Relationship between Thermal Diffusivity and Mechanical Properties of Wood

This paper describes an experimental study of the relationships between thermal diffusivity and mechanical characteristics including Brinell hardness, microhardness, and Young’s modulus of common pine (Pinus sylvestris L.), pedunculate oak (Quercus robur L.), and small-leaf lime (Tilia cordata Mill.) wood. A dependence of Brinell hardness and thermal diffusivity tensor components upon humidity for common pine wood is found. The results of the measurement of Brinell hardness, microhardness, Young’s modulus, and main components of thermal diffusivity tensor for three perpendicular cuts are found to be correlated. It is shown that the mechanical properties correlate better with the ratio of longitude to transversal thermal diffusivity coefficients than with the respective individual absolute values. The mechanical characteristics with the highest correlation with the abovementioned ratio are found to be the ratio of Young’s moduli in longitude and transversal directions. Our technique allows a comparative express assessment of wood mechanical properties by means of a contactless non-destructive measurement of its thermal properties using dynamic thermal imaging instead of laborious and material-consuming destructive mechanical tests.

Native seed dispersal by rodents is negatively influenced by an invasive shrub

Refuge–mediated apparent competition is the mechanism by which invasive plants increase pressure on native plants by providing refuge for generalist consumers. In the UK, the invasive Rhododendron ponticum does not provide food for generalist seed consumers like rodents, but evergreen canopy provides refuge from rodent predators, and predation and pilferage risk are key factors affecting rodent foraging and caching behaviour. Here we used a seed removal/ seed fate experiment to understand how invasion by an evergreen shrub can alter seed dispersal, seed fate and early recruitment of native trees. We used seeds of four species, small and wind–dispersed (sycamore maple Acer pseudoplatanus and European ash Fraxinus excelsior) and large and animal–dispersed (pedunculate oak Quercus robur and common hazel Corylus avellana), and monitored seed predation and caching in open woodland, edge habitats, and under Rhododendron. In the open woodland, wind–dispersed seeds had a higher probability of being eaten in situ than cached seeds, while the opposite occurred with animal–dispersed seeds. The latter were removed from the open woodland and edge habitats and cached under Rhododendron. This pattern was expected if predation risk was the main factor influencing the decision to eat or to cach a seed. Enhanced dispersal towards Rhododendron cover did not increase the prospects for seed survival, as density of hazel and oak saplings under its cover was close to zero as compared to open woodland, possibly due to increased cache pilferage or low seedling survival under dense shade, or both. Enhanced seed predation of ash and sycamore seeds close to Rhododendron cover also decreased recruitment of these trees. Rhododendron patches biased rodent foraging behaviour towards the negative (net predation) side of the conditional rodent / tree interaction. This effect will potentially impact native woodland regeneration and further facilitate Rhododendron spread due to refuge–mediated apparent competition.

Using the dendro-climatological signal of urban trees as a measure of urbanization and urban heat island

Using dendroclimatological techniques this study investigates whether inner city tree-ring width (TRW) chronologies from eight tree species (ash, beech, fir, larch, lime, sessile and pedunculate oak, and pine) are suitable to examine the urban heat island of Berlin, Germany. Climate-growth relationships were analyzed for 18 sites along a gradient of increasing urbanization covering Berlin and surrounding rural areas. As a proxy for defining urban heat island intensities at each site, we applied urbanization parameters such as building fraction, impervious surfaces, and green areas. The response of TRW to monthly and seasonal air temperature, precipitation, aridity, and daily air-temperature ranges were used to identify climate-growth relationships. Trees from urban sites were found to be more sensitive to climate compared to trees in the surrounding hinterland. Ring width of the deciduous species, especially ash, beech, and oak, showed a high sensitivity to summer heat and drought at urban locations (summer signal), whereas conifer species were found suitable for the analysis of the urban heat island in late winter and early spring (winter signal).The summer and winter signals were strongest in tree-ring chronologies when the urban heat island intensities were based on an area of about 200 m to 3000 m centered over the tree locations, and thus reflect the urban climate at the scale of city quarters. For the summer signal, the sensitivity of deciduous tree species to climate increased with urbanity.These results indicate that urban trees can be used for climate response analyses and open new pathways to trace the evolution of urban climate change and more specifically the urban heat island, both in time and space.

First Results of Monitoring the New Invasive Species Prunus serotina Ehrh. Population inside the Regeneration Area of Common Oak-Hornbeam Forest in Western Croatia

Black cherry ( Prunus serotina Ehrh., Rosaceae) is a widespread invader of the European temperate forests and a significant component of the human-caused part of the global environmental changes. Its successful invasion results from a complex interaction between the species life traits and the recipient ecosystem attributes. While it has been recorded to develop spontaneously in numerous European countries, in Croatia information details on its population distribution, as well as its current status, are still missing. The individuals of P. serotina were found in the pedunculate oak (Quercus robur L.) forest regeneration area of Jastrebarsko forest management unit in 2018. This alerted us to start to monitor its spreading area, status and impact on the native plant species in a four-year period (2018-2021). In order to investigate the habitat characteristics, phytosociological approach was applied. In addition, the area was surveyed using an unmanned aerial vehicle (UAV) DJI Mavic 2 Pro and DJI Ground Station Pro. The results showed that P. serotina spread considerably in the regeneration area, which indicates its invasive character. It also caused alteration in current vegetation. Fast initial expansion of P. serotina in 2019 was slowed down in the next 2 years due to performed tending activities, suggesting mechanical measures could help to control its invasive spreading at an early stage of development. This research brought up the first record of the Prunus serotina species in pedunculate oak forest regeneration area of western Croatia with a recommendation to continue the monitoring survey in order to help prevent its spread in the future.

The Influence of Nanoparticles on Fire Retardancy of Pedunculate Oak Wood

Traditional flame retardants often contain halogens and produce toxic gases when burned. Hence, in this study, low-cost, environmentally friendly compounds that act as fire retardants are investigated. These materials often contain nanoparticles, from which TiO2 and SiO2 are the most promising. In this work, pedunculate oak wood specimens were modified with sodium silicate (Na2SiO3, i.e., water glass) and TiO2, SiO2, and ZnO nanoparticles using the vacuum-pressure technique. Changes in the samples and fire characteristics of modified wood were studied via thermal analysis (TA), infrared spectroscopy (FTIR), and scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). The results of TA showed the most significant wood decomposition at a temperature of 350 °C, with a non-significant influence of the nanoparticles. A dominant effect of sodium silicate was observed in the main weight-loss step, resulting in a drop in decomposition temperature within the temperature range of 36–44 °C. More intensive decomposition of wood treated with water glass and nanoparticles led to a faster release of non-combustible gases, which slowed down the combustion process. The results demonstrated that wood modifications using sodium silicate and nanoparticle systems have potentially enhanced flame retardant properties.

Estimating Energy Concentrations in Wooded Pastures of NW Spain Using Empirical Models That Relate Observed Metabolizable Energy to Measured Nutritional Attributes

Wooded pastures serve as a traditional source of forage in Europe, where forest grazing is valued as an efficient tool for maintaining the diversity of semi-natural habitats. In a forest grazing setting with diverse diet composition, assessing the energy content of animal diets can be a difficult task because of its dependency on digestibility measures. In the present study, prediction equations of metabolizable energy (ME) were obtained performing stepwise regression with data (n = 297; 44 plant species) on nutritional attributes (Acid Detergent Fiber, lignin, silica, dry matter, crude protein, in vitro organic matter digestibility) from 20 representative stands of Atlantic dry heathlands and pedunculate oak woodlands. The results showed that the prediction accuracy of ME is reduced when the general model (R2 = 0.64) is applied, as opposed to the use of the specific prediction equations for each vegetation type (R2 = 0.61, 0.66, 0.71 for oak woodlands; R2 = 0.70 heather-gorse dominated heathlands, R2 = 0.41 continental heathlands). The general model tends to overestimate the ME concentrations in heaths with respect to the observed ME values obtained from IVOMD as a sole predictor, and this divergence could be corrected by applying the specific prediction equations obtained for each vegetation type. Although the use of prediction equations by season would improve accuracy in the case of a Winter scenario, using the general model as opposed to the prediction equations for Spring, Summer or Fall would represent a much smaller loss of accuracy.

Modelling the influence of biotic plant stress on atmospheric aerosol particle processes throughout a growing season

Most trees emit volatile organic compounds (VOCs) continuously throughout their life, but the rate of emission and spectrum of emitted VOCs become substantially altered when the trees experience stress. Despite this, models to predict the emissions of VOCs do not account for perturbations caused by biotic plant stress. Considering that such stresses have generally been forecast to increase in both frequency and severity in the future climate, the neglect of stress-induced plant emissions in models might be one of the key obstacles for realistic climate change predictions, since changes in VOC concentrations are known to greatly influence atmospheric aerosol processes. Thus, we constructed a model to study the impact of biotic plant stresses on new particle formation and growth throughout a full growing season. We simulated the influence on aerosol processes caused by herbivory by the European gypsy moth (Lymantria dispar) and autumnal moth (Epirrita autumnata) feeding on pedunculate oak (Quercus robur) and mountain birch (Betula pubescens var. pumila), respectively, and also fungal infections of pedunculate oak and balsam poplar (Populus balsamifera var. suaveolens) by oak powdery mildew (Erysiphe alphitoides) and poplar rust (Melampsora larici-populina), respectively. Our modelling results indicate that all the investigated plant stresses are capable of substantially perturbing both the number and size of aerosol particles in atmospherically relevant conditions, with increases in the amount of newly formed particles by up to about an order of magnitude and additional daily growth of up to almost 50 nm. We also showed that it can be more important to account for biotic plant stresses in models for local and regional predictions of new particle formation and growth during the time of infestation or infection than significant variations in, e.g. leaf area index and temperature and light conditions, which are currently the main parameters controlling predictions of VOC emissions. Our study thus demonstrates that biotic plant stress can be highly atmospherically relevant. To validate our findings, field measurements are urgently needed to quantify the role of stress emissions in atmospheric aerosol processes and for making integration of biotic plant stress emission responses into numerical models for prediction of atmospheric chemistry and physics, including climate change projection models, possible.

ANALYSIS OF THE ECOLOGICAL STATE OF THE AIR ENVIRONMENT IN THE CITY OF KINESHMA IN THE IVANOVSK REGION BY THE METHOD OF FLUCTUATING ASYMMETRY

Morphological changes occur in the leaves of trees under the influence of various air pollutants. Recording and assessing these changes reflects the state of the environment. The aim of the study was to assess the level of air pollution in the city of Kineshma, Ivanovo region, using the bioindication method. The technique of morphometry of pedunculate oak leaves and calculation of the index of fluctuating asymmetry were used. In all points of the city, a high asymmetry of oak leaf blades was noted, which indicates a critical level of atmospheric pollution. Ecotoxicants contained in emissions from enterprises and vehicles significantly violate the bilateral symmetry of oak leaf blades.

Norway maple (Acer platanoides) and pedunculate oak (Quercus robur) demonstrate different patterns of genetic variation within and among populations on the eastern border of distribution ranges

Norway maple (Acer platanoides L.) is a key species of broadleaved forests whose population genetics is poorly studied using modern genetic tools. We used ISSR analysis to explore genetic diversity and differentiation among 10 Russian populations on the eastern margin of the species range of distribution, and to compare the revealed patterns with the results of our population genetic studies of pedunculate oak (Quercus robur L.). In the first set comparatively high heterozygosity and allelic diversity were found (expected heterozygosity H_E = 0.160 ± 0.033, number of alleles n_a = 1.440 ± 0.080, effective number of alleles n_e = 1.271 ± 0.062) in comparison with strongly fragmented and geographically isolated small maple stands of the second set (H_E = 0.083 ± 0.011, n_a = 1.281 ± 0.031, n_e = 1.136 ± 0.019). A relatively high genetic differentiation among populations was detected (the proportion of the inter-population component of total genetic variation, G_ST = 0.558 ± 0.038). In the Cis-Urals, local groups of populations that are confined to the northern, middle and southern parts of the Urals were identified. On the contrary, the current significant fragmentation of the pedunculate oak distribution area in the same study area did not lead to any noticeable genetic differentiation among the majority of populations, the values of the population genetic diversity were very similar in different parts of the Southern Urals.

EMPIRICAL USE OF THREE OAK SPECIES IN AFFORESTATION: LESSONS FROM SOWING AND TRANSPLANTING EXPERIMENTS

The effects of different factors on the growth in height and diameter of oak saplings in comparative cultures were estimated: progeny from autumn and spring sowing of acorns (1); growing conditions of pedunculate oak (Quercus robur L.) mother plants (2); the initial planting density of sessile oak (Q. petraea Liebl.) (3); natural lightening level of downy oak (Q. pubescens Willd.) mother plants (4). The pedunculate oak seedlings obtained after spring sowing were characterized by faster growth compared with those obtained from the autumn sowing. The lower growth rate observed in seedlings sown in autumn was due to the prolonged frosty weather during winter, which led to a decrease in acorn viability and progeny vigour. Due to the higher genetic diversity of the progeny obtained from the free-pollinated pedunculate oaks, it is possible that their growth was more intense and stable in comparison to those of saplings obtained from the acorns of isolated trees. The planting under the forest canopy had a clear influence on the growth in height of saplings. At low density levels (1.0 x 1.0 m), the sessile oak saplings benefited from larger availability of soil nutrients and displayed the highest growth, contrasting with those planted at high density (0.5 x 0.5 m). The deep and moderate shading caused a substantial reduction in the growth of downy oak saplings. Therefore, when planting, it is recommended to avoid using fast-growing species, which, due to asymmetric competition, could drastically reduce the growth in height of the downy oak saplings. Prolonged regeneration of the pruned root system following the transplantation process of sessile and downy oak seedlings determined their very slow growth in the first years of life.