Fleur Longuetaud

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.

Crown plasticity reduces inter-tree competition in a mixed broadleaved forest

The objective of the study was to analyse to which extent horizontal crown plasticity reduces inter-tree competition at stand scale, and how it relates to species growth strategy. Two components of crown plasticity defined at the individual tree level (crown shape distortion, CSD and crown displacement relative to stem, CRD) were analysed and their relative importance in the reduction of competition was quantified. Inter-tree competition at stand scale was estimated using spatial pattern analysis and crown overlap estimation. Measurements were performed in a mixed broadleaved stand of Western Europe. Crown plasticity was shown to regularise the spatial distribution of crowns in comparison with the corresponding stems and to reduce inter-tree competition by optimising space occupation. A significant reduction in crown overlap was observed, mainly due to CRD and secondarily to CSD. At the species level, CSD and CRD were positively correlated. In addition, both were negatively correlated with species shade-tolerance scores. In particular, three European temperate tree species showed contrasting responses, which were related to their known specific ecological strategies. Fagus sylvatica, known to be a highly shade-tolerant species, showed large crowns, low CSD and CRD, indicating a low plasticity and suggesting a strong competitive ability. At the opposite, Quercus sp., known to be clearly less shade-tolerant, exhibited a reduced growth, associated with high CSD and CRD, indicating high crown plasticity and probably a lower competitive ability. For this species, plasticity could be described as passive. Last, Carpinus betulus, known to have a relatively good shade-tolerance, showed a contrasting behaviour with high CSD and CRD and a strong presence in the stand, suggesting high crown plasticity and a good competitive ability. In that case, plasticity was described as rather adaptive.

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.

Difference in shade tolerance drives the mixture effect on oak productivity

Assessing how species productivity in mixtures is influenced by species shade tolerance and phylogeny would be helpful to improve our general understanding of the relationship between tree species diversity and productivity in forests. We investigated the effects of differences in shade tolerance and phylogenetic distances between pairs of species on the productivity of Quercus petraea growing in 18 mixtures in lowland temperate forests. We calculated the mixture effect as the difference in productivity of Q. petraea in mixed vs. pure stands. Our analyses were based on data from seven annual campaigns of the French National Forest Inventory covering 1,573 plots. The mixture effect on Q. petraea productivity increased when the shade tolerance of the companion species decreased. Compared to its productivity in pure stands, Q. petraea productivity in mixed coniferous stands varied from -14.6% up to +39.6% as the shade tolerance of the companion species inversely varied from highest to lowest. With broadleaved companion species, the mixture effect varied from -10% up to +13.9% with decreasing shade tolerance. We found no effect of phylogenetic distance between Q. petraea and the companion species on the mixture effect. Synthesis: Our results confirm that shade tolerance is an important driver of the diversity effect on productivity at species level in temperate forests and that phylogenetic distance is not a relevant proxy for species functional dissimilarity. This article is protected by copyright. All rights reserved.

Pith : a marker of primary growth in Picea abies (L.) Karst.

The primary growth of trees may be studied either by following their development over time, which is costly and requires long-term monitoring, or by a posteriori growth analyses. Trees in temperate forests show rhythmic growth, which is characterised by morphological or anatomical markers. The study described here focuses on the pith of trees as an internal marker for the retrospective analysis of primary growth. Changes in pith size and density were quantified along a stem of Norway spruce [Picea abies (L.) Karst.] with high spatial resolution. The results showed that pith would appear to be a reliable marker of the annual growth rhythm even in the presence of polycyclism. Annual shoot limits were characterised by reductions in pith size associated, at the same time, with increases in pith density. In addition, pith size may provide information about tree ontogeny. The start of the competition with neighbouring trees was very likely responsible for an overall decrease in pith size. Regarding high frequency variations, pith size appeared to be less sensitive to local environmental fluctuations like climate than other studied variables such as annual shoot length and annual ring width. Finally, X-ray computed tomography proved to be a very promising method for the non-destructive detection of annual shoot limits in stems based on longitudinal changes in pith density, as demonstrated in a log of Norway spruce.

Patterns of within-stem variations in wood specific gravity and water content for five temperate tree species

Abstract• Key messageIntensive measurements of basic specific gravity and relative water content of lumens show that within-stem variations strongly depend on species and cannot be summarised through the typical patterns reported in the literature; breast height measurements are not always representative of the whole stem.• ContextKnowledge of the distribution of wood properties within the tree is essential for understanding tree physiology as well as for biomass estimations and for assessing the quality of wood products.• AimsThe radial and vertical variations of basic specific gravity (BSG) and relative water content of lumens (RWCL) were studied for five species: Quercus petraea/robur, Fagus sylvatica, Acer pseudoplatanus, Abies alba and Pseudotsuga menziesii. The observations were compared with typical patterns of variations reported in the literature.• MethodsWood discs were sampled regularly along tree stems and X-rayed in their fresh and oven-dry states.• ResultsAt breast height, BSG was found to clearly increase radially (pith to bark) for two species and to decrease for one species. For F. sylvatica and A. alba, the radial variations of BSG were rather U-shaped, with in particular inner wood areas showing respectively lower and higher BSG than the corresponding mature wood. RWCL increased generally from inner to outer area but wet sapwood was clearly distinguishable only for the coniferous species. Vertical variations of BSG and RWCL were strongly dependant on the species with usually non-linear patterns.• ConclusionThe observed variations of BSG were only partially in agreement with the reported typical radial patterns. Despite the vertical variations, the mean BSG of a cross-section at breast height appeared to be a good estimator of the mean BSG of the whole stem (although the difference was statistically significant for coniferous species), whereas breast height measurement of RWCL was not representative of the whole stem.

Robust Knot Segmentation by Knot Pith Tracking in 3D Tangential Images

This paper proposes a fast, accurate and automatic method to segment wood knots from images obtained by X-Ray Computed Tomography scanner. The wood knot segmentation is a classical problem where the most popular segmentation techniques produce unsatisfactory results. In a previous work, a method was developed to detect knot areas and an approach was proposed to segment the knots. However this last step is not entirely satisfactory in the presence of sapwood. This paper presents a novel approach for knot segmentation, based on the original idea considering slices tangential to the growth rings. They allow to track the knot from the log pith to the bark. Knots are then segmented by detecting discrete ellipses in each slice. A complete implementation is proposed on the TKDetection software available online.

Un algorithme robuste de segmentation des nœuds du bois sur des images obtenues par tomographie x

Les bois de résineux sont très largement utilisés en construction. La nodosité constitue le principal défaut de ces bois car, au-delà de l’aspect esthétique, les qualités mécaniques peuvent se trouver affectées par la présence de nœuds. Les nœuds du bois sont bien visibles sur des images tomographiques et certains industriels commencent à s’équiper de scanners à rayons X pour évaluer et classer leur ressource ou même optimiser le débit. Les algorithmes existants pour segmenter les nœuds dans des images tomographiques (voir la revue bibliographique de Longuetaud et al., 2012) fonctionnent en général mal dans l’aubier humide des résineux dont la densité se confond souvent avec celle des nœuds. Les travaux récents de Aguilera et al. (2012), Breinig et al. (2012) et Johansson et al. (2013) ont proposé différentes pistes pour segmenter les nœuds du bois humide. La méthode que nous avons développée (Krähenbühl et al., 2014) est une alternative à ces méthodes, robuste et adaptée aux conditions industrielles.

Une base de données unique en France de cubages d’arbres individuels (volumes, biomasses) au service d’une modélisation générique de la ressource en bois énergie

A base for volume and biomass data of the aerial woody compartments of individual trees was constituted under the ANR EMERGE (French acronym for ‘designing models for a robust, all-purpose estimation of wood energy’) project by seven bodies involved in forest research and management in France (ONF, INRA, Cemagref, IFN, FCBA, CNPF and CIRAD) so as to come up with a robust model of woody resources in forests. These measurements, taken for various logging diameters, sometimes down to the slenderest branches, have been performed since the beginning of the 20th century forming a unique data base in France. The data cover a broad range of age groups, sizes, species, stand structures and environmental factors (soil, climate). Of particular interest is the distribution of the available data in relation to French resources as estimated in the National Forest Inventory so as to use sampling campaigns to collect missing information under the EMERGE project. Another significant feature is the potential for designing robust, all-purpose models of volumes and biomass for various logging diameters depending on species, stage of development, geographic gradients, variations in silvicultural practises and possible effect of date of measurement.