• Background and Aims Forest tree saplings that grow in the understorey undergo frequent changes in their light environment to which they must adapt to ensure their survival and growth. Crown ...architecture, which plays a critical role in light capture and mechanical stability, is a major component of sapling adaptation to canopy disturbance. Shade-adapted saplings typically have plagiotropic stems and branches. After canopy opening, they need to develop more erect shoots in order to exploit the new light conditions. The objective of this study was to test whether changes in sapling stem inclination occur after canopy opening, and to analyse the morphological changes associated with stem reorientation. • Methods A 4-year canopy-opening field experiment with naturally regenerated Fagus sylvatica and Acer pseudoplatanus saplings was conducted. The appearance of new stem axes, stem basal diameter and inclination along the stem were recorded every year after canopy opening. • Key Results Both species showed considerable stem reorientation resulting primarily from uprighting (more erect) shoot movements in Fagus, and from uprighting movements, shoot elongation and formation of relay shoots in Acer. In both species, the magnitude of shoot uprighting movements was primarily related to initial stem inclination. Both the basal part and the apical part of the stem contributed to uprighting movements. Stem movements did not appear to be limited by stem size or by stem growth. • Conclusions Stem uprighting movements in shade-adapted Fagus and Acer saplings following canopy disturbance were considerable and rapid, suggesting that stem reorientation processes play a significant role in the growth strategy of the species.
The effects of population density and summer drought were analysed by means of diameter and height growth in sessile oaks (Quercus petraea) on the stand and individual tree scales. Dendrometric ...inventory data collected from two networks of silvicultural experimentation were used (LERFOB and GIS Coop networks, 9 sites, 31 plots, 99 inventories, ages from 10 to 120 years). These networks study the effects of a broad range of densities, from freely growing trees (relative density index, or RDI, close to 0) to maximum density situations where self-thinning occurs (RDI equal to or in excess of 1). Climate conditions vary from 660 to 850 mm per year with a heat gradient of 9.5 to 11.5 °C (average 1990-2010). Generally speaking, density very strongly affects tree and stand growth, with drought playing a secondary role that is nonetheless significant. Overtopped trees contribute very little to the growth of the stand, particularly when the stand is dense. Drought reduces growth, particularly that of non-dominant trees. Density and drought therefore have the same effect: they accentuate growth differences between trees when stresses are greater. By allocating more resources to diameter growth as compared to height growth, trees in open stands are more “stocky”. In contrast, in densely populated stands, there is “a race for light” making for greater height growth, especially that of overtopped trees. In all cases, drought has a greater effect in reducing height growth than in reducing diameter growth. Finally, following a particularly severe drought (1976), trees recovered most quickly at the drier sites (recovery in 2 years) while the overtopped trees in the higher density stands recovered very little (still no recovery 7 years later). These results suggest that sessile oak adapts better in drier conditions.
Les effets de la densité du peuplement et de la sécheresse estivale ont été analysés sur la croissance en diamètre et en hauteur du Chêne sessile (Quercus petraea) à l’échelle du peuplement et de l’arbre. Les données des inventaires dendrométriques issues de deux réseaux d’expérimentations sylvicoles ont été utilisées (réseaux LERFOB et GIS Coop, 9 sites, 31 placettes, 99 inventaires, âges de 10 à 120 ans). Ces réseaux étudient les effets de larges gradients de densité, depuis des arbres en croissance libre (relative density index, ou RDI, proche de 0) jusqu’à des situations de densité maximale avec des phénomènes d’autoéclaircie (RDI supérieur ou égal à 1). Les conditions climatiques varient de 660 à 850 mm par an pour un gradient thermique de 9,5 à 11,5 °C (moyenne 1990-2010). D’une façon générale, la densité module très fortement la croissance des arbres et du peuplement, la sécheresse jouant un rôle secondaire mais néanmoins significatif. Les arbres dominés participent peu à la croissance du peuplement et ceci est d’autant plus vrai que le peuplement est dense. La sécheresse réduit la croissance et ceci particulièrement pour les arbres non dominants. Ainsi densité et sécheresse ont le même effet, c’est-à-dire qu’elles accentuent les différences de croissance entre arbres quand les contraintes augmentent. En allouant davantage de ressources à leur croissance en diamètre par rapport à leur croissance en hauteur, les arbres dans les peuplements ouverts sont « trapus ». Au contraire, dans les peuplements denses, c’est la « course à la lumière » avec une croissance en hauteur accrue et ceci d’autant plus que l’arbre est dominé. Dans tous les cas, la sécheresse réduit davantage la croissance en hauteur que la croissance en diamètre. Enfin, après une sécheresse exceptionnelle (1976), la récupération des arbres a été la plus rapide sur les sites les plus secs (récupération après 2 ans) et elle fut très faible pour les arbres dominés dans les peuplements les plus denses (toujours pas de récupération après 7 ans). Ces résultats suggèrent une meilleure adaptation des chênes sessiles dans les conditions plus sèches.
• Premise of the study: Gravitropic movements are unexpected mechanical processes that could disturb tree design allometries derived from the physics of nonliving bodies. We investigated whether the ...scaling law of gravitropic performance (power of −2 of stem diameter) derived from integrative biomechanical modeling is disturbed by ontogeny or environment, then discuss the silvicultural and dendroecological consequences.• Methods: In a beech (Fagus sylvatica) plantation, four plots with different initial planting densities evolved without any intervention for 26 yr. Regular tree inventories and a silvicultural model were used to monitor competition over time in each plot. The radial production of tension wood was quantified using a cross-section of the stems at 1.30-m height, and an integrative biomechanical model computed the tree gravitropic performance over time.• Key results: All trees developed tension wood over the whole period, with higher amounts at the youngest age, resulting in theoretical lean corrections of ca. 20–30° on the first 4 m of the stem over the whole period. The scaling law of gravitropic performance is slightly larger than the power of −2 of stem diameter.• Conclusions: Gravitropic performance in forest ecosystems is mainly limited by size (diameter). Ontogenic acclimation of tension wood formation allows the youngest trees to be more reactive. No additional effect of spacing was found. However, silviculture influences size and, therefore, tree reactivity at a given age. Such results will be helpful for dendroecological approaches that use wood as a marker of environmental disturbances or a trait linked to plant strategies.
Numerous plant colonizations have been putatively attributed to deer, based on plant species traits, fur brushing or dung analyses. But, in woodlands, direct links between the expansion of zoochorous ...plant species and ungulate presence have seldom been reported. Based on coupled floristic and browsing surveys, repeated in time, we analysed the causes of the spatio-temporal progression of the epizoochorous species Cynoglossum germanicum over 30 years in a network covering an 11000 ha forested area in north-eastern France. In this area, deer populations reached a peak in the 1970s, then were reduced in order to meet forest management requirements. Although initially rare and protected locally, C. germanicum has displayed an unexpected fast colonization rate during the last few decades but only in the northern part of the forest, which previously had the highest animal populations. Absent in the initial 1976 survey, C. germanicum occurred in 8% of the plots in 1981, then 46% in 2006. Logistic regression models revealed that the probability of occurrence of C. germanicum in 2006 increased not only with light indicator values, in accordance with its ecological requirements, but also with past deer browsing pressure. This result provides direct evidence of long-lasting impacts of deer populations on plant species distribution. Combining two complementary traits, animal transport and herbivory avoidance, C. germanicum benefited from epizoochorous dispersal and, once established, was protected from deer browsing by the presence of toxic proteins in its tissues. Due to the triggering role of ungulates, this species switched from the status of rare to that of colonizer within only a few decades.
To understand key processes governing defense mechanisms in poplar (Populus spp.) upon infection with the rust fungus Melampsora larici-populina, we used combined histological and molecular ...techniques to describe the infection of Populus trichocarpa X Populus deltoides 'Beaupré' leaves by compatible and incompatible fungal strains. Striking differences in hosttissue infection were observed after 48-h postinoculation (hpi) between compatible and incompatible interactions. No reactive oxygen species production could be detected at infection sites, while a strong accumulation of monolignols occurred in the incompatible interaction after 48 hpi, indicating a late plant response once the fungus already penetrated host cells to form haustorial infection structures. P. trichocarpa whole-genome expression oligoarrays and sequencing of cDNAs were used to determine changes in gene expression in both interactions at 48 hpl. Temporal expression profiling of infection-regulated transcripts was further compared by cDNA arrays and reverse transcription-quantitative polymerase chain reaction. Among 1,730 significantly differentially expressed transcripts in the incompatible interaction, 150 showed an increase in concentration ≥3-fold, whereas 62 were decreased by ≥3-fold. Regulated transcripts corresponded to known genes targeted by R genes in plant pathosystems, such as inositol-3-P synthase, glutathione S-transferases, and pathogenesis-related proteins. However, the transcript showing the highest rust-induced up-regulation encodes a putative secreted protein with no known function. In contrast, only a few transcripts showed an altered expression in the compatible interaction, suggesting a delay in defense response between incompatible and compatible interactions in poplar. This comprehensive analysis of early molecular responses of poplar to M. larici-populina infection identified key genes that likely contain the fungus proliferation in planta.
Key message According to biomechanical processes, tree morphology (trunk inclination, height-to-diameter ratio and crown area) explains statistically silvicultural effects on growth stress ...variation.Abstract Growth stresses constitute the main mechanism allowing the tree to control its posture against its mechanical environment, but are also among the most important factors contributing to the depreciation of timber value. This study aimed at assessing the link between stand planting density and growth stress level in European beech (Fagus sylvatica) stands. Beech seedlings were planted in four plots corresponding to four planting densities: 2,500, 5,000, 10,000 and 40,000 stems/ha. They were left to grow for 26 years without any intervention, resulting in trees with highly different morphologies but of the same age and provenance. After 26 years of growth, both the tree morphology and growth stress indicators were measured on the standing trees in each plot and an attempt was made to establish a link between them. Our results showed that initial stand density influences growth stresses of the first order as a result of its impact on tree morphology. The best predictors of high growth stresses were high trunk inclination, high height-to-diameter ratio (slenderness factor) and low crown area. According to mechanosensing theories, these morphological criteria emphasised that growth stresses are due to a global mechanical stimulation rather than to local stem inclination alone. Research now has to be undertaken on new methods that combine the integrative assessment of tree morphology as well as its monitoring over time.
Forking is a frequent flaw in beech which can adversely affect the formation of high quality logs. Even though the hypothesis that late frosts increase forking is widely accepted by forest managers, ...it remains to be proved and quantified experimentally. Damage caused by a late frost on 15 May 1995 to young beech trees in an experimental site at Lyons-La-Forêt (France) and the consequences on the development of forking were analysed. The beech trees were 17 years old with heights between 1.5 and 9 m. Of all the plantation densities tested only the lowest density (625/ha) showed various and severe frost damage. Three levels of immediate damage to the growing terminal shoot were observed, with increasing intensity from: (1) no trace of frost damage, (2) reddened leaves and (3) frost-nipped shoots. The intensity of visible damage to the terminal shoot appeared to be very dependent on the height of the plant which justified our original experimental approach, based on an evaluation of the damage for each individual. Almost all of the beech trees less than 4 m high suffered frost damage and all those taller than 7 m were unaffected. Three-year-old forks due to frost which occurred in May 1995 were recorded at the end of 1997 using an objective definition based on dendrometric and age criteria. The worst frost damage resulted in a significant increase in the risk of fork emergence (71.7% of the plants were forked). With a risk related to forking in the presence of frost-nipped shoots equal to 2.15 and a fraction of the attributed risk of 0.36 it was concluded that the late frost observed played a significant role in the degradation of the shape of the beech affected by frost and the overall quality of the stand
Les dégâts de gel tardif sur la pousse terminale : un facteur de risque d’apparition de fourches chez le hêtre (Fagus sylvatica L.). La fourchaison est un défaut fréquent du hêtre qui peut nuire à la formation d’une grume de qualité. L’hypothèse d’un effet des gelées tardives contribuant à aggraver la fourchaison, bien que largement admise par les gestionnaires forestiers, restait pourtant à démontrer et à quantifier dans un cadre expérimental. Les dégâts occasionnés par la gelée tardive du 15 mai 1995 sur de jeunes plants de hêtre du dispositif expérimental de Lyons-La-Forêt (France) et leurs conséquences sur la mise en place de fourches ont été analysés. Les hêtres étaient alors âgés de 17 ans et de hauteur comprise entre 1,5 et 9 m. Parmi toutes les densités de plantation testées seule la plus faible (625/ha) présentait un impact fort et diversifié du gel. Trois niveaux d’intensité croissante de dégâts immédiats sur la pousse terminale en élongation ont pu être distingués : (1) aucune trace de gel, (2) feuilles roussies (3) pousse gelée. L’intensité des dégâts visibles sur la pousse terminale est apparue très dépendante de la hauteur du plant justifiant notre approche expérimentale originale centrée sur l’évaluation individuelle des dégâts. La quasi totalité des hêtres de hauteur inférieure à 4 m avaient gelé et tous ceux de hauteur supérieure à 7 m étaient indemnes. Les fourches imputables au gel ont été inventoriées fin 1997 selon une définition objective basée sur des critères dendrométriques et sur un critère d’âge. Le dégât de gel le plus intense a eu pour conséquence une augmentation significative du risque de fourchaison (71,7 % de plants fourchus). Avec un risque relatif de fourchaison en présence de pousse gelée égale à 2,15 et une fraction du risque attribuable de 0,36 on peut conclure que le gel tardif observé contribue notablement à la dégradation de la forme du hêtre touché par le gel et à la qualité globale du peuplement
The objective of this research was to evaluate the influence of vegetation control on the microclimate (light, air temperature, vapor-pressure deficit (VPD)) and on the growth of young planted, ...sessile oak seedlings. Three types of vegetation control, creating a range of above-ground interaction intensity, were compared. In the
open treatment, vegetation was chemically controlled and was maintained at a low height; in the
closed treatment, vegetation was manually controlled and a few dominant individuals that overtopped the oak seedlings were cut; and in the
sheath treatment, the vegetation in a 0.5-m diameter circle around each seedling was manually cut to a height equal to three quarters of the total seedling height. In all treatments, a strong reduction of incoming radiation was observed, as well as an increase in air temperature and VPD during the day, and a decrease in daily PET, compared to the reference located 4
m above the vegetation. However, the neighboring vegetation did not modify the microclimate around the seedling to a level that could have induced a significant reduction in seedling photosynthesis and, thus, in seedling growth. Seven years after planting, seedlings were shortest in the open treatment and tallest in the closed treatment (334, 372, 378
cm in the open, sheath and closed treatments, respectively). Seedlings in the open treatment allocated proportionally more biomass to diameter increment than to height growth, compared to seedlings in the sheath and closed treatments. The seedlings averaged 1.77, 1.10 and 1.00 forks in the open, sheath and closed treatments, respectively, and the average height of the lowest fork was 171, 206 and 226
cm in the same treatments. The reduction of the number of forks per seedling was not related to a reduction of the appearance of new forks, but rather to a reduction in the persistence of the existing forks. These changes in stem allometry and in fork development seemed to be related to the lateral shade afforded by the vegetation.
Research on the characteristics of pole-stage trees enables the prediction of their growth dynamics and qualitative development after thinning, and constitutes an important part of the management of ...(naturally regenerated) heterogeneous stands. This article presents the results of a study on the morphology of beech Fagus sylvatica and sessile oak Quercus petraea poles in multistorey stands (mixed stands and beech only stands) in northern France, where the aim is to implement sustainable management based on the prediction of the short-term (5-8 years) response of the poles to liberation felling. The first stage of the process was to define the morphotypes of poles present of each species by compiling detailed descriptions of over 800 beech poles at 12 sites and over 400 oak poles at 7 sites. A typology key is presented for each species, which shows 8 morphotypes for beech and 5 for oak. The second stage of the study (only reported for beech, and only for 1 year after treatment) put in place experiments to follow the growth dynamics and quality development of poles of the defined different morphotypes that had been liberated by felling, from which the plan is to develop response models for the different morphotypes.
La recherche d'éléments de diagnostic des perches permettant de prédire leur dynamique de croissance et leur évolution qualitative sous l'effet d'une éclaircie est une préoccupation forte des gestionnaires en futaie hétérogène. Elle est d'ailleurs commune à toutes les sylvicultures qui nécessitent de repérer les tiges de qualité, parfois très précocement, afin de travailler à leur profit. Nous présentons ici les résultats d'une étude sur la morphologie des perches de hêtre et chêne dans des peuplements multi-strates. Cette étude se poursuit par des expérimentations de "libération" de perches afin d'évaluer leur réactivité sur une période de 5 à 8 ans.
The production of woody biomass must consider the question of the impact of the accompanying vegetationon the development of the target species. Whenever the accompanying vegetation competes to the ...extentthat it might influence the yield of the dedicated biomass crop, it must be controlled. There is a range ofmanagement methods that can be used, some of which are well-documented and conventionally used,whereas others are at the design stage or under development. The benefits and drawbacks of several ofthese methods are described here. Constraints connected with management of competing vegetation varydepending on the region and are liable to change over time. It is therefore important to have a wide choiceof methods to meet production objectives. The choice of technique is determined by knowledge of theirdirect and indirect effects, costs and the related constraints.
La production de bois énergie nécessite de prendre en compte la question de l’impact de la végétationaccompagnatrice sur le développement de l’essence objectif. Toutes les fois où la compétition exercée par lavégétation est suffisamment intense pour risquer d’influer sur la production de biomasse de la culturedédiée, des opérations de gestion de cette végétation devront être mises en oeuvre. Il existe pour ce fairede nombreuses méthodes de gestion dont certaines sont bien documentées et utilisées classiquement tandisque d’autres sont en phase d’étude ou de développement. Plusieurs de ces méthodes, avec leurs intérêts etinconvénients, sont ici présentées. Les contraintes liées à la gestion de la végétation concurrente sontvariables selon les régions et évoluent dans le temps. Il est donc indispensable de disposer d’une largepalette de méthodes pour répondre aux objectifs de production, le choix des techniques à utiliser reposantsur la connaissance de leurs effets directs et indirects, de leurs coûts et des contraintes afférentes.
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