Variation in treatability of Scots pine sapwood: a survey of 25 different northern European locations

The treatability of Scots pine sapwood sampled from 25 locations in northern Europe, which was impregnated with an experimental furfuryl alcohol mix, was studied. A large variation in treatability was found between stands. The treatability was affected by anatomical properties of the trees and therefore also by the immediate climate, the sociological position of the tree in the stand, growth increments and on-stand competition. With the models applied, most parts of the differences in treatability between stands could be explained, while the treatability variation between trees within a stand remained mostly unexplained. Wider annual rings and higher latewood contents were found to increase the treatability. Models that included data on growth conditions and climate explain more of the variation in treatability, indicating that also other anatomical properties are influencing the treatability. Tree attributes and growth conditions that reduce annual ring width and latewood content decreased the treatability. Trees growing under warmer conditions and developing larger growth increments were easier to impregnate. Wood from trees growing near the timberline and under environmental conditions impairing wood growth was more difficult to treat.     

Climate influences the leaf area/sapwood area ratio in Scots pine

We tested the hypothesis that the leaf area/sapwood area ratio in Scots pine (Pinus sylvestris L.) is influenced by site differences in water vapor pressure deficit of the air (D). Two stands of the same provenance were selected, one in western Scotland and one in eastern England, so that effects resulting from age, genetic variability, density and fertility were minimized. Compared with the Scots pine trees at the cooler and wetter site in Scotland, the trees at the warmer and drier site in England produced less leaf area per unit of conducting sapwood area both at a stem height of 1.3 m and at the base of the live crown, whereas stem permeability was similar at both sites. Also, trees at the drier site had less leaf area per unit branch cross-sectional area at the branch base than trees at the wetter site. For each site, the average values for leaf area, sapwood area and permeability were used, together with values of transpiration rates at different D, to calculate average stem water potential gradients. Changes in the leaf area/sapwood area ratio acted to maintain a similar water potential gradient in the stems of trees at both sites despite climatic differences between the sites.     

Effects of chemical modification with glutaraldehyde on the weathering performance of Scots pine sapwood

Scots pine sapwood was treated with glutaraldehyde (GA) in aqueous solution using magnesium chloride as a catalyst in order to evaluate the durability towards weathering. Infrared spectroscopy suggested that GA treatment increased the photo-stability of lignin during artificial weathering of micro-veneers in a QUV over 168?h; photo-protection increased with increasing GA concentration. In comparison with the unmodified controls, GA-modified pine micro-veneer strips exhibited a lower tensile strength loss measured in a zero-span mode in the course of weathering. During 18?months of outdoor exposure, GA-modified pine wood boards exhibited a lower moisture content and water uptake than the unmodified ones. GA treatment also clearly restricted the penetration of blue stain fungi into deeper layers of wood. On the macroscopic scale, the surface of the GA-modified boards was significantly smoother due to less erosion, cracking and minor peeling of tracheids. Scanning electron microscopy further revealed that individual tracheids were detached from the cell compound and then washed away from the unmodified wood surface, whereas tracheids on surfaces of GA-modified wood remained in the tissue compound but displayed many axial and transversal cracks.     

Dimensional changes in Corsican and Scots pine sapwood due to reaction with crotonic anhydride

 The effects of the reaction temperature and varying level of weight gain on the dimensional stabilisation of crotonic anhydride modified Corsican and Scots pine sapwood were investigated. With Corsican pine at low levels of substitution, the reagent occupied larger molar volumes in the cell wall than at higher weight gains. With Scots pine the molar volume occupied by reagent was found to be temperature dependent at low levels of substitution. Dimensional stabilisation was determined by the water-soak/oven-dry method through a total of ten cycles in order to determine the stability of the ester bond to hydrolysis at neutral pH. It was found that the reaction temperature has no significant effect on dimensional stability provided the same weight gain level is obtained. At weight gain levels in excess of 30%, values of anti-shrink efficiency of 90% were obtained. Received 2 April 1999     

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.     

Neutral lipids and phospholipids in Scots pine (Pinus sylvestris) sapwood and heartwood

Variations in the concentration and composition of triacylglycerols, free fatty acids and phospholipids were analyzed in Scots pine (Pinus sylvestris L.) trees at five sites. Disks were taken at breast height or at a height of 4 m from the stems of 81 trees differing in diameter and growth rate. The mean concentration of triacylglycerols in sapwood was 26 mg g(-1) dry mass; however, variation among trees was large (16-51 mg g(dm)(-1)). The concentration of triacylglycerols was slightly larger at 4 m height in the stem than at breast height. Concentrations of triacylglycerols did not differ between the sapwood of young and small-diameter stems (DBH < 12 cm) and the sapwood of old stems (DBH > 36 cm). Concentrations of free fatty acids were negligible in the outer sapwood, but ranged between 5 and 18 mg g(dm)(-1) in the heartwood. The most abundant fatty acids of triacylglycerols were oleic (18:1), linoleic (18:2omega6, 18:2Delta5,9), linolenic (pinolenic, 18:3Delta5,9,12 and 18:3omega3) and eicosatrienoic acid (20:3Delta5,11,14 and 20:3omega6). The concentration of linoleic acid comprised 39-46% of the triacylglycerol fatty acids and the concentration was higher in the slow-growing stem from northern Finland than in the stems from southern Finland. Major phospholipids were detected only in sapwood, and only traces of lipid phosphorus were detected in heartwood.     

Variation in treatability of Scots pine (Pinus sylvestris) by the chemical modification agent furfuryl alcohol dissolved in water

Scots pine (Pinus sylvestris) sapwood was investigated for variation in treatability using the wood modifying agent, furfuryl alcohol (FA) in water. The variation in treatability within trees, between trees and between different stands of Scots pine was studied. Investigated variables that reduced the residual variance significantly were: site location, latitude of site, height of trees, annual ring width, vertical and horizontal position in the tree and method of drying. Linear mixed model statistics were used and tree number was handled as a random variable. The best model reduced the treatability residual variance by 67%. Location was the single factor affecting treatability most. Differences in latitude between locations may be the reason for that. Latitude correlated negatively with the treatability. Within the trees, the treatability of sapwood increased with distance from ground and with distance from heartwood border. A small, but significantly better treatability was found for kiln dried wood (60°C) compared to air dried wood (20°C).     

Electrical transport of endogenous mineral ions in green sapwood ofPinus sylvestris L. (Scots pine)

Summary The relative migration of the major endogenous ions (K⁺, Ca²⁺ Mg²⁺, Na⁺, Cl^– in green sapwood ofPinus sylvestris L. was measured in a modified Hittorf transference cell. The transference numbers obtained gave the fractions of the current carried by these ions when an electric field was applied across the wood samples under the conditions used.Potassium and calcium ions were always found to be the main endogenous current carriers, followed by magnesium, sodium and chloride ions. No significant differences in transference number were found between wood stored under refrigeration or in a deep freeze, nor was there any effect on prior -irradiation. Fungal contamination in a few non-irradiated specimens led to lower transference numbers. Changes in moisture content from 86 to 141% produced no significant change but the results did depend on the tree from which the samples had been taken. A decrease in the length of the wood sample from 100 to 50 mm had little effect on the transference numbers of calcium ions but caused a decrease in those of potassium when larger quantities of electricity were passed. Transversely- and longitudinally-oriented wood samples, however, gave very similar results. Visual observation of the anode compartment indicated that the ions followed the path of least resistance between cathode and anode and that the current passed along the grain of the wood.Symbols c_i molar concentration of ion i - F Faraday's constant (96 494 C/mol) - I current - t time - t_i transference number of ion i (also shown as t(i) in tables) - V volume of electrode compartment - Z_i charge number of ion i The authors thank SERC and Rentokil PLC for the award of a CASE Research Studentship to P.J.S. and the Leverhulme Trust for the award of an Emeritus Fellowship to M.S.     

Durability of thermally modified sapwood and heartwood of Scots pine and Norway spruce in the modified double layer test

In the present study, durability of untreated and thermally modified sapwood and heartwood of Scots pine and Norway spruce was examined using a modified double layer test. Base layer samples were partly on contact with ground where exposure conditions were harder than that in a double layer test above the ground. The base layer on ground contact gave results already after one year of exposure in Finnish climate, but the top layer of a double layer test element simulated more the situation of decking exposure.

Significant differences in durability and moisture content (MC) between the wood materials were detected after six years of exposure in the field. Thermally modified pine heartwood performed very well in all layers of the test element and only minor signs of decay were found in some of the base samples. Both sapwood and heartwood of thermally modified spruce were suffering only slight amounts of decay while thermally modified pine sapwood was slightly or moderately decayed. Untreated sapwood samples of pine and spruce were severely decayed or reached failure rating after six years in the field. Untreated heartwood samples performed clearly better. The highest MCs were measured from untreated and thermally modified pine samples. Thermal modification increased significantly the durability and decreased the MC values of all wood materials.     

Electrical migration of exogenous mineral ions through green sapwood ofPinus sylvestris L. (Scots pine)

Summary The electrical migration was studied of several cations passing longitudinally through cylindrical samples of green sapwood ofPinus sylvestris L. under the influence of an applied electric field. This led to values for the hindered ionic conductances within the wood of the cations Li⁺, K⁺ and CU²⁺ which were compared with data obtained previously (Simons et al., 1998) for several endogenous cations. There was satisfactory agreement for the conductance of the potassium ion, the only one to be determined by both methods. Copper ions were found to possess a higher conductance within the wood than calcium or magnesium, a factor relevant to its use as a wood preservative. Visual observation of the location of the blue-green colouration produced in the wood by copper ions indicated that they migrated via longitudinal resin ducts and tracheids. Elution and transport experiments were also carried out with sapwood which had been flushed with water, Li₂SO₄ or CuSO₄ solution.Symbols E potential gradient - F Faraday's constant (96, 494 C/mol) - I current - L length of wood sample - M molarity (mol/dm³) - Q quantity of electricity - R electrical resistance - S Siemens (reciprocal ohm) - t time - u ionic mobility (velocity under unit potential gradient) - v ionic velocity - z charge number of ion - ionic conductance The authors thank SERC and Rentokil PLC for the award of a CASE Research Studentship to P.J.S. and the Leverhulme Trust for the award of an Emeritus Fellowship to M.S.     

The influence of different soil substrates on the service life of Scots pine sapwood and oak heartwood in ground contact

Abstract

The durability of wood in ground contact is affected by numerous influences, such as substrate quality, climate and microflora of the soil, which need to be considered for the prediction of service life of wooden components to be used in the ground. In this study the influence of different soil substrates on the service life of Scots pine sapwood (Pinus sylvestris L.) and oak heartwood (Quercus petraea Liebl.) was investigated. Mini-stakes were exposed in six different soils at the test site of the Federal Research Centre for Forestry and Forest Products (BFH) in Hamburg, Germany. The effect of partly embedding the test samples in concrete or polyethylene films was also examined. After 3 years of exposure the decay rates for both wood species differed significantly between the soil substrates. Compost soil and fertilized test field soil induced the highest decay activity, whereas in pure sand the lowest decay rates were observed. Surprisingly, exposure in gravel also led to higher decay ratings than sand. Protective measures by means of concrete embedding and polyethylene films performed well during the first 2 years of exposure, but showed increasing decay rates in the third year. The overall decay rating for all soil types was higher for oak heartwood than for pine sapwood. The meaning of different soils, independent of other site influences, for service life prediction of wood is discussed, and the need for further studies on this topic is highlighted.     

Morphological and physiological differences in Scots pine seedlings of six seed origins

One-year-old seedlings of Scots pine (Pinus sylvestris L.) offour native seed origins (Loch Maree Islands, Glengarry/GlenMorriston, Glen Affric and Abernethy), a commercial Britishseedlot, and a seedlot from Hedesunda, in middle Sweden, werecompared at monthly intervals from October 1993 to April 1994.Seedling morphology, root condition, root frost hardiness andbud dry matter were determined at each date. There were clear morphological differences among seed origins.Seedlings raised from the commercial seedlot (A70) were largerbut had a poorer root:shoot ratio than the other seed origins.Of the native pines tested, the Loch Maree Islands origin allocateda larger proportion of its photosynthate to fine roots and needlesand smaller proportion to woody structures. Seedlings raised from the commercial British seedlot tendedto have poorer bud lignification than the other origins andalso, in autumn, higher electrolyte leakage rates from its fineroots. During winter, the Swedish origin had the lowest fineroot electrolyte leakage. Seedlings of all origins showed aprogressive increase in fine root hardiness towards mid-winterwith maximum hardiness (–7°C) in January. Dehardeningoccurred over subsequent months reaching –3°C in April.Differences among origins were evident. The Swedish seedlotdeveloped greater frost resistance than the other origins, hardeningbegan earlier in autumn and dehardening began later in spring.The commercial seedlot hardened later than the other originsbut reached a similar level of frost hardiness by January. Ofthe native pines, seedlings of the Loch Maree Islands originwere slowest to develop root hardiness.     

Recovery of photosynthetic capacity in Scots pine: a model analysis of forest plots with contrasting soil temperature

Both aboveground and belowground climate affects net primary production (NNP) and forest growth. Little is known about how above and belowground factors interact. The BIOMASS-model was tested to simulate photosynthetic recovery over a wide range of soil temperatures created by snow cover manipulations on tree-scale plots in a 20-year-old Scots pine stand in northern Sweden. The differences in timing of soil warming between the plots covered a span of two months. Carbon assimilation in needles, sap flow, needle water potential and climatic parameters were measured in the field. The simulations revealed that an early start of soil warming gave a relatively early photosynthetic recovery and a 7.5% increase of NPP. Late soil warming delayed the photosynthetic recovery and reduced the NPP by 13.7%. This indicated that soil temperature needed to be accounted for, as well as air temperature, when analysing photosynthetic recovery and NPP in boreal environment. The effects of differences in soil temperature were reflected in the simulated photosynthetic recovery. The model did not fully capture the delay of photosynthetic recovery caused by a late soil warming. It was possible to integrate the complexity of the soil climate effects into a threshold date for soil thaw, using sapflow measurements together with information about air temperature and a day degree sum, as long as water availability was not limiting water uptake by roots. Although a more realistic mechanism than that currently in BIOMASS is desirable as climate change shifts the typical patterns of interplay between air and soil temperature dynamics.     

The influence of different soil substrates on the service life of Scots pine sapwood and oak heartwood in ground contact

The durability of wood in ground contact is affected by numerous influences, such as substrate quality, climate and microflora of the soil, which need to be considered for the prediction of service life of wooden components to be used in the ground. In this study the influence of different soil substrates on the service life of Scots pine sapwood (Pinus sylvestris L.) and oak heartwood (Quercus petraea Liebl.) was investigated. Mini-stakes were exposed in six different soils at the test site of the Federal Research Centre for Forestry and Forest Products (BFH) in Hamburg, Germany. The effect of partly embedding the test samples in concrete or polyethylene films was also examined. After 3 years of exposure the decay rates for both wood species differed significantly between the soil substrates. Compost soil and fertilized test field soil induced the highest decay activity, whereas in pure sand the lowest decay rates were observed. Surprisingly, exposure in gravel also led to higher decay ratings than sand. Protective measures by means of concrete embedding and polyethylene films performed well during the first 2 years of exposure, but showed increasing decay rates in the third year. The overall decay rating for all soil types was higher for oak heartwood than for pine sapwood. The meaning of different soils, independent of other site influences, for service life prediction of wood is discussed, and the need for further studies on this topic is highlighted.     

Peroxidase activity, isoenzymes and histological localisation in sapwood and heartwood of Scots pine (Pinus sylvestris L.)

Peroxidase activity and isoenzymes of fresh wood samples of the third shoot of 12-year old trees and from the sapwood, transition zone and heartwood of c. 60-year old stems of Scots pine (Pinus sylvestris L.) were investigated. Wood samples were ground at −30°C, extracted, and the extracts concentrated c. 20-fold for peroxidase activity assays (guaiacol method) and for IEF-PAGE. At least 11 major isoenzymes could be found in the gels. Even the heartwood contained some peroxidase isoenzymes. Isoenzyme patterns of the juvenile wood did not change with the season. However, juvenile wood showed the highest peroxidase activity at the end of the growing season. Peroxidase activity decreased from the outer sapwood towards the heartwood. Thin sections of different wood zones stained for peroxidase revealed activity in ray parenchyma and resin canal epithelial cells. Intensive staining was localised in the bordered pits of vertical and ray tracheids, and in the end walls of ray parenchyma cells.     

Decay resistance of sapwood and heartwood of untreated and thermally modified Scots pine and Norway spruce compared with some other wood species

Abstract

Thermal modification has been developed for an industrial method to increase the biological durability and dimensional stability of wood. In this study the effects of thermal modification on resistance against soft- and brown-rot fungi of sapwood and heartwood of Scots pine and Norway spruce were investigated using laboratory test methods. Natural durability against soft-rot microfungi was determined according to CEN/TS 15083-2 (2005) by measuring the mass loss and modulus of elasticity (MOE) loss after an incubation period of 32 weeks. An agar block test was used to determine the resistance to two brown-rot fungi using two exposure periods. In particular, the effect of the temperature of the thermal modification was studied, and the results were compared with results from untreated pine and spruce samples. The decay resistance of reference untreated wood species (Siberian larch, bangkirai, merbau and western red cedar) was also studied in the soft-rot test. On average, the soft-rot and brown-rot tests gave quite similar results. In general, the untreated heartwood of pine was more resistant to decay than the sapwood of pine and the sapwood and heartwood of spruce. Thermal modification increased the biological durability of all samples. The effect of thermal modification seemed to be most effective within pine heartwood. However, very high thermal modification temperature over 230°C was needed to reach resistance against decay comparable with the durability classes of “durable” or “very durable” in the soft-rot test. The brown-rot test gave slightly better durability classes than the soft-rot test. The most durable untreated wood species was merbau, the durability of which could be evaluated as equal to the durability class “moderately durable”.     

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

The 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.