Summary
Trees are known to be atmospheric methane (CH4) emitters. Little is known about seasonal dynamics of tree CH4 fluxes and relationships to environmental conditions. That prevents the correct ...estimation of net annual tree and forest CH4 exchange.
We aimed to explore the contribution of stem emissions to forest CH4 exchange. We determined seasonal CH4 fluxes of mature European beech (Fagus sylvatica) stems and adjacent soil in a typical temperate beech forest of the White Carpathians with high spatial heterogeneity in soil moisture.
The beech stems were net annual CH4 sources, whereas the soil was a net CH4 sink. High CH4 emitters showed clear seasonality in their stem CH4 emissions that followed stem CO2 efflux. Elevated CH4 fluxes were detected during the vegetation season. Observed high spatial variability in stem CH4 emissions was neither explicably by soil CH4 exchange nor by CH4 concentrations, water content, or temperature studied in soil profiles near each measured tree. The stem CH4 emissions offset the soil CH4 uptake by up to 46.5% and on average by 13% on stand level.
In Central Europe, widely grown beech contributes markedly to seasonal dynamics of ecosystem CH4 exchange. Its contribution should be included into forest greenhouse gas flux inventories.
This work analyzes the influence of the composition of laminated materials based on solid and thermo-mechanically densified beech wood and the application of reinforcing elements in the form of ...reinforcing fibers. The paper investigates the behavior of the elastic, plastic, and total bending work and their ratios concerning the composition of the material. These characteristics are essential in determining the appropriate application of these materials in structural systems concerning the deformation energy in the elastic and plastic stress–strain areas. From the material point of view, factors such as the input thickness of beech lamellas (5 and 9 mm), the degree of densification of lamellas (references, 10%, 20%, 30%, and 40%), and the application of reinforcing fibers (carbon and glass) were observed and distinguished. There are several approaches to evaluate elastic and plastic work in bending. This paper deals with a more accurate method by integrating the curve of the force–deflection diagram. The output of the article points to a more efficient choice of beech wood modifications by densification concerning the formation of internal cracks in conjunction with the reinforcing fibers.
•4 years of species-oriented phenocamera and ground-based phenological observations.•Confirmed prolongation of growing season length due to a warmer climate.•Phenocamera-derived phenophases ...corresponded closely with field observations.•Greenup was advanced by above-average warm days, but leaf maturation was delayed.•Cold spell in 2017 showed marked effect on phenological shifts.
Phenological observations are important as indicators of global warming and as estimation tools for the terrestrial carbon balance in vulnerable ecosystems, such as the last fragments of floodplain forests in the Czechia. The aim of this paper was to compare ground-based phenological observations of three dominant species (European hornbeam, English oak and narrow-leaved ash) in this ecosystem, with the seasonal trajectory of the greenness index (Gcc) and thresholds extracted from images taken by phenocameras located on a meteorological mast. The average annual air temperature in the studied years 2014–2017 was 1 °C higher than the long-term average, and the precipitation deficit reached ⅓ of annual rainfall. We found a high proportion of above-average warm days in the warmest part of the growing season. Above-average air temperatures significantly accelerated the onset of budbreak in ash. Yet a higher proportion of above-average air temperatures prolonged the period between budbreak to fully developed leaf area, especially in ash and oak. In 2017, rapid cooling after exceptionally warm temperatures at the onset of spring had a detrimental effect on the stand productivity and showed a marked effect on the phenological shifts. The period when leaf area developed was in the range of DOY 66-286 for hornbeam, DOY 79-329 for oak and DOY 88-321 for ash in 2014–2017. The seasonal trajectory of Gcc showed differences between tree species that corresponded to the dynamics of the onset of phenophases observed in the field. According to image analyses, the phenophase of greenup and maturity for hornbeam and ash had minimal uncertainty. In contrast, the uncertainty was high in the determination of phenophases for oak. Our observations show that the modern method of phenological observation by phenocameras is suitable for mixed forests, but classical ground-based observations by a phenologist are still crucial in order to verify the results.
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Summary
The kinetics of wood formation in angiosperms are largely unknown because their complex xylem anatomy precludes using the radial position of vessels and fibers to infer their time of ...differentiation.
We analyzed xylogenesis in ring‐porous ash (Fraxinus angustifolia) and diffuse‐porous beech (Fagus sylvatica) over 1 yr and proposed a novel procedure to assess the period of vessel and fiber enlargement using a referential radial file (RRF).
Our approach captured the dynamics of wood formation and provided a robust estimation of the kinetics of vessel and fiber enlargement. In beech, fibers and vessels had a similar duration of enlargement, decreasing from 14 to 5 d between April and July. In ash, wide vessels formed in April enlarged at a rate of 27 × 103 μm2 d−1, requiring half the time of contemporary fibers (6 vs 12 d), and less time than the narrower vessels (14 d) formed in May.
These findings reveal distinct cell‐type‐dependent mechanisms for differentiation in diffuse‐porous and ring‐porous trees, enhancing our understanding of angiosperm wood cell kinetics. Our approach presents an effective method for investigating angiosperm wood formation and provides a more accurate representation of vessel and fiber morphogenesis in wood formation models.
The moisture behaviour of thermally modified Scots pine (Pinus sylvestris L.) exposed to cyclic conditions was analysed. Specimens of dimensions 15 × 15 × 5 mm³ were thermally modified at 180 °C ...(TM₁) and 220 °C (TM₂) using atmospheric pressure and superheated steam. Radial, tangential, volumetric swelling and anti-swelling efficiency (ASE) were calculated during six consecutive drying–soaking cycles. Afterwards, additional specimens were exposed to ten relative humidity cycles (0 and 95 %) at temperature 25 and 40 °C in order to analyse its influence on sorption behaviour. Application of thermal modification led to significant reduction of swelling from original 18.4–13.3 % for TM₁ and to 10.5 % for TM₂. However, after exposure to six consecutive soaking–drying cycles, the swelling of control specimens slightly decreased, whereas the swelling of thermally modified specimens increased. Due to the increased swelling after repeated cycles, the original ASE (28.6 and 42.7 %) decreased to 22.5 % for TM₁ and to 36.88 % for TM₂. The presence of leachable compounds and release of internal stresses are mainly attributed to that phenomenon. The EMC of the reference specimens decreases over the repeated humidity cycles for approximately 1 %–units. Same trend was found for the mild thermal modification TM₁, but decreasing only in the range of 0.5 %–units. However, the EMC of the TM₂ specimens during humidity cycles behaved differently. The results provide a better insight into details of thermal modification of wood and its behaviour under cyclic conditions.
Under the conditions of ongoing climate change, terrestrial ecosystems will be simultaneously exposed to a permanent rise in atmospheric CO2 concentration and increasing variability of such ...environmental factors as temperature, precipitation, and UV radiation. This will result in numerous interactions. The interactive effects caused by exposure to such multiple environmental factors are not yet well understood. We tested the hypotheses that enhanced UV radiation reduces the stimulatory effect of elevated CO2 concentration on plant biomass production and that it alters biomass allocation in broadleaved European beech (Fagus sylvatica L.) saplings. Our results after 2 years of exposure confirmed interactive effects of CO2 concentration and UV radiation on biomass production, and particularly on biomass allocation to roots and aboveground biomass. The strongest stimulatory effect of elevated CO2 on aboveground biomass and roots was found under ambient UV radiation, while both low and high UV doses reduced this stimulation. Nitrogen content in the roots and the distribution of nitrogen among leaves and roots were also significantly affected by interaction of CO2 concentration and UV radiation. The observed changes in leaf and root C:N stoichiometry were associated with altered morphological traits, and particularly with a change in the proportion of fine roots. As the biomass allocation and especially the proportion of fine roots can play an important role in effective water and nutrient use and acclimation to future climates, it is essential to obtain a deeper understanding of the links between C:N stoichiometry and biomass accumulation.
•Interactive effects of UV radiation and CO2 on root and shoot biomass were found.•Strongest stimulation by CO2 was found under ambient UV radiation.•N content and allocation were significantly influenced by CO2 and UV.•Changes in C:N stoichiometry are associated with altered morphological traits.
•FE analysis proved significance of soil properties and root volume in tree bending.•Asymmetrical defects significantly influence the measured inclinations/strains.•Marker tracking can evaluate ...overall tree response to loading from its deflection.•2nd derivative of the displacement reveals the effect of defects on stem deflection.
Despite continual development of the tree pulling test, there is no systematic study on the interaction of stem and root-plate stiffness in relation to tree assessment results. New methods involving numerical modelling and optical techniques provide tools for effective and deeper understanding of the interaction of stem and root-plate stiffness. Within this study, a finite element (FE) model of the tree response to static loading was developed, and the interaction between the stem and root-plate stiffness was analysed on three levels: longitudinal stem strains, root-plate inclinations and stem deflection curve. The model was validated at all three levels by comparison with experiment. Sensitivity analysis of the validated model showed a significant correlation of root-plate stiffness represented by the root volume and soil elastic modulus to the tree response. By analysing the defects in tree response, the importance of proper location for detection of strains and inclinations was demonstrated, especially regarding asymmetrical defects. A numerical estimate of the second derivative of displacement based on the Taylor approximation, was used to analyse the stem deflection curve.
Key message
Effect of drought during 2017 and 2018 resulted in radial stem increment reduction to 78% and 61%, respectively, of the levels occurring in normal year 2016 in Central Europe.
Norway ...spruce (
Picea abies
(L.) Karst.) is currently the most threatened commercial tree species in Central Europe. This is due to increased drought stress from advancing climate change as well as the species’ distribution outside its natural range. Tree water status and water movement through a tree are key parameters influencing tree growth and vitality. This study is focused on the growth and stress reaction of spruce to climatic conditions, analysing stem diameter variation along an elevation gradient (381–995 m a.s.l.) in the Czech Republic. Tree water deficit based on the zero-growth concept (TWD), calculated from high-frequency dendrometer records and the temporal dynamics of radial growth, was studied for 3 years (2016–2018). Two of these 3 years were affected by severe drought during the growing season. Contrary to our expectations, the observed TWD showed no clear linear decline with rising elevation. The most severe tree desiccation was observed in experimental sites at middle elevations of about 600 m a.s.l. Here, we show that both the timing and level of tree water deficit had an impact on annual stem radial increment (SRI
annual
). Severe drought had a substantial negative impact on SRI
annual
of Norway spruce in both 2017 and 2018. Drought conditions in 2017 and 2018 resulted in reduction of SRI
annual
relative to measurements for the wetter year in 2016 to 78% and 61%, respectively. We report the evidence that the current climatic conditions in the Central European region are not suitable for growing Norway spruce at lower and middle elevations and that forest management needs to react immediately to this situation.
The goal of the study was to investigate the influence of bark of Turkish hazel (
Corylus colurna
L.) on strain transfer from xylem to bark surface. The study addresses issues of tree biomechanics ...that calls for a high-quality deformation data measured on trees’ surfaces in a noninvasive way. For these purposes, the optical technique employing 3D digital image correlation (3D-DIC) was used and tested against extensometers commonly used for such applications. The measured tree was subjected to bending by two pulling tests to induce the strain in tree stem, during which the analyzed area of interest (AOI) on the tree was studied in both variants with and without bark. The DIC technique successfully provided strain fields on a tree with bark and without despite its highly complicated structure. The absolute values of vertical strain measured by both techniques agree with each other in order of magnitude. However, 3D-DIC returns generally lower values than extensometers. Statistical tests proved (at
p
< 0.05) that the vertical strain measured on a bark was lower than that measured on wood, which confirms the hypothesis that bark layers reduce the strain transfer from wood to tree surface. The extent of strain reduction is highly dependent on force and was statistically detectable when the force reached ca. 5 kN. This is an important fact especially for practical use of optical measurements that are to replace standard extensometers. Measured displacements agreed with each other for both variants within a whole range of loads.
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