Foliar elemental composition of spruce-fir in the southern blue ridge province

Data are presented for what we believe to be the first assessment of the elemental foliar status of red spruce (Picea rubens Sarg.) and Fraser fir [Abies fraseri (Pursh.) Poir.] trees in the high elevation forests of the southern Appalachian mountans. Needle samples were collected from September–November 1984. Needles were separated according to flush year for the 1984, 1983 and 1982 growing seasons. Each sample was analyzed without washing for 28 macro- and micronutrients and trace elements. Significant differences in foliar concentrations were observed between flush year for N, P, Ca, Mg, K, Cl, Cu, Ce, Th, Cs, Pb, Fe, La and Rb for Fraser fir (n=41), and P, Ca, K, Cl, Cu, Pb and Rb for red spruce (n=30). Nitrogen concentrations ranged from 11.2–20.2 mg g^?1 for Fraser fir, and 8.7–15.9 mg g^?1 for red pruce. The mean concentration of Ca observed in red spruce needles (1.4 mg g^?1 1984 growing season) fell at the low extreme of reported values for non-necrotic red spruce foliage in the northeastern United States (1.2–11.6 mg g^?1). The mean concentration of Ca in Fraser fir foliage (3.4 mg g^?1, 1984 growing season) was also lower than reported values for eastern fir, but not to the extent demonstrated for red spruce. Fraser fir needles had higher concentrations of Al than red spruce (310vs 91 mg kg^?1, respectively, 1984 growing season), but both values are higher than those reported for spruce or fir from the northeastern United States. Calcium:aluminum ratios in current foliage are the lowest yet reported for the eastern spruce/fir forest type, suggesting that Al toxicity and/or Ca deficiency may be important stresses in these stands. Comparison of Pb concentrations with those of other rare-earth elements known to be associated with dust on needle surfaces (Ce, La, Sc, Sm, and Th) suggested that a substantial portion of the Pb found was due to particulates on the needle surfaces. The significance of these results to the observed forest decline syndrome in high elevation forests of the eastern United States is also discussed.     

Characteristics of foliar chemistry in a commerical spruce-fir stand of northern New England,USA

Monthly foliage samples were evaluated for elemental composition from red spruce and balsam fir trees in a commercial, low elevation spruce-fir stand at Howland, Maine during the 1987 growing season. Balsam fir showed consistently higher concentrations in A1 and to a lesser extent N, Ca, Mg, and Fe when compared to red spruce. Red spruce exhibited consistently higher Mn and K concentrations. Both species showed a marked seasonal trend in the foliar concentrations of N, P, K, and Ca in current year foliage. For N, P, and K current year foliar concentrations declined rapidly during the early part of the growing season. Calcium concentrations steadily increased during the growing season for both species and age class of needles. Foliar concentrations of N and P in both species suggests that the availability of these nutrients is limited for this site.     

Effects of bud phenology and foliage chemistry of balsam fir and white spruce trees on the efficacy of Bacillus thuringiensis against the spruce budworm, Choristoneura fumiferana

Abstract 1 Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana was investigated in mixed balsam fir‐white spruce stands. Btk treatments were scheduled to coincide with early flaring of balsam fir shoots, and later with flaring of white spruce shoots. Btk efficacy on the two host trees was compared and examined according to the foliar content of nutrients and allelochemicals and the insect developmental stage at the time of spray. 2 Larvae fed white spruce foliage were less vulnerable to Btk ingestion than larvae fed balsam fir foliage. Higher larval survival on white spruce, observed 10 days after spray, was related to higher foliage content in tannins and a lower N/tannins ratio, which might have induced inactivation of Btk toxins. 3 Larval mortality due to Btk did not depend on spruce budworm larval age. 4 Foliage protection of both host trees was similar in plots treated with Btk: larval mortality due to Btk treatment reduced insect grazing pressure on balsam fir trees; meanwhile, suitability of white spruce foliage seemed to decrease very rapidly, which induced high larval mortality among spruce budworm fed on white spruce trees. Nevertheless, following Btk sprays, 50% more foliage remained on white spruce than on balsam fir trees, because of the higher white spruce foliage production. 5 Both spray timings achieved similar protection of white spruce trees, but Btk treatments had to be applied as early as possible (i.e. during the flaring of balsam fir shoots to optimally protect balsam fir trees in mixed balsam fir‐white spruce stands).     

Calcium addition at the Hubbard Brook Experimental Forest increases the capacity for stress tolerance and carbon capture in red spruce (Picea rubens) trees during the cold season

Red spruce (Picea rubens Sarg.) trees are uniquely vulnerable to foliar freezing injury during the cold season (fall and winter), but are also capable of photosynthetic activity if temperatures moderate. To evaluate the influence of calcium (Ca) addition on the physiology of red spruce during the cold season, we measured concentrations of foliar polyamines and free amino acids (putative stress-protection compounds), chlorophyll (a key photosystem component), and sapwood area (a proxy for foliar biomass), for trees in Ca-addition (CaSiO₃ added) and Ca-depleted (reference) watersheds at the Hubbard Brook Experimental Forest (NH, USA). Ca-addition increased concentrations of the amino acids alanine and γ-aminobutyric acid (GABA) and the polyamines putrescine (Put) and spermidine (Spd) in November, and Put in February relative to foliage from the reference watershed. Consistent with increased stress protection, foliage from the Ca-addition watershed had higher total chlorophyll and chlorophyll a concentrations in February than foliage from the reference watershed. In contrast, foliage from the reference watershed had significantly lower glutamic acid (Glu) and higher alanine (Ala) concentrations in February than foliage from the Ca-addition watershed. Imbalances in Ala:Glu have been attributed to cold sensitivity or damage in other species. In addition to concentration-based differences in foliar compounds, trees from the Ca-addition watershed had higher estimated levels of foliar biomass than trees from the reference watershed. Our findings suggest that Ca-addition increased the stress tolerance and productive capacity of red spruce foliage during the cold season, and resulted in greater crown mass compared to trees growing on untreated soils.     

Evidence of a direct chemical plant defense role for maltol against spruce budworm

This study examines the direct chemical defensive role of maltol, a previously identified secondary metabolite found in balsam fir, Abies balsamea (L.) Mill. (Pinaceae), that was detected during herbivory of spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). Although used extensively in many industries, in addition to being found in multiple plant species, its functional role in plants remains unknown. The objectives of this study were to quantify the amount of free maltol and its potential conjugated form, maltol glucoside, in various foliage age classes and to evaluate whether constitutive foliage levels of maltol have an impact on spruce budworm fitness in maltol supplementation assays. Gas chromatography–mass spectrometry (GC‐MS) analysis of balsam fir foliage showed that maltol is produced in all foliage age classes tested; however, concentrations were significantly higher in older foliage. Liquid chromatography–mass spectrometry–mass spectrometry (LC‐MS‐MS) analysis showed that maltol also exists in balsam fir in its glucosylated form, a unique discovery in conifers. Similar to maltol, maltol glucoside is also present in current and 1‐year‐old balsam fir foliage and in significantly higher concentration in older foliage. We investigated the impact of maltol‐treated diet on spruce budworm fitness. Maltol additions that reflected constitutive foliage concentrations caused a significant reduction in larval development rate and pupal mass, whereas higher concentrations were required to cause significant mortality. These results suggest that maltol may be an important component of a direct defense strategy in balsam fir against spruce budworm herbivory.     

Relationship between an exotic phloem feeder and balsam fir (Abies balsamea L. (Mill.)) foliar chemistry: implications for two native defoliators

The balsam woolly adelgid (Adelges piceae) is a gout-inducing hemipteran native to the silver fir forests of Europe. Introduced to eastern North America approximately 100 years ago, it is now found in most balsam fir forests in Atlantic Canada. When A. piceae feed, they trigger a reaction in the host branch that alters both xylem and phloem morphology. We conducted a field survey to examine the relationship between A. piceae gout density and balsam fir foliar chemistry and shoot growth in naturally unthinned and precommercially thinned stands. A. piceae gout density negatively affected branch growth and was related to changes in the chemistry of older, but not current-year foliage. Older foliage experienced decreases in camphene and bornyl acetate, while foliar concentrations of camphene, myrcene, phenolics, potassium and water differed between thinned and unthinned stands. Foliar chemistry was also influenced by interactions between thinning and A. piceae gout density in old foliage. This study suggests that changes in balsam fir associated with A. piceae gout density may force native defoliators that feed in highly gouted trees to adapt to diets of different chemical compositions and that thinning may alter these interactions.     

Interspecific variation in resistance of two host tree species to spruce budworm

Woody plants regularly sustain biomass losses to herbivorous insects. Consequently, they have developed various resistance mechanisms to cope with insect attack. However, these mechanisms of defense and how they are affected by resource availability are not well understood. The present study aimed at evaluating and comparing the natural resistance (antibiosis and tolerance) of balsam fir (Abies balsamea [L.] Mill.) and white spruce (Picea glauca [Moench) Voss] to spruce budworm, Choristoneura fumiferana (Clem.), and how drainage site quality as a component of resource availability affects the expression of resistance over time (6 years). Our results showed that there are differences in natural resistance between the two tree species to spruce budworm, but it was not significantly affected by drainage quality. Balsam fir exhibited higher foliar toxic secondary compounds concentrations than white spruce in all drainage classes, resulting in lower male pupal mass, survival and longer male developmental time. This, however, did not prevent spruce budworm from consuming more foliage in balsam fir than in white spruce. This response suggests that either natural levels of measured secondary compounds do not provide sufficient toxicity to reduce defoliation, or spruce budworm has developed compensatory mechanisms, which allow it to utilize food resources more efficiently or minimize the toxic effects that are produced by its host's defensive compounds. Larvae exhibited lower pupal mass and higher mortality in rapidly drained and subhygric sites. Drainage class also affected the amount of foliage destroyed but its impact varied over the years and was probably influenced by climatic variables. These results demonstrate the complexity of predicting the effect of resource availability on tree defenses, especially when other confounding environmental factors can affect tree resource allocation and utilization.     

Comparison of energy budgets for spruce budworm Choristoneura fumiferana (Clemens) on balsam fir and white spruce

Summary A determination was made of the differences in the utilization of energy by laboratory reared larval Choristoneura fumiferana fed either balsam fir or white spruce foliage. This enabled us to quantitatively measure the quality of these foliages vis a vis the spruce budworm.The larval strategy was to feed rapidly and develop quickly. Development time was longer on spruce than on fir. Total consumption was virtually identical on both foliage types though production was ca 20% greater on a white spruce diet. Calories/gram increased with insect development and with the development of balsam fir foliage but declined over time in white spruce. Assimilation efficiencies (A/C) were 33.9% to 40.2% while gross production efficiencies (P/C) were 9.5% to 13.3% and net production efficiencies (P/A) were 26.1% to 38.8%. The spruce fed insects gave higher values than those on fir, but all values were at the low end of the range for lepidopterous defoliators (possibly due to characteristics of conifer foliage).The enhanced growth found in spruce fed larvae contrasts the relationship between balsam fir and high insect densities. This is discussed together with the influence of spruce budworm on forest composition and the possible competitive benefits of spruce budworm induced tree mortality.Parts of this paper appeared in a Master's thesis (Koller 1978) submitted to the University of Maine     

Nodulating associations among rhizobia and legumes of the genus Glycine subgenus Glucine

Current and one-year-old foliage was collected from sixty-five red spruce trees growing in thirteen stands at different elevations in the Green Mountains of Vermont and Adirondacks of New York. Sample trees were randomly selected from visually healthy trees at each site. Foliage was analyzed for major and minor elements. In July 1984, foliar Ca, Mg, and Zn concentrations were significantly greater at low than at high elevations. In October 1984, Ca, Mg, and Zn concentrations were higher at low elevations and Ca and Mg concentrations varied significantly among locations within elevational groups. Nitrogen concentration was significantly higher in the high-elevation group in July but not in October. The average red spruce foliar Mg concentration at the end of the growing season in the high elevation stands (442 mg kg⁻¹) is much lower than values reported for other mature red spruce stands in the eastern United States.     

Impact of balsam fir flowering on pollen and foliage biochemistry in relation to spruce budworm growth, development and food utilization

The impact of balsam fir (Abies balsamea (L.) Miller) flowering on nutritional and allelochemical quality of pollen, current-year and one-year-old foliage is studied in relation to spruce budworm (Choristoneura fumiferana Clem.) (Lepidoptera: Tortricidae) growth, development and utilization of food and nitrogen. In the laboratory, using fresh food from the field, we simulated conditions of low larval population density, in which there is no current-year foliage depletion during the spruce budworm feeding period. Similarly, we simulated conditions of high larval population density when current-year foliage depletion occurs.Because of the high nutritive value of pollen (high amounts of amino acids and minerals, especially nitrogen; low monoterpene content), insects from flowering trees reached the fifth instar five days earlier than those from non-flowering trees, and had heavier dry- and nitrogen-weights at the beginning of the fifth instar. At budbreak, switching from pollen to current-year foliage negatively affected conversion efficiencies and digestibilities of food and nitrogen (AD; ADN; ECDN; ECI; ECIN). The switch from pollen to new foliage had a detrimental impact on fifth-instar survival and on newly-moulted sixth-instar dry- and nitrogen-weights. Moreover, during the fifth instar, balsam fir flowering reduced the nutritive value of current-year foliage, which in turn, might have contributed to the reduced larval growth. Nevertheless, during the sixth instar, balsam fir flowering affected the biochemistry of current-year foliage in ways that enabled larvae to compensate for their low fifth-instar biological performance; larvae also managed to reach pupal dry weight similar to larvae reared on non-flowering trees. Current-year foliage from flowering trees contained less nitrogen, total soluble sugars and total monoterpenes. Those foliar characteristics enabled larvae to increase food and nitrogen consumption rates (RCR; RNCR), because of lower repellency and/or post-ingestional feedback from monoterpenes.As for current-year foliage, balsam fir flowering reduced nitrogen, total soluble sugar and total monoterpene contents in one-year-old foliage during the sixth-instar feeding period. These characteristics enabled sixth-instar larvae, fed on old foliage from flowering trees, to have high relative food and nitrogen consumption rates (RCR; RNCR). Larvae were also able to reach higher relative growth rates (RGR) and relative nitrogen accumulation rates (RNAR) compared to larvae reared on one-year-old foliage from non-flowering trees. Finally, larvae on flowering trees had pupal dry weight similar to those from non-flowering trees, but reached the adult stage nine days earlier.Regardless the foliage type consumed by spruce budworm larvae during the sixth instar, pollen consumption during early larval stages reduced total development time, and thus exposure time to natural enemies. This phenomenon might increase larval survival. Balsam fir flowering changed the biochemistry of one-year-old and current-year foliages, but did not affect pupal dry weights of larvae reared on flowering trees compared to those reared on non-flowering trees. Thus, at low population density, spruce budworm populations in balsam fir flowering stands might be favoured over those in balsam fir non-flowering stands. In addition, when larvae consumed one-year-old foliage during the entire sixth instar, those on flowering trees are probably favoured over those on non-flowering trees. However, because flowering trees produce less new foliage than non-flowering trees, current-year foliage depletion may occur earlier on flowering trees than on non-flowering trees. Thus, at similar larval population density, larvae on flowering trees might have to feed on one-year-old foliage earlier than those on non-flowering trees. In that case, spruce budworm populations on non-flowering stands would be favoured over those on flowering stands.     

Recovery kinetics of photochemical efficiency in winter stressed conifers: the effects of growth light environment,extent of the season and species

Evergreens undergo reductions in maximal photochemical efficiency (F_v/F_m) during winter due to increases in sustained thermal energy dissipation. Upon removing winter stressed leaves to room temperature and low light, F_v/F_m recovers and can include both a rapid and a slow phase. The goal of this study was to determine whether the rapid component to recovery exists in winter stressed conifers at any point during the season in a seasonally extreme environment. Additional goals were to compare the effects of species, growth light environment and the extent of the winter season on recovery kinetics in conifers. Four species (sun and shade needle) were monitored during the winter of 2007/2008: eastern white pine (Pinus strobus), balsam fir (Abies balsamea), Taxus cuspidata and white spruce (Picea glauca). F_v/F_m was measured in the field, and then monitored indoors at room temperature and low light for 6 days. The results showed that all species showed a rapid component to recovery in early winter that disappeared later in the season in sun needles but was present in shade needles on most days monitored during winter. There were differences among species in the recovery kinetics across the season, with pine recovering the most slowly and spruce the most quickly. The results suggest an important role for the rapidly reversible form of energy dissipation in early winter, as well as important differences between species in their rate of recovery in late winter/early spring which may have implications for spring onset of photosynthesis.     

The effects of acid deposition on the biogeochemical cycles of major nutrients in miniature red spruce ecosystems

As part of an experimental study of air pollution effects on tree growth and health, we combined process studies with an ecosystem approach to evaluate the effects of acidic deposition on soil acidification, nutrient cycling and proton fluxes in miniature red spruce ecosystems. Ninety red spruce saplings were transplanted into 1-m diameter pots containing reconstructed soil profiles and exposed to simulated acid rain treatments of pH 3.1, 4.1 and 5.1 for four consecutive growing seasons. All the principal fluxes of the major elements were measured. During the first year of treatments, the disturbance associated with the transplanting of the experimental trees masked any treatment effects by stimulating N mineralization rates and consequent high N0₃ ⁻ cation, and H⁺ flux through the soil profile. In subsequent years, leaching of base cations and labile Al was accelerated in the most intensive acid treatment and corresponding declines in soil pH and exchangeable pools of Ca and Mg and increases in exchangeable Al concentrations were observed in the organic horizon. Leaching of Ca²⁺ and Mg²⁺ also was significantly higher in the pH 4.1 than in the pH 5.1 treatment. Flux of Ca from foliage and soil was increased in response to strong acid loading and root uptake increased to compensate for foliar Ca losses. In contrast, K cycling was dominated by root uptake and internal cycling and was relatively insensitive to strong acid inputs. Cation leaching induced by acidic deposition was responsible for the majority of H⁺ flux in the pH 3.1 treatment in the organic soil horizon whereas root uptake accounted for most of the H⁺ flux in the pH 4.1 and 5.1 treatments. Although no measurable effects on tree nutrition or health were observed, base cation leaching was significantly accelerated by acidic deposition, even at levels below that observed in the eastern U.S., warranting continued concern about acid deposition effects on the soil base status of forested ecosystems.     

Effect of nitrogen and light on nutrient concentrations and associated physiological responses in birch and fir seedlings

We grew seedlings of two co-occurring high elevation tree species in controlled light and nitrogen (N) environments to examine the effect on foliar N and P concentrations and the resulting correlation with photosynthesis and growth. Foliar N concentrations in both heart-leaf paper birch (Betula cordifolia) and balsam fir (Abies balsamea) seedlings were greater in low light treatments than in high light treatments. P concentrations, however, were lower in birch and fir foliage grown in low light than in high light. N-availability had no effect on foliar N in birch but tended to increase N concentration in fir needles at all but 100% ambient light. N-availability had no effect on P concentration in fir seedlings, but high N decreased foliar P in birch. There was a positive relationship between foliar N-concentration (mg g^–1) and mass-based maximum photosynthetic rate (Asat) in birch seedlings and a corresponding growth response to increased N-availability (suggesting N-limitation). Fir photosynthesis exhibited a positive correlation up to 22 mg g^–1 – N and a negative correlation above that point, suggesting that high N concentrations may be detrimental to photosynthesis in the fir seedlings. There was no significant effect of N-treatment on growth.     

Tree demography suggests multiple directions and drivers for species range shifts in mountains of Northeastern United States

Climate change is expected to lead to upslope shifts in tree species distributions, but the evidence is mixed partly due to land‐use effects and individualistic species responses to climate. We examined how individual tree species demography varies along elevational climatic gradients across four states in the northeastern United States to determine whether species elevational distributions and their potential upslope (or downslope) shifts were controlled by climate, land‐use legacies (past logging), or soils. We characterized tree demography, microclimate, land‐use legacies, and soils at 83 sites stratified by elevation (~500 to ~1200 m above sea level) across 12 mountains containing the transition from northern hardwood to spruce‐fir forests. We modeled elevational distributions of tree species saplings and adults using logistic regression to test whether sapling distributions suggest ongoing species range expansion upslope (or contraction downslope) relative to adults, and we used linear mixed models to determine the extent to which climate, land use, and soil variables explain these distributions. Tree demography varied with elevation by species, suggesting a potential upslope shift only for American beech, downslope shifts for red spruce (more so in cool regions) and sugar maple, and no change with elevation for balsam fir. While soils had relatively minor effects, climate was the dominant predictor for most species and more so for saplings than adults of red spruce, sugar maple, yellow birch, cordate birch, and striped maple. On the other hand, logging legacies were positively associated with American beech, sugar maple, and yellow birch, and negatively with red spruce and balsam fir – generally more so for adults than saplings. All species exhibited individualistic rather than synchronous demographic responses to climate and land use, and the return of red spruce to lower elevations where past logging originally benefited northern hardwood species indicates that land use may mask species range shifts caused by changing climate.     

Foliar chemistry of balsam fir and red spruce in relation to elevation and the canopy light gradient in the mountains of the northeastern United States

Red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea[L.] Mill) are the dominant conifer species at treeline in the mountains of the northeastern United States. The objective of this study was to investigate changes in foliar chemistry of these species along both elevational (below, at, and above treeline) and canopy light (sun vs. shade leaves) gradients. Nutrient concentrations (mass basis) did not show any significant (all P>0.05) differences among elevations, although mean concentrations of all macronutrients (N, P, K, Ca, Mg) tended to be higher at low elevation sites compared to high elevation. This result contradicts the traditional view that plants in cold growth environments are adapted to maintain high foliar nutrient concentrations, but it also gives only weak support for the hypothesis that nutrient limitation plays a role in determining treeline location. Foliar concentrations (mass basis) of lignin (both sun and shade needles) and cellulose (sun needles only) decreased sharply and significantly with increasing elevation, but foliar concentrations of hemicellulose did not change with elevation. These results are consistent with the hypothesis that as a result of carbon limitation at high elevation, synthesis of the most expensive fiber constituent (i.e. lignin) is reduced more than that of the least expensive fiber constituent (i.e. hemicellulose). The reduced lignin concentration at high elevation may have implications for nutrient cycling in this ecosystem where cold temperatures limit decomposition rates.     

Effects of tree age and stand thinning related variations in balsam fir secondary compounds on spruce budworm Choristoneura fumiferana development,growth and food utilization

• 1 The effect of tannins and monoterpenes on the development, mortality and food utilization of spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) was investigated under laboratory conditions using an artificial diet. Tannins were extracted from balsam fir foliage of thinned and unthinned stands to reproduce stand thinning related variations in tannins. A mixture of synthetic monoterpenes was utilized to simulate the concentration found in young and old balsam fir trees.
• 2 Longer development time and lower pupal weight were observed for insects fed on diets with a lower nitrogen concentration and a higher tannin concentration (unthinned treatment). Tannins induced higher insect mortality at a low nitrogen concentration compared with the diet with a higher nitrogen concentration.
• 3 Approximate digestibility was higher for larvae fed on diets with high concentrations of nitrogen at both low and high concentrations of tannins. Efficiency of conversion of digested food (ECD) decreased with an increase in tannin concentration. Tannins reduced both the relative consumption and growth rate (RCR and RGR).
• 4 Monoterpenes increased spruce budworm mortality and this mortality reached almost 50% under concentrations of monoterpene typical of the young trees compared with 20% under monoterpene concentrations found in old trees.
• 5 A higher digestibility was observed for larvae fed on diet with a higher concentration of monoterpenes, whereas efficiency of conversion of ingested food (ECI), ECD, RCR, and RGR decreased with an increase in monoterpenes in the diet.
• 6 The results obtained in the present study are consistent with the defensive role of secondary compounds such as tannins and monoterpenes in the spruce budworm–balsam fir system.

     

FACTORS AFFECTING RED SPRUCE REGENERATION IN DECLINING AREAS OF CAMELS HUMP MOUNTAIN,VERMONT

Scarcity of red spruce (Picea rubens Sarg.) seedlings in declining spruce-fir forests of Camels Hump mountain, Vermont, prompted a study on some contributing factors involved in failure of spruce regeneration. Cones were shorter than those from low elevation red spruce trees from unaffected sites. Seed number in cones collected in declining areas of Camels Hump was low as were seed sizes and weights. Seed germination was at control levels only in good seed years. Capacity of seeds to form seedlings was reduced relative to that of controls, although seedling growth was normal. Coniferous litter contains presumed allelopathic substances leachable by contemporary precipitations that affect seed germination and seedling root development in red spruce, but not in balsam fir. Shield fern contains leachable substances that reduce seed germination and seedling root development in red spruce, but not balsam fir. Roots of red spruce germlings have lower capacity to penetrate through the increased forest duff depths of declining forests than do balsam fir roots. It is anticipated that substantial reproduction of red spruce will not occur in declining montane conifer forests under present conditions.     

Photosynthetic Action Spectra of Trees: II. The Relationship of Cuticle Structure to the Visible and Ultraviolet Spectral Properties of Needles from Four Coniferous Species

The relative reflectance spectra for control and treated (surface wiped) current-year foliage of Douglas fir, and Sitka, Colorado, and Blue spruce (Pseudotsuga menziesii [Mirb.] Franco, Picea sitchensis [Bong.] Carr., Picea pungens Engelm., and Picea pungens Engelm. var. hoopsii, respectively) were obtained from 220 to 700 nm. The green color of the control foliage of both Douglas fir and Sitka spruce was unaffected by the treatment whereas the blue-green and blue-white foliage of control Colorado and Blue spruce, respectively, became “green” as a result of the wiping. The relative reflectance curves for all green foliage, including the treated Colorado and Blue spruce, were all very similar with a peak in the green (540-560 nm), minima in the red (660-680 nm) and blue (450-500 nm), and very low reflectivities in the ultraviolet (λ < 400 nm). In contrast, the control foliage for Colorado and Blue spruce both showed a generally higher relative reflectance over most of the visible spectrum (400-700 nm) with a marked increase in the blue region (400-500 nm). At wavelengths below 420 nm, their relative reflectances increased sharply with decreasing wavelength, the reflectance at 220 nm for Blue spruce being over four times that at 540 nm.     

Factors affecting oral regurgitation by larval spruce budworm

This study evaluated factors that influence the regurgitation behaviour of sixth instar spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), reared on balsam fir, Abies balsamea (L.) Mill. (Pinaceae), under various experimental conditions in the laboratory. Upon physical disturbance, larvae discharged a median volume of regurgitant of 0.4 μl when fed and 1.6 μl when food‐deprived. Larvae deprived of food for 24 or 48 h disgorged more regurgitant than larvae feeding on balsam fir foliage, and the effect was consistent for laboratory‐reared and field‐collected larvae. The water content of the foliage fed upon by larvae had no immediate impact on the volume of regurgitant; following a 24‐h period of food deprivation, however, larvae that previously fed on fresh foliage discharged >2.5 times more regurgitant than larvae that previously fed on dry foliage. Self‐regulated regurgitation by larvae, measured using the number of regurgitant stains on filter paper, was >10 times higher when larvae had access to balsam fir foliage than when they were starved. The number of larvae confined inside the Petri dish (one or four individuals) had a relatively small effect on regurgitation. Larvae were deterred from feeding when balsam fir needles were entirely covered with regurgitant, but not when only a portion of the foliage was treated. These results suggest that the regurgitant does not serve as resource marking or spacing pheromone. The high level of regurgitation by larvae after contact with ants suggests that the regurgitant has evolved in part as a defence mechanism against natural enemies.     

Macrocharcoal-Based Chronosequences Reveal Shifting Dominance of Conifer Boreal Forests Under Changing Fire Regime

Balsam fir (Abies balsamea) and black spruce (Picea mariana) forests are the main conifer forest types in the North American boreal zone. The coexistence of the two species as well as their respective canopy dominance in distinct stands raises questions about the long-term evolution from one forest type to the other in relation to environmental factors including climate and stand disturbance. We tested the hypothesis that repetitive fire events promote the succession of balsam fir forest to black spruce forest and vice versa. Postfire chronosequences of one black spruce (BSP) and one balsam fir (BFI) sites were reconstructed based on the botanical composition and ¹⁴C-dated soil macrocharcoals. The results support the hypothesis of a successional dynamics. The BSP site has been affected by fires for the last 7600 years, whereas the BFI site, after having been impacted by several fires during the first half of the Holocene, evolved in a fire-free environment for the last 4400 years. Periods of fire activity facilitated the dominance of black spruce forests. The cessation of fires around 4400 cal. years BP on BFI site marks the beginning of the transition from black spruce to balsam fir stands. This succession is a long process, due to the ability of black spruce to regenerate by layering in the absence of fire. The resulting balsam fir stands are ancient and precarious ecosystems, since fire generally leads to the return of black spruce. The increase in balsam fir to the detriment of black spruce in boreal forests is a response to a decrease in fire frequency.