Analysis of the pore-size distribution and fiber saturation point of native and thermally modified wood using differential scanning calorimetry

The aim of this paper was to investigate pore-size distributions in the nano-diameter range of wood and their alteration due to thermal modification of wood using thermoporosimetry, and to find out what consequences can be derived regarding the biological durability. Thermoporosimetry is a technique that is based on the measurement using differential scanning calorimetry (DSC). The method is based on the fact that frozen water contained within small pores is at elevated pressure and therefore has a depressed melting temperature as a function of the appropriate pore diameter. In addition, the fiber saturation points (FSP) were determined by DSC. The former were performed in an isothermal-step method and the latter using the continuous heating-up method. Native and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.), Sycamore maple (Acer pseudoplatanus L.) and European ash (Fraxinus excelsior L.) were analyzed. The results clearly show that the pore shares of wood for the measurable diameter range between 4 and 400 nm decrease considerably in all studied wood species due to thermal modification of the wood. Furthermore, thermal modification of wood leads to a decreased FSP for all studied wood species. For evaluation as well as reproducibility of the results of pore-size distribution and FSP, the consideration of sensible heat and specific heat of fusion plays an important role. If this is not done, it can lead to misinterpretations.     

Toward improved understanding of the cell-wall density and porosity of wood determined by gas pycnometry

The main objective of this study was to evaluate the effect of sample preparation on cell-wall density and porosity using gas pycnometry. Native and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.), sycamore maple (Acer pseudoplatanus L.), and European ash (Fraxinus excelsior L.) were analyzed. The samples differed in terms of shape, geometry, and climatic state. On the one hand, the samples were oven dry as usual and, on the other hand, conditioned at 22 °C and 95 % relative humidity. Furthermore, the samples were processed using solvent exchange drying. In addition to helium, nitrogen was used as a displacement gas. The tests show i.a. how this can lead to misinterpretation of the cell-wall density or porosity of wood determined by gas pycnometry. The results show that native spruce has a lower cell-wall density and higher porosity compared with native maple and ash. Due to thermal modification, the cell-wall densities are decreased. The investigations show that the determined cell-wall density and porosity of the wood are strongly dependent on the sample geometry and climatic state. The cell-wall densities of all investigated wood species in the conditioned state at 22 °C and 95 % relative humidity are significantly higher compared with the oven-dry cell-wall densities.     

Impact of thermal modification on color and chemical changes of spruce and oak wood

Thermal modification of wood is an environment-friendly alternative method for improving several properties of wood without the use of chemicals. This paper deals with the examination of color and chemical changes in spruce (Picea abies L.) and oak wood (Quercus robur F.) that occur due to thermal treatment. The thermal modification was performed at 160, 180, and 210 °C according to thermowood process. The color changes were measured by the spectrophotometer and described in the L*a*b* color system. Chemical changes were examined by wet chemistry methods, infrared spectroscopy and liquid chromatography. During the experiment, oak samples showed smaller color changes than spruce samples at all temperature values. During thermal modification, the content of cellulose, lignin, and extractives increases; however, the hemicellulose content drops by 58.85% (oak) and by 37.40% (spruce). In addition to deacetylation, new carbonyl and carboxyl groups are formed as a result of oxidation. Bonds in lignin (mainly β-O-4) and methoxyl groups are cleaved, and lignin is condensed at higher temperatures.     

Canopy disturbance and intertree competition: implications for tree growth and recruitment in two yellow birch–conifer stands in Quebec, Canada

Composition, structure, and species-specific patterns of recruitment and growth were characterized in two yellow birch (Betula alleghaniensis Britt.)–conifer stands in Quebec, Canada, to improve our understanding of the dynamics of these complex ecosystems. The mixture of mid- and shade-tolerant species in the canopy, the inverse J-shape stem diameter distribution, and the age distribution were indicative that the two stands were in a late-successional stage. Recruitment of mid-tolerant species above 1.3 m in height appeared to be periodic and synchronized with historical spruce budworm (Choristoneura fumiferana Clem.) outbreaks, while the coniferous component of these mixedwood stands recruited continuously. Results suggest that recruitment of yellow birch and red maple (Acer rubrum L.) requires disturbances of a certain intensity that affect at least 25 % of the forest cover. In contrast, balsam fir (Abies balsamea (L.) Mill.) and red spruce (Picea rubens Sarg.) can recruit under the canopy without relying on moderate or large canopy disturbances. Results suggest that the historical disturbance regime, and differences in shade tolerance between species, largely govern the contemporary composition of these stands. This study improves the comprehension of mechanisms that regulate the dynamics of yellow birch-conifer stands and will be useful for the subsequent elaboration of forest management strategies.     

Estimating the maple syrup production potential of American forests: an enhanced estimate that accounts for density and accessibility of tappable maple trees

This paper examines the maple syrup production potential of American forests by analyzing Forest Inventory & Analysis (FIA) data provided by the US Forest Service on the resource of sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) trees in twenty states. The analysis is based on tree species and size (diameter at breast height, or dbh), ownership category, jurisdiction, the density of maple trees in a stand, and the distance of the stand to an access road. Although there are over 2 billion sugar and red maple trees of tappable size growing in US forests, when narrowed down according to the attributes of an optimal ‘sugarbush’, there are 100 million potential taps from sugar maples alone and 286 million potential taps with sugar and red maples combined. Overall, 45 % of the tappable-size maple trees are found in stands whose density is not high enough to support commercial sap extraction whereas only 6 % are found in stands that are at least 1.6 km from an access road. The ten states with commercial maple syrup industries have a much higher percentage of their maple trees occurring in stands of optimal density and also contain a higher percentage of sugar maple than red maple trees. States that are utilizing the highest percentage of their potential sugarbushes include Vermont and Maine, whereas states that have significant room for expansion include Michigan, New York, and Pennsylvania.     

Effect of gap size on mid-rotation stand structure and species composition in a naturally regenerated mixed broadleaf forest

This paper is an assessment of the effect of gap size on stand structure and species composition 48 years following treatment in a mixed broadleaf upland forest. Established in 1960, the study tests three circular openings, 15.2 m (0.02 ha), 45.7 m (0.16 ha), and 76.2 m (0.46 ha). Forty-eight years following treatment (2008) basal area, top height, and quadratic mean diameter were significantly lower in 15.2 m openings. Maple (Acer spp.) species had the highest mean importance value across treatments (0.40). Trends suggest that species composition of dominant and codominant trees among opening sizes may have been influenced by shade tolerance adaptations of the species groups present. Whereas 15.2 m openings were dominated by shade tolerant maple species, 45.7 and 76.2 m openings produced a mixture of commercial species including shade intolerant species such as yellow-poplar (Liriodendron tulipifera L.), trees of intermediate shade tolerance like oak (Quercus spp.), and shade tolerant maple. Data further suggest the density of overstory oak was highest in the intermediate opening size (45.7 m), while yellow-poplar increased in the larger opening sizes. Evaluation of species shifts between 1981 and 2008 showed that relative basal area of maple increased across all treatments. Relative basal areas from 45.7 to 76.2 m openings suggest declines in yellow-poplar and other non-commercial species were balanced by increases in oak and maple.     

Evaluation of thermally modified beech and spruce wood and their properties by FT-NIR spectroscopy

Quality assessment of thermally modified spruce (Picea abies (L.) Karst) and beech (Fagus sylvatica L.) wood and of the corresponding reference samples was carried out by means of non-destructive FT-NIR spectroscopic measurements and PLS regression. Oven-dry and basic density as well as MOE and MOR determined by 3-point bending tests were evaluated. The focus was put on specimens produced from material that had been thermally modified in an industrial scale kiln. Modelling results range from poor to very good. The results of the spectra taken from the spruce samples resulted in better prediction results than the spectra of the beech samples. This could be due to different proveniences or variation in the industrial modification process. The results indicate that FT-NIR surface measurements of sound thermally modified wood samples could be applied to evaluate several characteristics before and after the modification process. The method could be used for screening during pre-sorting of thermally modified wood.     

Forest regeneration 50 years following partial cutting in mixedwood ecosystems of southern Quebec,Canada

The impact of winter harvesting on regeneration 50 years after an experimental diameter-limit cutting was examined in mixed deciduous–coniferous ecosystems of southern Quebec, Canada. The study was conducted in La Mauricie National Park, Quebec, Canada. Regeneration data in two balsam fir (Abies balsamea (L.) Mill.), red spruce (Picea rubens Sarg.), sugar maple (Acer saccharum Marsh.), and yellow birch (Betula alleghaniensis Britt.) ecosystem types were analyzed. Comparisons between uncut and cut stands were obtained from a total of 63 sample plots. For both ecosystems, there were no significant differences between uncut and cut plots for regeneration density and stocking. The most abundant regeneration species were balsam fir, red spruce, sugar maple, red maple (Acer rubrum L.), yellow birch and American beech (Fagus grandifolia Ehrh.). The type of diameter-limit cutting described in the study did not affect regeneration density and stocking but its impact on productivity, timber quality and genetics is still unknown.     

Gap dynamics in the Western Carpathian mixed beech old-growth forests affected by spruce bark beetle outbreak

Understanding how species-specific disturbances affect the dynamics of mixed forests is becoming increasingly important due to rapidly changing disturbance regimes. This study estimated the effect of Norway spruce (Picea abies (L.) Karst.) mortality on the disturbance processes in two mixed beech stands of the Western Carpathians that were affected by a bark beetle outbreak. We evaluated the size distribution, fraction of canopy and expanded gaps, the characteristics of gapmakers and the contribution of different species to gap size. The measured canopy gap fraction was <5%, and most canopy gaps were small (<100 m²). Spruce was the most abundant gapmaker, and its share among gapmakers was 3–6 times higher than its share in the canopy. We found that the increase in spruce mortality due to the outbreak resulted in a fine-scale mortality pattern. However, spruce gapmakers did not contribute much to gap area size, as shown by a weak correlation between the number of spruce gapmakers and the area of expanded gaps. Diameter distribution of living versus recently dead trees showed that beech mortality occurred disproportionately in large size classes. However, dead spruce trees were equally frequent in all diameter classes, which means beetles did not exclusively attack larger trees in these stands during the outbreak. We conclude that spruce mortality may have influenced successional processes by giving a competitive advantage to two other species that were not affected by the outbreak, provided that a high deer browsing intensity does not hinder the regeneration of new seedlings.

     

Distribution of preservatives in thermally modified Scots pine and Norway spruce sapwood

Studying the impregnation and distribution of oil-based preservative in dried wood is complicated as wood is a nonhomogeneous, hygroscopic and porous material, and especially of anisotropic nature. However, this study is important since it has influence on the durability of wood. To enhance the durability of thermally modified wood, a new method for preservative impregnation is introduced, avoiding the need for external pressure or vacuum. This article presents a study on preservative distribution in thermally treated Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) sapwood using computed tomography scanning, light microscopy, and scanning electron microscopy. Secondary treatment of thermally modified wood was performed on a laboratory scale by impregnation with two types of preservatives, viz. Elit Träskydd (Beckers) and pine tar (tar), to evaluate their distribution in the wood cells. Preservative solutions were impregnated in the wood using a simple and effective method. Samples were preheated to 170 °C in a drying oven and immediately submerged in preservative solutions for simultaneous impregnation and cooling. Tar penetration was found higher than Beckers, and their distribution decreased with increasing sample length. Owing to some anatomical properties, uptake of preservatives was low in spruce. Besides, dry-induced interstitial spaces, which are proven important flow paths for seasoned wood, were not observed in this species.     

Radial growth of Norway spruce and Scots pine: effects of nitrogen deposition experiments

The growth patterns of annually resolved tree rings are good indicators of local environmental changes, making dendrochronology a valuable tool in air pollution research. In the present study, tree-ring analysis was used to assess the effects of 16 years (1991–2007) of chronic nitrogen (N) deposition, and 10 years (1991–2001) of reduced nitrogen input, on the radial growth of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) growing in the experimental area of Lake Gårdsjön, southwest Sweden. In addition to the ambient input of c. 15 kg N ha^?1 year^?1, dissolved NH₄NO₃ was experimentally added to a 0.52-ha watershed at a rate of c. 40 kg ha^?1 year^?1. Atmospheric N depositions were reduced by means of a below-canopy plastic roof, which covered a 0.63-ha catchment adjacent to the fertilized site. The paired design of the experiment allowed tree growth in the N-treated sites to be compared with the growth at a reference plot receiving ambient N deposition. Nitrogen fertilization had a negative impact on pine growth, while no changes were observed in spruce. Similarly, the reduction in N and other acidifying compounds resulted in a tendency towards improved radial growth of pine, but it did not significantly affect the spruce growth. These results suggest that spruce is less susceptible to changes in the acidification and N status of the forest ecosystem than pine, at least in the Gårdsjön area.     

Evaluating the suitability of nine shelterbelt species for dendrochronological purposes in the Canadian Prairies

Shelterbelts have played an important role in prairie agriculture since the late 1800s; however, little is known about how these shelterbelts may be affected by climate change. The objective of this study was to determine if shelterbelt species, which are heavily influenced by human activity, express a common radial-growth signal within and between trees. The study focused on the annual tree-ring growth of the nine most common shelterbelt species of the Canadian Prairies: Salix acutifolia (Acute willow), Caragana arborescens (caragana, or Siberian pea shrub), Picea pungens (Colorado spruce), Fraxinus pennsylvanica (green ash), Populus sp. (hybrid poplar), Acer negundo (Manitoba maple), Pinus sylvestris (Scots pine), Ulmus pumila (Siberian elm) and Picea glauca (white spruce). Tree core samples were collected near Saskatoon, Saskatchewan using traditional dendrochronological methods. The standardized growth of each species was compared with historical homogenized climate data in order to determine the key monthly climate variables impacting each species. Prior to this analysis, little was known about the suitability of six of these nine species for dendrochronological purposes. It was found that all species crossdate at a significant level, and that the three most significantly correlated climate factors are able to account for up to 37 % of the annual variation in tree-ring growth. The findings of this study suggest that all nine species are suitable, to varying degrees, for future dendrochronological research in the Canadian Prairies as well as having implications for shelterbelt systems elsewhere in the world. The top four species based on four ranking criteria (interseries correlation, mean sensitivity, climate explanatory power, and commonality) were white spruce, acute willow, caragana, and Manitoba maple, and initial results suggest that all species have the potential to be investigated in greater depth.     

Effects of enhanced nitrogen deposition on foliar chemistry and physiological processes of forest trees at the Bear Brook Watershed in Maine

Effects of enhanced nitrogen deposition on nutrient foliar concentrations and net photosynthesis of sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Ehrh) and red spruce (Picea rubens Sarg.) were evaluated at the Bear Brook Watershed in Maine (BBWM). The BBWM is a paired-watershed forest ecosystem study with one watershed treated since 1989 with bimonthly dry ammonium sulfate ((NH₄)₂SO₄) additions at a rate of 25.2 kg N ha⁻¹ year⁻¹, while the other watershed serves as a reference. The (NH₄)₂SO₄ treatment resulted in significant increases in foliar N concentrations for all three species and significant reductions in foliar Ca, Mg and Zn concentrations for American beech and red spruce. Treatment effects on foliar concentrations of other nutrients were not significant in any species. Despite higher N concentrations in all species, only treated sugar maple showed significantly higher photosynthetic rates. The non-response in net photosynthesis to higher foliar N in American beech and red spruce might be attributed to their low foliar Ca and/or Mg concentrations. Higher net photosynthetic rates in sugar maple might be explained by the higher foliar N and by the ability of this species to maintain an adequate Ca and Mg supply. Results suggested that nutrient imbalances due to inadequate supply of Ca and Mg might have counteracted a potential increase in net photosynthesis induced by higher N concentrations in American beech and red spruce.     

Decaying wood and tree regeneration in the Acadian Forest of Maine,USA

We examined the effect of management history on the availability of decayed downed wood and the use of downed wood as a regeneration substrate in mixed-species stands in the Acadian Forest of Maine. Regeneration of red spruce (Picea rubens Sarg.), eastern hemlock (Tsuga canadensis (L.) Carr.), balsam fir (Abies balsamea L. Mill), and red maple (Acer rubrum L.) was quantified. Treatments included variants of selection cutting, commercial clearcutting (unregulated harvesting), and no harvesting for >50 years (reference). Area of wood substrate (wood ≥ Decay Class III and ≥10 cm on at least one end) was less in the commercial clearcut than in the reference; other treatments were not differentiated. Spruce and hemlock seedlings were found at higher densities on wood than paired forest floor plots of equal area, regardless of treatment. Conversely, fir and maple were less abundant on wood than forest floor plots in reference and selection treatments, but more or equally abundant on wood than forest floor plots in the commercial clearcut. These findings suggest that silvicultural treatment affects both the availability of decayed downed wood and seedling-substrate relationships, and that forest management in the Acadian Region should consider availability of downed woody material.     

Modification of three hardwoods with an N-methylol melamine compound and a metal-complex dye

This study evaluated the combined modification and staining of ash, beech and maple wood with a low molecular weight N-methylol melamine compound (NMM) and a metal-complex dye. Wood samples were treated with aqueous solutions of 10, 20 and 30 wt% NMM and 5 wt% of the dye. The treatment caused the fixation of the water-soluble dye by the NMM resin. Vacuum pressure impregnation of unsealed wood blocks did not result in different solution uptake and weight percent gain after curing among the three species, but sealing of the surfaces of the wood blocks to allow penetration only into one direction revealed easiest penetrability of beech followed by maple and ash. UV micro-spectrophotometry and light microscopy indicated that NMM was partly deposited in the cell wall and partly in the lumens. Penetration of the metal-complex dye was shown by means of X-ray micro-analysis (SEM–EDX). The study shows that a combined resin modification and staining of the three wood species tested is possible and that NMM causes fixation of the water-soluble dye.     

Modelling primary branch frequency and size for five conifer species in Maine,USA

Quantitative models of crown structure have been developed for several conifer species, but these studies have rarely simultaneously fit the models across multiple species. This study used extensive crown structure data for the five primary conifer species in Maine to test for species differences in maximum branch diameter profile, branch density, and relative branch diameter distribution. The species included balsam fir [Abies balsamea (L.) Mill], northern white-cedar [Thuja occidentalis (L.)], eastern hemlock [Tsuga canadensis (L.) Carr.], eastern white pine [Pinus strobus (L.)], and red spruce [Picea rubens (Sarg.)]. After accounting for key covariates, significant species differences were found in all crown structural attributes examined in this study. Profiles for the mean tree indicated that northern white-cedar had the smallest maximum branch diameters throughout the crown and white pine had the largest, except near the base of the crown where the species switched in rank. The density of live branches in a crown had the widest range of variation of the examined crown structural attributes. Red spruce had a significantly higher density of primary branches than the other conifers, particularly in the upper crown. The relative branch diameter distribution indicated that balsam fir had a distribution more skewed towards larger relative branch sizes, while eastern hemlock and red spruce had distributions shifted towards smaller relative branches. This study highlights the range of variability in key crown structural attributes due to inherent species differences, but indicates that models fit across multiple species can perform quite well as the amount of explained variation was relatively high.     

Effects of soil moisture and species composition on growth and productivity of trembling aspen and white spruce in planted mixtures: 5-year results

Aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench.) Voss) were planted 0.5 m apart in intimate mixtures in 5 × 4 m plots, with two moisture regimes—irrigation versus control—and five species compositions—pure aspen (Aw100), mixed aspen and spruce (Aw83Sw17, Aw50Sw50, Aw17Sw83), and pure spruce (Sw100), replicated six times. Fifth-year assessments indicated that irrigation increased individual tree growth (height, RCD, crown width), plot leaf area index (LAI), and wood biomass. Increased aspen composition reduced the availability of soil moisture and consequently the growth of individual trees. With increased aspen composition more growth was allocated to stem in aspen and to foliage in white spruce. Comparatively, aspen responded more to irrigation and thus their growth is more dependent on precipitation than that of spruce. Among the three growth variables assessed, height responded more to irrigation in both species. Equal mixtures and aspen-dominated mixtures in control plots had higher productivity in terms of total wood biomass in both absolute and relative terms. The implications of these findings are discussed in relation to managing aspen and white spruce mixedwood forests under increasing drought expected as a result of climate change.     

Impact of bark wounds on sapwood in Norway spruce and silver fir

Bark wounds by damage during harvesting are a serious problem in forestry due to fungi infection and wood deterioration. This paper presents results of an investigation about the influence of the wounds on the internal structure of such injured stems. In an experiment, bark wounds were artificially created at the stem base of Norway spruce [Picea abies (L.) Karst.] and silver fir (Abies alba Mill.). 2 years later, the injured stems along with undamaged controls were cut and the trunk portion below breast height subjected to computer tomographic (CT) analysis. Analysis of the CT-images revealed a substantial impact of wounding on sapwood properties in spruce: directly adjacent to the wound surface in all examined trees, a large disturbance zone was detected affecting on average 17% of the potential sapwood area. With increasing distance from the wound, the size of this disturbance zone diminished, but was still detectable in all trees at breast height ca. 1 m above the bark wound.     

Growth and mortality in underplanted tree seedlings in response to variations in canopy closure of Norway spruce stands

Six broadleaved tree species and Picea abies (L.) Karst. wereplanted under spruce plantations of varying densities, in Sweden.Treatments included control (994 stems ha^–1), dense (538stems ha^–1), sparse (294 stems ha^–1) and gap (0stems ha^–1) overstory treatments. There was an increasein height and diameter growth from control to sparse overstorytreatment of all underplanted tree species except for ash (Fraxinusexcelsior L.) and Norway maple (Acer platanoides L.). Site conditionsmay have hampered the growth of these species, as well as wildcherry (Prunus avium L.). Both oak (Quercus robur L.) and sprucehad greater growth in the gap treatment, relative to the othertreatments. Insecticide application did not influence seedlinggrowth or survival. The performance of beech (Fagus sylvaticaL.), lime (Tilia cordata Mill.), spruce and oak was consistentwith shade tolerance ranking. Beech and lime had a very highsurvival rate, even under the densest canopy. The growth andmortality of ash, maple and wild cherry differed significantlyfrom what was expected. This experiment demonstrated significantvariation in interspecific growth and mortality between sevenplanted tree species in relation to canopy density. Correctsite and species selection is crucial when underplanting inshelterwood systems.     

Understory dynamics after disturbance accelerate succession from spruce to beech-dominated forest—the Siggaboda case study

??Context

It is assumed that climate change will favour European beech (Fagus sylvatica L.) to Norway spruce (Picea abies [L.] Karst.) at its northern range margins due to climate change and induced disturbance events.

??Aims

An old-growth mixed forest of spruce and beech, situated near the northern beech margin, was studied to reveal effects of disturbances and response processes on natural forest dynamics, focussing on the understory.

??Methods

We carried out analyses on understory dynamics of beech and spruce in relation to overstory release. This was done based on a sequence of stand and tree vitality inventories after a series of abiotic and biotic disturbances.

??Results

It became apparent that beech (understory) has a larger adaptive capacity to disturbance impacts and overstory release (68 % standing volume loss) than spruce. Understory dynamics can play a key role for forest succession from spruce to beech-dominated forests. Disturbances display an acceleration effect on forest succession in the face of climate change.

??Conclusion

Beech is poised strategically to replace spruce as the dominant tree species at the study area. Due to an increasing productivity and a lower risk of stand failure, beech may raise into the focus of forestry in southern Sweden.