Stem Wood Density Research Articles

Diversity of deciduousness and phenological traits of key Indian dry tropical forest trees

• In seasonally dry tropical forests deciduousness (leaflessness) is an important strategy of trees to survive in water stress period during summer. Deciduousness is a reflection of interacted effect of seasonal drought, tree characteristics and soil moisture conditions. • The present study aims to document the diversity in leaf pheno-phases in terms of duration of deciduousness (which is reciprocal to growing season length), wood density, leaf mass per area (LMA) and leaf strategy index in 24 important tree species growing in the Vindhyan dry tropical forest in India. • On the basis of phenological observations, the tree species were categorized into two main groups: leaf exchanging species exhibiting overlapping periods of leaf fall and leaf flush, and deciduous species whose timings of leaf flush and leaf fall differ resulting in a time lag (deciduousness) between the completion of leaf fall and initiation of leaf flush. Presence of wide range of deciduousness duration (from ca. a week to 7 months) among dry tropical trees indicates large variations in their growing season length. In the tree species studied, as the duration of deciduousness increased, leaf flushing period decreased significantly but leaf fall period showed little variation. • Differing deciduousness in tree species exhibited substantial differences in their leafing (vegetative growth) pattern, as reflected by ratio of durations of leaf flush to leaf fall (leaf strategy index). Across different species, duration of deciduousness was significantly positively correlated with leaf strategy index, and significantly negatively correlated with both wood density and LMA. • Wide variations in deciduousness, leaf strategy index, wood density and LMA in the 24 species investigated indicate considerable functional diversity in tree species growing in Vindhyan dry tropical region. Variation in seasonal duration of deciduousness among species is reflections of differences in tree functional traits like stem wood density, leaf strategy index and LMA.

The relationship between stem biomechanics and wood density is modified by rainfall in 32 Australian woody plant species

*Stem mechanical properties are critically linked to foliage deployment and growth strategy, yet variation in stem mechanics across species and habitats is poorly understood. *Here, we compared 32 plant species growing across four sites of contrasting rainfall and soil nutrient availability in Australia. *The modulus of elasticity (MOE) and modulus of rupture (MOR) were tightly correlated with dry sapwood density within sites, but species from low-rainfall environments had higher wood density for a given MOE and MOR compared with species growing in high-rainfall environments. The ratio of MOE to MOR was slightly lower for species at low-rainfall sites, suggesting that wood was stronger for a given elasticity. Most species had thick bark, but the mechanical contribution of bark to stem MOE was small. *Our results suggest that arid-adapted species would need to deploy more dry mass to support stems. Our results also highlight the importance of understanding how the biomechanics-wood density relationship evolves under different environmental conditions to better understand plant growth across diverse habitats.

Age trends in genetic parameters for growth and wood density in Eucalyptus globulus

Genetic parameters for stem diameter and wood density were compared at selection (4–5 years) and harvest (16–17 years) age in an open-pollinated progeny trial of Eucalyptus globulus in Tasmania (Australia). The study examined 514 families collected from 17 subraces of E. globulus. Wood density was assessed on a subsample of trees indirectly using pilodyn penetration at both ages and directly by core basic density at harvest age. Significant additive genetic variance and narrow-sense heritabilities ( $$ h_{\text{op}}^2 $$ ) were detected for all traits. Univariate and multivariate estimates of heritabilities were similar for each trait except harvest-age diameter. Comparable univariate estimates of selection- and harvest-age heritabilities for diameter masked changes in genetic architecture that occurred with stand development, whereby the loss of additive genetic variance through size-dependent mortality was countered by the accentuation of additive genetic differences among survivors with age. Regardless, the additive genetic (r a) and subrace (r s) correlations across ages were generally high for diameter (0.95 and 0.61, respectively) and pilodyn penetration (0.77 and 0.96), as were the correlations of harvest-age core basic density with selection- and harvest-age pilodyn (r a −0.83, −0.88; r s −0.96, −0.83). While r s between diameter and pilodyn were close to zero at both ages, there was a significant change in r a from adverse at selection age (0.25) to close to zero (−0.07) at harvest age. We argue that this change in the genetic correlation reflects a decoupling of the genetic association of growth and wood density with age. This result highlights the need to validate the use of selection-age genetic parameters for predicting harvest-age breeding values.

Plant–water relationships and growth strategies of Jatropha curcas L. seedlings under different levels of drought stress

Although Jatropha curcas, an important tropical biofuel crop, is reputed for its drought resistance, its ability to perform under dry conditions has hardly been investigated. In a greenhouse experiment we investigated the plant–water relationships of Jatropha seedlings from different accessions under different levels of drought stress. There was little difference in plant–water relations between accessions. Drought significantly reduced leaf area, biomass and relative growth rate, but had no effect on specific leaf area, daily range in leaf water potential, leaf water content, transpiration efficiency or aboveground biomass water productivity, corrected for atmospheric conditions. Stem wood density was equally low (0.26 g cm −3) for all treatments. Stem water content was lowest for dry treatment seedlings. Based on these results, Jatropha could be characterized as a stem-succulent tree. In contrast to other stem-succulent deciduous trees, leaves were not shed immediately after the seedlings were confronted with drought. Instead, at the onset of drought, leaves with a higher adaxial stomatal density were formed, after which leaves were only gradually shed. The role of the succulent stem in the water economy of Jatropha was confined to balancing the small water losses of the leaves during drought.

Introduction to a Virtual Special Issue on plant ecological strategy axes in leaf and wood traits

Introduction to a <i>Virtual Special Issue</i> on plant ecological strategy axes in leaf and wood traits

Predicting timber properties from tree measurements at felling: Evaluation of the RetroSTEM model and TreeViz software for Norway spruce

The RetroSTEM model was developed for predicting three-dimensional stem and wood quality characteristics in conifer stems from simple measurements at felling. The model has been previously parameterised and tested for Scots pine. This study adapts the model to Norway spruce and evaluates its prediction power regarding stem and wood quality simulations from tree base to tree top, with the objective of identifying any systematic errors in the estimation. This information will be used for future model development. The selected quality factors – stem taper, branch size, ring width and wood density distributions – are critical for visual and strength-based timber grading and for timber yield estimations. The wood density simulations provided through visual tool, TreeViz, were embedded in the RetroSTEM. The model testing indicated that the height growth model embedded in RetroSTEM should be revised regarding growth at early ages. The predicted early height growth was too fast, which led to bias in the number of annual rings at the middle and lower parts of the stem and in stem diameter at the middle stem. However, the average bias in stem diameter was relatively small (−0.3 cm) at tree level. Similarly the average bias of branch maximum diameters was low (0.2 cm) at tree level, but RetroSTEM underestimated branch diameters in trees with long crowns. Overestimation in the number of annual rings also led to underestimation of average ring width. The TreeViz estimates of wood density seem realistic. At this stage the model is applicable to estimating stem quality distributions at stand level, particularly in dense stands younger than 100 years of age.

Growth and Wood/Bark Properties of Abies faxoniana Seedlings as Affected by Elevated CO2

Growth and wood and bark properties of Abies faxoniana seedlings after one year's exposure to elevated CO2 concentration (ambient + 350 (+/- 25) micromol/mol) under two planting densities (28 or 84 plants/m(2)) were investigated in closed-top chambers. Tree height, stem diameter and cross-sectional area, and total biomass were enhanced under elevated CO2 concentration, and reduced under high planting density. Most traits of stem bark were improved under elevated CO2 concentration and reduced under high planting density. Stem wood production was significantly increased in volume under elevated CO2 concentration under both densities, and the stem wood density decreased under elevated CO2 concentration and increased under high planting density. These results suggest that the response of stem wood and bark to elevated CO2 concentration is density dependent. This may be of great importance in a future CO2 enriched world in natural forests where plant density varies considerably. The results also show that the bark/wood ratio in diameter, stem cross-sectional area and dry weight are not proportionally affected by elevated CO2 concentration under the two contrasting planting densities. This indicates that the response magnitude of stem bark and stem wood to elevated CO2 concentration are different but their response directions are the same.

ESTIMATING AVERAGE STEMWOOD DENSITY FROM BREAST HIGHT DENSITY IN THREE SPECIES OF FOREST TREES

Simple regression was used to obtain a mathematical equations for estimating the total stemwood density in three species of forest tree, namely: Pinus brutia Ten, Casuarina equestifolia, and Eualyptus Camaldulensis Dehn; by connecting the total stemwood density in its orginal form as dependent variable with the density values at breast height. A sample of 44 Pine trees, 34 Casuarina and 32 eucalyptes were used in this study. An equation was obtained for each type of wood characterized by having a very high R2 and a low S.E.% which confirmed the high accuracy of the obtained equations, the equation are:

Influence of stand density, thinning and elevated CO&lt;sub&gt;2&lt;/sub&gt; on stem wood density of spruce

Stem wood density (SWD) of young Norway spruce trees (&lt;i&gt;Picea abie&lt;/I&gt;s [L.] Karst.) growing at ambient (A variant, 350 &amp;micro;mol(CO&lt;sub&gt;2&lt;/sub&gt;)/mol) and elevated (E variant, A + 350 &amp;micro;mol(CO&lt;sub&gt;2&lt;/sub&gt;)/mol) atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentration inside of the glass domes with adjustable windows was estimated after six and eight years of the cultivation. Stand density of two subvariants (s – sparse with ca 5,000 trees/ha and d – dense with ca 10,000 trees/ha) and thinning impact (intensity of 27%) on SWD and its variation along the stem vertical profile were investigated. After six years of CO&lt;sub&gt;2&lt;/sub&gt; fumigation, stems of sparse subvariant had about 10% lower values of SWD comparing to dense ones, although the difference was not statistically significant. In 2004 (two years after thinning), the SWD values were higher in all subvariants along the whole stem vertical profile. This increase was more obvious in E variant (about 6% in d subvariant and only 3% in s subvariant). The highest increase of SWD values was found in Ed subvariant, particularly in the middle stem part (about 8%, statistically significant increase).

Predicting growth and sequestration of carbon by plantations growing in regions of low-rainfall in southern Australia

In regions of Australia of low–medium rainfall (500–800 mm/year), there is growing community and land-owner support for re-planting trees to achieve multiple environmental objectives, particularly amelioration of soil salinity. Sequestration of carbon by newly established trees is not only another important environmental benefit, but also a potential commercial benefit. To obtain estimates of carbon sequestered by species of commercial potential in such regions, we calibrated the carbon (C) accounting model FullCAM to Eucalyptus cladocalyx and Corymbia maculata plantations. This was achieved by harvesting trees of a range in sizes to determine the allometric relationships that most accurately predict biomass and stem density from measures of stem diameter. Predictions of stem diameter were obtained from a forest growth model (3-PG) previously calibrated for these two species. By applying these predictions of changes in stem diameter as the stand matures in our allometric relationships, we estimated changes in partitioning of biomass (between stem, branches, bark, foliage and roots) and stem wood density as the stand matures under scenarios of 500, 600 and 750 mm mean annual rainfall. We found that for both species, regardless of annual rainfall, throughout the rotation 37–50% of carbon sequestered in the total tree biomass was in the stem, 18–27% in both branches and roots, and the remainder in foliage or bark. However, rate of accumulation of carbon was dependent on annual rainfall, with average annual rate of sequestration of carbon in tree biomass and litter during the first rotation of E. cladocalyx (or C. maculata) increasing from 3.68 (or 4.17) to 4.72 (or 4.86) Mg C ha −1 yr −1 as annual rainfall increased from about 500 to 750 mm. Although it was predicted that decomposition negated any accumulation of debris between successive rotations, carbon was predicted to accumulate in sawlog products, given that assumed rates of product decomposition were slightly less than their rate of accumulation. This resulted in a slight increase (<8 Mg C ha −1) in predicted total sequestration of carbon between successive rotations.

Genotypic variation in wood density and growth traits of poplar hybrids at four clonal trials

Wood density is considered as one of the most important wood properties which affects the properties and value of both fibrous and solid wood products. The present study was intended for evaluating the possibilities of improving wood quality and growth of poplar hybrids. Wood density components of individual growth rings (minimum and maximum wood density, average ring density) and growth traits (tree height, dbh, stem volume) were measured in four 10- and 12-year-old clonal trials of four poplar hybrids, Populus deltoides × P. nigra, P. trichocarpa × P. deltoides, P. maximowiczii × P. balsamifera, and P. balsamifera × P. nigra, as well as P. deltoides. Wood density components of individual growth rings were obtained from microdensitometeric profiles measured with a direct reading X-ray densitometer. Site had a moderately significant effect on wood density and a highly significant effect on tree growth. The hybrid effect was highly significant ( P < 0.001) for most traits. Minimum, maximum and weighted wood densities were found to be under strong genetic control, with clonal repeatabilities varying between 0.45 and 0.81. The coefficient of genotypic variation (CV G) for wood density at individual sites ranged from 4.0 to 6.8%, whereas CV G for dry fiber weight (mass) reached 32.8% with repeatabilities of up to 0.67. A small but significant ( P = 0.028) hybrid × environment interaction was found for dry fiber weight. The highest ecological sensitivity was found for P. deltoides × P. nigra, with ecovalence reaching 32.3%. Clonal × environment interaction was significant for weighted, average, and minimum wood density. Significant negative genotypic correlations between stem volume and wood density ranged from −0.39 to −0.74. One possible strategy in tree breeding would be to maximize wood fiber production through selection for dry fiber weight.

Effects of leaf and branch removal on carbon assimilation and stem wood density of Eucalyptus grandis seedlings

The rate of leaf CO2 assimilation (Al) and leaf area determine the rate of canopy CO2 assimilation (Ac) can be thought proportional to assimilate supply for growth and structural requirements of plants. Partitioning of biomass within plants and anatomy of cells within stems can determine how assimilate supply affects both stem growth and wood density. We examined the response of stem growth and wood density to reduced assimilate supply by pruning leaf area. Removing 42% of the leaf area of Eucalyptus grandis Hill ex Maiden seedlings did not stimulate leaf-level photosynthesis (Al) or stomatal conductance, contrary to some previous studies. Canopy-level photosynthesis (Ac) was reduced by 41% immediately after pruning but due almost solely to continued production of leaves, and was only 21% lower 3 weeks later. Pruning consequently reduced seedling biomass by 24% and stem biomass by 18%. These reductions in biomass were correlated with reduced Ac. Pruning had no effect on stem height or diameter and reduced wood density to 338 kg m−3 compared to 366 kg m−3 in control seedlings. The lower wood density in pruned seedlings was associated with a 10% reduction in the thickness of fibre cell walls, and as fibre cell diameter was invariant to pruning, this resulted in smaller lumen diameters. These anatomical changes increased the ratio of cross-sectional area of lumen to area cell wall material within the wood. The results suggest changes to wood density following pruning of young eucalypt trees may be independent of tree volume and of longer duration.

Calibration and Uncertainty Analysis of a Carbon Accounting Model to Stem Wood Density and Partitioning of Biomass for Eucalyptus globulus and Pinus Radiata

There is a need to calibrate models for carbon accounting in forest systems if they are to be applied for carbon trading and off-set schemes. One such model, Full Carbon Accounting Model (FullCAM), calculates stem mass by taking annual inputs of tree growth in stem volume and multiplying these by basic stem wood density. Stem mass is then multiplied by user-entered coefficients to determine the mass of other tree components. Using datasets of Pinus radiata and Eucalyptus globulus that comprised of between 73 and 187 observations, we determined empirical relationships that can be used in FullCAM to relate basic stem wood density to stand age, and masses of bark, foliage or branches to mass of stem wood for these two species. All fitted relationships were highly significant (p < 0.001), explaining between 35 and 89% of the variance. These calibrations were then tested using three case studies where data on volume yield curves and repeated measures of biomass of stand components were available: one of P. radiata and two of E. globulus. Although accumulation of biomass in foliage and branches were not well predicted by the model, sensitivity analysis showed that this was relatively unimportant to total carbon storage because of the dominance of the stem, particularly once the stand is older than 5 years. Indeed, FullCAM accounted for 99% of the variance in measured above-ground biomass at all three sites because calibrations for the mass of stem was reasonably well constrained. Uncertainty analysis showed that despite the standard errors of parameters used in relationships for basic density and biomass partitioning, and for estimates of carbon contents of tree components, we can be 95% confident that sequestration of carbon in trees and debris of Pinus radiata and Eucalyptus globulus plantations are, on average, within 13% of that predicted by FullCAM.

Association of the cad-n1 allele with increased stem growth and wood density in full-sib families of loblolly pine

Stem growth and wood density associated with a mutant null (cad-n1) allele were examined in three 15-year-old loblolly pine half-diallel tests established on two sites in the southern United States. In each half-diallel test, one or two cad-n1 heterozygous parents were crossed with five unrelated wild-type parents to produce five or ten full-sib families. In all, 839 trees from 20 full-sib families in four genetic backgrounds (a cad-n1 heterozygote × five unrelated trees) were sampled, genotyped at the cad locus, and assessed for growth and wood density traits. In a combined analysis of all four genetic backgrounds, we found evidence for effects of increased wood density associated with the cad-n1 allele at age 15 years (p=0.03) and height growth at ages 6 (p=0.03) and 15 (p=0.005). There were differences in the cad-n1 effects for the various growth and wood traits among the half-diallel tests. This variation may be due to either different genetic backgrounds among the parents of the different half-diallel tests or for different growing environments at the field sites. Even though the cad-n1 effect on growth and wood density was significant across genetic backgrounds, the effect was variable among full-sib families within backgrounds. We speculate that certain wild-type alleles from second parents specifically interact with cad-n1 producing large positive effects. In addition, pleiotropic effects on growth and wood density appear to be associated with the cad-n1 allele. While substantial gains are possible through deployment of trees carrying cad-n1, these gains may be family-specific and should be verified for each cross through field-testing.

Why does phosphorus limitation increase wood density in Eucalyptus grandis seedlings?

Wood density influences both the physiological function and economic value of tree stems. We examined the relationship between phosphorus (P) supply and stem wood density of Eucalyptus grandis Hill ex Maiden seedlings grown with varying soil P additions and determined how changes in wood anatomy and biomass partitioning affect the relationship. Plant height, stem diameter and total biomass increased by 400-500% with increasing P supply. Stem wood density decreased sharply from 520 to 380 kg m(-3) as P supply increased to 70 mg P kg(soil) (-1). Further increases in P supply to 1000 mg P kg(soil) (-1) had no effect on wood density. The increase in wood density at low soil P supply arose principally from enhanced secondary wall thickening of stem fiber cells. Cell wall thickness increased from 3.6 to 4.5 microm as soil P supply decreased. Because fiber cell diameter was independent of soil P (12 microm +/- 0.3), the proportion of the stem occupied by cell wall material increased as P supply declined. The enhanced secondary wall thickening of stem fiber cells at low P supply was not associated with changes in whole-plant biomass partitioning. Instead, low P supply appeared to alter biomass partitioning within the stem in favor of secondary wall thickening. Thus, increased wood density in E. grandis seedlings grown at low P soil supply was associated with inhibited stem cambial activity, resulting in an increased proportion of photoassimilates available for secondary wall thickening of fiber cells.

Molecular targets of elevated [CO2] in leaves and stems of Populus deltoides: implications for future tree growth and carbon sequestration.

We report the first comprehensive analysis of the effects of elevated [CO2] on gene expression in source leaf and stem sink tissues in woody plants. We have taken advantage of coppiced Populus deltoides (Bartr.) stands grown for 3 years under three different and constant elevated [CO2] in the agriforest mesocosms of Biosphere 2. Leaf area per tree was doubled by elevated [CO2] but although growth at 800 v. 400 µmol mol-1 CO2 resulted in a significant increase in stem biomass, growth was not stimulated at 1200 µmol mol-1 CO2. Growth under elevated [CO2] also resulted in significant increases in stem wood density. Analysis of expression data for the 13 490 clones present on POP1 microarrays revealed 95 and 277 [CO2]-responsive clones in leaves and stems respectively, with the response being stronger at 1200 µmol mol-1. When these [CO2]-responsive genes were assigned to functional categories, metabolism-related genes were the most responsive to elevated [CO2]. However within this category, expression of genes relating to bioenergetic processes was unchanged in leaves whereas the expression of genes for storage proteins and of those involved in control of wall expansion was enhanced. In contrast to leaves, the genes up-regulated in stems under elevated [CO2] were primarily enzymes responsible for lignin formation and polymerisation or ethylene response factors, also known to induce lignin biosynthesis. Concomitant with this enhancement of lignin biosynthesis in stems, there was a pronounced repression of genes related to cell wall formation and cell growth. These changes in gene expression have clear consequences for long-term carbon sequestration, reducing the carbon-fertilisation effect, and the potential for increased lignification may negatively impact on future wood quality for timber and paper production.

Models for vertical wood density of Scots pine, Norway spruce and birch stems, and their application to determine average wood density

The purpose of this study was to investigate the vertical dependence of the basic density of Scots pine, Norway spruce, and birch stems, and how such dependence could be applied for determining the average stem wood density. The study material consisted of 38 Scots pine (Pinus sylvestris), 39 Norway spruce (Picea abies [L.] Karst.) and 15 birch (Betula pendula and Betula pubescens) stands located on mineral soil sites in southern Finland. The stem material mainly represented thinning removal from stands at different stages of development. The linear mixed model technique, with both fixed and random effects, was used to estimate the model. According to the fixed part of the model, wood density was dependent on the vertical location along the stem in all three tree species. Wood density in pine decreased from the butt to the top, and the gradient in wood density was steep at the butt but decreased in the upper part of the stem. The vertical dependence was similar in birch, but the density gradient was much smaller. For spruce the vertical dependence of the basic density was moderate. The model can be calibrated for a tree stem when one or more sample disks are measured at freely selected heights. Using treewise calibrated predictions of the vertical density dependence and measured stem diameters, almost unbiased estimates, and lower prediction errors than with traditional methods, were obtained for the average stem wood density. The advantages of the method were greater for pine with a strong vertical dependence in basic density, than for spruce and birch.

Variation and Correlations Among Stem Growth and Wood Traits of Calycophyllum spruceanum Benth. from the Peruvian Amazon

Abstract Calycophyllum spruceanum Benth. is an important tree for timber and energy in the western Amazon, with expanding national and international markets for its wood. There is relatively little information, however, about geographic variation in tree growth and wood properties, and correlations among these traits. The first provenance trial was established with farming communities in the Peruvian Amazon. Seven provenances, sampled from regions near the equator, were tested in three planting zones located in one watershed. Variation and correlations were investigated in stem growth at 30 and 42 months, wood density (in the lower and upper parts of the stem) and mean heat content of stem wood at 32 months. Stem height varied significantly among provenances and planting zones, but zones accounted for much more variation than provenances. Stem wood traits did not vary significantly among provenances. Wood density was greater in the lower than in the upper stem. Wood density in the upper stem and the difference in density between the lower and upper stem varied significantly among planting zones: density in the upper stem was lowest, and the difference in density between the lower and upper stem was largest in the zone where trees grew most rapidly. Phenotypic correlations between stem growth and wood density differed in sign among planting zones, suggesting that selecting fastgrowing trees could indirectly reduce wood density in environments where trees grow slowly, and increase the difference in wood density between the lower and upper stem in environments where trees grow very rapidly. Correlations between stem growth and wood heat content were stable across zones, and indicated that larger trees tended to have wood with higher heat content. Stem-wood heat content varied with provenance latitude/ longitude in the sample region, but none of the other traits varied clinally. Results indicate that there is potential to select faster-growing provenances at an early age, but this could affect wood density in certain environments.

Developing general allometric relationships for regional estimates of carbon sequestration—an example using Eucalyptus pilularis from seven contrasting sites

General non-site-specific allometric relationships are required for the conversion of forest inventory measurements to regional scale estimates of forest carbon sequestration. To determine the most appropriate predictor variables to produce a general allometric relationship, we examined Eucalyptus pilularis aboveground biomass data from seven contrasting sites. Predictor variables included diameter at breast height (dbh), stem volume, dbh 2 × H, dbh × H and height ( H). The data set contained 105 trees, ranging from 6 to over 20,000 kg tree −1, with dbh ranging from 5 to 129 cm. We observed significant site differences in (1) partitioning of biomass between the stem, branch wood and foliage; (2) stem wood density and (3) relationship between dbh and height. For all predictor variables, site had a significant effect on the allometric relationships. Examination of the model residuals of the site-specific and general relationship indicated that using dbh alone as the predictor variable produced the most stable general relationship. Furthermore, the apparent site effect could be removed by the addition of a constant value to the measured diameter (dbh + 1), to account for the differing diameter distribution across the seven sites. Surprisingly, the inclusion of height as a second predictor variable decreased the performance of the general model. We have therefore demonstrated that for E. pilularis a general allometric relationship using dbh alone as the predictor variable can be as accurate as site-specific allometry, whilst being applicable to a wide range of environments, management regimes and ages. This simplifies regional estimates of aboveground biomass from inventory measurements, eliminating the need for site-specific allometric relationships or modifiers such as height, wood density or expansion factors.

Effects of tree selection on strength properties and distribution of structural roots of clonal Sitka spruce

An examination was made into the effects of tree breeding on the properties of the root systems associated with anchorage. Comparisons between the strength properties of root and stem wood were also made. Five selected clones of 11-year-old Sitka spruce ( Picea sitchensis (Bong.) Carr.) were used along with control trees grown from unimproved cuttings and transplants. The trees had been established on a shallow unploughed but relatively homogeneous soil to limit directional distribution of the roots. Results suggest that tree selection primarily based on improved stem growth, form and wood density did not have a negative effect on the strength properties of the structural roots. Significant correlations between a number of stem and large root wood parameters suggest that selecting for stem strength should have a positive effect on the strength of the wood of the large roots. Despite clonal differences in cross-sectional root area, there was no difference in the proportion of large roots, which provide most of the anchorage, to small roots between treatments. There was also no difference in the cross-sectional area of root plate apportioned to north, east, south and west directions. The wide variation in strength characteristics observed suggests that both stem and root wood strength could be improved through clonal selection.