Norway Spruce Sapwood Research Articles

Mechanical properties of Norway spruce (Picea abies) infested by the bark beetle (Ips typographus)

ABSTRACT This study considered the mechanical properties of primary blue-stained sapwood of Norway spruce infested by the bark beetle Ips typographus. Nineteen stems from Stammerberg (ZH, Switzerland) were harvested in three different seasons and after different periods of bark beetle outbreaks. Density, Brinell hardness including elastic recovery after load, and key strength properties were tested on blue-stained wood and non-infected controls. Differences in mechanical properties were analysed according to the stand and storage time of the stems after the bark beetle attack. Spruce harvested at a late stage after the bark beetle attack (2–3 months) showed a clear reduction in impact bending strength, a significant loss in surface elastic recovery after indentation during Brinell hardness test, and a striking number of specimens with brittle fracture behaviour during Three-Point-Bending. Light microscopy and the results of the mechanical tests give clear evidence to suggest that wood-degrading fungi are already active in addition to the sap-staining fungi. Especially after larger outbreaks of bark beetles, it must be assumed that sapwood of Norway spruce does not only show the typical blue stain, but also incipient stages of wood degradation by wood-degrading fungi.

Thin kerf cutting forces of frozen and non-frozen Norway spruce and Scots pine wood

ABSTRACT Reducing the kerf width in bandsawing has potential in reducing waste while optimising the yield. To be able to reduce the kerf width, understanding the cutting forces becomes critical. In this work, nine cutting teeth with varying band-body thicknesses and side clearances were tested by cutting both heartwood and sapwood of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) in frozen and non-frozen conditions. Single cutting teeth were moved into rotating wood samples in the 90–90° cutting direction, with chip thicknesses of 0.9 mm per cut. The main and normal cutting forces were measured. Scots pine had a higher density than Norway spruce and, therefore, a higher main cutting force. Non-frozen sapwood, non-frozen heartwood and frozen heartwood resulted in similar main cutting forces, but frozen sapwood resulted in significantly higher main cutting forces. Reducing the cutting width by about 45% resulted in an approximately 40% reduction in the main cutting force. The normal forces were not significantly affected by the species or cutting width. Frozen heartwood, non-frozen heartwood and non-frozen sapwood had similar normal cutting forces. Frozen sapwood had negative normal forces, and thus self-feeding was observed.

Humidity-dependence of the hydroxyl accessibility in Norway spruce wood

This study aimed at a better understanding of the wood-water interaction, in particular the role of the hydroxyl accessibility during the humidity-dependent change in moisture content. Thin sections (80 µm) of never-dried Norway spruce sapwood that contained early- and latewood were used for the experiments. Sorption isotherm measurements confirmed the humidity-dependent moisture content changes and the effect of the first drying of the wood sections. Changes in hydroxyl accessibility were then determined by deuteration of the sections using deuterium oxide, followed by their re-protonation in water (H2O) vapor at different relative humidity: 15, 55 or 95%. The deuteration and re-protonation of the wood sections were quantified by dry mass changes as well as by changes in the OH and OD stretching vibrations in the Fourier transform infrared spectra. The results showed that the deuterated sections could be almost completely re-protonated in H2O vapor, nearly irrespective of the applied relative humidity. Therefore, changes in hydroxyl accessibility were not the driving force for the humidity-dependent changes in moisture content. However, a slow re-protonation rate at low relative humidity had to be considered. Nonetheless, a small quantity of OD groups persisted the re-protonation in H2O vapor and liquid H2O, which was not related to the drying of the wood.Graphic abstract

Tree species identification via 1H NMR fingerprinting of supercritical carbon dioxide wood extractives

Six tree species were examined using 1H NMR spectroscopy of sap extracted by supercritical CO2. A metabolomic approach was developed to evaluate the sap extracted from sapwood of Norway spruce (Picea abies), Sitka spruce (Picea sitchensis), radiata pine (Pinus radiata), macrocarpa (Cupressus macrocarpa), and two Eucalyptus species—shining gum and mountain ash (Eucalyptus nitens and Eucalyptus regnans. The sap extraction patterns in the different species were visualised using 1H magnetic resonance imaging. In softwoods with distinct annual rings, water was first removed from the latewood bands, and then gradually from the earlywood bands. In the case of the hardwood species an almost random water redistribution, rather than water expulsion, was observed. Analysis of the principal component analysis loading plots showed that the significant differences in the sap between each species were due to the carbohydrate region. Key discriminators were identified as pinitol, sucrose, glucose, and fructose.

Determination of Pleurotus abieticola ligninolytic activity on Norway spruce wood

Abstract The effect of Phlebiopsis gigantea treatment in control of Heterobasidion parviporum in Norway spruce is less effective than that in control of Heterobasidion annosum in pine. It is necessary to apply other fungi, for example, Pleurotus abieticola in Norway spruce stands. Thus, it is necessary to assess the activity of major ligninolytic enzymes, that is, laccase, lignin peroxidase (LiP), manganese peroxidase (MnP) and versatile peroxidase (VP) produced by P. abieticola, which may be effective in the fast degradation of Norway spruce wood. Three strains of P. abieticola (Pa1-3) were grown on pieces of Norway spruce sapwood and heartwood for 50 days in laboratory conditions. Enzymatic activity was determined using spectrophotometry. Pleurotus abieticola produced laccase, LiP, MnP and VP. The activity of laccase was low, ranging 0–3.696 and 0–0.806 mU/μg of protein in sapwood and heartwood, respectively. The highest activity in Pa1 = 3.696 mU/μg of protein in sapwood and in Pa3 = 0.806 mU/μg of protein in heartwood was observed after 30 and 50 days of incubation, respectively. The activity of LiP was also low, ranging 0–0.188 and 0–0.271 mU/μg of protein in sapwood and heartwood, respectively. The highest activity in Pa1 = 0.271 mU/μg of protein in sapwood and in Pa2 = 0.188 mU/μg of protein in heartwood was observed after 40 and 20 days of incubation, respectively. The activity of MnP ranged 0–17.618 and 0–12.203 mU/μg of protein in sapwood and heartwood, respectively. This enzymatic activity peaked at the 50th day of culture on sapwood for the Pa3 strain (17.618 mU/μg of protein) and at the 20th day of culture on heartwood for the Pa1 strain (12.203 mU/μg of protein). The activity of VP with manganese-oxidising properties was found to be high in all strains of P. abieticola, ranging 0–39.19 and 0–59.153 mU/μg of protein in sapwood and heartwood, respectively, whereas the activity of VP with guaiacol-oxidising properties was very low for all P. abieticola strains, ranging 0–0.248 and 0–0.225 mU/μg of protein in sapwood and heartwood, respectively. The values of released hydroxyphenols in P. abieticola strains ranged 24.915–139.766 and 25.19–84.562 µg of protocatechuic acid/ml in sapwood and heartwood, respectively. The values of released methoxyphenols for the evaluated strains of P. abieticola ranged 7.225–23.789 and 1.953–20.651 µg of vanillic acid/ml in sapwood and heartwood, respectively. Further studies with a higher number of strains of this species as well as an optimisation of conditions for the measurement of ligninolytic activity are needed.

The cell wall composition of Norway spruce earlywood and latewood revisited

ABSTRACTThe xylem of gymnosperm trees consists mainly of tracheids, which generally have larger radial diameters and thinner walls in earlywood than in latewood. Information on possible chemical differences is limited, but according to a few studies, earlywood normally contains more lignin relative to cellulose than latewood. However, for methods giving results per gram dry matter, this result is expected since a larger part of the earlywood cell wall material consists of lignin-rich middle lamella. In this study, we used Raman microspectroscopy to assess relative biopolymer composition of earlywood and latewood secondary cell walls from mature sapwood of Norway spruce (Picea abies (L.) Karst.). In addition, infrared spectroscopy of isolated earlywood and latewood from the same growth rings as well as additional growth rings was performed. Both methods showed significantly higher relative lignin content in the earlywood which confirms results from earlier studies.

Hydraulic and mechanical dysfunction of Norway spruce sapwood due to extreme summer drought in Scandinavia

Abstract Projected climate change scenarios such as frequently occurring dry summer spells are an enormous threat to the health of boreal conifer forests. We identified visible features indicating wood with tracheids predisposed for hydraulic and mechanical dysfunction in Norway spruce, suggest why this is formed during severe summer drought and hypothesised on mechanism that would cause tracheid collapse and stem cracks. Trees from southern Sweden that showed signs of severe reaction to drought, i.e. stem cracks along the trunk, were compared to healthy, undamaged trees. Rings investigated included those formed in 2006, a year with an extremely dry summer season in the study region. In southern Norway, we investigated trees with and without drought-induced top dieback symptoms. We analysed anatomical features such as tracheid lumen diameter, thickness of cell wall and its various layers (S1, S2 and S3), applied Raman imaging in order to get information on the lignin distribution in the cell wall and the compound middle lamellae and performed hydraulic flow and shrinkage experiments. Although tracheids in annual rings with signs of collapse had higher tangential lumen diameters than those in “normal” annual rings, we conclude that collapse of tracheid walls depends mainly on wall thickness, which is genetically determined to a large extent. Spruce trees that produce earlywood with extremely thin cell walls can develop wall collapse and internal cracks under the impact of dry spells. We also present a new diagnostic tool for detecting individuals that are prone to cell wall collapse and stem cracks: Lucid bands, i.e. bands in the fresh sapwood with very thin cell walls and inhomogeneous lignin distribution in the S-layers and the compound middle lamellae that lost their hydraulic function due to periods of severe summer drought. The detection of genotypes with lucid bands could be useful for an early selection against individuals that are prone to stem cracks under the impact of severe summer drought, and also for early downgrading of logs prone to cracking during industrial kiln drying.

The sorption of monovalent cations onto wood flour and holocelluloses of Norway spruce: molecular interactions during LiCl impregnation

Abstract Active functional groups and interactions involved in the sorption of Li+ ions from an aqueous LiCl solution onto the Norway spruce sapwood (sW) flour have been investigated. To this purpose, sW was delignified by peracetic acid (PAA) treatments and the resulting holocelluloses (HC6 h, HC24 h, HC51 h, HC72 h, where the lower case data indicate the PAA treatment time) with various lignin contents were immersed in aqueous solution of LiCl and the sorption effects were studied by flame atomic emission spectroscopy (FAES), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The Brunauer- Emmett-Teller (BET) specific surface area increased from 1.5±0.0 m2g−1 to 2.4±0.1 m2g−1 for HC6 h, and from 1.6±0.03 m2g−1 to 2.7±0.6 m2g−1 for HC72 h upon LiCl treatment. It was found that Li+/Cl− retention occurs predominantly via O-containing functionalities and the carbohydrate-rich samples sorbed more Li+. Upon LiCl treatment, the mobility and accessibility of the wood matrix was enhanced, possibly by interference of the introduced ions with the existing intermolecular bonds.

Wood density as a proxy for vulnerability to cavitation: Size matters

In this study, vulnerability to cavitation, P50 (i.e. the water potential causing 50 % loss of hydraulic conductivity), of Norway spruce trunkwood at different cambial age was related to wood density. Wood density was calculated from mass in the oven dry state related either to volume at the oven-dry state (dry wood density) or to volume at full saturation (basic wood density). Dry wood density and basic wood density were strongly linearly related (r² = 0.99); there was however a shift from the 1:1 reference line with increasing dry wood density. Dry wood density as well as basic wood density had similar high predictive qualities for P50 (r² = 0.85). The quadratic regression lines took however a quite different course below -4 MPa because volume shrinkage increased with increasing dry wood density. For Norway spruce sapwood with high dry wood density, mixing up different wood density traits would thus result in a predicted overestimation or underestimation of vulnerability to cavitation. Gravimetrically wood density measurements at different moisture contents (starting at full saturation) are easily to achieve on standard size specimens and the conversion curves obtained will be of high value for future ecological studies on other species and across species.

Hydraulic traits of Norway spruce sapwood estimated by Fourier transform near-infrared spectroscopy (FT-NIR)

The potential of Fourier transform near-infrared (FT-NIR) spectroscopy to predict hydraulic traits in Norway spruce (Picea abies (L.) Karst.) sapwood was evaluated. Hydraulic traits tested were P50 (applied air pressure causing 50% loss of hydraulic conductivity) and RWL50 (applied air pressure causing 50% relative water loss). Samples came from 24-year-old spruce clones. FT-NIR spectra were collected from the axial (transverse) and radial surface of each solid wood sample for the prediction of P50 and RWL50. Partial least squares regression (PLS-R) models with cross validation were used to establish relationships between the FT-NIR spectra and the reference data from hydraulic properties analysis. The impact of the wavenumber range and the pretreatment during the PLS-R model development and the differences between the axial and radial surfaces were shown. Based on the values of the coefficient of determination (r2) and the root mean square error of cross validation, predicted results were evaluated as acceptable. The models from the axial surface gave better results than the models from the radial surface for P50 (r2 = 0.65), as well as for RWL50 (r2 = 0.77). The first approach to predict hydraulic properties such as P50 and RWL50 by FT-NIR spectroscopy can be regarded as successful. We conclude that the method has high potential to be put into practice as a rapid, reliable, and nondestructive method to determine P50 and RWL50.

The mobility of nitrogen across tree-rings of Norway spruce (Picea abies L.) and the effect of extraction method on tree-ring δ¹⁵N and δ¹³C values.

The use of stable nitrogen (N) isotope ratios (δ(15)N values) in dendroecological studies is often preceded by an extraction procedure using organic solvents to remove mobile N compounds from tree-rings. Although these mobile N compounds may be capable of distorting potential environmental signals in the tree-ring δ(15)N values, recent investigations question the necessity of such an extraction. We used an on-going experiment with simulated elevated N deposition previously labelled with (15)N, in conjunction with control trees, to investigate the necessity of extracting mobile N compounds (using a rapid extraction procedure) for tree-ring δ(15)N and δ(13)C studies, as well as N and C concentration analyses. In addition, we examined the magnitude of radial redistribution of N across tree-rings of Norway spruce (Picea abies). The (15)N label, applied in 1995/96, was found in tree-rings as far back as 1951, although the increased N availability did not cause any significant relative increase in tree growth. The rapid extraction procedure had no significant effect on tree-ring δ(15)N or δ(13)C values in either labelled or control trees, or on N concentration. The C concentrations, however, were significantly higher after extraction in control samples, with the opposite effect observed in labelled samples. Our results indicate that the extraction of mobile N compounds through the rapid extraction procedure is not necessary prior to the determination of Norway spruce δ(15)N or δ(13)C values in dendrochemical studies. δ(15)N values, however, must be interpreted with great care, particularly when used as a proxy for the N status of trees, due to the very high mobility of N within the tree stem sapwood of Norway spruce over several decades.

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 Traskydd (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.

Within-ring movement of free water in dehydrating Norway spruce sapwood visualized by neutron radiography

Abstract This study is a first approach to visualize moisture distribution and movement between annual rings during sapwood drying by neutron imaging (NI). While Norway spruce [Picea abies (L.) Karst.] sapwood beams were allowed to dehydrate on a balance at ambient conditions, NI was performed in 1–10 min time steps. From NI raw files, radial dimensional changes were calculated during dehydration and transmission profiles were drawn for different relative moisture content (MC) steps from full saturation until equilibrium moisture content. The NI technique proved to be a useful tool to visualize the movement of free water within, and between, annual rings. Removal of free water in the middle part of the wood beam did not proceed continuously from the surface to the central part, but was strongly influenced by wood anatomy. Water is removed from earlywood during early stages of dehydration and later, at higher moisture loss (<50% MC), from the main latewood parts. It is therefore concluded that the radial dimensional changes measured at moderate moisture loss are not only caused by cell wall shrinkage of the outer wood parts located beneath the wood surface, but a result of elastic deformation of earlywood tracheids under the influence of negative hydrostatic pressures.

Defence-related gene expression in bark and sapwood of Norway spruce in response to Heterobasidion parviporum and methyl jasmonate

We compared gene expression in Norway spruce secondary phloem (bark) and developing xylem (sapwood) in response to the necrotrophic pathogen Heterobasidion parviporum, wounding and methyl jasmonate (MeJ). The pathogen induced systemic and local up-regulation of PaPX3, PaPX2 and PaChi4 in both bark and sapwood that returned to constitutive levels as the plants recovered from the infection, whereas the local responses to MeJ were similar in both tissues but was longer lasting for PaPX3 and PaChi4. Genes involved in lignin biosynthesis (PaPAL1, PaPAL2, PaC4H3/5 and PaHCT1) were up-regulated locally in the bark in response to pathogen and wounding whereas MeJ induced a similar but stronger local response. The ethylene biosynthesis related transcripts PaACO and PaACS did not increase in response to MeJ treatment or the pathogen, however it increased both locally and systemically as a response to wounding in the sapwood. These results demonstrate that the local and systemic host responses to pathogen infection and wounding largely correspond and reveal striking similarities between the local response to a necrotroph, wounding and MeJ treatment in both bark and living wood.

Ophiostomatoid fungi associated with Ips typographus (L.) on Picea abies [(L.) H. Karst.] and Pinus sylvestris L. in north-eastern Poland

This study dealt with the species distribution and frequency of ophiostomatoid fungi associated with the bark beetle Ips typographus on Norway spruce and Scots pine in north-eastern Poland. At all locations high spruce bark beetle damage has occurred in 2002-2003. Fungi were isolated from beetles and from brood systems of trees infested by the spruce bark beetle. The ophiostomatoid fungi were represented by 13 species. A similar spectrum of ophiostomatoid fungi as that recorded from <em>Picea abies</em> was associated with <em>I. typographus</em> on <em>Pinus sylvestris</em> trees. The most frequent ophiostomatoid species isolated from beetles, phloem and sapwood of Norway spruce were <em>O. bicolor</em> and <em>O. penicillatum</em>. The frequency of occurrence of ophiostomatoid fungi varied significantly among the examined locations. <em>O. bicolor</em> was the most frequently found species on Scots pine infested by <em>I. typographus</em>. The potential role of ophiostomatoid fungi in the epidemiology of <em>I. typographus</em> is discussed. Additionally, we also recorded how the ophiostomatoid fungi associated with spruce bark beetle could grow into phloem and sapwood of <em>Pinus sylvestris</em> trees.

Radial shrinkage and ultrasound acoustic emissions of fresh versus pre-dried Norway spruce sapwood

Acoustic emission (AE) and radial shrinkage were compared between fully saturated fresh and pre-dried Norway spruce sapwood during dehydration at ambient temperature. Hydraulic conductivity measurements, anatomical investigations on bordered pits and X-ray computed tomography (CT) scans were done to search for possible AE sources other than the breakage of the water columns inside the tracheids. Both fresh and pre-dried specimens showed radial shrinkage due to drying surface layers right from the beginning of dehydration, which induced almost no AE. Whereas no dimensional changes occurred in pre-dried wood thereafter, fresh wood showed a rapid shrinkage increase starting at 25% relative water loss. This dimensional change ceased when further moisture got lost and was even partially reversed. AE of fresh wood showed much higher activity and energy, which is a waveform feature that describes the strength of the acoustic signal. Extremely high single AE energy events were detected at this critical stage of dehydration. After partial recovery from shrinkage, neither dimensional changes nor AE activity showed differences between fresh and pre-dried wood after more than 80% relative moisture loss. Our results suggested that fresh sapwood is more prone to dehydration stresses than pre-dried sapwood. Differences in AE and shrinkage behavior might be due to the weakening or distortion of the pit membranes (cavitation fatigue), pit aspiration, structural changes of the cell walls and micro-checks, which occurred during the first dehydration cycle.

Fungi isolated from Picea abies infested by the bark beetle Ips typographus in the Białowieża forest in north‐eastern Poland

SummaryThe assemblage of fungi occurring in the sapwood of Norway spruce (Picea abies) and in bark beetle galleries following attack by the Eurasian spruce bark beetle Ips typographus was investigated in the Białowieża forest in north‐eastern Poland. Fungi were isolated from blue‐stained sapwood of beetle‐infested spruce trees in June 2002, and a few isolates were also obtained from ascospores and conidia taken from perithecia and asexual structures occurring in the gallery systems of the insects. The mycobiota of I. typographus in the Białowieża forest was dominated by ophiostomatoid fungi, which were represented by seven species. Four species, including Ceratocystis polonica, Grosmannia penicillata, Ophiostoma ainoae and Ophiostoma bicolor were isolated at high frequencies, whereas three other taxa, Ceratocystiopsis minuta, Ceratocystiopsis alba and a Pesotum sp. were rare. The anamorphic fungus Graphium fimbriisporum and yeasts also occurred occasionally. In addition, the basidiomycete Gloeocystidium ipidophilum was relatively common. The pathogenic blue‐stain fungus C. polonica was the dominant fungal associate of I. typographus in the Białowieża forest, which is consistent with a previous study at this area in the 1930s. Ceratocystis polonica was the most frequently isolated species at the leading edge of fungal colonization in the sapwood and had on an average penetrated deeper into the wood than other fungal associates. This suggests that it acts as a primary invader into the sapwood after attack by I. typographus in the Białowieża forest, followed by O. bicolor, O. ainoae, G. ipidophilum and G. penicillata. Thus far, the Białowieża forest is one of the few areas in Europe, where C. polonica has been reported as a dominate fungal associate of I. typographus.

Degradation of Norway spruce (Picea abies) heartwood and sapwood during 5.5 years’ above-ground exposure

Differences in durability between heartwood and sapwood of Norway spruce [Picea abies (L.) Karst.] were investigated to determine wood qualities most favourable for use in outdoor constructions above ground. Trees grown on sites with either good or poor access to water were used. Seventy-eight specimens measuring 20 × 50 × 300 mm3 separated into heartwood and sapwood, half untreated, half painted, were exposed horizontally outdoors above ground for 5.5 years with the pith side up and the bark side down. Crack length and crack number were measured. Fungus growth and surface changes were visually estimated. Fungus type was determined by microscopic analysis. The main finding was that spruce heartwood had fewer and shorter cracks and less surface-discolouring fungus growth than sapwood. This was valid for both painted and untreated wood. After 2 years’ exposure, the cracks in sapwood (upper surface) were more than three times longer and about five times more numerous than in heartwood for both painted and untreated boards. Microscopic study showed that surface discoloration was due mainly to Aureobasidium pullulans, together with a few other discolouring fungi. After 5.5 years, initial decay was established on the surface and in the end grain of four untreated test objects.

Local water vapor diffusion coefficient when drying Norway spruce sapwood

In this article, a one-dimensional and a two-dimensional approach to the evaluation of local diffusion coefficients for Norway spruce sapwood from measured moisture content (MC) values are presented. A studied wood sample was dried from the initial green condition to about 15% mean MC, but here only the diffusive part of the drying process between approximately 25% and 15% mean MC was treated. Measured local MC values were based on nondestructive X-ray computed tomography data. Finite element calculations were performed with two alternative diffusion coefficients to test the appropriateness of the diffusion coefficients that were evaluated from the measured MC values. The evaluated diffusion coefficients show interesting dependence on MC and distance from the evaporation surface. The advantage of using the methods presented is that the diffusion coefficient is calculated on a local level without having to define a function for the diffusion coefficient’s dependency on other parameters.

Initial reactions in sapwood of Norway spruce and Scots pine after wounding and infection by Heterobasidion parviporum and H. annosum

SummaryThe xylem surface of seedlings, stem material and roots of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) were inoculated with strains of Heterobasidion annosum s. str. and H. parviporum s. str. The depth of necrosis in wounded spruce increased at a linear rate for at least seven weeks of incubation, but the rate of necrotic spread was significantly faster in infected wounds. In wounded pine the necrosis was maintained at a more superficial level for several weeks. Both spruce and pine sapwood were initially infected by hyphae of both species. In spruce, the hyphae advanced at a constant rate behind the necrotic front. On the contrary, after 1–2 weeks living H. parviporum hyphae were rare in pine rays. Heterobasidion annosum hyphae survived in pine rays, phloem and tracheids, despite a heavy accumulation of phenolics and resins and were able to penetrate into the sapwood at a linear rate although slower than infections in spruce. Histochemistry and quantitative estimates demonstrated that peroxidase activity was initially higher in spruce sapwood than in pine. Within three days of incubation, the activity in spruce sapwood disappeared concurrently with deepening necrosis. However, in pine, in both control and infected samples, there was a significant increase in peroxidase activity in the area surrounding the superficial necrosis, up to the wound surface and in the cambium and phloem around the wound. After wounding and infection, the content of soluble protein increased significantly in wood of older trees but not in seedlings. Infection resulted in an increased formation of lipophilic extractives in both spruce and pine but to a significantly greater degree in the latter, whereas the amount of hydrophilic compounds decreased in both. High‐performance liquid chromatography (HPLC) analyses of lipophilic extracts showed that inoculation of pine with the two species of Heterobasidion increased the amounts of pinosylvin, its monomethylether and several other phenolics as also resinous compounds. The results obtained may be relevant in explaining the known higher resistance of Scots pine to H. parviporum.