John R. Moore

Radial Variation in Wood Structure and Function in Woody Plants, and Hypotheses for Its Occurrence

Woody stems, branches, and roots display large progressive changes in structure and function from the pith outwards, a pattern known as the core/outerwood or juvenile/mature wood pattern. For example, the typical radial pattern (TRP), characterized mostly for commercial softwoods, includes increases in wood density by a factor of up to 1.5, tracheid width by a factor of 2, and tracheid length by a factor of up to 4. These large changes will have substantial effects on the success or failure of the plant. Our knowledge of the drivers and the universality of the typical radial pattern are minimal in spite of 150 years of research that has been concentrated mostly on commercial softwoods. This chapter (1) provides a brief description of the nature and magnitude of the structural and functional changes along the radius of woody stems, (2) clarifies whether ring number from the pith or size best explain the typical radial pattern, and (3) introduces and briefly evaluates hypotheses for the functional significance of the radial patterns, with developmental, hydraulic, and mechanical hypotheses. The chapter indicates major knowledge gaps in different biomes and plant types, and provides examples of systems in which research advances could be made. An improved knowledge of why wood develops into the structures we observe will provide a basis for better predictions of woody plant behavior across environments. It is also essential for tree breeders in developing adapted stock for different environments, and foresters and wood processors in predicting end-product quality.

Natural sway frequencies and damping ratios of trees: concepts, review and synthesis of previous studies

Previous studies that measured the natural frequencies and damping ratios of conifer trees were reviewed and results synthesized. Analysis of natural frequency measurements from 602 trees, belonging to eight different species, showed that natural frequency was strongly and linearly related to the ratio of diameter at breast height to total tree height squared (i.e., DBH/H2). After accounting for their size, pines (Pinus spp.) were found to have a significantly lower natural frequency than both spruce (Picea spp.) and Douglas-fir (Pseudotsuga spp.). Natural sway frequencies of de-branched trees were significantly higher than those of the same trees with the branches intact, and the difference increased with an increasing ratio of DBH/H2. Damping mechanisms were discussed and methods for measuring damping ratio were presented. Analysis of available data suggested that internal damping ratios were typically less than 0.05 and were not related to tree diameter. External damping was mainly due to aerodynamic drag on the foliage and contact between the crowns of adjacent trees. Analysis of data from previous wind-tunnel studies indicated that damping due to aerodynamic drag is a nonlinear function of velocity. Damping due to crown contact has been suggested by a previous author to be a function of both the distance to and the size of adjacent trees. Therefore, in uniformly spaced stands it may be possible to model crown contact damping as a function of stand density index (SDI), a common forestry measure which incorporates both of these variables.

Natural sway frequencies and damping ratios of trees: influence of crown structure

Natural frequency and damping ratio were measured for nine plantation-grown Douglas-fir (Pseudotsuga menziesii Mirb. Franco) trees from the Oregon Coast Range under different levels of crown removal. Natural frequency of trees, in both their unpruned and completely de-branched states, was linearly related to the ratio of diameter at breast height to total tree height squared (i.e., DBH/H2), as expected from the theory governing the oscillation of a cantilever beam. Pruning resulted in an increase in natural frequency; however, at least 80% of the crown mass needed to be removed before this increase was noticeable. A single equation was developed that enabled the natural frequency of a tree of given size and pruning intensity to be predicted. Damping ratios of unpruned trees varied considerably from 8% to almost critical, while those for completely de-branched trees ranged from 1% to 8%. Two different trends in damping ratio were observed during pruning. Some trees exhibited an increase in damping ratio with initial crown removal, followed by a sharp decrease when the uppermost portion of the crown was removed. Others showed little or no change in damping ratio followed by a sharp reduction upon removal of the uppermost portion of the crown. Damping was mainly due to aerodynamic drag and preventing interference with neighbouring trees had little effect. Theoretical analysis using the finite element method indicated that changes in natural frequency as a result of pruning are not due to changes in damping ratio, but rather changes in mass distribution. This analysis also suggested that treating branches as lumped masses rather than individual cantilevers attached to the main stem may not be appropriate.

Wood properties of juvenile Pinus radiata growing in the presence and absence of competing understorey vegetation at a dryland site

Pinus radiata D. Don trees were grown in the presence and absence of the woody weed broom (Cytisus scoparius L.) on a dryland site for 2 years to determine the effects of competition from weeds on wood properties in juvenile trees. Wood property measurements made on cross-sections from the bark to the pith were scaled to convert results from distance to a time basis using sigmoidal equations fitted to monthly measurements of tree diameter. When averaged across the 2 years, the presence of the weeds significantly increased wood density (+11%), wall thickness (+6%) and modulus of elasticity (MOESS, +93%), and significantly reduced microfibril angle (MFA, −21%) and radial diameter (−8%). Radial growth rate was significantly correlated to wood density, and this relationship held across both treatment and age. At the seasonal scale, there was close correspondence between changes in MFA and growth rate. Ring width was significantly related to both MFA and MOESS at the annual scale. Although both of these relationships held across treatments, year significantly influenced the value of coefficients in the relationships. The results highlight the direct effects of the presence of weeds on wood properties and the need to consider silvicultural treatments appropriate for balancing gains in productivity with losses in wood quality for timber production.

Allometric equations to predict the total above-ground biomass of radiata pine trees

Abstract• Radiata pine (Pinus radiata D. Don) is the main exotic plantation tree species grown in New Zealand for wood production and as such represents a significant component of the terrestrial carbon cycle.• Using data for 637 trees collected in 13 different studies, a series of equations was developed that enable the total above-ground biomass of individual radiata pine trees to be estimated from information about height and diameter. A mixed-effects modelling approach was used when fitting these equations in order to account for random fluctuations in model parameters between studies due to site and methodological differences. Linear models were fitted to logarithmically transformed data, while weighted linear and non-linear models were fitted to data on the original arithmetic scale.• Based on a modified likelihood statistic (Furnival’s Index of Fit), models fitted to transformed data were found to perform slightly better than weighted models fitted to data on the original arithmetic scale; however, the latter do not require a means for correcting for the bias that occurs when estimates of biomass obtained from transformed models are back transformed to the original scale.• Recommendations for further development of these models including additional data collection priorities are given.

A comparison of the relative risk of wind damage to planted forests in Border Forest Park, Great Britain, and the Central North Island, New Zealand.

Abstract The risk of wind damage was assessed for Sitka spruce growing in the Border Forest Park, Great Britain and radiata pine growing in the Central North Island, New Zealand using a quantitative wind risk model (FORESTGALES). The model has been adapted for the two species using estimates of maximum resistive bending moment from historical tree winching studies performed in the two regions, drag coefficients obtained from wind tunnel tests, and wind data from representative meteorological stations. The risk is calculated as the probability that the threshold wind speed for damage will be exceeded at a particular site. This approach enables the effect of different growth rates, soil types, management regimes and wind climates to be investigated. The threshold wind speed for tree failure was calculated for stands of both species grown under standard regimes on typical soils and characteristic topography. The probability that the threshold wind speed is exceeded was determined using a recurrence function fitted to time-series of annual maximum hourly wind speeds from a representative long-term meteorological station for each region. The two species are grown over substantially different rotation lengths, so comparisons were made between the profile of risk over a single rotation, and also as cumulative risk over a time-span sufficient to contain multiple rotations. The results demonstrate substantial differences in the probability of wind damage between forests in the two regions as they are currently managed. Contrary to expectation, the risk is lowest for forests in the region of the most severe wind climate, because of the selection of a risk-minimising strategy. This finding emphasises the degree to which management of forests can affect the frequency and amount of damage that they experience. The model was portable and provided objective estimates of risk for two very different locations and silvicultural regimes. Further development should provide a tool of practical importance for those seeking to make comparisons between very different situations, such as multi-national companies and re-insurers.

Predicting the longitudinal modulus of elasticity of Sitka spruce from cellulose orientation and abundance

Abstract Sitka spruce (Picea sitchensis) is the most widely planted commercial tree species in the United Kingdom and Ireland. Because of the increasing use of this species for construction, the ability to predict wood stiffness is becoming more important. In this paper, a number of models are developed using data on cellulose abundance and orientation obtained from the SilviScan-3 system to predict the longitudinal modulus of elasticity (MOE) of small defect-free specimens. Longitudinal MOE was obtained from both bending tests and a sonic resonance technique. Overall, stronger relationships were found between the various measures of cellulose abundance and orientation and the dynamic MOE obtained from the sonic resonance measurements, rather than with the static MOE obtained from bending tests. There was only a moderate relationship between wood bulk density and dynamic MOE (R2=0.423), but this relationship was improved when density was divided by microfibril angle (R2=0.760). The best model for predicting both static and dynamic MOE involved the product of bulk density and the coefficient of variation in the azimuthal intensity profile (R2=0.725 and 0.862, respectively). The model parameters obtained for Sitka spruce differed from those obtained in earlier studies on Pinus radiata and Eucalyptus delegatensis, indicating that the model might require recalibration before it can be applied to different species.

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.

Influence of earlywood/latewood and ring position upon water vapour sorption properties of Sitka spruce

Abstract Variation in the water vapour sorption kinetics of the stemwood of Sitka spruce (Picea sitchensis (Bong.) Carr.) has been studied, with respect to possible variations between earlywood and latewood and between different annual ring positions from pith to bark. The sorption kinetics was analysed using the parallel exponential kinetics (PEK) model that has recently been introduced by this laboratory for studies with wood. Significant differences in kinetic parameters were found between ring positions, corresponding to differences between juvenile wood and mature wood that contrast with previously reported work in the literature. Differences were also found in the sorption kinetics of earlywood and latewood in agreement with the literature. Thus far, there has been no satisfactory explanation as to the physical interpretation of the PEK model and in this paper it is argued that the kinetic behaviour is consistent with what would be expected for sorption with a viscoelastic material. Analysis of the PEK data using the Kelvin–Voigt model has proved that it is possible to obtain values for the wood cell wall stiffness and viscosity that are in broad agreement with previously published values in the literature.

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.