Fertilization effects on mean stomatal conductance are mediated through changes in the hydraulic attributes of mature Norway spruce trees

Stomatal conductance was quantified with sap flux sensors and whole-tree chambers in mature Norway spruce (Picea abies (L.) Karst.) trees after 3 years of exposure to elevated CO(2) concentration ([CO(2)]) in a 13-year nutrient optimization experiment. The long-term nutrient optimization treatment increased tree height by 3.7 m (67%) and basal diameter by 8 cm (68%); the short-term elevated [CO(2)] exposure had no effect on tree size or allometry. Nighttime transpiration was estimated as approximately 7% of daily transpiration in unchambered trees; accounting for the effect of nighttime flux on the processing of sap flux signals increased estimated daily water uptake by approximately 30%. Crown averaged stomatal conductance (g(s)) was described by a Jarvis-type model. The addition of a stomatal response time constant (tau) and total capacitance of stored water (C(tot)) improved the fit of the model. Model estimates for C(tot) scaled with sapwood volume of the bole in fertilized trees. Hydraulic support-defined as a lumped variable of leaf-specific hydraulic conductivity and water potential gradient (K(l)DeltaPsi) -was estimated from height, sapwood-to-leaf area ratio (A(s):A(l)) and changes in tracheid dimensions. Hydraulic support explained 55% of the variation in g(s) at reference conditions for trees across nutrient and [CO(2)] treatments. Removal of approximately 50% of A(l) from three trees yielded results suggesting that stomatal compensation (i.e., an increase in g(s)) after pruning scales inversely with K(l)DeltaPsi, indicating that the higher the potential hydraulic support after pruning, the less complete the stomatal compensation for the increase in A(s):A(l).     

Intra-annual variations in climate influence growth and wood density of Norway spruce

Intra-annual radial growth variations of two Norway spruce trees (Picea abies (L.) Karst.) were monitored over 4 years, at four heights up the stem, by means of point-dendrometers. The trees were then felled and radial wood samples were cut from the radii that had been monitored by the dendrometers and analyzed for density. From the radial growth measurements recorded by the dendrometers, we related positions within the rings to dates, thus making possible investigation of the relationships between changes within the rings in wood density and fluctuations in climate or growth rate. Radial growth started in early April and ended, with large intra-annual differences, in August or September. Short-term variations in growth rate were related to fluctuations in climate parameters and soil water reserves. The sensitivity of radial growth to climate decreased with stem height. Wood density responded strongly to drought events, and a dry period in June 1996 induced false-ring formation. Wood density was relatively independent of growth rate and climatic conditions during the first part of the growing season, but increased with decreasing radial growth rate later in the growing season.     

A density management diagram for Norway spruce in the temperate European montane region

Norway spruce is one of the most important conifer tree species in Europe, paramount for timber provision, habitat, recreation, and protection of mountain roads and settlements from natural hazards. Although natural Norway spruce forests exhibit diverse structures, even-aged stands can arise after disturbance or as the result of common silvicultural practice, including off-site afforestation. Many even-aged Norway spruce forests face issues such as senescence, insufficient regeneration, mechanical stability, sensitivity to biotic disturbances, and restoration. We propose the use of Density Management Diagrams (DMD), stand-scale graphical models designed to project growth and yield of even-aged forests, as a heuristic tool for assessing the structure and development of even-aged Norway spruce stands. DMDs are predicated on basic tree allometry and the assumption that self-thinning occurs predictably in forest stands. We designed a DMD for Norway spruce in temperate Europe based on wide-ranging forest inventory data. Quantitative relationships between tree- and stand-level variables that describe resistance to selected natural disturbances were superimposed on the DMD. These susceptibility zones were used to demonstrate assessment and possible management actions related to, for example, windfirmness and effectiveness of the protective function against rockfall or avalanches. The Norway spruce DMD provides forest managers and silviculturists a simple, easy-to-use, tool for evaluating stand dynamics and scheduling needed density management actions.     

Using drill resistance to quantify the density in coarse woody debris of Norway spruce

To evaluate the mass of coarse woody debris (CWD), it is necessary to quantify its density. Drill resistance measurements are introduced as a approach to estimate the density of CWD in different stages of decay. Dead logs of Norway spruce [Picea abies (L.) Karst.] from a Central European mountainous site were used as a test system to compare the new method with conventional predictors of wood density such as fast quantitative field estimates (e.g., knife probe) and classification of decay classes based on a set of qualitative traits and quantitative estimates. The model containing only drill resistance as a predictor explained 65% of the variation in wood density and was markedly better than models containing one or more of several conventional predictors. However, we show that the relationship between drill resistance and gravimetric wood density relationship is sensitive to the decay status. Therefore, the best model combines drill resistance and decay class (adj. R2 = 0.732). An additional experiment showed that drill resistance is also sensitive to the moisture state (fresh vs. oven-dry) of the sample. The major potential of the method lies in its non-destructive nature which allows repeated sampling in long-term ecosystem studies or in protected areas where destructive sampling is prohibited. The limitations of the method are discussed and recommendations for applications are given.     

Wood volume yield and stand structure in Norway spruce understorey depending on birch shelterwood density

Wood volume yield and stand structure were investigated for Norway spruce understorey growing at 1500 trees ha⁻¹ under birch shelters of two different densities, 300 and 600 trees ha⁻¹, and Norway spruce growing without shelter, in a field trial in the boreal coniferous forest, 56 years after the establishment of the stand and 19 years after establishment of the trial.Wood volume yield in sheltered spruce (mean annual increments of 1.87 and 1.78 m³ ha⁻¹ year⁻¹ under the dense and sparse shelterwoods, respectively) was significantly lower than that of unsheltered spruce (mean annual increment 2.43 m³ ha⁻¹ year⁻¹). The loss in wood volume yield for sheltered spruce was more than compensated for by the additional wood volume yield in the shelterwoods (mean annual increments 3.26 and 1.88 m³ ha⁻¹ year⁻¹ for the dense and sparse shelterwood respectively).Shelterwood density did not produce any significant differences in inequality of the understorey stands, measured as skewness and the Gini coefficient for the wood volume distributions. This implies that two-sided competition for nutrients and water was more significant than competition for light.Immediately after trial establishment, trees in the no shelterwood treatment (i.e. where all overstory trees had been removed) showed a marked increase in diameter growth. Over time, the growth rate of unsheltered Norway spruce was reduced to a level comparable to that of sheltered spruce. The difference in average diameter has persisted during the trial period. There was no similar effect on height growth, resulting in an increased slenderness index (h/d) with increased shelterwood density for the understorey trees.     

Examining age- and altitude-related variation in tree architecture and needle efficiency in Norway spruce using trend surface analysis

The aim of this study was to examine the variation in tree architecture and needle efficiency in stemwood production in Norway spruce in relation to tree age and altitude of growing site. The data, which were obtained from the literature, described individual Norway spruce (Picea abies (L.) Karst.) trees from even-aged stands in Switzerland. Second-order trend surface models, with tree age and altitude as independent variables, were used in the analysis. The fitted models for stem, branch and needle dry masses explained 95%, 75% and 64% of the variation, respectively. The model for the estimated mean branch density in the crown (kg m⁻³) explained 64% of the variation and the model for mean needle density in the crown (kg m⁻³) only 28% of the variation. Crown structural characteristics, which showed age- and altitude-related variations, included live crown ratio (59% of variation explained), number of living whorls (43% of variation explained), mean weight of single needle (40% of variation explained) and specific needle area (27% of variation explained). Tree age had a strong effect on needle efficiency in stemwood production, so that needle efficiency increased up to the age of 50–70 years, depending on altitude.     

A model for spatial wood density gradients in Norway spruce stems and stochastic between-stem dissimilarities for basic and dry density

Density is a fundamental softwood quality trait. The aim of this paper is to identify a spatial model for wood density variation in spruce stems, with the main focus on basic density. Six thousand 20-mm-wide cubes systematically sampled from 85 trees in western Norway were analysed. The overall radial density pattern was the J shape with local maximum in the pith and increasing density outwards from a minimum at some distance from the pith. The minimum appeared closer to the pith further up in the tree. The stochastic nature of the six tree-wise parameters defining density gradients from pith to surface and from base to top was analysed and described. The results provide information needed to simulate density variation inside stems and between stems in a population. Considering the fundamental influence of density on a range of wood traits, such simulation should be of great significance for scientific and industrial analyses.     

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.     

Crown density changes of Norway spruce and the influence from increased age on permanent monitoring plots in Norway during 1988–1997

On the ‘local county monitoring plots’ located throughout Norway a reduction of crown density has been noted during the period 1988–1997. The aim of this study was to determine whether this change could be attributed to normal effects due to the increased age of trees in the plots. The dataset comprised around 580 plots and 27 000 single trees of Norway spruce (Picea abies), with 10 years of crown density measurements available for each tree. A two-step approach was used, first to search for an expectancy for normal reduction of crown density by age derived from the dataset, and then to compare this with the actual reduction. The interpretation was somewhat complicated as the various results were dependent upon each other. Highly significant correlations were found between crown density and age. The relationship indicated an annual reduction of crown density of around 0.12%. However, the relationship varied both between years and between regions, and it was not possible to definitely determine whether the relationship was best described by linear or nonlinear models. Of major importance here is that the relationship appeared to be influenced by the presence of stresses, whose effects tended to be more severe in old stands. On this basis it seems questionable whether an expectancy for normal ageing can be properly defined. In the present study, however, it could still be definitely determined that the mean crown density change of—0.41% annually was too negative to be attributed to normal ageing, as it was clearly below all the suggested expectancies from the various models. This suggests that the amount of stress in the period under study has been higher than normal, and this encourages the search for causal agents in further studies. Changes in silviculture may have had some influence. The results were valid for most of Norway, with the exception of western and northern regions. Crown density assessments are subjective, which may possibly give erroneous time trends. However, it is argued that this is less likely to be of major importance in the present data.     

Boron retranslocation in Scots pine and Norway spruce

We previously traced 10B-enriched boric acid from shoots to roots to demonstrate the translocation of boron (B) in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings. To gain a more detailed understanding of B translocation, we sought: (1) to demonstrate B retranslocation directly, by showing that foliar-applied 10B is located in the new growth after dormancy; and (2) to assess whether shoot-applied B affects growth in the long term. We applied 10B-enriched boric acid to needles of Scots pine and Norway spruce seedlings. After a dormancy period and 9 weeks of growth, small but significant increases in the 10B isotope were found in the new stem and needles of both species. In Scots pine, the total B concentration of the new stem was also increased. Both species contained polyols, particularly pinitol and inositol. Boron-polyol complexes may provide a mechanism for mobilizing B in these species. To determine the long-term effects of applied B, seedlings were grown for two growing seasons after the application of 10B to shoots. In Norway spruce, the proportion of 10B in the root systems and current needles of the harvest year was slightly higher than in the controls, and in Scots pine root systems, marginally so. The B treatment had no effect on growth of Norway spruce seedlings. In Scots pine seedlings, the B treatment caused a 33% increase in total dry mass and significantly increased the number of side branches.     

Influence of planting density and rotation age on the profitability of timber production for Norway spruce in Central Europe

When forest stands are established by planting, the initial density is often chosen based on recommendations of specific plant numbers. Since forest owners typically face different alternatives for the employment of their opportunities and since market situations often change more rapidly and on a smaller scale than the characteristics of forest sites, the question arises whether these factors are reflected in one or within a small range of planting densities. Even though some advised densities might be profitable for some forest owners and market situations, the shift of profitable timber production as a result of changes in the circumstances surrounding the investment is unclear. In this paper, the influence of the planting density on the profitable production of timber is analysed with the explicit inclusion of price differentials as these offer incentives for the choice of the planting density in Central Europe. Since numerical calculations based on empirical data are required for an analysis of the complex facets of price differentials, the specific statements are restricted to the tree species Norway spruce (Picea abies Karst.). By means of typical calculation examples, the effects of changes in investment parameters are exemplified and discussed against the background of a sensitivity analysis. The results reveal the boundaries for the profitable production of high-quality timber and show that forest owners might compensate changes in the investment situation by adjustments of either or both the rotation age and the planting density.     

Ectomycorrhizas and cadmium toxicity in Norway spruce seedlings

We studied the effects of ectomycorrhizal colonization by Laccaria bicolor (Maire) Orton S238 and Paxillus involutus (Batsch) Fr. 533 on cadmium (Cd) toxicity in Norway spruce seedlings (Picea abies (L.) Karst.). Both mycorrhizal and nonmycorrhizal seedlings were exposed to 0 (control), 0.5 or 5 &mgr;M CdSO(4) for 9 weeks in a sand culture system with frequent addition of nutrient solutions. In pure culture, P. involutus and L. bicolor showed similar Cd tolerance. However, in symbiosis, the Cd treatments decreased colonization by L. bicolor but not by P. involutus. Paxillus involutus ameliorated the negative effects of 0.5 &mgr;M Cd on shoot and root growth and chlorophyll content of old needles, whereas L. bicolor did not. Mycorrhizal colonization did not affect Cd concentrations of old needles and roots of seedlings. Despite differences between the ectomycorrhizal fungi in colonization and ability to alleviate Cd toxicity of seedlings, both species reduced Cd concentrations of young needles to a similar degree compared with nonmycorrhizal seedlings. However, in the 0.5 &mgr;M Cd treatment, the Cd content of needles of seedlings colonized by P. involutus was increased, whereas the Cd content of needles of seedlings colonized by L. bicolor was similar to that of needles of nonmycorrhizal seedings. When the amount of Cd translocated to needles was expressed on a root length basis to account for differences in the size of the root systems, the amount of Cd translocated to the needles was similar in seedlings mycorrhizal with P. involutus and in nonmycorrhizal seedlings. All mycorrhizal seedlings were similarly affected by 5 &mgr;M Cd, indicating that the amelioration efficiency of ectomycorrhizal fungi is dependent on the metal concentration to which the roots are exposed. Concentrations of P, K, Ca, Mg and Mn were decreased by 5 &mgr;M Cd to a similar extent in both nonmycorrhizal and mycorrhizal seedlings. In contrast to L. bicolor, P. involutus increased P uptake and altered patterns of root branching. We conclude that mycorrhizas alleviate Cd-induced reductions in growth of Picea abies seedlings. Although the two mycorrhizal fungi examined differed in their ability to alleviate Cd toxicity, these differences were not related to differences in Cd uptake or translocation to the shoot of the mycorrhizal seedlings. We suggest that amelioration of Cd toxicity by P. involutus may be a result of improved P nutrition or changes in root morphology, or both.     

Ceratocysts polonica inoculated in Norway spruce: Blue-staining in relation to inoculum density,resinosis and tree growth

When Norway spruce trees were inoculated with Ceratocystis polonica, a dose-dependent response was recorded. Local resinosis near the inoculation sites decreased with increasing inoculum density; parallelled by an increasing degree of sapwood staining, and tree mortality. Suppressed trees, and trees showing growth decline appeared more susceptible than trees suffering less competition.     

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.     

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.     

Three-dimensional elastic behaviour of common yew and Norway spruce

In view of its high density, yew wood has a remarkably low longitudinal Young’s modulus, which makes it unique among coniferous woods. However, the elastic response of yew related to other load directions is largely unknown. Therefore, our goal was to comprehensively characterise the three-dimensional elastic behaviour of yew wood. To achieve this, we performed tensile tests on dog-bone-shaped yew specimens and determined the three Young’s moduli and six Poisson’s ratios using a universal testing machine and a digital image correlation technique. All tests were also applied to spruce as reference species. After including the shear moduli determined in a prior study by our group, all elastic engineering parameters of yew and spruce were ascertained. Based on these values, the three-dimensional elastic behaviour was describable with deformation bodies and polar diagrams. Evaluating these illustrations revealed that yew had a lower stiffness only in the longitudinal direction. In all other three-dimensional directions, spruce was clearly more compliant than yew. Particularly, in the radial–tangential plane, both species varied largely in their degree of anisotropic elasticity. All mentioned differences between yew and spruce originate at the microstructural level.     

Life cycle of Lophodermium piceae in Norway spruce needles

The spruce needle inhabiting ascomycete Lophodermium piceae can live symptomless for several years, before it completes its life cycle within less than one year as detailed studies have shown.     

Effects of repeated fertilization in young Norway spruce forests

Several studies have shown the positive effect of nitrogen fertilization on conifer growth. In young Norway spruce (Picea abies) stands, an additional effect of including a mixture of other nutrients has often, but not always, been found. We studied effects of repeated fertilization in 28 stands with young Norway spruce in central Norway. The treatments consisted of plots without nutrient addition (Control), fertilization with 150?kg?N?ha^?1 (150?N), and fertilization with 150?kg?N plus addition of P, K, Mg, B, Mn and Cu (150?N?+?mix), repeated three times with approximately eight years interval. There was a clear positive effect on volume increment of the 150?N and 150?N?+?mix treatments compared to Control, and the effect was significantly higher for 150?N?+?mix than for 150?N. Fertilization had a stronger effect in the first fertilization period than in the second, while the third period was intermediate. The effect of 150?N?+?mix was strongest at plots?>?300?m a.s.l. However, this correlation may be due to geological conditions rather than elevation. Further studies are needed to find out under which edaphic conditions a nutrient mixture will increase growth substantially in young spruce stands.     

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.