles (MFAs) of the S2 layer of the cell wall were measured by the iodine deposition method and their relationships with growth strain examined. The magnitude of the compressive stress on the lower side of trunks with a basal sweep was greater than that of the tensile stress at the surface of straight trunks. However, transverse compressive stress was similar around the trunk regardless of whether normal wood or compression wood was present. The released surface growth strains varied with MFA. At MFAs of 20-25 degrees , growth stress changed from tension to compression, and compressive stress increased dramatically in the compression wood region. Branches suffer bending stress due to self-loading. This stress is superimposed on the growth stress. Growth strains on the upper or lower sides of branches were larger than those in the trunks, suggesting that generation of growth stress on the lower sides of branches with extensive compression wood is affected by the gravitational bending stress due to self-loading. We conclude that branch form is affected by the interaction between the bending moment due to self-loading and that due to the asymmetric distribution of growth stress. Growth strain distribution in a branch differed depending on whether the branch was horizontal, upward bending or downward bending.     

Age- and position-related changes in hydraulic versus mechanical dysfunction of xylem: inferring the design criteria for Douglas-fir wood structure

We do not know why trees exhibit changes in wood characteristics as a function of cambial age. In part, the answer may lie in the existence of a tradeoff between hydraulic properties and mechanical support. In conifers, longitudinal tracheids represent 92% of the cells comprising the wood and are involved in both water transport and mechanical support. We used three hydraulic parameters to estimate hydraulic safety factors at several vertical and radial locations in the trunk and branches: vulnerability to cavitation; variation in xylem water potential (psi); and xylem relative water content. The hydraulic safety factors for 12 and 88 percent loss of conductivity (S(H12) and S(H88), representing the hydraulic safety factors for the air entry point and full embolism point, respectively) were determined. We also estimated the mechanical safety factor for maximum tree height and for buckling. We estimated the dimensionless hydraulic and mechanical safety factors for six seedlings (4 years old), six saplings (10 years old) and six mature trees (> 110 years old) of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Over the natural range of psi, S(H12) decreased linearly from treetop to a minimum of 0.95 at the tree base. Young and mature trees had S(H12) values 1.4 and 1.3 times higher, respectively, at their tips (juvenile wood) than at their bases (mature wood). Modeling analyses indicated that if trees were made entirely of mature wood, S(H12) at the stem base would be only 0.7. The mechanical safety factor was 1.2 times higher for the base of the tree than for the rest of the tree. The minimum mechanical safety factor-1.6 for the critical buckling height and 2.2 for the critical buckling load-occurred at the base of the live crown. Modeling analysis indicated that if trees were made only of mature wood, these values would increase to 1.7 and 2.3, respectively. Hydraulic safety factors had values that were less than half those for mechanical safety factors, suggesting that wood structure in Douglas-fir has evolved primarily as a result of selection for hydraulic safety rather than mechanical safety. The results suggest that forest managers must consider the role of juvenile wood in tree physiology to avoid producing plantations vulnerable to drought.     

Ethylene and tension wood formation in Eucalyptus gomphocephala

Summary Eucalyptus gomphocephala A.DC seedlings grown horizontally for 103 days had less terminal shoot elongation and higher internal and emanated ethylene levels in the basal portion of the stem than seedlings grown vertically under otherwise identical conditions. Horizontal seedlings had greater radial growth in the upper stem half than in the lower half of the basal portion of the stem. Upper halves contained 60–80 percent tension wood by volume, lower halves 0–10 percent tension wood. Radial growth in vertical seedlings was symmetrical, and they contained negligible tension wood. Upper halves of the basal portion of the stem of horizontal seedlings had greater amounts of internal and emanated ethylene than lower halves and vertical seedling halves. Ethylene differences between random halves of vertical seedlings were smaller than differences between upper and lower halves of horizontal seedlings. The data suggest an association between increased ethylene levels and tension wood formation.This work was made possible through the award of a Fulbright Postdoctoral Fellowship and an Honorarium to N. D. Nelson by the Australian-American Educational Foundation and CSIRO Division of Building Research, respectively, and is part of a larger body of research by the authors on hormonal aspects of wood quality in rapidly grown Eucalyptus spp. Appreciation is experssed to Peter Fitzgibbon and Jugo Ilic for competent technical assistance.     

Photosynthetic and leaf water potential responses of Alnus glutinosa saplings to stem-base inoculaton with Phytophthora alni subsp. alni

Three-year-old Alnus glutinosa (L.) Gaertn. (alder) saplings were single or double inoculated at the stem base with Phytophthora alni subsp. alni Brasier & S.A. Kirk under natural climatic conditions. Lesion formation on the bark showed a biphasic pattern of development, with extension occurring at a moderate rate in spring, and more rapidly during late summer. However, large variability was encountered in pathogen development within the population of infected saplings, ranging from high susceptibility to almost complete resistance. Infection resulted in severe growth retardation, and death within two years of inoculation in 75% of the saplings. During disease development, rates of transpiration and CO(2) uptake were significantly reduced. Consequently, minimum leaf water potentials were less negative in infected saplings than in control saplings. Surviving saplings matched control trees in photosynthetic capacity, transpiration rate and water potential during the second year of infection. Leaf starch concentration of infected saplings was significantly higher than in control saplings, possibly indicating that the destruction of bark tissue by the pathogen impaired phloem transport from leaves to roots.     

Effect of stand and tree attributes on growth and wood quality characteristics from a spacing trial with Populus xiaohei

The effect of stand density (1000 stems/ha, 500 stems/ha and 250 stems/ha) on tree growth and wood quality characteristics was studied in a 27-year-old plantation species of Populus xiaohei in China. Results indicated that stand density had significant effects on tree radial growth and crown size, and the lowest stand density produced trees with the largest stem taper. In terms of wood quality characteristics, there was no significant effect of stand density on either wood basic density or fiber length. However, significant differences were found between different stand densities for wood mechanical properties. A positive relationship between modulus of elasticity, compression strength and stand density was observed, while the highest modulus of rupture was recorded at a moderate density of 500 stems/ha. Stand density was responsible for highly significant effects on both juvenile wood and wet heartwood basal areas in individual trees, and there was an obvious tendency towards increasing juvenile wood and wet heartwood basal areas with decreasing stand density. In addition, the relationships between wood quality characteristics and tree and stand characteristics were also examined. Some wood quality characteristics, namely mechanical properties and juvenile wood and wet heartwood basal areas, were quantified successfully in relation to selected tree characteristics using a regression approach with various degrees of goodness of fit. Based on comprehensive consideration of various factors, such as wood quality, tree growth, and establishment cost, results from this study suggest that a density of 500 stems/ha is optimum for wood production.     

Apical control of branch movements in white pine: Compression wood action

Summary The movements of branches or control stem girdled white pine (Pinus strobus L.) were analyzed using beam theory. The stresses generated in the compression wood (CW) produced bending moments to counter the added bending moments due to new branch growth. The branches on the treated trees produced additional CW after untreated trees stopped elongation and diameter growth. The intensity of the stresses in this additional CW was greater than in the other CW. Thus, branches on treated trees moved up vertically well beyond their initial orientation due to both more CW and more active CW. The branches on untreated trees all deflected downward as branch weight continued to increase after CW production stopped.     

Utilization of polar metabolite profiling in the comparison of juvenile wood and compression wood in loblolly pine (Pinus taeda)

Juvenile wood (JW) of conifers is often associated with compression wood (CW), with which it is sometimes believed to be identical. To determine whether JW and CW can be distinguished metabolically, we compared gas chromatographic profiles of 25 polar metabolites from rooted cuttings of a single loblolly pine (Pinus taeda L.) clone raised in controlled environment chambers and subject to three treatments: (1) grown erect with minimal wind sway (control); (2) swayed by wind from oscillating fans; and (3) with 30-cm growth increments successively bent at an angle of 45 degrees to the vertical. Profiles were compared by principal component analysis. Substantial increases in abundances of coniferin and p-glucocoumaryl alcohol separated immature JW-forming xylem tissues of the control trees from the CW-forming xylem of the bent and swayed trees.