Mature Norway Spruce Trees Research Articles

Mitigating Norway spruce mortality through the combined use of an anti-attractant for Ips typographus and an attractant for Thanasimus formicarius

This study investigates the efficacy of combined treatment strategy, incorporating pheromones for bark beetle I. typographus (IT) and attractant of its natural enemy T. formicarius (TF), along with anti-attractants for IT (containing 1-hexanol, 1-octen-3-ol, 3-octanol, eucalyptol, trans-thujanol, and trans-conophthorin), to enhance protection methods for Picea abies against biotic disturbances. Two field experiments—trapping experiment and tree protection experiment—were conducted in June 2023 in managed spruce-dominated beetle-affected stands in Czechia. We anticipated higher catches of IT in traps baited with IT pheromone (containing s-ipsdienol, s-cis-verbenol, and 2-methyl-3-buten-2-ol) and TF attractant compared to traps using IT pheromone alone, since compounds intrinsic to IT pheromone, namely 2-methyl-3-buten-2-ol, ipsenol, and ipsdienol, are integral components of the attractant designed for TF. We hypothesized that application of TF attractant and IT anti-attractant would enhance the treatment's protective properties, assuming that attracted TF would function as a predator, reducing bark beetle population and increasing tree survival rates. Semiochemical composition declared by the producers was verified using gas chromatography-mass spectrometry analysis. In the trapping experiment, EcoTrap-type traps were baited with six combinations of lures and anti-attractant. In the tree protection experiment, 28 mature Norway spruce trees situated at newly created forest edges underwent four treatment types: TF attractant, IT anti-attractant, their combination, and no treatment (“control”). Traps baited solely with TF attractant did not capture either beetle, whereas traps lured with IT pheromone, TF attractant and anti-attractant showed no captures of IT but recorded the highest numbers of TF, suggesting significant potential for combined treatment efficacy. Surprisingly, tree mortality was observed exclusively among trees treated only with TF attractant and in their vicinity, suggesting unique bark beetles' response to the mixture of predator's attractant and host tree kairomones, a phenomenon that was not previously reported. Application of anti-attractant and TF treatment effectively prevented tree mortality, demonstrating the repellent potential of IT anti-attractant against bark beetles. However, mortality rates showed no significant differences among control trees, those treated with anti-attractants, or those treated with the combination of anti-attractants and TF attractant, underscoring necessity for further research to optimize treatment efficacy.

Drought impacts on tree carbon sequestration and water use - evidence from intra-annual tree-ring characteristics.

Summary The impact of climate extremes on forest ecosystems is poorly understood but important for predicting carbon and water cycle feedbacks to climate. Some knowledge gaps still remain regarding how drought‐related adjustments in intra‐annual tree‐ring characteristics directly impact tree carbon and water use.In this study we quantified the impact of an extreme summer drought on the water‐use efficiency and carbon sequestration of four mature Norway spruce trees. We used detailed observations of wood formation (xylogenesis) and intra‐annual tree‐ring properties (quantitative wood anatomy and stable carbon isotopes) combined with physiological water‐stress monitoring.During 41 d of tree water deficit, we observed an enrichment in 13C but a reduction in cell enlargement and wall‐thickening processes, which impacted the anatomical characteristics. These adjustments diminished carbon sequestration by 67% despite an 11% increase in water‐use efficiency during drought. However, with the resumption of a positive hydric state in the stem, we observed a fast recovery of cell formation rates based on the accumulated assimilates produced during drought.Our findings enhance our understanding of carbon and water fluxes between the atmosphere and forest ecosystems, providing observational evidence on the tree intra‐annual carbon sequestration and water‐use efficiency dynamics to improve future generations of vegetation models.

High resilience of carbon transport in long-term drought-stressed mature Norway spruce trees within 2weeks after drought release.

Under ongoing global climate change, drought periods are predicted to increase in frequency and intensity in the future. Under these circumstances, it is crucial for tree's survival to recover their restricted functionalities quickly after drought release. To elucidate the recovery of carbon (C) transport rates in c. 70-year-old Norway spruce (Picea abies [L.] KARST.) after 5years of recurrent summer droughts, we conducted a continuous whole-tree 13 C labeling experiment in parallel with watering. We determined the arrival time of current photoassimilates in major C sinks by tracing the 13 C label in stem and soil CO2 efflux, and tips of living fine roots. In the first week after watering, aboveground C transport rates (CTR) from crown to trunk base were still 50% lower in previously drought-stressed trees (0.16±0.01mh-1 ) compared to controls (0.30±0.06mh-1 ). Conversely, CTR below ground, that is, from the trunk base to soil CO2 efflux were already similar between treatments (c. 0.03mh-1 ). Two weeks after watering, aboveground C transport of previously drought-stressed trees recovered to the level of the controls. Furthermore, regrowth of water-absorbing fine roots upon watering was supported by faster incorporation of 13 C label in previously drought-stressed (within 12±10h upon arrival at trunk base) compared to control trees (73±10h). Thus, the whole-tree C transport system from the crown to soil CO2 efflux fully recovered within 2weeks after drought release, and hence showed high resilience to recurrent summer droughts in mature Norway spruce forests. This high resilience of the C transport system is an important prerequisite for the recovery of other tree functionalities and productivity.

Foliage Biophysical Trait Prediction from Laboratory Spectra in Norway Spruce Is More Affected by Needle Age Than by Site Soil Conditions

Scaling leaf-level optical signals to the canopy level is essential for airborne and satellite-based forest monitoring. In evergreen trees, biophysical and optical traits may change as foliage ages. This study aims to evaluate the effect of age in Norway spruce needle on biophysical trait-prediction based on laboratory leaf-level spectra. Mature Norway spruce trees were sampled at forest stands in ten headwater catchments with different soil properties. Foliage biophysical traits (pigments, phenolics, lignin, cellulose, leaf mass per area, water, and nitrogen content) were assessed for three needle-age classes. Complementary samples for needle reflectance and transmittance were measured using an integrating sphere. Partial least square regression (PLSR) models were constructed for predicting needle biophysical traits from reflectance—separating needle age classes and assessing all age classes together. The ten study sites differed in soil properties rather than in needle biophysical traits. Optical properties consistently varied among age classes; however, variation related to the soil conditions was less pronounced. The predictive power of PLSR models was needle-age dependent for all studied traits. The following traits were predicted with moderate accuracy: needle pigments, phenolics, leaf mass per area and water content. PLSR models always performed better if all needle age classes were included (rather than individual age classes separately). This also applied to needle-age independent traits (water and lignin). Thus, we recommend including not only current but also older needle traits as a ground truth for evergreen conifers with long needle lifespan.

Tree-ring volatile terpenes show potential to indicate fungal infection in asymptomatic mature Norway spruce trees in the Alps

Volatile terpenes (VTs) content in tree-ring resin, in response to natural infection by Heterobasidion spp. in asymptomatic mature Norway spruce (Picea abies) trees was investigated. Twenty-three randomly selected mature trees were sampled in a stand in the Western Italian Alps by extracting cores using an increment borer. Based on fungal isolations from cores and molecular typing using taxon-specific competitive-priming (TSCP)-polymerase chain reaction, 12 out of the 23 trees were identified as infected by Heterobasidion parviporum. Tree-ring growth patterns and VT content in tree rings were determined. Analysis of VT content was performed by means of gas chromatography mass spectrometry on a subset of trees. Results show slightly but not significantly lower tree-ring width in infected compared with non-infected trees in the past two decades. Total concentrations of sesquiterpenes (SQTs) and relative proportions of α-pinene, β-pinene and longifolene were significantly greater in infected trees; while relative proportions of camphene, 3-carene, ρ-cymene, sesquiterpene 15.90 and α-farnesene were significantly lower. This is the first study showing that VTs in tree-ring resin may indicate infection of trees by a fungal forest pathogen, even when trees are mostly asymptomatic.

Bark-scratching of storm-felled trees preserves biodiversity at lower economic costs compared to debarking

The simultaneous control of insect pests and compliance of conservation targets in conifer-dominated forests has intensified public debate about adequate post-disturbance management, particularly in protected areas. Hence, mechanical bark treatments, such as debarking, of disturbance-affected trees have been widely promoted as an on-site method of pest control that accounts for conservation targets because woody biomass is retained. However, the effects of debarking to non-target biodiversity remain unclear. We analyzed data from a two-and-a-half-year field survey of wood-inhabiting fungi, saproxylic beetles and parasitoid wasps in twelve artificial windthrows, created by pulling down mature Norway spruce trees (Picea abies) with winches. Each experimental windthrow comprising one control tree, one completely debarked tree and one bark-scratched tree. Insects were sampled using stem emergence traps. Fruiting bodies of wood-inhabiting fungi, number of wood wasp emergence holes, and number of holes made by foraging woodpeckers were assessed by visual counts. We recorded the amount of time needed to complete debarking by machine, bark-scratching by machine and bark-scratching by chainsaw each on 15 separate trees to estimate the economic costs of mechanical bark treatments.Our results revealed that both debarking and bark-scratching significantly decreased numbers of the emerging target pest Ips typographus to in median 4% (debarked) and 11% (scratched bark) of the number of individuals emerging from untreated control trees. Compared to control trees, debarking significantly reduced the species density of wood-inhabiting fungi, saproxylic beetles, and parasitoid wasps. By contrast, bark-scratching did not reduce the overall species density of wood-inhabiting fungi, saproxylic beetles or parasitoid wasps. The time needed for bark-scratching by machine was significantly lower than debarking, whereas bark-scratching by chainsaw needed a similar amount of time as conventional debarking. However, bark-scratching did have some negative effects in common with debarking, such as the significant reduction of wood wasps emergence holes and the reduction of holes made by foraging woodpeckers. Hence, bark-scratching of downed trees, like debarking, might affect higher trophic levels of biodiversity and should be applied only if pest management is urgently needed. We urge policy makers and natural resource managers to rapidly shift current pest management toward new techniques of bark-scratching, particularly in protected areas. Such a shift in post-disturbance pest-control will foster ecosystem integrity at lower economic cost compared to debarking.

Biomass of external mycelium of ectomycorrhizal fungi in Norway spruce stands in Poland

<p>Biomass of extramatrical mycorrhizal mycelium (EMM) was examined under canopies of mature Norway spruce trees grown in different forest stands in Poland. Two mountain forest sites (Brenna and Salmopol), one upland site (Zwierzyniec) and one lowland site (Mirachowo) have been investigated, using sand-filled mesh-bags method. The in-grow mesh-bags were buried in the soil for 12 months (since October up to the next October) or for 4 months (since June up to October) at four depths at each site: 5, 15, 30 and 45 cm (Brenna and Salmopol) or 60 cm (Zwierzyniec and Mirachowo). The mycelium biomass was estimated from the ergosterol content determined in the mesh-bags. The results indicated significant differences in EMM production and their vertical distribution between the mountain and the upland and lowland forest sites. The lowest EMM biomass was found at the experimental plot in the mountainious site Brenna. Considerable decrease of EMM biomass with the soil depth was recorded after 12 months of the mesh-bags incubation in soil in the upland and lowland sites, while in the mountain forests decrease of the EMM biomass in the lower soil depths diminished more gradually EMM biomass determined in the mesh-bags placed in soil at the upper 5 and 15 cm tended to be higher after 4 months than after 12 months of incubation period. Such results suggest that the time necessary for evaluation of EMM biomass in soil may be limited to the summer–autumn months, when the production of EMM is the highest. Variable stress factors can influence decreased ectomycorrhizal mycelium production and/or their destruction. Further research in different forest types and regions are needed for better understanding factors determining EMM biomass production and surviving in soil.</p>

Nest site selection by the hazel dormouse Muscardinus avellanarius: is safety more important than food?

Vegetation parameters determining nest site selection by the hazel dormouse Muscardinus avellanarius were studied in a typical habitat where dormice are relatively common in Lithuania, the northern periphery of its distributional range. Dormice preferred nest sites with a better-developed understory, particularly with a good cover of hazel shrubs taller than 4 m and plentiful bird cherry trees, a high diversity of woody plant species in the understory and overstory, and better connectivity of the nest tree with its surroundings. They avoided sites with a high number of mature Norway spruce trees in the canopy and a high density of young trees. In a stepwise multiple regression analysis, three vegetation parameters of the number of shrub species, the cover of hazel shrubs, and the number of Norway spruce trees in the canopy determined over 85% of the index of nestbox use by M. avellanarius. The number of shrub species in the surroundings of the nest site had the highest impact of all. Nest sites used by dormice for breeding were distinguished by a better-developed understory, particularly by a significantly higher number of bird cherry trees and a lower number of Norway spruce trees in the canopy, as well as a higher diversity of plants in the understory and overstory. Selection of nest sites by M. avellanarius is a combination of safety from predators and the presence of food. A well-developed inter-connected understory ensures the safety of nest sites from predators, and the diversity of understory and overstory species guarantees continuity of the food supply in the vicinity of nest sites.

Xylem defense wood of Norway spruce compromised by the pathogenic white-rot fungus Heterobasidion parviporum shows a prolonged period of selective decay

Heterobasidion parviporum, a common pathogenic white-rot fungus in managed Norway spruce forests in northern and central Europe, causes extensive decay columns within stem heartwood of the host tree. Infected trees combat the lateral spread of decay by bordering the heartwood with a fungistatic reaction zone characterized by elevated pH and phenol content. To examine the mode of fungal feeding in the reaction zone of mature Norway spruce trees naturally infected by H. parviporum, we conducted spatial profiling of pectin and hemicellulose composition, and established transcript levels of candidate fungal genes encoding enzymes involved in degradation of the different cell wall components of wood. Colonized inner heartwood showed pectin and hemicellulose concentrations similar to those of healthy heartwood, whereas the carbohydrate profiles of compromised reaction zone, irrespective of the age of fungal activity in the tissue, indicated selective fungal utilization of galacturonic acid, arabinose, xylose and mannose. These data show that the rate of wood decay in the reaction zone is slow. While the up-regulation of genes encoding pectinases and hemicellulases preceded that of the endoglucanase gene during an early phase of fungal interaction with xylem defense, the manganese peroxidase gene showed similar transcript levels during different phases of wood colonization. It seems plausible that the reaction zone components of Norway spruce interfere with both lignin degradation and the associated co-hydrolysis of hemicelluloses and pectin, resulting in a prolonged phase of selective decay.

Asexual reproduction of Hygrophorus olivaceoalbus by intracellular microsclerotia in root cells of Picea abies – A winner of ozone stress?

Hygrophorus olivaceoalbus has long been known as an ectomycorrhizal fungus, formerly designated with the artificial binomen Piceirhiza gelatinosa. Recently, it has been found to be abundant and very frequent under double ambient ozone free air fumigation of mature Norway spruce trees. As it has already been reported that this fungus can form intercellular hyphae within the root meristem, a more detailed study was performed to clarify its type of root colonization. The present study not only revealed intercellular hyphae within the meristematic zone but also intracellular hyphae within root cortex cells which grow towards and into large tannin droplets—phenolic compounds usually deposited as defensive aids—to finally fill them completely. The hyphal assemblages become globular which at first sit as separated hyphal balls within cells still containing cytoplasm. Later on, they are apparently released from the root cells, presumably as microsclerotia for dispersal of the species. Old ectomycorrhizae (ECM) show an apical pore, and later a large orifice of a tube-like cylinder formed by the thick, persistent hyphal mantle. The root tissue is progressively degrading towards proximal parts. Disintegrating root cells apparently liberate the microsclerotia through the orifice. Further studies have to find out the mechanism by which the microsclerotia are liberated and whether they operate as asexual propagules and lastly how and by whom they are propagated. As these ECM are found under ozone stress, and with identical features at higher altitudes, stress impact on trees might be the causative agent for the high frequency and abundance of Hygrophorus olivaceoalbus ECM.

Modelling the potential impact of global warming on Ips typographus voltinism and reproductive diapause

The Eurasian spruce bark beetle, Ips typographus, is one of the major forest insect pests in Europe, capable of mass-attacking and killing mature Norway spruce trees. The initiation and development of a new generation are strongly controlled by temperature and a warmer climate may affect the number of generations that is produced per year and hence the outbreak dynamics. Experimental knowledge regarding reproductive diapause adaptations is, however, too sparse for large-scale assessments of future trends. We developed a model description of diapause induction, and used gridded observational temperature data to evaluate multiple combinations of day length and temperature thresholds to find the model parameterisation most coherent with I. typographus monitoring data from Scandinavia. The selected model parameterisation is supported by European literature data, though further experimental studies are required to analyse population specific adaptations and capacity for adjustments to changing climate conditions. Implementing the model description of reproductive diapause in a temperature driven model of bark beetle phenology (swarming activity and development from egg to mature bark beetle), enabled us to assess the length of the late summer swarming period that is a critical determinant of the risk of forest damage. By using regional climate model data we show that higher temperatures can result in increased frequency and length of late summer swarming events, producing a second generation in southern Scandinavia and a third generation in lowland parts of central Europe. Reproductive diapause will not prevent the occurrence of an additional generation per year, but the day length cues may restrict the length of the late summer swarming period.

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).

Does timing of boron application affect needle and bud structure in Scots pine and Norway spruce seedlings?

Loss of apical dominance is a well-known boron (B) deficiency symptom in trees. Recent field studies indicate that B deficiency may cause irreversible damage in emerging leader buds leading to bushy growth, and changes in developing needles in mature Norway spruce trees. We experimentally studied if timing of B application affects needles and buds of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings with low initial B levels. The treatments were: no B (B0); B supply from the beginning of the simulated summer (B1); starting soon after bud burst (B2) and starting at the occurrence of first needle primordia in new spruce buds (B3). At the end of the experiment, B concentration in B1 was 23 mg kg−1 (pine) or 17 mg kg−1 (spruce) and lower in the later applications. In B0 it was at deficiency limit. In B0, B2 and B3, there were fewer sclerenchyma cells, and cavities occurred in vascular cylinders in pine needles, and in spruce buds there were more tanniferous cells in the primordial shoots compared to B1. Furthermore, in all but B1 there was cell collapse in the bud apex of some spruce seedlings. The experimentally induced changes were the same as earlier reported in B deficient conifers in the field, and indicate, similarly as in the field that adequate B is necessary throughout the growing season for healthy growth, particularly for spruce. The differences between spruce and pines are due, at least partly, to the differences in time frame of needle development and in the differences in development of conducting tissues in the buds.

Negative impact of ozone on the stem basal area increment of mature Norway spruce in south Sweden

The relative annual basal area increment of mature Norway spruce trees in south-central Sweden during 9 years was used as the response variable and analysed in relation to ozone exposure, meteorological conditions, soil moisture and stand characteristics. The method used was a modified multiple regression analysis, allowing for dependencies between observations from the same plots. The selected statistical model explained 91% of the variation in the annual relative basal area increment. The strongest explanatory variable was the stand basal area, followed by the temperature sum and the soil moisture index. After these three variables, the ozone index was the most important variable. Its effect was negative and highly significant. The average daylight ozone concentration gave a slightly better model fit as compared to the accumulated exposure during daylight hours above a threshold of 40 nmol mol −1 (AOT40). The predicted effect of ozone within the range of annual ozone exposures found in this study (1800–8700 nmol mol −1 h AOT40), was in absolute values a 0.8% decrease in the relative annual basal area increment. This could be compared with the mean relative annual increment measured during the study period of 4.6%. Our results provide statistical evidence that ground level ozone can have a negative impact on the stem growth of mature Norway spruce trees under field conditions.

Shoot growth processes, assessed by bud development types, reflect Norway spruce vitality and sink prioritization

Crown defoliation, is a product of the tree crown status from the past several years of growth, which can be misleading if used as a stress indicator when assessing current Norway spruce vitality. To evaluate recovery processes in previously damaged trees a newly developed macroscopic indicator based on proportions of bud development types was investigated. In 1998 and 1999, 474 mature Norway spruce trees were sampled for macroscopic measurements, 293 trees for tree-ring increments and 40 trees for study of metabolic markers (concentration of chlorophylls, phenolic compounds and lignin). Study sites were located in the Czech Republic, in the Sumava Mts, a relatively unpolluted and undisturbed area, and in the Krusne hory Mts, which exhibited a whole range of tree damage corresponding to a gradient of increasing air pollution load. Three categories of trees were identified which reflect current levels of intensity of shoot formation and capacity to replace potential needle loss by activation of buds with growth potential: accelerated, stabilized and decreased shoot growth. Relative to sink prioritization, we concluded that the highest vitality occurred in trees with stabilized shoot growth and the lowest vitality in trees with accelerated shoot growth. In conifers, the amount of allocated assimilates to low priority carbon sinks (such as stem growth, production of protective chemical compounds and reproductive organs) depends on what is remaining from the shoot growth processes which are of the highest priority. Significant inverse relationships were found between the intensity of shoot growth, tree-ring increments, production of reproductive organs and concentration of phenolic compounds in the needles. The highest allocation of assimilates to crown recovery occurred in trees with crown defoliation of 50–69% indicating forest recovery was observed in the most heavily damaged areas impacted by air pollution in the past. The present criterion of bud development types has potential for forestry management applications as it is easily applied in the field and, in contrast with standard forestry measurement of crown defoliation, it reflects accurately tree recovery and decline processes under multiple stress impacts.

Response of Ips typographus (Scolytidae: Coleoptera) and other bark- and wood-boring beetles to a flash-flood event

On 30–31 August 1997, a thunderstorm accompanied by heavy rain caused flood erosion on the forest-covered slopes of Mt Fulufjäll in central Sweden. Large numbers of mature Norway spruce trees [Picea abies (L.) Karst.] were uprooted and deposited along streams in the area. Attacks by bark-and wood-boring beetles in lying spruces were recorded along three flooded and three unflooded streams in the three years following this flooding event. The bark beetles Ips typographus (L.), Pityogenes chalcographus (L.), Orthotomicus sp. and the cerambycid Monochamus sp. were found to be much more abundant along flooded than unflooded streams. In contrast, the bark beetle Hylurgops glabratus (Zett.) showed the opposite pattern. Mortality among standing trees peaked in the second year following the flooding event. A considerable proportion of this additional tree mortality could be attributed to attacks by I. typographus. In contrast, no trees killed by this species were found along the three unflooded streams.

Xylem sap flow of Norway spruce after inoculation with the blue‐stain fungus Ceratocystis polonica

In a field experiment, the sap flow of Norway spruce (Picea abies) was measured in response to inoculation with Ceratocystis polonica, a virulent fungal associate of the spruce bark beetle Ips typographus. Four vigorous, mature Norway spruce trees were mass‐inoculated with C. polonica at a density of four inoculations per dm2 within a 120‐cm‐wide band on the lower bole. Two other trees were inoculated with sterile agar and served as controls. Sap flow of the six trees was measured by the thermal dissipation method from three weeks prior to inoculation until five months after inoculation. In three trees that had been inoculated with the fungus, sap flow density decreased dramatically within the first weeks after inoculation until no sap flow was measurable 4–6 weeks after inoculation. No marked changes in sap flow density were recorded in the fourth tree that had been inoculated with C. polonica, and this tree survived the inoculation. Inoculation with sterile agar did not have any apparent influence on the sap flow of the control trees. The results confirm the ability of C. polonica to kill mature Norway spruce trees. Sap flow measurements by the thermal dissipation method provided a direct and nondestructive method for monitoring the effects of fungal infection on sapwood functionality. Its application for further studies on vascular wilt and vascular stain diseases of trees is therefore recommended.

Problems and options in modelling fine-root biomass of single mature Norway spruce trees at given points from stand data

In a 75-year-old Norway spruce (Picea abies (L.) Karst.) stand, three different single-tree models were tested to predict the fine-root biomass of root samples. This approach is based on the assumption that the fine-root biomass at a given point determines the availability of belowground resources as, for example, soil water. All models assume a monotonously decreasing function describing the distribution of the fine-root biomass of a subject tree depending on the distance to the trunk of the tree. To the contrary, the models differ in the maximum distance from the stem where roots can be found. There were high correlations between the observed and the predicted fine-root biomasses for all models in a part of the stand where the trees are distributed less uniformly and where root biomasses are most heterogeneous. In a section with medium stand density, the model of diameter at breast height dependent root spread yields higher correlation coefficients compared with the fixed-distance approach of the two other models. Significant correlations between model predictions of root distributions and measured soil water potential supported the validity of the models. The results of the model estimations imply differences in the maximum distance of lateral root spread dependent on stand density.

Changes in the content and constituents of the cuticular wax of Picea abies (L.) Karst. in relation to needle ageing and tree decline in five European forest areas

Cuticular wax composition of healthy and and declining mature Norway spruce trees [Picea abies (L.) Karst.] was investigated in five European forest areas. The amount of extracted wax and the content of alkanes and secondary alcohols were analysed as a function of the factors “sample area” (five areas, detailed below), “needle age” (current year to 2 years) and “decline class” (Class O to Class 2). Using a GC-MS, alkanes from C20 to C31 and the following alcohols were quantified: 10-nonacosanol, 5,10-nonacosandiol, 4,10-nonacosandiol and the triterpenol 24-methylenecycloartanol. According to our results, the total wax content as well as the alkane and alcohol content of waxes show a large variation corresponding to sample area and needle age. Ageing caused a highly significant increase in alkane content and a highly significant decrease in total wax and alcohol content. The decline class significantly influenced only the content of the long chain alkane C31 (increase), the secondary alcohol 10-nonacosanol (decrease), and the triterpenic alcohol (decrease). Total wax weight was not influenced by tree damage. Thus, according to our results, needle ageing and progressive tree damage are correlated to different changes in the examined parameters.

Field studies on Norway spruce trees at high altitudes

summaryThe present study was performed on mature Norway spruce trees (Picea abies L.) with needle losses in the range of 25–35 %. The trees were growing at three altitudes (870, 1270, and 1700 m above sea level) in a mountain forest in the Calcareous Alps of Bavaria. The objectives were to assess the role of climate and pollution in addition to nutrient disorders for damage to spruce trees. During the growing season the average temperature was up to 5 °C lower and the average ozone concentration was about twofold higher at the high altitude in comparison to the low altitude (13 and 18 °C, and 60 and 35 nl I−1 ozone, respectively); the average NOx and SO2 concentrations did not exceed 5 nl I−1. Foliar analysis of pollutants did not indicate critical levels of Pb, Cd, Cl, F and S. Biometrical parameters, foliar element composition, pigment and protein content of the needles were determined during four seasons. Average dry:fresh weight ratios, specific needle weights, projected needle areas, soluble protein and carotenoid contents were similar within the 20 % range for needles from all three altitudes. Foliar analysis of nutrients indicated a low nutrient status especially for nitrogen, and showed a phosphorus deficiency in needles from the three sites. The chlorophyll content of the needles decreased with increasing altitude. Since nutrient imbalances were greatest in needles from the lowest site, it was concluded that the greater damage to spruce trees and lower chlorophyll content of the needles at altitudes > 1000 m above sea level were not caused by nutrient disorders.