Effects of nutrition and soil water availability on water use in a Norway spruce stand

We investigated effects of nutrition and soil water availability on sap flux density, transpiration per unit leaf area (EL), and canopy stomatal conductance (GS) of Norway spruce (Picea abies L. (Karst.)) in northern Sweden during the 1996 growing season. Our objectives were to determine (1) if artificially imposed drought (65% rain diversion) reduces soil water sufficiently to cause physiological limitations to whole-tree and plot-scale water transport, and (2) whether increased capacity for water transport resulting from fertilization-induced increases in leaf (> 3-fold) and sapwood areas (> 2.3-fold) deplete soil water sufficiently to cause a negative feedback on GS and EL. We monitored soil water content (theta) and soil water potential (PsiS) in control (C), drought (D), fertilized (F) and irrigated + fertilized (IL) treatment plots, along with site meteorological conditions. Ten trees per plot were monitored for sap flow. Although there were significant treatment differences in mean daily EL (C > D > F; P < 0.01) and GS (C > D > F; P < 0.05), variation in absolute magnitudes was small. Therefore, transpiration differences on a unit ground area basis (EC) were nearly proportional to leaf area differences. Precipitation was well distributed throughout the study period and so PsiS remained high, except during short dry periods in Plot F when it declined rapidly. Thus, although soil water was not limiting to GS, EL or EC when precipitation was uniformly distributed throughout the growing season, we cannot conclude that water availability would not limit GS in fertilized stands if the seasonal distribution of precipitation were altered.     

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.     

Predicting regeneration establishment in Norway spruce plantations using a multivariate multilevel model

This study predicts the regeneration establishment on 3-year-old Norway spruce (Picea abies (L.) Karst.) plantations in southern Finland using regeneration survey data. Regeneration establishment was described by seven response variables: number of planted spruces, natural Scots pines (Pinus sylvestris L.), natural spruces, natural seed-origin birches (Betula pubescens Ehrh. and B. pendula Roth.) and other broadleaves (i.e. sprout-origin birches and other broadleaves than birch), as well as height of crop-tree spruce and dominant height of broadleaves. Due to the multivariate (several responses for each plot) and multilevel (plot, stand, municipality, forest centre) structure, regeneration establishment was modelled by fitting a multivariate multilevel model with explanatory variables such as temperature sum, site fertility, soil quality and method of site preparation. In the model, the numbers of tree seedlings were modelled using over-dispersed Poisson distributed equations, and the tree heights were modelled using normally distributed linear equations. The estimated fixed and random parameters of the equations were logical, and there was no serious bias in predicting the regeneration establishment in the independent test data set. This modelling approach can be used to predict the regeneration establishment stochastically by taking into account the large unexplained variation in regeneration models.     

Dissolution and dispersion of spruce wood components into hot water

Summary The dissolution and dispersion of components from Norway spruce (Picea abies) wood were examined in laboratory experiments to determine the factors influencing variations in dissolved and colloidal substances in mechanical pulp suspensions. Finely ground, fresh spruce wood was suspended in water at 90 °C and was agitated intensively for up to 12 h, after which the concentrations of dissolved and dispersed lipophilic extractives, lignans, carbohydrates and lignins were determined. Sapwood and heartwood were studied separately. Effects of pH and added electrolytes on the dissolution and dispersion of wood components were also investigated.Higher amounts of lipophilic extractives, and especially of triglycerides, were dispersed from sapwood than from heartwood. The release of lipophilic extractives continued for up to 3 h, after which the concentrations in the suspensions leveled off. At this stage the composition of the dissolved and dispersed lipophilic extractives equaled that of the wood. The amount of lipophilic extractives in the suspensions increased with increased pH, in the range of 4.5–6.7, but was lower in the presence of electrolytes. The dissolution of carbohydrates continued even beyond 3 h of agitation. The high water temperature induced hydrolytic reactions, thereby releasing especially arabinose. The release of arabinose through the hydrolytic cleavage from polysaccharides was more extensive at pH 4.5 than at pH 5.5 and 6.7. More polysaccharides containing galacturonic acid units (pectins) were dissolved at a higher pH. Much more polysaccharides containing glucose, most probably starch, were present in the sapwood suspensions. The dissolution of lignins also continued throughout the 12 h experiment. The measured UV-absorption, after extraction of lignans, was roughly the same for sapwood and heartwood suspensions. Slightly less lignins were released in the presence of electrolytes. Lignans were released only from heartwood.     

Cytology of Norway spruce needles

The structural changes in the albuminous, endodermal and mesophyll cells in the ageing needles of different aged healthy spruces (Picea abies [L.] Karst.) were studied on material collected in Germany and in Finland in winter. The results are considered as background information for the studies dealing with the structural changes in spruces suffering from biotic or abiotic stresses e. g., from the polluted air. Both light and electron microscopes were used.     

Isolation and characterisation of water soluble polysaccharides from Norway spruce and Scots pine

Water soluble polysaccharides from Norway spruce, Scots pine, and Siberian larch were compared. For all species the total amount of polysaccharides isolated from the heartwood was higher than that from the sapwood. The heartwood polysaccharides had a high content of galactose and arabinose units, and some glucuronic acid units, suggesting the presence of acidic arabinogalactans. The total amounts of recovered water-soluble arabinogalactans were 1.9 mg/g for spruce heartwood, 5.3 mg/g for pine heartwood, and as much as 106 mg/g for larch heartwood. The other water-soluble polysaccharides were mainly glucomannans. The average ratio of Gal:Ara:GlcA in the water-soluble arabinogalactans of spruce heartwood was about 4.3:1:1, pine heartwood about 4.5:1:0.2, and larch heartwood about 6.7:1:0.1. The corresponding molar ratios then being about 3.6:1:0.8 for spruce, 3.8:1:0.2 for pine, and 5.6:1:0.08 for larch. Thus, the content of glucuronic acid units was especially high in the spruce heartwood arabinogalactans. The content of arabinose was slightly higher in spruce and pine than in larch heartwood arabinogalactans.     

Radial velocity profiles of water flow in trunks of Norway spruce and oak and the response of spruce to severing

Trunk-tissue heat balance, volumetric and staining methods were used to study xylem water flow rates and pathways in mature Norway spruce (Picea abies (L.) Karst.) and pedunculate oak (Quercus robur L.) trees. The radial profile of flow velocity was confirmed to be symmetrical in spruce, i.e., maximum flow velocity was in the center of the conducting xylem and tailed with low amplitude (about 30 cm h(-1)) in the direction of the cambium and heartwood. Variability around the trunk was high. In contrast, in oak, the radial profile of flow velocity was highly asymmetrical, reaching a peak of about 45 m h(-1) in the youngest growth ring and tailing centripetally for about 10 rings, but variability around the trunk was less, under non-limiting soil water conditions, than in spruce. In spruce, the flow rate increased abruptly within seconds when the tree was severed while immersed in water, and then decreased gradually, showing significant root resistance. We conclude that water flow through an absorbing cut surface differs from the flow higher in a tree trunk because of the presence of hydraulic capacitances in the conductive pathways. The staining technique always yielded higher estimates of flow velocity than the non-destructive tree-trunk heat balance method.     

Effects of experimental drought on the fine root system of mature Norway spruce

Norway spruce (Picea abies (L.) Karst.) is an economically important, but relatively drought-sensitive tree species that might suffer from increasing drought intensities and frequencies, which are predicted to occur in parts of central Europe under future climatic change. In a throughfall exclusion experiment using sub-canopy roofs, we tested the hypothesis that enhanced drought leads to an increase in fine root mortality, and also to a higher, subsequent fine root growth. Fine root production and mortality were assessed using two independent approaches, sequential soil coring (organic layer) and direct observations in minirhizotrons (organic layer plus upper mineral soil). Six weeks of throughfall exclusion resulted in mild drought stress, i.e. a reduction in average soil moisture from 20 to 12 vol.% during the treatment. Based on the sequential coring data, experimental drought did not result in significant changes in fine root biomass during the 6-week treatment period, but caused an increase in fine root mortality by 61% in the 6 weeks following the drought treatment. Remarkably, fine root production showed a synchronous increase in this period, which more than compensated for the loss due to increased mortality. The minirhizotron data confirmed that the drought treatment increased fine root loss in the organic layer. Based on this method, however, root loss occurred during the drought period and was not compensated by increased root production. The mild drought stress was mainly restricted to the organic layer and did not significantly influence fine root dynamics in the mineral soil. We calculated that the drought event resulted in an extra input of about 28 g C m⁻² and 1.1 g N m⁻² to the soil due to increased fine root mortality. We conclude that even periods of mild drought significantly increase fine root mortality and the associated input of root-derived C to the soil organic matter pool in temperate Norway spruce forests.     

Summer drought: a driver for crown condition and mortality of Norway spruce in Norway

Summer drought, i.e. unusually dry and warm weather, has been a significant stress factor for Norway spruce in southeast Norway during the 14 years of forest monitoring. Dry and warm summers were followed by increases in defoliation, discolouration of foliage, cone formation and mortality. The causal mechanisms are discussed. Most likely, the defoliation resulted from increased needle‐fall in the autumn after dry summers. During the monitoring period 1988–2001, southeast Norway was repeatedly affected by summer drought, in particular, in the early 1990s. The dataset comprised 455 ‘Forest officers’ plots’ with annual data on crown condition and mortality. Linear mixed models were used for estimation and hypothesis testing, including a variance–covariance structure for the handling of random effects and temporal autocorrelation.     

Potential production of Norway spruce in Sweden

In this paper, the potential stem wood production for Norway spruce was estimated for different regions in Sweden. This was done by using basic physiological relationships of intercepted radiation versus biomass production and knowledge of how a water deficit reduces the potential production, derived from results of field experiments on nutrient optimisation. To scale these relationships up to regional and national levels, data of incident radiation and humidity during the growing season for all of Sweden were used. The figures for potential and attainable production indicate that the temperate to boreal climate allows considerably higher production than the current production, if availability of water and nutrients is non-limiting. In northern Sweden, the attainable production is ca. 300% higher than the current production and in southern Sweden, the yield can be increased by ca. 100%. In absolute numbers, as a mean for a whole rotation period, it is possible to achieve an annual stem-wood dry mass production of 7–9 Mg ha⁻¹ in southern and central and ca. 5–6 Mg in northern Sweden. This increased production would mean that rotation periods can be shorter than they are now by 20–30 years in southern Sweden and by ca. 50–60 years in northern Sweden.     

Quality of timber products from Norway spruce

Summary The overall aim of this study and series of papers is to address the key variables for timber quality and to optimize the utilization of Norway spruce timber with respect to construction purposes. It is the end-user's degree of overall satisfaction that determines the quality of a product. Therefore, the performance of structural timber cannot solely be defined by mechanical properties. Geometric performance (warp) must be improved if timber is to continue as an important building material.An experimental study of the spatial variation in warp and bending properties of fast-grown Norway spruce is introduced. In this paper, the growth characteristics are presented as a function of stand and location in the tree. The knot area ratio (KAR) was considerably higher in the core (0.31) compared with timber closer to bark (0.21). The top log studs had higher KAR (0.38) than the corresponding butt log studs (0.31). The average grain angle was 3.5% ( 2°) and appeared not to vary radially. The presence of compression wood was much more common in the top log timber (75%) than in the butt log (44%). However, no consistent radial variation in compression wood was found.The authors gratefully acknowledge the support from EEC Forest programme, Contract No. MA2B-0024 and from Södra Timber AG from NUTEK project No. 9100554     

Prediction of longitudinal shrinkage and bow in Norway spruce studs using scanning techniques

Straightness is one of the most important properties for making timber an attractive material for modern mechanized building. Several studies have shown that a lack of straightness is one of the main reasons for choosing materials other than timber in the construction industry. This paper presents a way to model moisture-induced bow from longitudinal shrinkage data predicted from an analysis of images of the surface of Norway spruce studs. For this study, eight studs (45 × 95 × 2500mm and 45 × 120 × 3000mm) of Norway spruce timber were selected. Bow in these studs was measured at two moisture contents below the fiber saturation point. The studs were then split into three slices 11mm thick, and the surfaces of these slices were scanned to obtain color information and images of the tracheid effect. The slices were cut into sticks with dimensions of 10 × 10 × 200mm. The longitudinal shrinkage coefficient of these sticks was measured. A multivariate model was created to model the longitudinal shrinkage coefficient data from the information in the images. The predicted longitudinal shrinkage data was used to model bow. The mean value of the measured longitudinal shrinkage was 0.0121 (SD 0.0123). The root mean square error of prediction (RMSEP) for the multivariate model was 0.0079, which is regarded as good. Thus, it was possible to model moisture-induced bow with good accuracy using the predicted longitudinal shrinkage data.     

Quality of timber products from Norway spruce

Summary Strength and stiffness together with some properties characterizing the stand and the growth of trees were studied. Specimens (45 × 70 × 2900 mm³) were cut from different radial and longitudinal positions, from fast-grown trees from two stands in southern Sweden. These trees had relatively large annual rings (4–6 mm) and were not representative of Norway spruce in Sweden but are an example of the intensivelymanaged stands which will probably constitute a substantial part of the raw material supply in the future.The results indicate that the mean values for strength and stiffness were lowest for the core studs and increased further away from the pith. This radial variation in strength and stiffness appears to be associated with the variation in ring width. Density alone, on the other hand, does not explain the radial variation but should be used together with either ring width or knot area ratio to explain the stiffness and strength respectively. The increase in the strength and stiffness of the core studs from the butt logs to the top logs was significant. Density alone was found to be the best variable to explain the longitudinal variation between the butt logs and the top logs. The heartwood formation in the butt log juvenile core appeared not to have a positive effect on strength and stiffness. The occurrence of compression wood, the magnitude of grain angle and the margin knot area ratio had only a minor effect on strength and stiffness.The authors gratefully acknowledge the support received from the EEC forest research programme, Contract no MA2B-0024, from NUTEK, project no 9100554 and from Södra Timber AB     

Pathogenicity of Ceratocystis resinifera to Norway spruce

The blue‐stain fungus Ceratocystis resinifera colonizes wounds on living Picea spp. and other conifers in Europe and North America. Little is known regarding the pathogenicity of this fungus and consequently, four Norwegian C. resinifera isolates were inoculated on to Norway spruce (Picea abies) using two different techniques. These included single‐point inoculations on young trees (two inoculations per tree on 14‐year‐old trees) and mass‐inoculations on older trees (～200 inoculations per tree on 34‐year‐old trees). In both experiments, C. resinifera induced minor symptoms that in most cases did not differ significantly from inoculation with sterile agar. The virulent blue‐stain fungus C. polonica, which was inoculated for comparative purposes, induced extensive symptoms, causing 83% dead cambium circumference and 82% blue‐stained sapwood, and long necrotic lesions in the phloem. The results suggest that C. resinifera is non‐pathogenic or only mildly pathogenic to Norway spruce and does not present a threat to these trees.     

Quality of timber products from Norway spruce

Summary In a previous paper in this series it was concluded that the warp (twist, crook and bow) of structural timber products is of utmost importance for end-user satisfaction. In this paper, a study of the spatial variation of warp of fast-grown Norway spruce is presented. The material, 372 studs (45 × 70 × 2900 mm²), was cut from different radial and longitudinal positions in trees from two stands.The results indicated that twist and crook were at maximum near the pith. However, twist decreased much more rapidly with the distance from pith compared with crook. Crook associated with core studs was larger in the butt log than in the top log, while twist and bow in core studs appeared not to vary longitudinally. Heartwood formation in the butt log juvenile core did not diminish warp propensity. Twist was rather well correlated to the distance between pith and centroid of cross section. The ratio of grain angle to pith distance was the best parameter to predict twist. Presence of compression wood increased bow and crook significantly, while ring width, density and knot area ratio did not substantially contribute to explain warp variation.A moisture content change from 18% to 12% decreased the overall acceptability, expressed by stud grade yield, from 76% to 43%. Thus, timber products should be delivered at a moisture level close to the one expected in the finalized building in order to avoid excessive warp after delivery.The authors gratefully acknowledge the support from EEC Forest programme, Contract No MA2B-0024, from NUTEK project No 9100554 and from Södra Timber AB     

Optimal management of uneven-aged Norway spruce stands

An optimization model is specified to analyze forest management without any restrictions on the forest management system. The data on forest growth comes from unique field experiments and is used to estimate a nonlinear transition matrix or size-structured model for Norway spruce. The objective function includes detailed harvesting cost specifications and the optimization problem is solved in its most general dynamic form. In optimal uneven-aged management, stand density is shown to be dominated by limitations in natural regeneration. If the goal is volume maximization, even-aged management with artificial regeneration (and thinnings from above) is superior to uneven-aged management. After including regeneration and harvesting costs, the interest rate, and the price differential between saw timber and pulpwood, uneven-aged management becomes superior to even-aged management. However, in the short term the superiority is conditional on the initial stand state.     

Liquid water absorption in dried Norway spruce timber measured with CT scanning and viewed as a percolation process

Liquid flow in dried wood is complicated to study, since wood is a nonhomogeneous, hygroscopic-porous, anisotropic material. However, liquid flow is important to understand, since it has an influence on the durability of wood and on such processes like impregnation, drying, surface treatment, etc. In this study, simulations of liquid water absorption in wood as a fibre network, percolation, were compared with experimental water absorption in the longitudinal direction in spruce timber. With CT scanning, water distribution during liquid flow can be shown visually and measured by image processing. Liquid water absorption in end grain of spruce was measured with CT scanning after 1, 3, 7 and 14?days of liquid water absorption and shown as moisture content (MC) profiles in heartwood and sapwood. It was found that the amount of water absorbed could be expressed as a linear function of the square root of time. The slopes of the lines differed between sapwood and heartwood and also varied depending on the growth condition of the trees. The simulations according to the percolation method show generally good agreement with the measured results for sapwood.     

Allometry varies among related families of Norway spruce

Key message

Slopes and intercepts of allometric equations for organs’ biomass varied among half-sib families of Norway spruce and between age categories in a family-dependent manner. Genetic variation should be accounted for when applying allometric analysis to mixtures of genetic groups.

Context

Genetic variation in relationships among plant biomass components was rarely addressed in trees, though depending on deployment strategies in tree improvement programs, variation among genetic groups in plant organs’ growth rates, and thus biomass allocation, would affect forest growth and carbon balance.

Aims

We investigated growth and biomass distribution in Norway spruce (Picea abies [L.] H. Karst) half-sib families. We assumed invariance among families in allometric relationships, and stability in growth rates of different organs between ages 2 and 8 years in the subset of those families. We also tested for ontogenetic trend in allometry using the independent dataset of biomass at age 21 years.

Methods

We analyzed allometric relationships among plant components using standardized major axis regression.

Results

Slopes and intercepts of allometric relationships varied among families, indicating variation in both organs’ growth rates and biomass partitioning at a given plant size. Variation in scaling exponents between age categories was also dependent on the family and plant organ considered.

Conclusion

Variation in slopes of allometric relationships indicates that a single scaling coefficient should not be applied when different genetic groups are compared. For the interpretation of age effect on biomass partitioning, both slopes and intercepts of allometric relationships should be examined.

     

Fresh-stem bending of silver fir and Norway spruce

The bending and growth characteristics of large fresh stems from four silver fir (Abies alba Mill.) and three Norway spruce (Picea abies (L.) Karst.) trees were studied. Twenty logs taken from different stem heights were subjected to four-point bending tests. From the bending test records, we calculated stress-strain curves, which accounted for detailed log taper, shear deformation and self weight. From these curves we determined, among other parameters, the modulus of elasticity (MOE), the modulus of rupture (MOR) and the work absorbed in bending (W). No significant differences were found between species for the wood properties examined. Values of MOE, MOR and W generally decreased with stem height, with MOR in the range of 43 to 59 MPa and MOE ranging from 10.6 to 15.6 GPa. These MOE values are twice or more those reported for stems of young Sitka spruce (Picea sitchensis (Bong.) Carr.) trees. Based on the radial growth properties measured in discs from the logs, we calculated predicted values of MOE and MOR for the stem cross section. The predictions of MOE were precise, whereas those of MOR were approximate because of a complex combination of different failure mechanisms. Methods to test and calculate MOE, MOR and W for the stems of living trees are discussed with the aim of improving analyses of tree biomechanics and assessments of forest stability protection.     

Estimating percentile-based diameter distributions in uneven-sized Norway spruce stands using airborne laser scanner data

Abstract

A model for prediction of stand basal area and diameters at 10 percentiles of a basal area distribution was estimated from small-footprint laser scanner data from primeval conifer forest using partial least squares regression. The regression explained 44–80% and 67% of the variability of the 10 percentiles and stand basal area, respectively. The predicted percentiles, scaled by the predicted stand basal area, were used to compute diameter distributions. A cross-validation showed that the mean differences between the predicted and observed number of stems by diameter class were non-significant (p>0.05) for 22 of 29 diameter classes. Moreover, plot volume was calculated from the predicted diameter distribution and cross-validation revealed a non-significant deviation between predicted and observed volume of ?3.3% (of observed volume). An independent validation showed non-significant mean differences for 20 of 21 diameter classes for data corresponding to the model calibration data. Plot volumes calculated from the predicted diameter distributions deviated from observed volume by ?4.4%. The model reproduced diameter distributions corresponding to the model calibration data (uneven-sized forest) well. However, the model is not flexible enough to reproduce normal and uniform diameter distributions. Volume estimates derived from predicted diameter distributions were generally well determined, irrespective of the observed distribution.