Dave Cown

Modelling variation in wood density within and among trees in stands of New Zealand-grown radiata pine

BackgroundDensity is an important wood property due to its correlation with other wood properties such as stiffness and pulp yield, as well as being central to the accounting of carbon sequestration in forests. It is influenced by site, silviculture, and genetics, and models that predict the variation in wood density within and among trees are required by forest managers so that they can develop strategies to achieve certain wood density targets. The aim of the study presented here was to develop a wood density model for radiata pine (Pinus radiata D. Don) growing in New Zealand.MethodsThe model was developed using an extensive historical dataset containing wood density values from increment cores and stem discs that were obtained from almost 10,000 trees at over 300 sites. The model consists of two sub-models: (1) a sub-model for predicting the radial variation in breast-height wood density and (2) a sub-model for predicting the distribution of density vertically within the stem.ResultsThe radial variation in breast-height wood density was predicted as a function of either ring number or both ring number and ring width, with the latter model better accounting for the effects of stand spacing. Additional model components were also developed in order to convert from annual ring density values to a whole-disc density, predict log density from disc densities, and account for the variation in wood density among individual trees within in a stand. The model can be used to predict the density of discs or logs cut from any position within a tree and can utilise measured outerwood density values to predict the density by log height for a particular stand. It can be used in conjunction with outerwood density to predict wood density distributions by logs for stands of any specified geographic location and management regime and is designed to be able to incorporate genetic adjustments at a later stage.ConclusionsThe analysis has confirmed and quantified much of the previous knowledge on the factors that affect the variation in wood density in radiata pine, particularly the influences of site factors and silviculture. It has also quantified the extent and patterns of variation in wood density within and among trees.

Effects of site, silviculture and seedlot on wood density and estimated wood stiffness in radiata pine at mid-rotation

BackgroundTo understand the underlying control of patterns of important wood properties is fundamental to silvicultural control of wood quality and genetic selection. This study examines the influences of site, silviculture and seedlot on diameter growth, wood density and estimated wood stiffness in mid-rotation radiata pine (Pinus radiata D Don) stands across New Zealand.MethodsSelected treatment combinations were assessed across five sites in a 17-year-old experiment comparing silvicultural treatments and improved breeds of radiata pine. Diameter at breast height (DBH), and stress-wave velocity (an indicator of wood stiffness) and outerwood (outermost five growth rings) basic density at breast-height were assessed for ten trees from each plot in the experiment.ResultsThere were large differences in DBH and wood properties between sites. Silviculture (stand density) had a stronger influence than seedlot on DBH and stress-wave velocity, while the converse applied to outerwood density. There was a positive relationship between stand density and both stress-wave velocity and outerwood density. Trees in the un-pruned 500 stems ha−1 treatment had larger DBH, lower outerwood density and lower stress-wave velocity than trees in the 400 stems ha−1 pruned treatment. This suggests that silvicultural manipulation (pruning) of green crown length is important for controlling both growth and wood properties.ConclusionsResults from this study support previous research which indicates that thinning, and to a lesser extent pruning, have a strong impact on DBH, stress-wave velocity and outerwood density. Increasing stand density is consistently associated with stiffer and denser outerwood.

Modelling microfibril angle variation in New Zealand-grown radiata pine

BackgroundMicrofibril angle (MFA) is a property of wood cell walls that has a strong influence on end-product quality, particularly for solid timber. Forest managers, tree breeders and wood processors require more quantitative information on the inter- and intra-stem variation in MFA in order to understand the impacts of their decisions on wood quality. The aim of this study was to develop parametric models that can be used to predict the intra- and inter-stem variation in MFA in radiata pine (Pinus radiata D. Don) trees growing in New ZealandMethodsEmpirical models were developed using a dataset that contained records from 347 trees in which radial profiles of MFA have been measured at different heights up the stem. Radial variation in MFA was modelled as a function of cambial age using both a modified logistic function and a modified Michaelis-Menten equation. Additional terms were added to these models to account for differences in MFA with relative height up the stem.ResultsValues of MFA ranged from more than 40° near the pith to approximately 10-15° in the outerwood. Values greater than 30° were largely confined to the inner rings of the butt logs. A variance components analysis showed that most of the variation in MFA occurred within stems, with less than 15% of the variation due to differences between sites. The final models were able to account for 57-63% of the variation in MFA and inclusion of a relative height term significantly improved the model fit.ConclusionsRadiata pine has a region of high microfibril angle in the first 10-15 growth rings from the pith, particularly at the base of the tree. Growth rate had a small positive influence on average MFA (wider rings resulting in higher MFA values). Site differences were small, indicating that regional variation in wood stiffness is due more to the known trends in wood density. The models developed here can be coupled to growth models to examine how the combination of site productivity and silvicultural regime affect the size of the central zone containing high MFA wood.

Stand, stem and log segregation based on wood properties: a review

There are many log and wood properties of interest to wood processors. There is also high variability in important attributes between and within growing regions and between and within individual stems which influence financial returns to wood processors. This review summarises recent studies of segregation technologies and techniques which have shown that: regional or stand level attribute models will facilitate a coarse level of segregation but not account well for the between and within stem variation; many tools and techniques are available for segregating wood based on internal properties but few have been implemented commercially. Some are better suited for application in mills than in forests; the benefits of segregating stands, stems and logs based on wood properties are not clear due to high variability in wood properties, poor market signals (in terms of price) for wood with superior properties, and poor understanding of the costs across the value chain; and most of the existing economic models tend to look at the economics of segregation from the perspective of a single participant in the value chain, e.g. a structural mill or a central processing yard. Only a few models look across the value chain and these have limitations often poorly representing some participants in the value chain.

Effects of induced drought and tilting on biomass allocation, wood properties, compression wood formation and chemical composition of young Pinus radiata genotypes (clones)

Abstract Eight genotypes (clones) of Pinus radiata were subjected to drought and stem inclination to assess genotype response to common stressors. While drought stress reduced diameter growth, height growth and total biomass accumulation, root to shoot (R/S) ratios were unaffected. Drought-stressed plants had significantly lower average acoustic velocity, but longitudinal shrinkage (LS) and density were not different from those of the control plants. Radial diameter growth and R/S ratios were unaffected by tilting. Inclined stems had significantly lower acoustic velocity, and significantly higher LS and density than control stems. Acoustic velocity had a strong negative correlation with LS (r2=0.79). Compression wood (CW) content was much higher in tilted plants, compared to control and drought treatment plants. The CW of tilted trees had different chemistry than that of the CW of drought and control plants. Genotypes differed significantly in the amount of CW formed as a response to tilting, demonstrating that the formation and extent of CW is genetically influenced. Mechanical perturbation in conjunction with acoustic methods for assessing stiffness would be a useful approach for early-age selection of genotypes less prone to form CW.

Effects of stand density and seedlot on three wood properties of young radiata pine grown at a dry-land site in New Zealand

BackgroundManipulation of stand density and choice of genetic material are two key mechanisms through which forest managers can influence tree growth and wood properties. Past silvicultural practices in New Zealand have been characterised by early thinning to relatively wide spacing, while tree improvement programmes have primarily focussed on growth and form. The aim of this study was to quantify the impacts of stand density and past genetic selections on the wood properties of radiata pine (Pinus radiata D. Don).MethodsStress-wave velocity, wood density, microfibril angle (MFA) and modulus of elasticity (MOE) were measured on trees and wood samples taken from a 15-year-old silvicultural and tree breeds trial located in Canterbury, New Zealand. The focus of this study was comparison of seedlots with genetic ratings of GF6 and GF25. Data from pruned stands with final densities of 100, 200 and 400 stems ha−1 were compared as were data from unpruned stands with stand densities of 200, 400, 600 and 1000 stems ha−1.ResultsStress-wave velocity of trees was affected by final stand density, with the lowest values recorded from trees in the 100 and 200 stems ha−1 treatments. Values for wood MFA and MOE both showed the greatest amount of change when final stand density was less than 400 stems ha−1. Trees from the GF25-rated seedlot had wood density that was approximately 34 kg m−3 lower than trees from the GF6-rated seedlot.ConclusionVery high stand densities are not required in order to influence wood properties, but early thinning to low stand densities should be avoided. Such results are of practical importance to forestry managers.

Corewood (Juvenile Wood) and Its Impact on Wood Utilisation

Purpose of ReviewCorewood (‘juvenile wood’) is found within the first 10–20 annual rings adjacent to the pith. This review focuses on describing the characteristics of corewood, the factors affecting its occurrence within a tree and the implications for wood utilisation.Recent FindingsCorewood has been extensively researched across a wide range of commercial trees species, with a large focus on loblolly pine (Pinus taeda L.) and radiata pine (Pinus radiata D. Don). Recent studies have focussed on understanding the degree to which corewood extent and properties are affected by environmental, silvicultural and genetic factors. The impacts of corewood on dimension lumber, panel products and pulp and paper are generally well known, and recent research has examined the impact of corewood on the performance of newer products.SummaryAn increase in the proportion of corewood in the planted forest resource is inevitable due to an intensification of forestry practises and a drive for more cost-effective raw material production. The implications for wood processing can be positive or negative depending on the end product in question. Solving the problems posed by corewood may depend heavily on wood processors adapting their systems to accommodate the increased proportion of corewood in the future resource or changing the performance specifications for their products.

ASSESSING SPIRAL GRAIN ANGLE BY LIGHT TRANSMISSION - Proof of Concept -

Spiral grain measurements are subject to a high degree of variation and interpretation, depending on the assessment method used. A new measurement approach was tested whereby light was directed through disc samples on a flatbed scanner and the deviation along the grain assessed by means of a template to allow the mapping of grain angle variation radially and tangentially within discs. Initial results showed that the approach was valid for green discs up to 35 mm thick and small enough to fit on an A4 scanner. Comparisons with traditional scribing and cleaving methods were favourable, indicating that the light transmission approach could allow much faster and more accurate data acquisition. The possibility of using larger discs would enhance the ability to assess spatial variation in grain angle and minimise the effects of sample reference geometry with respect to the tree axis (disc tilt and parallax). Further work may also be required to ensure that reliable spiral grain values are obtained from both sapwood and heartwood. The ultimate goal is to develop an automated system for reconstructing stem characteristics from measurements on large fresh green discs to enable the 3-dimensional mapping of individual stem variations in key wood properties and modelling the impacts of silviculture and genetics on wood products.

Sawn timber grade recovery from a planted coast redwood stand growing in New Zealand

BackgroundTimber from old-growth stands of coast redwood (Sequoia sempervirens (D.Don) Endl.) is dimensionally stable, resistant to surface checking and splitting, and has been widely used for outdoor purposes such as decking and cladding. Restrictions on the supply of redwood timber from Californian stands have increased the focus on timber from plantations grown elsewhere in comparatively short rotations. Little is known about the quality of timber produced from plantations of redwood in New Zealand.MethodsIn this study trees from a 38-year-old pruned stand in Mangatu Forest near Gisborne, New Zealand, selected to cover the range of stem diameters present, were cross-cut into logs. Each log was then sawn into boards and each board was graded according to a simplified United States redwood grading system.ResultsTotal timber volume (50 logs) was 16.2 m3, valued at USD 7,835 (2008 prices). This was less than might be expected in a well-managed stand. The 13 pruned logs accounted for 38% of the total volume recovered and 50% the total financial value of the timber. Pruned log quality assessed according to a pruned log index (PLI) was low, due to untimely pruning and the presence of epicormic shoots. Only 12% of the timber was graded clear and 32% of this came from pruned logs. Despite low PLI scores, the relationships between PLI, proportion of clear timber and pruned log value were reasonably strong.ConclusionsRecoveries from individual stems were variable. The most important determinants of log value were log size, which affected timber recovery; pruning quality, which governed the volume of clear wood; the proportion of heartwood, (valued for durability and appearance); and to a lesser extent, mid-stem branch vitality. High incidence of dead (bark-encased) knots in most of the unpruned logs contributed to the poor timber grade recovery results. Other defects (insect tunnels, rot and traumatic resin pockets) were associated with a 7% reduction in financial value. Accurate prediction of the pattern of distribution of heartwood inside a redwood log could play a major role in maximising the value of recovered timber.

Differences in intra-tree variation in spiral grain angle for radiata pine

BackgroundSpiral grain angle (SGA) is an important factor affecting the distortion and utilisation of solid timber. Little research has investigated how SGA varies at a fine scale within trees and whether this fine-scale three-dimensional variation is similar between genotypes. The objectives of this research were to (i) characterise three-dimensional variation in SGA within stems and clones, and (ii) understand how intra-stem variation in SGA varies between genotypes.MethodsDetailed measurements of SGA were taken from 12 radiata pine (Pinus radiata D. Don) clones. Analyses were undertaken to characterise variation in three dimensions and determine if this variation significantly differed between genotypes.ResultsSpiral grain varied significantly with distance from the pith, showing a sharp initial increase with distance from the pith, followed by a gradual decline. Values of SGA increased significantly with height up the stem, reaching a maximum at ca. 5 m. Circumferential variation in SGA showed no significant trend. There was significant variation in mean SGA between clones; however, the within tree patterns in SGA did not significantly vary between clones.ConclusionIf further research confirms the uniformity of within tree patterns in SGA between clones this may greatly simplify efforts to model three-dimensional variation in SGA.