Plant-soil feedback in spruce (Picea abies) and mixed spruce-beech (Fagus sylvatica) stands as indicated by dendrochemistry

Ten pairs of secondary pure spruce (Picea abies) and adjacent mixed spruce-beech (Fagus sylvatica) stands on comparable sites were selected on two different bedrocks for soil formation (Flysch: nutrient rich and high soil pH; Molasse: poor nutrient supply and acidic) to study how an admixture of beech to spruce stands affects nutrient cycling and consequently soil chemistry. Soil analyses indicated accumulation of Ca under the mixed stands while the top soil under pure spruce was acidified. It was hypothesized that changes of soil chemical properties due to species composition over the last six decades are reflected in the stem wood of spruce. Three healthy dominant spruce trees per plot were selected for coring. Cores were crossdated and half-decadal samples were analyzed for Ca, Mg, Mn and Al. Calcium and Mg concentrations in stem wood of spruce were significantly higher for the pure spruce than for the mixed stands in spite of lower Ca and Mg stores in the soil. We assume that acidification caused by pure spruce mobilized these cations temporarily, increasing soil solution contents and consequently stem wood concentrations. It was possible to reconstruct soil pH from the element ratios Ca/Al (pure stands) and Ca/Mg (mixed stands), since these ratios in the stem wood of the last half-decade did correlate with soil pH for selected soil depths. Reconstructed soil pH showed a decline over the last 60 years under both species compositions due to accumulation of base cations in the increasing biomass. Comparisons of reconstructed soil pH in 0–5 and 10–20 cm soil depth indicated more pronounced top soil acidification (lower soil pH in 0–5 cm) by spruce on the nutrient rich soil (Flysch) than on the acidic soil (Molasse). However, admixture of beech caused higher pH values in 0–5 cm than in 10–20 cm soil depth on Flysch due to the observed Ca-pump effect of beech (uptake of Ca from deeper soil horizons).     

Interactions between calcium and copper or cadmium in Norway spruce

The accumulation of calcium (Ca), copper (Cu) and cadmium (Cd) in roots and stem of Norway spruce (Picea abies [L.] Karst) was examined. Two-year-old Norway spruce seedlings were treated with elevated concentrations of Ca, Cd or Cu, or as combinations of Ca with Cu or Cd in nutrient solutions for three months. The stem was divided into bark, wood formed during the treatment period (new wood), and wood formed before the treatment period (old wood). The accumulation of the metals in stem and roots increased with addition of the respective metal into nutrient solution. Addition of Cu decreased the accumulation of Ca in roots and wood, and Ca addition decreased the accumulation of Cu in the new wood. By adding Ca in combination with Cu the accumulation of Cu in the stem was decreased even more by Ca and the negative effect of Cu on the Ca content in the stem was diminished. Addition of Cd decreased the accumulation of Ca in wood, especially the old wood, and Ca addition decreased the accumulation of Cd in roots, bark and new wood. By adding Ca in combination with Cd the Ca content was reduced in the bark, instead of in the old wood.     

Effect of initial fertilisation on biomass and nutrient contentof Norway spruce and Douglas-fir plantations at the same site

Norway spruce (NS) and Douglas-fir (DF) are among the main species used for production forestry in France. In low-elevation mountains and under-acidic conditions, they often occupy the same ecological situations. It is therefore of paramount interest to have a good understanding of how the two species behave under similar conditions and how they react to site improvement by fertilisation. The study stands are part of an experimental stand located in the estate forest of Breuil-Chenue in the Morvan (east central part of France). Its aim is to compare the impact of change in species on ecosystem functions. Destructive sampling of 10 trees per stand, distributed over the whole spectrum of inventoried classes of circumference at breast height (c _1.30), was carried out within four stands, e.g., fertilised and control (non-fertilised) NS; fertilised and control (non-fertilised) DF. Allometric relationships between c _1.30 and biomass or nutrient content per tree compartment were calculated. These equations were applied to the stand inventory for quantifying stand biomass and nutrient content on a hectare basis. The standard deviations of results were estimated using Monte-Carlo simulations. Specific emphasis was given to explain the origin of differences observed between species and treatments, i.e., changes in carbon allocation leading to specific allometric relationships, changes in stand structure (tree size distributions) and changes in stand density due to mortality.DF was more productive than NS (+28% for total tree biomass, +50% for ligneous biomass and +53% for stem wood). Both NS and DF were affected by fertilisation but in the case of NS, effects on the crown_c _1.30 relationship and on average tree growth were predominant while in the case of DF, the stem_c _1.30 relationship and stand density were affected by changes in soil fertility. The general fertilisation effect was an increment of 40% of ligneous dry matter for DF and only 22% for NS. In both cases, the amount of wood biomass produced per unit of leaf biomass (on a tree basis and, to a lesser extent, on a per hectare basis) was greater in fertilised plots. However, in the case of NS, the same amount of wood biomass was produced from a smaller quantity of leaves while in the case of DF, the same amount of leaves produced more wood biomass.The amount of nutrients in total ligneous biomass was higher for N, P and K, but lower for Ca and Mg, in DF than in NS. A high variability was observed between nutrient content of the different compartments, e.g., DF < NS for needles (except Mg), DF < NS for K, Ca and Mg for stem wood and DF > NS for N and P of stem wood. Fertilisation did not considerably change the hierarchy. On the basis of this study, all the indexes concerning stand production, wood density, nutrient use efficiency and response to fertilisation gave a net advantage to DF. This information is highly relevant for both ecological and practical purposes.     

Enhanced growth and ethylene increases spiral grain formation in Picea abies and Abies balsamea trees

Spiral grain angle in Norway spruce (Picea abies) trees and balsam fir (Abies balsamea) seedlings was investigated in relation to growth rate, endogenous and applied ethylene. Trees from stands of Norway spruce, which were irrigated and fertilised in order to enhance growth, and trees having different growth rates in non-treated stands were studied. Stem growth rate at the stand level (m³ ha^-1 year^-1) was measured annually, or by means of microscopy on stem sections as the number and size of tracheids produced. Enhanced growth increased ethylene evolution and maintained a high level of left-handed spiral grain angle in comparison to slower-growing trees. An increased number of earlywood tracheids in fast growing trees was correlated to a more left-handed spiral grain angle. Ethrel, applied to stems of balsam fir seedlings, increased the internal ethylene levels in parallel with increased left-handed spiral grain angle. The results indicate that ethylene regulates the extent of spiral grain angle.     

Effect of elevated [CO2] on stem wood properties of mature Norway spruce grown at different soil nutrient availability

The objective of the present study was to investigate the interactive effects of elevated [CO₂] and soil nutrient availability on secondary xylem structure and chemical composition of 41‐year‐old Norway spruce (Picea abies (L.) Karst.) trees. The nonfertilized and irrigated‐fertilized trees were, for 3 years, continuously exposed to elevated [CO₂] in whole‐tree chambers. Elevated [CO₂] decreased concentrations of soluble sugars, acid‐soluble lignin and nitrogen in stem wood, but the effects were not consistent between sampling height and/or fertilization. The effect of 2*ambient [CO₂] on wood structure depended on the exposure year and/or fertilization. Radial lumen diameter decreased and annual ring width increased in the second year of exposure (1999) in elevated [CO₂]. In the latter, the CO₂ effect was significant only in the nonfertilized trees. Stem wood chemistry and structure were significantly affected by fertilization. Fertilization increased the concentrations of nitrogen and gravimetric lignin, annual ring width, and radial lumen diameter. Fertilization decreased C/N ratio, mean ring density, earlywood density, latewood density, cell wall thickness, cell wall index, and latewood percentage. We conclude that elevated [CO₂] had only minor effects on wood properties while fertilization had more marked effects and thus may affect ecosystem processes and suitability of wood for different end‐use purposes.     

The effect of nutrition on the seasonal course of needle respiration in Norway spruce stands

 Respiration of 1-year-old needles of 30-year-old Norway spruce trees [Picea abies (L.) Karst.] was studied in a nutrient optimisation experiment in northern Sweden. Respiration rates of detached needles, from ten control (C) and ten irrigated-fertilised (IL) trees, were measured on 16 occasions from June 1992 to June 1993. The aim of the study was to determine the influence of temperature on the seasonal course of needle maintenance respiration, and the effect of nitrogen concentration [N] and carbohydrate content on needle respiration in young Norway spruce trees subjected to long-term fertilisation. The IL treatment significantly affected needle size, in terms of dry mass and length, but not specific needle length (SNL). There was, however, a strong tree-specific effect on SNL (P<10^–9, R ² = 0.75). Needle starch content varied markedly with season (0–25% of total dry mass). This, unless accounted for, would cause erroneous estimates of nutrient concentrations, and of rates of needle respiration, within and between treatments. There was considerable seasonal variation in needle respiration, both in terms of maintenance respiration and temperature dependence (Q₁₀). Q₁₀ had its highest value (2.8) during winter and its lowest (2.0) in the middle of summer. In early autumn (August, September), respiration rate and needle [N] were significantly related (C: P = 0.001, IL: P<0.0005). There was no significant difference in the slope between the two regression lines, but a difference in intercept. At the same needle [N], needles from IL-plots always had a lower respiration rate than needles from control plots. No obvious explanation for the observed difference in intercept was found, but some plausible assumptions are put forward and discussed. Received: 24 January 1997 / Accepted: 1 July 1997     

Stem wood properties of mature Norway spruce after 3 years of continuous exposure to elevated [CO2] and temperature

The objective of the study was to investigate the interactive effects of elevated atmospheric carbon dioxide concentration, [CO₂], and temperature on the wood properties of mature field-grown Norway spruce ( Picea abies (L.) Karst.) trees. Material for the study was obtained from an experiment in Flakaliden, northern Sweden, where trees were grown for 3 years in whole-tree chambers at ambient (365 μmol mol⁻¹) or elevated [CO₂] (700 μmol mol⁻¹) and ambient or elevated air temperature (ambient +5.6 °C in winter and ambient +2.8 °C in summer). Elevated temperature affected both wood chemical composition and structure, but had no effect on stem radial growth. Elevated temperature decreased the concentrations of acetone-soluble extractives and soluble sugars, while mean and earlywood (EW) cell wall thickness and wood density were increased. Elevated [CO₂] had no effect on stem wood chemistry or radial growth. In wood structure, elevated [CO₂] decreased EW cell wall thickness and increased tracheid radial diameter in latewood (LW). Some significant interactions between elevated [CO₂] and temperature were found in the anatomical and physical properties of stem wood (e.g. microfibril angle, and LW cell wall thickness and density). Our results show that the wood material properties of mature Norway spruce were altered under exposure to elevated [CO₂] and temperature, although stem radial growth was not affected by the treatments.     

Effect of wood ash and nitrogen fertilization on soil chemical properties, soil microbial processes, and stand growth in two coniferous stands in Finland

The aim of our study was to investigate long-term effects of wood ash fertilization, given together with nitrogen, on soil chemical properties, soil microbiological processes related to C and N cycling, and tree growth. The study was carried out in a 31-year-old Scots pine stand and in a 45-year-old Norway spruce stand 15 years after application. The treatments were (1) a control with no ash or nutrient addition, (2) wood ash + N (WAN), and (3) a stand-specific fertilization (SSF) formulated on the basis of analyses carried out on needle and soil samples taken from the stand. The SSF treatments included N, Cu and B, and in the spruce stand also P. WAN decreased acidity and increased the extractable Ca, Mg and P concentrations in the organic layer in both stands, but SSF had no effect. The microbial processes reacted more strongly to the treatments in the pine stand, whereas the growth response, although only relatively slight during the third 5-year period after fertilization, was detected only in the spruce stand. WAN increased the NH₄-N concentrations in the organic layer compared to the control and SSF treatments on both sites. In the pine stand, amount of N in microbial biomass and both the C and net N mineralization rates were significantly higher in the WAN treatment than in the SSF treatment. On both sites net nitrification was negligible in all treatments. Soil microbial biomass, microbial respiration and N availability have been used as indices for assessing the biological activity and health of soil, and these parameters either increased or were not affected by the WAN treatment. Hence, with regard to these parameters there are justifiable grounds for applying wood ash.     

Tree allometry of Douglas fir and Norway spruce on a nutrient-poor and a nutrient-rich site

Research related to the allometric relationships of tree height and projected tree crown area to diameter at breast height was conducted to look at the biological suitability and timber production potential of Douglas fir under the conditions present in central Europe. The dependence of allometric relationships on soil nutrient conditions were described in forest stands of Douglas fir and Norway spruce. The studied sites were climatically similar but differed in soil nutrient availability. A significant difference was found in the allometric relationships of Norway spruce trees from the nutrient poor and nutrient rich site. In contrast to the Norway spruce, there was no significant effect of site fertility on allometric relationships for Douglas fir suggesting that its allocation patterns were less sensitive to site nutrient conditions. Stem growth increment, which was measured weekly during two consecutive seasons for both species, was related to the weather conditions and available soil moisture. Stem growth of Douglas fir began about 2 weeks earlier than in the Norway spruce at both sites. At the nutrient rich site, most of the stem growth of both species occurred at the beginning of the season, while growth at the other site was more evenly distributed throughout the season. Data obtained in this study will be useful for modeling stem growth and analysis of water use efficiency of these two tree species.     

Overexpression of the endogenous peroxidase-like gene spi 2 in transgenic Norway spruce plants results in increased total peroxidase activity and reduced growth

Peroxidases constitute a large family of proteins found in all higher plants. Owing to the complexity of the peroxidase isoenzyme family it has been difficult to assess the precise function of individual peroxidase enzymes. In this work we have studied the effects of an endogenous peroxidase-like gene from Norway spruce [Picea abies (L.) Karst], spi 2, on the development and growth of Norway spruce somatic embryo plants. Embryogenic cells of Norway spruce transformed with spi 2 under control of the maize ubi-1 promoter showed up to 40 times higher total peroxidase activity than the control cells; regenerated plants overexpressing spi 2 showed an increased total peroxidase activity. Based on these results and the overall sequence similarity with cationic peroxidases we conclude that spi 2 encodes a peroxidase. Overexpression of spi 2 resulted in increased sensitivity to stress, leading to a reduction in epicotyl formation and in height growth compared with control plants. The plants overexpressing spi 2 also showed a deeper phloroglucinol staining but similar levels of Klason lignin.     

Decomposition and element concentrations of Norway spruce needle litter with differing B, N, or P status

Adequate boron (B) nutrition may decrease concentrations of phenolic compounds and enhance structural integrity and lignification in plants, compared with suboptimal B. This could affect decomposition in areas where B deficiencies are common. The mass loss and changes in element concentrations in Norway spruce needle litter were studied with combinations of litter from high-B and low-B trees, incubated for 29 months, in either B fertilised or control plots without B addition. The litter originated from the same Norway spruce field experiments. Additionally, the field experiments included long-term N and P treatments. Initially, lowest lignin concentrations were found in Norway spruce litter from the treatment P and particularly in the combination B?+?P, and highest in the B?+?N fertilised plots. The mass loss of Norway spruce litter was not affected by the treatments. However, B_litter increased Cu accumulation. The litter from the B?+?P fertilised plots accumulated considerably more Al, Ca, S and Zn than the other treatments, whereas B together with N reduced the remaining amounts of these elements. Reduced nutrient release from litter may have far-reaching consequences on nutrient cycles in forests.     

Mechanical properties of spruce and beech wood grown in elevated CO2

Biomechanical responses of stems of 6- to 7-year-old spruce [Picea abies (L.) Karst.] and beech (Fagus sylvatica L) trees were studied after 4 years of growth in elevated atmospheric CO₂ in combination with a nitrogen treatment and on two different soil types. At the end of the treatment, stems were harvested and tested in fresh and air-dried status. Bending characteristics of juvenile wood (modulus of elasticity, termed rigidity) were determined by bending tests. Fracture characteristics (termed toughness) were determined by stroke-pendulum tests. From the base disk of each stem densitometric data were obtained. In spruce, wood produced under elevated CO₂ was tougher on both soil types; enhanced N deposition made wood less rigid only on acidic soils. In contrast, beech wood samples showed no significant reaction to CO₂ but were significantly tougher under high nitrogen depositions on acidic soil. Effects on wood density of both CO₂ and N treatments were not significant, but wood density was higher on acidic soil and so were rigidity and toughness (soil effect). Different genotypes of spruce and beech reacted significantly differently to the treatments. Some genotypes reacted strongly to CO₂ or N, whereas others did not react or showed interactions between CO₂ and N. This underlines the importance of genetic diversity in tree communities.     

Biomass, morphology and nutrient contents of fine roots in four Norway spruce stands

Fine root systems may respond to soil chemical conditions, but contrasting results have been obtained from field studies in non-manipulated forests with distinct soil chemical properties. We investigated biomass, necromass, live/dead ratios, morphology and nutrient concentrations of fine roots (<2 mm) in four mature Norway spruce (Picea abies [L.] Karst.) stands of south-east Germany, encompassing variations in soil chemical properties and climate. All stands were established on acidic soils (pH (CaCl₂) range 2.8–3.8 in the humus layer), two of the four stands had molar ratios in soil solution below 1 and one of the four stands had received a liming treatment 22 years before the study. Soil cores down to 40 cm mineral soil depth were taken in autumn and separated into four fractions: humus layer, 0–10 cm, 10–20 cm and 20–40 cm. We found no indications of negative effects of N availability on fine root properties despite large variations in inorganic N seepage fluxes (4–34 kg N ha⁻¹ yr⁻¹), suggesting that the variation in N deposition between 17 and 26 kg N ha⁻¹ yr⁻¹ does not affect the fine root system of Norway spruce. Fine root biomass was largest in the humus layer and increased with the amount of organic matter stored in the humus layer, indicating that the vertical pattern of fine roots is largely affected by the thickness of this horizon. Only two stands showed significant differences in fine root biomass of the mineral soil which can be explained by differences in soil chemical conditions. The stand with the lowest total biomass had the lowest Ca/Al ratio of 0.1 in seepage, however, Al, Ca, Mg and K concentrations of fine roots were not different among the stands. The Ca/Al ratio in seepage might be a less reliable stress parameter because another stand also had Ca/Al ratios in seepage far below the critical value of 1.0 without any signs of fine root damages. Large differences in the live/dead ratio were positively correlated with the Mn concentration of live fine roots from the mineral soil. This relationship was attributed to faster decay of dead fine roots because Mn is known as an essential element of lignin degrading enzymes. It is questionable if the live/dead ratio can be used as a vitality parameter of fine roots since both longevity of fine roots and decay of root litter may affect this parameter. Morphological properties were different in the humus layer of one stand that was limed in 1983, indicating that a single lime dose of 3–4 Mg ha⁻¹ has a long-lasting effect on fine root architecture of Norway spruce. Almost no differences were found in morphological properties in the mineral soil among the stands, but vertical patterns were apparently different. Two stands with high base saturation in the subsoil showed a vertical decrease in specific root length and specific root tip density whereas the other two stands showed an opposite pattern or no effect. Our results suggest that proliferation of fine roots increased with decreasing base saturation in the subsoil of Norway spruce stands.     

Stem radius changes and their relation to stored water in stems of young Norway spruce trees

Changes in the stem radius of young Norway spruce [Picea abies (L.) Karst.] were related to changes in stem water content in order to investigate the relationship between diurnal stem size fluctuations and internally stored water. Experiments were performed on living trees and on cut stem segments. The defoliated stem segments were dried under room conditions and weight (W), volume (V), and xylem water potential (O_s) were continuously monitored for 95 h. Additionally, photos of cross-sections of fresh and air-dried stem segments were taken. For stem segments we found that the change in V was linearly correlated to the change in W as long as O_s was >-2.3ǂ.3 MPa (phase transition point). Stem contraction occurred almost solely in the elastic tissues of the bark (cambium, phloem, and parenchyma), and the stem radius changes were closely coupled to bark water content. For living trees, it is therefore possible to estimate the daily contribution of "bark water" to transpiration from knowledge of the stem size and continuous measurements of the stem radius fluctuations. When O_s reaches the phase-transition point, water is also withdrawn from the inelastic tissue of the stem (xylem), which - in the experiment with stem segments - was indicated by an increasing ratio between (V and (W. We assume that for O_s below the transition point, air is sucked into the tracheids (cavitation) and water is also withdrawn from the xylem. Due to the fact that in living P. abies O_s rarely falls below -2.3ǂ.3 MPa and the xylem size is almost unaffected by radius fluctuations, dendrometers are useful instruments with which to derive the diurnal changes in the bark water contents of Norway spruce trees.     

Vibrational spectroscopy and X-ray diffraction methods to establish the differences between hardwood and softwood

FT-IR spectrometry and X-ray diffraction were applied to probe the differences between pulp fibers from Eucalyptus wood (hardwood) and Norway spruce wood (softwood). Wood processing was found to induce certain structural alterations within its components depending on the type of wood and the applied procedure. These differences were established by using techniques such as; spectral comparison of wood samples with those of individual component fractions, derivative spectroscopy, bands deconvolution, etc. FT-IR spectroscopy was shown to be an important tool that provided details about the structural characteristics of hardwood and softwood samples. Using second-derivative spectra and deconvolution processes small differences between spectra became apparent that allowed correlations to be made related to wood composition. In addition a correlation was established between the integral absorptions for the various bands and lignin content as well as the lignin/carbohydrate content. Relations between various spectral characteristics and the degree of crystallinity and sample composition were established.     

Effects of growth differences due to geographic location and N-fertilisation on wood chemistry of Norway spruce

We studied the effect of long-term nitrogen fertilisation on wood chemistry at two boreal sites in Finland: the northern site (Kemijärvi) and the southern site (Heinola). N-fertilisation was repeated in five-year intervals from the 1960s. Norway spruce (Picea abies L. Karst.) trees that had been planted in 1938 and 1954, in the northern and the southern site, respectively, were harvested in October 2002. Altogether 20 trees, in five different size classes, either unfertilised or fertilised, were felled. Wood sections at breast height, consisting of five consecutive annual rings, from six (Kemijärvi) or five (Heinola) points with different distances from the pith were examined. Differences in growth between the northern and southern sites were marked in favour of the southern site. In the northern site fertilisation had clearly increased the diameter growth, while in the southern site fertilisation had no effect. Nitrogen fertilisation resulted in slight changes in wood chemistry that included increased nitrogen concentrations in the northern site and extractives in the southern site. Stem wood had higher concentrations of extractives, starch, and uronic acids, and lower concentration of cellulose, in the northern than in the southern site. Changes in the stem wood chemistry along radial axis were marked. The changes in wood chemistry are discussed in relation to the physiological function and also how the changes can influence the suitability of wood for different end-use purposes.     

Below-ground response of Norway spruce to climate conditions at Mt. Brocken (Germany)—A re-assessment of Central Europe's northernmost treeline

Alpine treelines at medium high mountains are less abundant and thus have been less frequently studied than at high-elevation mountain ranges of the world. We studied mature Norway spruce stands along an extended elevation transect at Mt. Brocken (Harz Mountains, Central Germany) to analyse the altitudinal changes in climate-related growth conditions, and to evaluate the prevailing climate conditions at the treeline of medium high Mt. Brocken. A particular aim was to analyse the change in fine root biomass partitioning along the transect towards the treeline. Microclimate conditions at the treeline of Mt. Brocken were very similar to other treeline sites worldwide. Tree height and stem biomass strongly decreased from middle elevations towards the treeline. On the contrary, fine root biomass and the ratio of fine root/stem biomass strongly increased towards the treeline indicating a marked shift in carbon allocation in favour of the fine root system with elevation. A meta-analysis of literature data revealed that the elevation-related increase in dry mass partitioning to the fine root system is a general phenomenon for Norway spruce stands in northern and central European mountains. We conclude that the particularly large fine root system of Norway spruce at cold sites represents a mechanism to cope with unfavourable soil conditions such as reduced or temporally variable nutrient supply.     

Methyl jasmonate induces traumatic resin ducts,terpenoid resin biosynthesis,and terpenoid accumulation in developing xylem of Norway spruce stems

Norway spruce (Picea abies L. Karst) produces an oleoresin characterized by a diverse array of terpenoids, monoterpenoids, sesquiterpenoids, and diterpene resin acids that can protect conifers against potential herbivores and pathogens. Oleoresin accumulates constitutively in resin ducts in the cortex and phloem (bark) of Norway spruce stems. De novo formation of traumatic resin ducts (TDs) is observed in the developing secondary xylem (wood) after insect attack, fungal elicitation, and mechanical wounding. Here, we characterize the methyl jasmonate-induced formation of TDs in Norway spruce by microscopy, chemical analyses of resin composition, and assays of terpenoid biosynthetic enzymes. The response involves tissue-specific differentiation of TDs, terpenoid accumulation, and induction of enzyme activities of both prenyltransferases and terpene synthases in the developing xylem, a tissue that constitutively lacks axial resin ducts in spruce. The induction of a complex defense response in Norway spruce by methyl jasmonate application provides new avenues to evaluate the role of resin defenses for protection of conifers against destructive pests such as white pine weevils (Pissodes strobi), bark beetles (Coleoptera, Scolytidae), and insect-associated tree pathogens.