The mechanics of wood as a material for construction, furniture, pulp and other uses have been addressed in a very large number of papers and are a well-established field for both research and technical applications (for example among many others, see Pöhler et al., 2006 for beechwood). In addition to such approaches that derive from material sciences, further developments based on similar physical concepts addressed the questions raised by the biomechanics of the standing and the growing tree which requires some degree of postural control and sensing of specific signals (gravity, movements…; see for instance Fournier et al. 2013; Dlouha et al., 2025). Within this field of research, the question of the correlation of wood anatomy (diameter of xylem tracheids or vessels, fibre content and angles, vessel wall thickness… ) and biomechanical properties is of prime importance, and specific responses of wood and bark components have been identified over the last decades. In particular the occurrence of reaction wood generates local strains and contributes to the postural control (Ruelle, 2014).

In this preprint, Almeras et al. address a complementary question related to the properties of juvenile wood in trees. During the first years of the growth of young trees, the annual tree rings display quite specific properties (large tree rings, less dense wood, …) that gradually change with age and dimensions of the trees until reaching a range of values typical for adult trees. During the first years, the interannual changes might follow an ontogenetic trajectory mainly related to age (and dimensions) while in later stages, they appear to be strongly controlled by environment (wind, soil fertility, site index, irradiance, water availability, ...). All these changes result in radial profiles along tree rings (from the pith to the bark) of three main features that govern the biomechanical properties of wood, namely the width of the annual tree ring, the local specific gravity (wood density), and the specific modulus which contributes with density to the local modulus of elasticity (Fournier et al. 2013). Such gradients of local wood properties within stems have been analysed and synthesised in the last years (Lachenbruch et al. 2011, Meinzer et al. 2014). 

Here, the authors address the question of local variations of such properties within tree stems as a function of the distance to the pith (inversely related to the age of the trees when the ring was formed) in a broadleaved species, European Beech (Fagus sylvatica L.). They checked whether ring width, specific gravity and specific modulus display systematic trends from pith to bark across tree stems, and whether these trends enable the detection of a general ontogenic (age-related) effect with very similar patterns in juvenile wood of different individuals, or whether adaptive factors (modulated by the environment and by the mechanical constraints induced by the postural control of growth) dominate already in juvenile wood, like it does at later stages. Such questions were already analysed in the wood of some coniferous species (softwood with tracheids), but less frequently in hardwood species (angiosperms, like Beech with its diffuse porous wood anatomy).

Before starting the analysis of age-related tree ring properties in juvenile wood, the authors addressed the potential impact of duraminisation, which affects the oldest tree rings in the inner wood (that is those formed during the juvenile growth stages). Duraminisation results from local deposition of a number of secondary metabolites and results in the build-up of heartwood; in the case of beech however, reddish heartwood is less present than in other species (Knoke, 2003). Almeras et al showed here that the occurrence of reddish wood did only marginally affect the mechanical properties and contributed only marginally to the observed variations among trees 

The very solid experimental design enabled the authors to clearly assign a fraction of the observed variation in the three parameters to (i) the site where trees had grown, (ii) to the individuals within these sites and (iii) to the position of the ring within the stem. The intraindividual component of the variation was much larger than the former. However, the observed asymmetry in the patterns of ring properties in juvenile wood, and the large variability in these patterns among trees led the authors conclude that the ontogenic juvenility effects, visible in ring width were largely dominated by other effects influenced by the local environment. In this respect, the results differ from those that were recorded earlier with Pinus taeda L. in a plantation (i.e., trees of the same age and homogenous spatial distribution, Bendtsen and Senft, 1986). 

The recommended version of the preprint is very original as it shows how local (radial) variations of biomechanical wood properties can be addressed in a systematic way. This lead to novel approaches that share light on the processes governing wood formation in trees.

The first version of the preprint was submitted over a year ago. The recommended version differs in many respects from the initial one. The two rounds of reviews with external reviewers, and the additional one with the recommender resulted in an in-depth reorganisation of the statistical analysis and of the demonstration. This took some time, but shows also the benefits that may be gained during an open peer review process like the one developed by the Peer Community in…. 

References

Bendtsen BA, Senft J. 1986. Mechanical and anatomical properties in individual growth rings of plantation-grown eastern cottonwood and loblolly pine. Wood Fiber Sci 18: 23-38. 

Dlouhá J, Moulia B, Fournier, M et al. 2025 Beyond the perception of wind only as a meteorological hazard: importance of mechanobiology for biomass allocation, forest ecology and management. Ann For Sci 82, 1. https://doi.org/10.1186/s13595-024-01271-6 

Fournier M, Dlouha J, Jaouen G, Alméras T. 2013. Integrative biomechanics for tree ecology: beyond wood density and strength. J Exp Bot, 64, 4793-4815. https://doi.org/10.1093/jxb/ert279

Knoke T. 2003 Predicting red heartwood formation in beech trees (Fagus sylvatica L.)? Ecol. Model. 169, 289-312. https://doi.org/10.1016/S0304-3800(03)00276-X 

Lachenbruch, B., Moore, J.R., Evans, R. (2011). Radial Variation in wood structure and function in woodypPlants, and hypotheses for its occurrence. In: Meinzer, F., Lachenbruch, B., Dawson, T. (eds) Size- and age-related changes in tree structure and function. Tree Physiology, vol 4. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-1242-3_5 

Longuetaud F, Mothe F, Santenoise P, Diop N, Dlouha J, Fournier M, Deleuze C. 2017. Patterns of within-stem variations in wood specific gravity and water content for five temperate tree species. Ann For Sci 74:64. https://doi.org/10.1007/s13595-017-0657-7

Meinzer, F., Lachenbruch, B., Dawson, T. (eds). 2014. Size- and age-related changes in tree structure and function. Tree Physiology, vol 4. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-1242-3_5 

Pöhler E, Klingner R, Künniger T. 2006. Beech (Fagus sylvatica L.) - Technological properties, adhesion behaviour and colour stability with and without coatings of the red heartwood. Ann For Sci 63: 129-137. https://doi.org/10.1051/forest:2005105

Ruelle J. 2014. Morphology, anatomy and ultrastructure of reaction wood. In: Gardiner B, Barnett J, Saranpää P, Gril J (eds) The Biology of Reaction Wood. Springer Series in Wood Science. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-10814-3_2 

Cite the recommended preprint: 

Almeras Tancrède, Jullien Delphine, Liu Shengquan, Loup Caroline, Gril Joseph, Thibaut Bernard (2025) The diversity of radial variations of wood properties in European beech reveals the plastic nature of juvenile wood. HAL, ver.6 peer-reviewed and recommended by PCI Forest and Wood Sciences https://hal.science/hal-04133248

This interesting preprint develops a new model with a quite strange name (see below why this name was used by the authors) that aims at describing the growth of mixed forests (it may also be used for monospecific forests with a regular or irregular structure). It is based on two main features: it is a process-based model that integrates a tree-tree interaction module. The model derives from the modelling framework « Physio-demo-genetics model PDG » developed earlier at INRAE-Avignon, and « Castanea », developed at Orsay and Avignon as a widely used stand-level process-based model. « Arena » underlines the competition between trees in mixed stands. The « PDG-Arena » model was developed on the Capsis platform (https://capsis.cirad.fr/capsis/presentation), which is a shared platform for the development of tree growth models under a very open framework maintained by several French institutions.

The reviewers and the recommender saw two important strengths in the preprint : (i) PDG-Arena is definitely a significant improvement when compared to the existing models and may be used for accurately predicting the growth and dynamics of mixed stands ; (ii) it was validated against an impressive data set gained in a quite impressive network of mixed stands of beech (Fagus sylvatica L.) and silver fir (Abies alba Mill.) with a 5-year growth analysis at individual tree level (based on two detailed surveys at individual tree level. PDG-Arena could properly predict the growth of these stands and showed significant improvements for the existing models.

During the review process, many important questions were raised, some directly related to the manuscript (which the authors addressed very convincingly during the revision of the first version of the preprint), and some refering to more general debates around predictive forest growth models able to integrate long-term changes. For instance, the long-lasting debate opposing the proponents of process-based forest growth models (that might require a large number of sometimes difficult-to-document processes leading to growth predictions, Forrester et al. 2016) and phenomenological models that directly link actual (recorded) growth and stand dynamics to climate and soil variables, is not yet settled. Both approaches display strengths and weaknesses. Similarly, the ability of both families of models to predict the impact of extreme events induced by climate change (like severe drought episodes associated to high temperatures likely to happen at higher frequencies in the near future) remains to be assessed and is the main challenge for this area of research. 

A second question that raises large interest is whether mixed forest stands display a larger resilience to future climate changes than monospecific and homogenous stands. Camille Rouet and his colleagues present convincing results that this is the case (both using their model and from the recorded data). However, there is still debate whether the observed over-yielding in mixed forests under favourable conditions will be maintained under severe drought episodes and after a return to more favourable water availability and moderate temperatures (Jourdan et al, 2019; Jourdan et al, 2020).

The model is available for testing under the condition of participating to the CAPSIS community (which gives access to the shared resources available on the platform. The codes and data used to test the performance of the model can be accessed on the Zenodo data repository. 

This preprint should open the way for fruitful cooperation and further improvements in a very important area for forest science in the near future.

References

Camille Rouet, Hendrik Davi, Arsène Druel, Bruno Fady, Xavier Morin (2024) PDG-Arena: An ecophysiological model for characterizing tree-tree interactions in heterogeneous and mixed stands. bioRxiv, ver.3 peer-reviewed and recommended by PCI Forest and Wood Sciences https://doi.org/10.1101/2024.02.09.579667

Jourdan, M., Kunstler, G., Morin, X., 2020. How neighbourhood interactions control the temporal stability and resilience to drought of trees in mountain forests. Journal of Ecology 108, 666–677.  https://doi.org/10.1111/1365-2745.13294 

Jourdan, M., Lebourgeois, F., Morin, X., 2019. The effect of tree diversity on the resistance and recovery of forest stands in the French Alps may depend on species differences in hydraulic features. Forest Ecology and Management 450, 117486. https://doi:10.1016/j.foreco.2019.117486 

Forrester, D.I., Bauhus, J., 2016. A Review of Processes Behind Diversity Productivity Relationships in Forests. Current Forestry Reports 2, 45–61. https://doi:10.1007/s40725-016-0031-2  

Mey, R., Zell, J., Thürig, E. et al. , 2022. Tree species admixture increases ecosystem service provision in simulated spruce- and beech-dominated stands. European Journal of Forest Research 141, 801–820 (2022). https://doi.org/10.1007/s10342-022-01474-4 

This preprint (Bouffier et al, 2023) analyses different biological (tree genotype, age, flowering phenology) and environmental factors (vicinity with external pollen sources, orchard structure, soil type, climatic conditions) with influence on the of seed lots in seed orchards of an important forest tree species (Pinus pinaster Ait.).  The analysis is based on an optimized set of 60 SNP markers that constitute a new tool for characterizing improved material in the breeding program of the species.

One of the main questions when managing seed orchard is to obtain a precise estimation of pollen contamination, as it causes major losses to genetic improvement from selection and breeding (Di Giovanni and Kevan, 19911) but also will determine the adaptive potential of the species (Kremer et al. 2012). The results indicate that contamination rates were highly variable between seed lots (from 20 to 96%), with a mean value of 50%). The main factors determining these rates include the distance between the seed orchard and external pollen sources, rain during the pollination period, seed orchard age, soil conditions and seed parent identity. 

A second point of interest in this paper is the determination of the overall self-fertilization rate. This factor also determines the quality of the seed-lots and was estimated as 5.4%, with high variability between genotypes (from 0% to 26%). The overall value is of the same order of magnitude than in other species. 

These results are used to define some recommendations for managing seed orchards in the French breeding program, but that can be generalized to other species (eg. Mullin and Lee, 2013). As an example, they recommend that sampling 100 seeds annually should be sufficient to estimate pollen contamination (with a standard error of 5%). Also, they suggest that one of the main measures to reduce pollen contamination is carefully selecting the location of the orchard, in terms of its distance from external pollen sources and soil conditions, and not collecting seeds from young trees (below 8 years old). 

The present preprint revisits an important topic of research with interest for the biology of tree species, but also with great implications in applied breeding activities. The main conclusions are essential to understand the importance of different factors in managing seed orchards and in the future performance of the reproductive material. 

In conclusion, this paper stresses the need for more studies, taking advantage of new genomic tools, to advance the knowledge of factors influencing the success of breeding programs.

REFERENCES

Bouffier L, Debille S, Alazard P, Raffin A, Pastuszka P, Trontin JF (2023). Pollen contamination and mating structure in maritime pine (Pinus pinaster Ait.) clonal seed orchards revealed by SNP markers. bioRxiv, 2022.09.27.509769, ver. 2 peer-reviewed and recommended by Peer Community in Forest and Wood Science. https://doi.org/10.1101/2022.09.27.509769

Di-Giovanni F, Kevan PG (1991) Factors affecting pollen dynamics and its importance to pollen contamination: a review. Can J For Res 21(8):1155-1170.
https://doi.org/10.1139/x91-163
 
Kremer A, Ronce O, Robledo-Arnuncio JJ, Guillaume F, Bohrer G, Nathan R, Bridle JR, Gomulkiewicz R, Klein EK, Ritland K, Kuparinen A, Gerber S, Schueler S (2012) Long-distance gene flow and adaptation of forest trees to rapid climate change. Ecol Lett 15(4):378-92.
https://doi.org/10.1111/j.1461-0248.2012.01746.x

Mullin TJ, Lee SJ (2013) Best practice for tree breeding in Europe. Skogforsk, Uppsala, Sweden. ISBN: 530 978-91-977649-6-4. https://www.skogforsk.se/contentassets/42acda01f83843bf925f690bd0a6ed37/best-practice-hela-low.pdf

​​​​​Fires in the Anthropocene, whether natural or human-induced, are among the main factors of deforestation, threatening forest resilience and biodiversity (Kelly et al. 2020). Fire events have also increased in occurrence and severity worldwide in the past decade (e.g. Whitman et al. 2022, Ribeiro et al. 2020). In this context, we need to better understand the links between fire occurrence and their impact on forest loss, especially in countries where such knowledge is lacking.

The work by Martinez-Batlle addresses this need as it thoroughly describes forest loss and fire patterns across the forests of the Dominican Republic (DR), and systematically tests their spatial and temporal correlations across the DR regions since 2001. To this end, the author combines two independent databases from NASA: the Global Forest Change 2000-2018 data service, and remotely sensed data on fire/hotspot occurrence. The author then provides a state-of-the-art analysis pipeline that first shows significant spatial autocorrelations in both forest loss and fire density over the whole period, and each year across the period. Detailed maps of zonal statistics across hexagonal grids also illustrate clusters of either high or low forest loss and fire points, and distinguish small or large clearings. Second, these spatial dependencies are accounted for in spatial autoregressive models, and congruent patterns of forest loss and fire density are shown across the 2001-2018 period in the DR. This is consistent with the initial working hypothesis of a link between deforestation and slash and burn agriculture. Third, detailed time-series analyses and modelling show common cyclical patterns for forest loss areas in large clearings, number of small clearings, and fire density in the first 14 years, with no increasing trends. In contrast, fire density does not predict extensive forest loss in the eastern half of the country for most years. Finally, yearly maps clearly depict uncontrolled wildfires that impacted larger areas in recent years in both the central and southern mountain ranges of the DR.

This work, therefore, provides a solid, detailed, and rigorous account of the current status of forest loss across the DR, and of its causes, either from recurrent fires due to shifting agriculture or from farming linked to tourism expansion. These results could be very useful for designing strategies adapted to each particular zone of the DR, for preventing human-induced fires or managing wildfires, and for planning post-fire reforestation. This is true, especially for core protected areas where an increasing trend of forest loss is identified in the last 8 years (up to 25% in some mountainous and inaccessible areas of the DR). In those areas, the author suggests implementing a natural regeneration program. Indeed, recent scientists’ warnings stress that fires should be accounted for when planning reforestation for climate change mitigation (Leverkus et al. 2022), with evidence in different ecosystems, that natural regeneration with local seed banks would benefit their post-fire recovery. As proposed by the author, this new knowledge for the DR should also help develop policies for managing forest fires and biodiversity, which are lacking in areas close to tourism facilities. More generally, this study offers methods and graphical representations that are likely to inspire future work with similar databases in other countries where data are scarce, on either spatial trends or temporal evolution of forest cover, or fire activities, or both.

References

Kelly LT, Giljohann KM, Duane A, Aquilué N, et al. (2020). Fire and biodiversity in the Anthropocene. Science, 370(6519), eabb0355. https://doi.org/10.1126/science.abb0355

Leverkus AB, Thorn S, Lindenmayer DB, Pausas JG (2022) Tree planting goals must account for wildfires. Science 376(6593): 588-589. https://doi.org/10.1126/science.abp8259

Martinez Batlle JR (2022) Fire and forest loss in the Dominican Republic during the 21st Century. bioRxiv, 2021.06.15.448604, ver. 4 peer-reviewed and recommended by Peer Community in Forest and Wood Science. https://doi.org/10.1101/2021.06.15.448604

Ribeiro LM, Viegas DX, Almeida M, McGee TX, et al. (2020) 2 - Extreme wildfires and disasters around the world: lessons to be learned. In F. Tedim, V. Leone, T.K. McGee (Eds.), Extreme Wildfire Events and Disasters, Elsevier Inc. 31-pp. 51. https://doi.org/10.1016/B978-0-12-815721-3.00002-3

Whitman et al. (2022) Climate-induced fire regime amplification in Alberta, Canada. Environ. Res. Lett. 17(5): 055003. https://doi.org/10.1088/1748-9326/ac60d6

Trees are constantly subjected to mechanical stresses (gravity, wind, storms) but they have a remarkable ability to remain upright despite their great size. Straightness is also major characteristic that greatly determines the quality and market value of a log. For some species, maritime pine in particular, this is even a default that geneticists are trying to correct through dedicated breeding programs (Bartholomé et al. 2016). If trees are able to maintain a straight trunk, or to return to straightness after a growth accident, for example, it is thanks to an "engine" whose mechanisms are now better known (Moulia et al. 2021). This mechanism lies in the structure of the trunk itself and the ability of trees to produce cells and tissues that display different mechanical properties during their maturation. Some fibers will "pull" the trunk in one direction, known as tension wood, while others will « push » it in the opposite direction (compression wood). The posture control of a tree is therefore directly related to the growth process of the trees and the placement of this reaction wood at specific points in the trunk. The internal structure of the trunk will therefore retain the memory of these growth constraints throughout its life and, if we are able to read it, we can envisage reconstructing its history over the years. This source of information contained in tree rings is still largely unexplored. However, it can reveal insights into the evolution of the climate, or help foresters to select the most valuable trees. Sophisticated approaches exist to measure these growth forces in wood, but the major difficulty remains our ability to read the mechanical properties with simpler, more widely used methods. The article by Thibaut and Gril (2021) proposes such a methodology.

The approach used here is similar to the one used for other wood functions, such as sap transport: linking the mechanical function of wood to its structural properties. The transport capacity of wood is for example well explained by the distribution of vessel sizes. However, other interesting properties, such as resistance to cavitation, are only very weakly explained by the same anatomical characteristics. The authors, after analyzing the wood properties of many species, both tropical and temperate, conclude that growth forces can be deduced from variables that are relatively simple to measure, such as wood density or moduli of elasticity.  The article provides a series of generic and more specific equations and relationships that allow these growth forces to be estimated. 

I recommend this article to people who want to learn about the principles and concepts of tree biomechanics. I also recommend it to people who want to further explore the mechanical properties of trees and who will be able to characterize them thanks to the method proposed here by the authors.  

References

Bartholomé J, Bink MC, Heerwaarden J van, Chancerel E, Boury C, Lesur I, Isik F, Bouffier L, Plomion C (2016) Linkage and Association Mapping for Two Major Traits Used in the Maritime Pine Breeding Program: Height Growth and Stem Straightness. PLOS ONE, 11, e0165323. https://doi.org/10.1371/journal.pone.0165323

Thibaut B, Gril J (2021) Tree growth forces and wood properties. HAL, hal-02984734, ver. 4 peer-reviewed and recommended by Peer community in Forest and Wood Sciences. https://hal.archives-ouvertes.fr/hal-02984734

Moulia B, Douady S, Hamant O (2021) Fluctuations shape plants through proprioception. Science, 372. https://doi.org/10.1126/science.abc6868