Existing models for describing knot morphology are typically based on polynomial functions with parameters that are often not biologically interpretable. Hence, they are difficult to integrate into tree growth simulators due to the limited possibilities for linking knot shape to external branch and tree characteristics. X-ray computed tomography (CT) images taken along the stems of 16 jack pine (Pinus banksiana Lamb.) trees and 32 black spruce (Picea mariana (Mill.) B.S.P.) trees were used to extract the three-dimensional shape of 3450 and 11 276 knots from each species, respectively. Using a nonlinear approach, we firstly fitted a model of knot geometry adapted from a Weibull function. Separate equations were used to describe both the curvature and the diameter of the knot along its pith. Combining these two equations gave an accurate representation of knot shape using only five parameters. Secondly, to facilitate the integration of the resulting model into a tree growth simulator, we extracted the parameters obtained for each knot and modelled them as functions of external branch and tree characteristics (e.g., branch diameter, insertion angle, position in the stem, tree height, and stem diameter). When fitted to a separate data set, the model residuals of the black spruce knot curvature equation were less than 2.9 mm in any part of the knot profile for 75% of the observations. The corresponding value from the diameter equation was 2.8 mm. In jack pine, these statistics increased to 5.4 mm and 3.2 mm, respectively. Overall, the ability to predict knot attributes from external tree-and branch-level variables has the potential to improve the simulation of internal stem properties.Résumé : Les modèles utilisés actuellement pour décrire la morphologie des noeuds sont généralement basés sur des fonctions polynomiales dont les paramètres sont difficilement interprétables. Ainsi, ils sont difficiles à intégrer dans les simulateurs de croissance en raison de la difficulté à relier la forme des noeuds et les caractéristiques externes des branches et des arbres. Des images de tomographie à rayons-X le long des tiges de 16 pins gris (Pinus banksiana Lamb.) et de 32 épinettes noires (Picea mariana (Mill.) BSP) ont été utilisées pour extraire, respectivement pour chaque espèce, la forme tridimensionnelle de 3450 et 11 276 noeuds. Dans un premier temps, nous avons utilisé une approche de modélisation non linéaire basée sur une fonction de Weibull afin de décrire la géométrie de chaque noeud. Des équations distinctes ont été utilisées afin de décrire à la fois l'évolution de la courbure et du diamètre du noeud de la moelle à l'écorce. Cette combinaison de deux équations a permis une représentation exacte de la forme noeud en utilisant seulement cinq paramètres. Dans un second temps, les paramètres obtenus pour chacun des noeuds ont été extraits et modélisés en fonction des caractéristiques externes de la branche et de l'arbre (p. ex. le diamètre de la branche, l'angle d'inclinaison, la position dans la tige, la hauteur et le ...
White spruce breeding has traditionally focused on genetic improvement for high productivity, targeting mostly stem volume. However, new challenges, such as the effects of climate change on individual trees and ecosystems and the changing nature of forest products markets, require action to address these issues while providing improved stock for seed and seedling production. This work aims to define the relative importance of white spruce wood traits for the lumber industry, with the intent of guiding tree breeding programs. This manuscript examines: (1) wood features that are important for lumber, (2) the genetics of wood traits and their improvement and (3) the level of acceptance of raw material with optimal traits, as obtained from a survey conducted with sawmills. Stem diameter at stump height, wood density, bending strength and stiffness were determined as the most important properties for sawmills. Decay proportion, knot diameter, slope of grain and the proportion of compression wood were also determined as important for sawmills, but to a lesser extent. Breeding efforts aiming to produce lumber should focus on stems with improved growth that are capable of sustaining the production of dense wood in greater proportion.
Radial trends in black spruce wood density can show an age-and growth-related decline.Abstract & Context Wood density variation affects structural timber performance and is correlated with several potentially confounding factors, such as cambial age, position in the stem and growth rate. To date, these relationships have not been comprehensively quantified in black spruce (Picea mariana (Mill.) B.S.P.). & Aims The aim of this study was to describe the variation in annual ring density in black spruce as a function of cambial age, stem height and growth rate. & Methods Radial density profiles from 107 black spruce trees were analysed using a two-stage modelling approach. First, the parameters of a nonlinear function were estimated separately for individual samples. Linear regression was then used to model the parameters obtained in the first stage as functions of internal and external tree descriptors. & Results Annual ring density was high near the pith and declined rapidly in the first 15 annual rings before increasing to more stable values between rings 25 and 60. However, just below 25 % of the samples showed a gradual decline towards the bark, typically after ring 60. & Conclusion Describing and quantifying radial density patterns, including the decline close to the bark, will help further our understanding of the links between tree growth and ring density over the life of the tree.
& Key Message A model describing species composition, density and diameter distribution of saplings was developed from operational inventory data. It could be used as an input into growth models calibrated exclusively with merchantable trees to correct some recruitment bias. Important differences in distributions were found between plantations and naturally regenerated stands. Longer-term monitoring would be required to observe the effects of thinning treatments on saplings. & Context Saplings play important ecological and structural roles in forest stands. They also constitute the pool of candidate trees that are responsible for recruitment of merchantable sized trees. However, sapling information is often absent from regular inventory measurements (e.g. where no saplings are measured) even though they could be used as inputs in predicting recruitment in merchantable trees. & Aims The objectives were to develop models describing density and diameter distribution of saplings from operational inventories, e.g. having only merchantable tree inventory, and to evaluate how stand type (naturally regenerated stands and plantations) and various thinning treatments influence these distributions. & Methods Using data from both white spruce (Picea glauca [Moench] Voss) plantations and naturally regenerated balsam fir (Abies balsamea (L.) Mill.) stands having been commercially thinned, a zero-inflated poisson regression was used to model the stand density and a gamma regression to predict the two parameters of the Weibull used to characterize the diameter distribution. & Results Despite the fact that the operational inventory data is often limited (e.g. species, dbh, height), the accuracy of the models was good and unbiased. It could be integrated into growth models to complete missing sapling distributions and help to correct some recruitment bias. Important differences in species composition, density and diameter distribution were found between plantations and naturally regenerated stands, but only a moderate response in diameter distribution was observed with thinning treatments. & Conclusion These models will enable managers to estimate saplings in intermediate aged softwood forests of eastern Quebec using harvesting inventories or National Forest Inventory. Characterization of differences between plantations and naturally This article is part of the Topical Collection on Mensuration and modelling for forestry in a changing environment Contributions of the co-authors Emmanuel Duchateau: designed figures and tables in the manuscript. Stéphane Tremblay, Robert Schneider: conceived and designed the experiments. Emmanuel Duchateau, Laurie Dupont-Leduc: analyzed the data.
The branch autonomy principle, which states that the growth of individual branches can be predicted from their morphology and position in the forest canopy irrespective of the characteristics of the tree, has been used to simplify models of branch growth in trees. However, observed changes in allocation priority within trees towards branches growing in light-favoured conditions, referred to as ‘Milton’s Law of resource availability and allocation’, have raised questions about the applicability of the branch autonomy principle. We present models linking knot ontogeny to the secondary growth of the main stem in black spruce (Picea mariana (Mill.) B.S.P.), which were used to assess the patterns of assimilate allocation over time, both within and between trees. Data describing the annual radial growth of 445 stem rings and the three-dimensional shape of 5377 knots were extracted from optical scans and X-ray computed tomography images taken along the stems of 10 trees. Total knot to stem area increment ratios (KSR) were calculated for each year of growth, and statistical models were developed to describe the annual development of knot diameter and curvature as a function of stem radial increment, total tree height, stem diameter, and the position of knots along an annual growth unit. KSR varied as a function of tree age and of the height to diameter ratio of the stem, a variable indicative of the competitive status of the tree. Simulations of the development of an individual knot showed that an increase in the stem radial growth rate was associated with an increase in the initial growth of the knot, but also with a shorter lifespan. Our results provide support for ‘Milton’s Law’, since they indicate that allocation priority is given to locations where the potential return is the highest. The developed models provided realistic simulations of knot morphology within trees, which could be integrated into a functional-structural model of tree growth and above-ground resource partitioning.
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