Frédéric Mothe

Picea abies sapwood width: Variations within and between trees

Abstract This study focused on the amount of sapwood and its variation by means of computed tomographic (CT) imaging. Twenty-four trees were selected from four Norway spruce [Picea abies (L.) Karst.] stands in north-eastern France, varying in age, density and fertility. In each stand, sampled trees represented the dominant, co-dominant and suppressed strata. The heartwood/sapwood boundary was detected from the CT images, and the heartwood and sapwood amount and their variations were then evaluated. At the within-tree level sapwood width was relatively constant along the tree stem above the butt swelling and below the living crown. The between-tree sapwood width variations were partially explained by the total cross-sectional area of living branches. This result opens up the possibility of investigating within-tree allometric relationships. Sapwood width was found to be highly correlated with tree slendemess (tree height/breast height diameter) and with the relative height of the crown. This suggests that sapwood width could be readily predicted from conventional forest inventory measurements. The number of sapwood rings within the stem was largely dependent on cambial age, and could be determined dynamically using the concept of mean lifetime of sapwood rings.

Cutting forces in wood machining – Basics and applications in industrial processes. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Abstract The data available in the literature concerning wood cutting forces permits to build models or to simulate the main wood machining processes (milling, sawing, peeling, etc.). This approach contributes to a better understanding of formation of wood surfaces and chips and the data may be helpful to optimise cutting geometry, reduce tool wear, improve tool material, and to size tool-machines. The models may also be useful for industrial application in two ways: (1) providing data to optimise the settings for a given operation (batch approach), and (2) building predictive models that could be the basis of an online control system for the machining processes (interactive approach). A prerequisite for this is that numerous machining tests on different wood materials are performed based on experiences with different kind of tools and experimental devices. With a focus on potential industrial applications, the emphasis of this review was on the wood peeling process, which is a very demanding special case of wood cutting. Although not so many industrial machines are equipped with expensive force sensors, there is a lot of high quality information available about cutting forces which may be useful to improve the scientific or technological knowledge in wood machining. Alternative parameters, such as vibration or sound measurements, appear to be promising substitutes in the praxis, particularly to feed online control systems of any wood cutting process.

Detailed analysis of the geometric relationship between external traits and the shape of red heartwood in beech trees (Fagus sylvatica L.)

Frequently occurring red heartwood decisively restricts the volume of light-coloured beech wood, which can be processed to high-grade appearance products. Forestry and wood industry lack suitable means for maximising the yield of light timber, since the intra-tree extent of red heartwood varies considerably. The present study characterised in detail the intra-tree shape of red heartwood and its relationships to tree-external traits (dead branches, branch scars), considered as possible initiation points of red heartwood formation. An experimental method based on log scanning and image analysis was developed and applied. Using its output for three-dimensional visualisation and data analyses, external traits being linked to the local red heartwood shape were identified. Furthermore geometric relationships were established for characterising these external traits and for deriving discriminating criteria.

A digital photographic method for 3D reconstruction of standing tree shape

A digital photographic method is presented which is able to reconstruct the profile of the stem on standing trees up to a height of 12 m and to provide a fine level of detail. The method uses two digital photographs taken at 90° to each other and does not require special illumination conditions. A method is proposed to perform the data acquisition process from the two photographs and to transform the stem dimensions and 3-D position from pixels to units of length. The accuracy of this method for measuring tree shape was tested by comparing the results with those obtained from a laser system. The comparison showed that the photographic method provides a good assessment of standing tree shape.RésuméLa méthode photographique présentée dans cet article permet la reconstruction en 3D du profil du tronc d’arbres sur pied jusqu’à une hauteur de 12 m. On utilise un appareil photo numérique pour faire deux prises de vue orientées à 90° l’une de l’autre. Il n’y a pas de contrainte particulière d’éclairage. Le traitement des images conduit à la représentation tridimensionnelle des tiges et à la mesure des indicateurs de forme. La précision de la méthode proposée est évaluée par référence à des mesures réalisées avec un théodolite à visée laser. Les résultats montrent que la méthode photographique permet des mesures précises de la forme des arbres.

Knot Detection in X-Ray CT Images of Wood

This paper presents an original problem of knot detection in 3D X-ray Computer Tomography images of wood stems. This image type is very different from classical medical images and presents specific geometric structures. These ones are characteristic of wood stems nature. The contribution of this work is to exploit the original geometric structures in a simple and fast algorithm to automatically detect and analyze the wood knots. The proposed approach is robust to different wood qualities, like moisture or noise, and more simple to implement than classical deformable models approaches.

Knot segmentation in 3D CT images of wet wood

This paper proposes a fully automatic method to segment wood knots from images obtained by an X-ray Computed Tomography scanner. Wood knot segmentation is known to be a difficult problem in the presence of sapwood because of the quite similar density of knots and wet sapwood. Classical segmentation techniques produce unsatisfactory results due to the very weak distinction between these two intensities. To overcome this limitation caused by physical characteristics, we propose to exploit the geometric properties of both the knot shapes and knot-sapwood interface. Based on previous work related to automatic knot detection, a new segmentation algorithm is proposed that uses a robust curvature estimation of 2D digital contours. The segmentation process is fast, easily parallelizable and produces better segmentation results than other state-of-the-art algorithms. It may be reproduced from the precise description given here or from source code available online.

Approach to the estimation of red heart occurrence in Fagus sylvatica based on geometric relationships between branch scar development and knot dimensions

Abstract The effect of branch scars on the initiation and occurrence of red heart in beech (Fagus sylvatica L.) was studied on 17 trees with red heartwood and 14 trees with no discoloured heartwood, all of which were selected from a 120-year-old high-forest stand in Germany. Logistic regression was used to predict the probability of red heart occurrence for a given tree. The model was based on individual probabilities derived from geometric relationships between scar and knot morphologies, and integrated the diameter at breast height. Using this model, 27 of 31 trees were correctly classified, and the two groups of trees were clearly distinguished by probabilities below 0.25 and above 0.85 (with one exception). Given the constitution of the model, only 17 of 616 scars were found to initiate red heart formation, and the parameters of mechanistic variables were strongly correlated. The results suggest specifying the relationship between scars, knots and red heart, and extending the scope of the model.

Does past emergence of epicormic shoots control current composition of epicormic types

Abstract• ContextWhile past studies on epicormics in oak (Quercus sp.) have focused on the effect of thinning on epicormic shoots emergence, the consequences of this emergence on the epicormic ontogeny and future wood quality have rarely been asked.• AimsThis paper aims to quantifying the relationship between past emergence and current composition of epicormics.• MethodsThree thinning experiments with Quercus petraea (Matt.) Liebl. or Quercus robur L. were investigated. Epicormic shoots were regularly tallied and epicormic composition recorded recently. Some logs were scanned using X-ray computed tomography (CT).• ResultsPast tallies on both species were mainly and positively related to the current frequency of bud clusters and burls. This was due to the production of buds by epicormic shoots for only certain trees, as evidenced by CT, and mainly to correlated numbers of current epicormic shoots, bud clusters and burls, all originating from a past common set of buds and bud clusters.• ConclusionThe important tree effect on both species suggests that oak silviculture can be optimized by the early selection of crop trees with few epicormics and/or eventually a first and heavy thinning that helps in spotting remaining individuals being prone to the development of multiple epicormics.

A PROCEDURE BASED ON CONDITIONAL PROBABILITIES TO ESTIMATE PROPORTIONS AND DENSITIES OF TISSUES FROM X-RAY IMAGES OF QUERCUS PETRAEA SAMPLES

This paper describes a procedure to estimate within-ring proportions and densities of earlywood vessels, fibres and parenchyma, and then validates the procedure for each tissue type. The procedure uses conditional probabilities for these estimates. It was developed using 16 annual growth rings of contrasting anatomy sampled from five mature sessile oaks (Quercus petraea Liebl.). The X-ray images of the sampled rings were converted into density maps and the two components of the rings (i.e. earlywood and latewood) were delimited manually. First, mean tissue densities of individual rings were estimated from anatomical characteristics combined with a simple analysis of the frequency histograms of density in earlywood and latewood. Second, the procedure used the radial position and density of each point of a digitised ring to calculate a probability for a point belonging to either vessels, multiseriate wood rays, fibres or axial parenchyma. The procedure was evaluated using i) measurements of tissue proportions from anatomical sections and ii) measurements of tissue densities performed on X-ray images. The validation demonstrates that the procedure provides an accurate estimation of the proportion and density of earlywood vessels, fibres and axial parenchyma in earlywood and latewood. However, it also demonstrates that the procedure is not sufficiently effective to estimate the proportion of multiseriate wood rays.

Variations in the natural density of European oak wood affect thermal degradation during thermal modification

Key messageThermogravimetric analysis, performed on small samples of earlywood (EW) or latewood (LW), indicated that earlywood is more susceptible to thermal degradation than latewood. These results suggest a direct relationship between wood density (which depends on the EW/LW ratio and indirectly on silviculture) and the response of wood during thermo-modification processes.ContextOne of the main difficulties in developing thermo-modified wood products at an industrial scale lies in the difficulty of obtaining consistent products with a stable quality (durability, dimensional stability, color). This may be due either to the thermal treatment process itself or to inter- or intra-specific heterogeneity of wood properties.AimsWe investigated the effect of the natural variability of oak wood, particularly in density, on the degree of thermo-degradation during thermal treatments.MethodsX-ray computed tomography was used to assess the effect of initial wood density of oak boards on their thermo-degradation. Intra-ring wood density was estimated using thermogravimetric analysis and micro-densitometry.ResultsX-ray CT did not allow establishment of a clear correlation between initial wood density and mass loss due to thermo-degradation, while thermogravimetric analysis, performed separately on earlywood and latewood samples, revealed a larger susceptibility to thermal degradation of the less dense earlywood samples compared to more dense latewood samplesConclusionInitial wood density, which is directly controlled by the earlywood/latewood ratio modulated by silvicultural practices, directly influences thermo-degradation during thermal treatment. Initial wood density therefore appears to be a potential parameter influencing industrial thermal treatment processes.