Petr Čermák

Radial Growth and Health Condition of Norway Spruce (Picea Abies (L.) Karst.) Stands in Relation to Climate (Silesian Beskids, Czech Republic)

Radial Growth and Health Condition of Norway Spruce (Picea Abies (L.) Karst.) Stands in Relation to Climate (Silesian Beskids, Czech Republic) The research was conducted in selected spruce stands of the Silesian Beskids aged over 70 at altitudes from 403 m a.s.l. to 794 m a.s.l. in 2008. The samples were taken and processed in compliance with standard dendrochronological methodology. Tree rings were measured and the tree-ring curves were synchronized using the PAST4 application. The age trend was removed in the ARSTAN application and the climatic influences were modelled in the DendroClim application. The regional standard tree-ring chronology shows an obvious decrease in the radial increment from the beginning of the 1970s to the mid-1990s. The gradual increase in radial increment which followed in the second half of the 1990s was interrupted in 2000, 2003, and 2006. Most of the years with the decreased radial increment have been confirmed by the analysis of significant negative years. The radial increment statistically significantly correlates with the precipitation in July and September of the previous year, precipitation in June of the year in question and precipitation during the vegetation period. Moreover, the growth of spruce is statistically significantly affected by temperatures in October of the previous year and March of the year in question. Additionally, the paper includes habitual monitoring of trees and the volume of salvage cutting in these districts. The condition of the habit of trees and the development of salvage cuttings agree with the hypothesis about strong stress load or its considerable increase in 2003 and the following years.

Comparison of selected physical and mechanical properties of densified beech wood plasticized by ammonia and saturated steam

Gaseous ammonia treatment in combination with densification of wood has been known for several decades, but these days there is no industrial production of materials modified in this way; also, little has been published in this area of wood science. In this study, selected physical and mechanical properties, i.e. density profile, bending strength, hardness and moisture absorption were investigated for Lignamon (1), which was obtained from the Czech industrial production. Selected properties were also investigated using steam-densified beech (2) and native beech (3) and compared with each other. Densitometry of Lignamon showed a large variability in the density profile compared to that of only densified beech. It is affected by the degree of densification, temperature and moisture gradients, and their relationship to the glass transition of the wood cell wall. Modulus of elasticity, hardness, moisture exclusion and anti-swelling efficiency of Lignamon are enhanced compared to densified beech. The enhanced dimensional stability and lower hygroscopicity of Lignamon are probably caused by heat treatment during the process. Further investigation will be carried out with self-produced Lignamon samples.

Exploring Growth Variability and Crown Vitality of Sessile Oak (Quercus Petraea) in the Czech Republic

Abstract Unraveling climatic effects on growth of oak - Europe’s most ecologically and economically important forest species - has been the subject of many recent studies; however, more insight based on field data is necessary to better understand the relationship between climate and tree growth and to adapt forest management strategies to future climate change. In this report, we explore the influence of temperature, precipitation and drought variability on the productivity and vitality of oak stands in the Czech Highlands. We collected 180 cores from mature oaks (Quercus petraea) at four forest stands in the Czech Drahany Highlands. Standard dendromethods were used for sample preparation, ring width measurements, cross-dating, chronology development, and the assessment of growth-climate response patterns. Crown vitality was also evaluated, using the modified ICP Forests methodology. Late spring precipitation totals between May and June as well as the mean July temperature for the year of ring formation were found to be the most important factors for oak growth, whereas crown condition was significantly affected by spring and summer drought. This study is rep-resentative for similar bio-ecological habitats across Central Europe and can serve as a dendroclima-tological blueprint for earlier periods for which detailed meteorological information is missing

The effect of heat and ammonia treatment on colour response of oak wood (Quercus robur) and comparison of some physical and mechanical properties

In this paper the effect of heat and ammonia treatment on the change in colour of oak wood (Quercus robur.) and comparison of physical and mechanical properties were investigated. Wood specimens were made from heartwood and sapwood in dimensions 30×30×30 mm3. The specimens were subjected to heat treatment at 180°C and 230°C for 2 and 4 hours, others were treated by ammonia for 24 hours. After these processes, CIELAB colour, hardness, EMC, density and MOE of wood were tested in comparison with untreated samples. The results show that the heat treatment contributed to darkening of sapwood and heartwood and the total colour change increased up to 38.47 units (CIELAB) in the radial direction and 37.75 units (CIELAB) in the tangential direction. Previous research into ammonia treatment shows that the most significant changes were noticed after 1 day. The colour changes between sapwood and heartwood were more noticeable in ammonia treatment than in the case of heat treatment. All other observed properties were decreased in the case of heat treatment. Ammonia treatment does not have a significant influence on the other observed properties. The results proved that ammonia treatment is a modification that improves the decorative value but has a minimal effect on technologically relevant properties of solid wood. Nevertheless, the heat treatment can be used as comparable process for colour change of wood.

Measured temperature and moisture profiles during thermal modification of beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) wood

Abstract The temperature and moisture profiles during thermal modification of beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) wood have been investigated. Specimens with dimensions of 80×80×200 mm3 were heat treated based on ThermoWood technology. Heat transfer was continuously measured by several thermocouples placed into various positions of the samples. In the course of the treatment, samples were removed from the chamber at different times, and their moisture content (MC) was measured by the so-called slicing technique. The complete data of heat and moisture movement during the heat treatment process are presented. Significant temperature gradients occur in the initial and modification stages of the process. In the latter, the chamber temperature was 200°C for 3 h, but exothermic reaction increased the sample temperatures to 240°C (beech) and 215°C (spruce). Thermodiffusion (Soret effect) at the beginning of the process was observed. Therefore, the MC under surfaces (in transverse and in longitudinal direction) was increasing ∼0.5%–3% for 5 h. The results provide a better insight into details of thermal modification of wood.

Growth responses of Norway spruce (Picea abies (L.) Karst.) to the climate in the south-eastern part of the Českomoravská Upland (Czech Republic)

The research was conducted in selected 80- to 110-year-old spruce stands in the south-eastern part of the Českomoravská Upland at altitudes from 350 m a.s.l. to 465 m a.s.l. The regional standard tree-ring chronology shows very low increments for years 1974, 1976 and 1992. After 1992, there is a sharp rise in increments with a climax in 1997. Afterwards, increments gradually decrease, reaching minima in 2003 and 2008. The years with low increments were also confirmed by the analysis of negative pointer years when over 80% of the analysed trees responded by a sharp decrease in increment, mainly in years 1976 and 1992. We can usually find values of monthly precipitation or monthly temperature average which can explain or help explain these falls in the radial growth. The correlations of diameter increments with average monthly precipitation gain only positive statistically significant values, namely for the months of May, June, July and August of the particular year. The correlations of diameter increments with average monthly temperatures gain only negative statistically significant values, namely for the months of June, July and September of the previous year and January and August of the particular year. In the examined area there is a significant negative correlation between average temperatures and monthly precipitation in July, August and September. The results of the habitual diagnostics show that with respect to the climatic conditions the health condition of the monitored stands is relatively good. On average, the defoliation does not exceed the values ascertained in different territories of the Czech Republic.

Norway Spruce Fine Roots and Fungal Hyphae Grow Deeper in Forest Soils After Extended Drought

Global warming will most likely lead to increased drought stress in forest trees. We wanted to describe the adaptive responses of fine roots and fungal hyphae, at different soil depths, in a Norway spruce stand to long-term drought stress induced by precipitation exclusion over two growing seasons. We used soil cores, minirhizotrons and nylon meshes to estimate growth, biomass and distribution of fine roots and fungal hyphae at different soil depths. In control plots fine roots proliferated in upper soil layers, whereas in drought plots there was no fine root growth in upper soil layers and roots mostly occupied deeper soil layers. Fungal hyphae followed the same pattern as fine roots, with the highest biomass in deeper soil layers in drought plots. We conclude that both fine roots and fungal hyphae respond to long-term drought stress by growing into deeper soil layers.

Reducing the moisture sensitivity of linear friction welded birch (Betula pendula L.) wood through thermal modification

Linear friction welding of wood is a bonding process applied to wood and during which a stiff bond line is formed by the softening and rehardening of wood components to form a composite material composed mainly of wood fibres embedded in a modified lignin matrix. Unfortunately, the bonds tend to spontaneously delaminate or lose their strength when exposed to moist conditions. Some approaches were previously applied to overcome this problem, but so far a suitable solution has not been found. This paper presents results of applying post-welding thermal modification to reduce the moisture sensitivity of welded wood. The experiments included welding of birch wood, thermal modification under superheated steam at atmospheric pressure, internal bond (IB) and tensile-shear strength testing and soaking tests. As supposed, the non-modified reference specimens performed poorly after the seven days soaking test (on average 0.33 MPa IB strength), whereas the thermally modified specimens yielded almost the same IB strength in dry and wet condition (on average e.g. 1.15 and 0.93 MPa, respectively). Such a similar load bearing capacity in very different moisture conditions was previously reported only in the case of paduk wood. Similar to the reduction of IB strength occurred during the soaking test, also delamination was observed more clearly in non-modified reference specimens (e.g. 4 vs. 0 total delaminations after seven days soaking). Therefore, the authors suggest that post-welding thermal modification could provide a suitable bond-stabilisation method against moisture, although the process parameters must be optimised in further research, for instance, to ensure scalability.

Sorption-Related Characteristics of Surface Charred Spruce Wood

Surface charring of wood is a one-sided thermal modification process that can be used to create a hydrophobic, durable surface to exterior claddings. Spruce (Picea abies L.) wood samples were charred with a hot plate and several time-temperature combinations while using simultaneous surface compression. Temperature profile, water sorption, cupping after water exposure and density profile were measured. Furthermore, changes in the microstructure and surface functional groups were investigated by scanning electron microscopy and photoacoustic FT-IR spectroscopy. Results show that surface charring notably improves the hydrophobicity measured by contact angle, water floating and dynamic vapour sorption. Increased holding time during charring reduced the sorption but at the same time increased the dimensional instability measured by cupping. The density profile showed a shifting density peak with more severe modification regimes, indicating a more porous surface. The PAS-FTIR showed increased aromaticity of the surface that was also present in the pyrolysis zone beneath the surface in samples modified with longer holding time. Higher modification temperature affected the sorption as well as cupping positively but it is possible similar results can be obtained with lower temperature and longer holding time.

Numerical analysis of temperature profiles during thermal modification of wood: chemical reactions and experimental verification

Abstract Numerical analysis of temperature profiles during thermal modification of wood was carried out. The numerical solution – based on finite element analysis, FEA – of the 3D problem of transient nonlinear heat transfer model is presented for wood as a typical anisotropic material. The numerical model was enhanced for describing chemical reactions of cellulose, hemicelluloses and lignin (pyrolysis model), which takes into account the exothermic reactions as an internal source of heat energy. Experimental as well as theoretical process schedules were applied and the influence of sample dimensions (sample geometry) and wood species was studied. The influence of wood species was negligible on heating time to reach the highest temperature, i.e., the temperature differences were about 2°C during the drying phase. A expected, the sample size played an important role in the heating duration and in terms of the exothermic reactions of wood. The experimental and numerical data are generally in good agreement. The numerical error increased in the range of higher temperatures. The results can be improved by consideration of wood species (mass of wood compounds) and boundary conditions in the pyrolysis model, thus, better insight into details of thermal modification of wood could be reached.