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Abstract: Many studies have focused on the influence of needle defense compounds that are produced when trees are attacked. Spruce budworm is the most important defoliator of conifers in eastern North America causing tree mortality. Volatile components such as terpenes are of importance as they are known to be agents of defense in plants and trees against many aggressors like spruce budworm. In this study, the static headspace gas chromatography (HS-GC) method was used to evaluate volatile compounds in the foliage of balsam fir (Abies balsamea) in order to compare the results obtained with the traditional GC–MS method. An advantage of analyzing plant volatile compounds with the HS-GC was the simplicity of execution, allowing a large number of samples to be treated. The most abundant volatile molecules were identified on the HS-GC chromatogram, except for some compounds such as α-thujene, fenchone, terpin-1-en-4-ol and α-terpineol. In addition to the qualitative analysis of terpene, a quantitative analysis of β-phellandrene was done to compare the variation of this compound between a control and a defoliated site. This study suggests that β-phellandrene was released as a response to injuries when the site was heavily defoliated by spruce budworm. [Copyright &y& Elsevier]

A 20–40% reduction in soil moisture is projected for the boreal forest of Eastern Canada for the period 2070–99 relative to 1971–2000. In order to better predict the effects of a reduced water supply on the growth of balsam fir (Abies balsamea (L.) Mill.), a dominant tree species of the boreal forest, we simulated 2 consecutive years of summer droughts (starting in July) by means of throughfall exclusion. Four 100-m2 plots were established in 2010 with polyethylene sheets maintained 1.3–2 m aboveground and redirecting the water outside the plots. Wood microcores were extracted weekly from mature trees from April to October 2011 to analyse the time dynamics of wood formation in that year. The number of tracheids formed during and before treatment and their anatomical characteristics were determined through microscopic analyses. The growth of lateral and terminal branches and the water potential of balsam fir seedlings were also monitored. Throughfall exclusion significantly reduced soil water content by 5.8% in 2010 and 10.5% in 2011. Xylogenesis was affected significantly by the treatment. Tracheids were 16.1% smaller in diameter and their cell wall was 14.1% thicker during both years. The treatment delayed by more than a week the start of the tracheid differentiation process in the second year with a concomitant decrease (26%) in the number of tracheids produced. The seedlings displayed a 32% reduction in growth and a 40% reduction in leaf water potential. Our results suggest that a future regime of increased frequency and intensity of droughts could have negative effects on the duration of xylogenesis and the production of xylem cells in balsam fir. [ABSTRACT FROM PUBLISHER]

Two experiments were conducted to understand the effect of light emitting diodes on postharvest abscission in balsam fir (Abies balsamea L.) branches. In one experiment, branches were pre-exposed to the fluorescent light, LEDs, or darkness for 1, 4, 8, 12, 24, or 48 h. In a second experiment, branches were constantly exposed to fluorescent lights, LEDs, or darkness. The response variable was needle retention duration (NRD). A 48-hour exposure time to red, white, or blue LEDs significantly (P < 0.001) increased NRD by approximately 75, 118, or 127%, respectively, compared to a cool white fluorescent lighting or darkness. Constant exposure to any LED significantly (P < 0.001) improved NRD compared to fluorescent lights or darkness, though white and red LEDs were most effective. It is speculated that LED-promoted needle retention could possibly be due to changes in carbohydrate synthesis similar to those observed during cold acclimation. [ABSTRACT FROM AUTHOR]

Field trials and assessments of the balsam fir sawfly (Neodiprion abietis) nucleopolyhedrovirus (NeabNPV: Baculoviridae, Gammabaculovirus) against its natural host were conducted in July and August 2002 near Corner Brook, Newfoundland and Labrador, Canada, in naturally regenerated, precommercially thinned stands dominated by balsam fir (Abies balsamea). Two experimental blocks, each with its own untreated control, were established. The purpose of the Island Pond block was to examine the spread of NeabNPV from a 313-ha aerial treatment block out into adjacent populations of balsam fir sawflies. The purpose of the Old Man's Pond block (2,093 ha) was to determine whether NeabNPV could disperse into populations of balsam fir sawflies within a 200-m zone between spray swaths. NeabNPV was applied to treatment blocks by a Cessna 188B AgTruck aircraft equipped with MicronAir AU4000 rotary atomizers at an application rate equivalent to 1 x 109 NeabNPV occlusion bodies/ha in 2.5 L of 20% aqueous molasses. At Island Pond, NeabNPV infection increased with time following the spray, especially for individuals close to the treatment block, and infection rate decreased to a measured distance of 400 m from the treatment block. At Old Man's Pond, NeabNPV infection rose higher (80% vs. 15%) and sawfly densities declined more (84% vs. 60%) in the area between spray swaths than in the control block. [ABSTRACT FROM AUTHOR]

Nucleopolyhedroviruses (NPV: Gammabaculovirus: Baculoviridae) of diprionid sawflies (Diprionidae: Hymenoptera) are highly host specific and only infect the midgut epithelium. While still alive, infected sawfly larvae excrete NPV-laden diarrhea that contaminates food sources. The diarrhea can then be consumed by conspecific larvae, resulting in rapid horizontal transmission of the virus. To better understand the efficacy of Gammabaculovirus-based biological control products, the horizontal spread of such a virus (NeabNPV) within cohorts of balsam fir sawfly (Neodiprion abietis) larvae was studied by introducing NeabNPV-treated larvae into single-cohort groups at densities similar to those observed during the increasing (field study) and peak (laboratory study) phases of an outbreak. In field studies (∼200 N. abietis larvae/m² of balsam fir (Abies balsamea) foliage), NeabNPV-induced mortality increased positively in a density-dependent manner, from 23% (in control groups) to 51% with the addition of one first-instar NeabNPV-treated larva, to 84% with 10 first-instar-treated larvae. Mortality was 60% and 63% when one or 10 NeabNPV-treated third-instar larva(e), respectively, were introduced into groups. Slightly higher levels of NeabNPV-induced mortality occurring when NeabNPV-treated larvae were introduced into first- rather than third-instar cohorts suggests that early instars are more susceptible to the virus. In the laboratory (∼1330 N. abietis larvae/ m² of foliage), NeabNPVcaused mortality increased from 20% in control groups to over 80% with the introduction of one, five or 10 NeabNPV-treated larvae into treatment groups of first-instar larvae. [ABSTRACT FROM AUTHOR]

* Premise of the study: In ecosystems where seed production is low and masting years are sporadic, or with species that have short-lived seeds, regeneration is assured by seedling banks rather than seed banks. Seedling establishment and survival play a critical role in determining the composition of these plant communities by supplying new individuals for their maintenance. Seedling emergence and mortality were investigated to test the hypothesis that recruitment into the seedling bank is periodic. * Materials and methods: Seed production and seedling emergence and survival was monitored during 1994-2007 in balsam fir (Abies balsamea) and white spruce (Picea glauca) in four pristine stands of the boreal forest of Quebec, Canada. Measurements were collected twice per month by sampling one permanent plot of 20 x 20 m per stand. * Key results: Seed-rain abundance reached 9 x 10³ seeds m-2 year-1, and was characterized by synchronous sequences of low and high seed production. New seedlings appeared only during the year following a seed production of at least 1 x 10³ and 1.5 x 10² seeds m-2 year-1 for balsam fir and white spruce, respectively. Seedlings emerged in July and survived 34-52 d on average, with balsam fir showing a longer lifespan and lower mortality, although 85-99% of seedlings died before completing one year of life. * Conclusions: The emergence of young seedlings was coupled with massive seed rains, which allowed synchronous replenish ment of the seedling banks among stands and species, and generated different cohorts, yielding a discontinuous age structure. [ABSTRACT FROM AUTHOR]

Ethylene accumulation increases after harvest and culminates in needle abscission in balsam fir [Abies balsamea (L.) Mill.]. We hypothesize that water deficit induces ethylene evolution, thus triggering abscission. The purpose of this research was to investigate the role of temperature and humidity on postharvest needle abscission in the presence and absence of exogenous ethylene and link vapor pressure deficit (VPD) to postharvest needle abscission in balsam fir. In the first experiment, branches were exposed to 30%, 60%, or 90% humidity while maintained at 19.7 °C (VPD of 1.59, 0.91, or 0.23 kPa, respectively); in the second experiment, branches were exposed to 5, 15, or 25 °C (VPD of 0.35, 0.68, or 1.26 kPa, respectively) while maintained at 60% relative humidity. Needle retention duration, average water use, xylem pressure potential relative water content, and ethylene evolution were response variables. Reducing water loss or xylem tension by changing temperature or humidity effectively delayed needle abscission, although the 90% humidity treatment had the most profound effects. In the absence of exogenous ethylene, branches placed in 90% humidity had a fivefold increase in needle retention, 67% decrease in average water use, and had a final xylem pressure potential of -0.09 MPa. There was a near perfect relationship between VPD and needle retention (R² = 0.99). These findings suggest that increasing xylem tension or decreasing water status may trigger ethylene synthesis and needle abscission. In addition, these findings demonstrate an effective means of controlling postharvest needle abscission by modifying temperature and/or relative humidity. [ABSTRACT FROM AUTHOR]

The article presents compares pre-settlement and modern forest dynamics of subboreal wilderness and analyzing whether spruce budworm enhance fire risk. The study employs LANDIS-II process-based model, extension Age-list Succession, remote sensing. Result reveal that budworm-mortality increased spread rates and facilitated escalation of fires to crown fires.

The article discusses a study which tested whether there were attributes of trees that may have influenced whether a tree fell or was left standing due to Hurricane Igor. The hurricane was a Category I when it passed the island of Newfoundland on September 21, 2010. The cities of St. John's and Mount Pearl and the town of Paradise were included in the study. Trees were arranged into native/non-native classes.

The northernmost balsam fir forest in eastern Canada forms disjunct stands far beyond the extensive balsam fir forest zone of southern Canada. The northern balsam fir stands are distributed in the subalpine belt of high plateaus and coexist locally with white spruce stands. These subalpine stands contrast greatly with black spruce forest stands located in lowlands. Given that subalpine stands are remnants of an earlier northern expansion of the balsam fir forest, the main objective of this study is to assess whether white spruce stands are distinct communities having diverged from the balsam fir forest community earlier in the Holocene or if they rather correspond to a different stage of the chronosequence within the subalpine belt. Macrofossil analysis of charcoal in mineral soils was used to compare the stand-scale fire histories and taxonomic fossil composition of subalpine, old-growth balsam fir stands and white spruce stands. No significant differences of mean number of observed fires (mean = 6.35 fires per site), Holocene fire recurrence at the landscape scale and mean fire-return interval (mean = 580 years) were found between white spruce stands and balsam fir stands. The botanical composition of charcoal fragments from mineral soils showed that Abies, Betula and Picea were present throughout the fire period from 5600 cal. BP to present, and no difference was found in the fossil composition of the balsam fir and white spruce stands. No historical change in the botanical composition of charcoal from soils of both stand types was observed indicating that the initial floristic composition remained through the period of recurrent fires. Charcoal data suggest that white spruce stands are not divergent community types. Rather, the two community types are arranged along a chronosequence of different successional stages within the subalpine relict flora. [ABSTRACT FROM AUTHOR]

Spruce budworm (Choristoneura fumiferana Clem.) (SBW) outbreaks have caused considerable damage to coniferous forests dominated by balsam fir (Abies balsamea [L.] Mill.) or black spruce (Picea mariana [Mill.]). Hence, forecasting SBW-caused mortality of these species is an important step in allowable annual cut calculations of the forest industry in northeastern North America. This study developed prediction models of balsam fir and black spruce mortality caused by SBW and compared SBW-caused mortality of fir and spruce that were growing under similar stand conditions. Zero-inflated models were estimated for the entire range of balsam fir and black spruce in Quebec, Canada, using historical records of insect defoliation and permanent sample plot inventories from 1970 to 2006. Fir and spruce mortality caused by SBW was successfully related to historical records of defoliation through a growth reduction index. Fir mortality increased with the number of years of severe defoliation and was always greater than that of spruce, which appeared to be weakly affected by SBW defoliation. In mixed spruce-fir stands, the total volume of mortality decreased almost linearly with increasing proportions of black spruce. This suggests that thinning aimed to increase spruce proportions could be efficient in reducing overall stand mortality during an SBW outbreak. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to understand the effect of light emitting diodes on postharvest abscission in balsam fir (Abies balsamea L.) branches. In one experiment, branches were pre-exposed to the fluorescent light, LEDs, or darkness for 1, 4, 8, 12, 24, or 48 h. In a second experiment, branches were constantly exposed to fluorescent lights, LEDs, or darkness. The response variable was needle retention duration (NRD). A 48-hour exposure time to red, white, or blue LEDs significantly (P < 0.001) increased NRD by approximately 75, 118, or 127%, respectively, compared to a cool white fluorescent lighting or darkness. Constant exposure to any LED significantly (P < 0.001) improved NRD compared to fluorescent lights or darkness, though white and red LEDs were most effective. It is speculated that LED-promoted needle retention could possibly be due to changes in carbohydrate synthesis similar to those observed during cold acclimation. [ABSTRACT FROM AUTHOR]

Abstract: The intensity and duration of Neodiprion abietis outbreaks have recently increased in forests of North America that were precommercially thinned more than a decade earlier. We tested the hypotheses that changes in stand structure following thinning increase the fitness (i.e., survival rate×fecundity) of N. abietis by either (a) increasing foliar availability and/or quality (i.e., increased availability of primary metabolites and/or reduced foliar defenses) or (b) by reducing any negative effects on foliar quality and/or availability resulting from herbivory that occurred during the preceding season(s). Effects of thinning and previous herbivory on N. abietis and its host plant (Abies balsamea) were determined through (i) a manipulative field experiment that evaluated the effects of experimental defoliation on N. abietis in a thinned stand, (ii) a manipulative field experiment that examined the effects of thinning on N. abietis in undamaged and naturally defoliated stands, and (iii) a field survey to estimate survival of N. abietis in natural populations. Defoliation caused reductions in the availability of different-aged foliage available to larvae and in the fitness of a subsequent N. abietis generation feeding on defoliated branches, but decreases in fitness were smaller in thinned than unthinned stands. In thinned stands, defoliation was associated with increases in foliage production and foliar contents of monoterpenes and nitrogen, as well as with a decrease in foliar contents of water. Conversely, only small changes in plant growth and foliar contents of nutrients and secondary chemicals were observed in defoliated unthinned stands. This suggests that deleterious effects of defoliation on sawfly fitness were offset by an increase in the foliar content of nitrogen, a primary compound known to improve larval growth in sawflies, which supports the hypothesis that thinning moderates negative effects of previous defoliation on sawfly fitness. The present study demonstrates that forestry practices that alter stand structure by reducing tree density may increase herbivory by affecting the way trees respond to insect attack, even after crown closure, with consequences on the buildup of herbivore populations in attacked trees. [Copyright &y& Elsevier]

In balsam fir ( Abies balsamea)-dominated boreal forests of Gros Morne National Park, Newfoundland (Canada), non-native Cirsium arvense (Canada thistle) has invaded forest gaps. Its management is complicated by the lack of viable control techniques and an overarching issue of gap regeneration failure attributed to browsing by non-native moose ( Alces alces). This study identifies the impacts of thistle invasion on balsam fir regeneration and explores protocols to re-establish fir in gaps invaded by thistle and moose. Fir seeds were planted into ten gaps (five natural; five anthropogenic) and the emergence, growth, herbivory damage, and survival of fir was determined for 2 years amongst five treatments ( n = 50 plots; 32 seeds/plot): (1) thistle monocultures in gaps; (2) where aboveground thistle biomass was removed; (3) where above- and below-ground thistle biomass was removed; (4) non-invaded areas in gaps; and, (5) adjacent uninvaded forest edges. In addition, 432 fir seedlings (aged 15 months) were transplanted into four forest gaps within the above treatments and followed for 1 year. Results indicate that invasion of C. arvense negatively affects fir emergence and early survival, and may further contribute to continued balsam fir regeneration failure independent of future moose densities. However, older fir seedlings transplanted into thistle monocultures experienced a positive facilitative effect due to the protection thistle provided against small mammal herbivory. Restoration actions that combine moose density reductions with the planting of fir seedlings offers the most viable long-term strategy to re-establish the native forest canopy in thistle-invaded gaps and would likely lead to the eventual decline of shade-intolerant C. arvense. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Forestry Chronicle is the property of Canadian Institute of Forestry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: This research aims at uncovering the stand-scale Holocene fire history of balsam fir forest stands from two bioclimatic zones of the boreal forest and assessing the existence of a sub-continental shift in past fire activity that could have triggered a change in the Holocene zonal pattern. In eastern Canada, the extant closed-crown boreal forest corresponds to two ecological regions separated along 49°N, the northern black spruce zone and the southern balsam fir zone. We sampled balsam fir stands from the southern fir zone (n =7) and among the northernmost patches of fir forest located far beyond the fir zone boundary, into the spruce zone (n =6). Macrofossil analysis of charcoal in mineral soils was used to reconstruct both the stand-scale and regional Holocene fire histories. Data were interpreted in the context of published palaeoecological evidence. Stands of the balsam fir zone were submitted to recurrent fire disturbances between c. 9000 and 5000cal.yrB.P. Local fire histories suggested that four sites within the fir zone escaped fire during the Holocene. Such fire protected sites allowed the continuous maintenance of the balsam fir forest in the southern boreal landscape. Stands of the spruce zone have been affected by recurrent fires from 5000cal.yrB.P. to present. Local fire histories indicated that no site escaped fire in this zone. Published palaeoecological data suggested that balsam fir migrated to its current northern limit sometime between 7300 and 6200cal.yrB.P. A change of the fire regime 5000 years ago caused the regional decline of an historical northern balsam fir forest and its replacement by black spruce forest. The consequence was a sub-continental reshuffling of the fir and spruce zones within the closed-crown boreal forest. The macrofossil analysis of charcoal in mineral soils was instrumental to the reconstruction of stand-scale Holocene fire history at sites where no other in situ fire proxies were available. [Copyright &y& Elsevier]

Abstract: Hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) is an economically damaging defoliator that undergoes periodic outbreaks in Newfoundland, Canada. It defoliates and causes extensive tree mortality to its primary host, balsam fir (Abies balsamea [L.] Mill.). We quantified tree survival using data from permanent sample plots (PSPs) and growth reduction or release using dendrochronology, and related these impacts to defoliation severity determined from annual aerial defoliation survey data. Such impact relationships are necessary as a fundamental input to a Decision Support System. Growth and survival of balsam fir, black spruce (Picea mariana (Mill.) B.S.P.) and white birch (Betula papyrifera Marsh.) were assessed from 1996 to 2008 in 48 Newfoundland Forest Service PSPs, selected based on four classes of defoliation severity. Two years of severe (71–100%) defoliation resulted in almost complete mortality for balsam fir, 10 years after defoliation, whereas survival was 70–80% for black spruce and white birch. Lower defoliation severity (1–2 years of moderate (31–70%) or 1 year of severe) resulted in approximately 60% survival for balsam fir and no reduction in survival for black spruce and white birch. Maximum growth reduction of balsam fir was 10–15% with 1 year of moderate-severe defoliation, 35–40% with 2 years of moderate defoliation, and about 50% with 2 years of severe defoliation. Growth recovered to pre-defoliation rates 5 years after defoliation ceased in all severity classes. Growth reduction and recovery of black spruce were more variable and lower than for balsam fir, and white birch exhibited only minor (<10%) growth reduction during the defoliation year or 1 year after defoliation. Control measures should focus on avoiding severe defoliation for two consecutive years. [Copyright &y& Elsevier]

Stem or branch failure is a recurrent problem in silviculture and arboriculture. The risk of rupture varies with species in relation to the inherent mechanical properties of the species and the presence of defects. In general, calculations of critical loads for breakage are based on mechanical properties determined from defect-free samples and adjustment factors that try to scale up to full trees that include defects. This study aims at developing an objective method to scale up mechanical resistance to breakage from defect-free samples to full trees, including different types of defects. It combines two approaches. In the first one, a correction factor is determined from a meta-analysis of various tree-pulling studies involving balsam fir [ Abies balsamea (L.) Mill.], white spruce [ Picea glauca (Moench) Voss], jack pine [ Pinus banksiana Lamb.], and black spruce [ Picea mariana (Mill.) B.S.P.]. The second approach consists in obtaining empirical data from three-point bending tests using 8-foot (2.44 m) logs with various amounts of decay. Results show that the correction required varies according to the species and the presence of some defects. For balsam fir, which was the species showing the most important difference between whole log and small sample values, differences in correction factors were found between tree-pulling tests and three-point bending tests. Data from winching tests tend to underestimate the stem's resistance to breakage since they likely represent the weakest trees among those tested. No relationship was found between the adjustment factors and different indices used in arboriculture to account for decay, showing the complexity of mechanical resistance at the stem level. [ABSTRACT FROM AUTHOR]

Post-harvest needle abscission is a major challenge for Christmas tree and greenery industries. It was hypothesized that ethylene triggers abscission in balsam fir. Three experiments were conducted to test this hypothesis. In experiment 1, 70 balsam fir branches were collected, placed in water, and ethylene evolution was observed over time. In experiment 2, a 2 × 5 factorial experiment was designed to determine the effect of exogenous ethylene and an ethylene receptor blocker, 1-methylcyclopropene (1-MCP), on needle abscission. In experiment 3, a 2 × 6 factorial experiment was designed to determine the effect of exogenous ethylene and an ethylene inhibitor, aminoethoxyvinylglycine (AVG), on needle abscission. It was found that ethylene evolution was the highest 1–2 days prior to needle abscission, which was consistent in untreated branches and branches exposed to exogenous ethylene. Exposure to exogenous ethylene significantly decreased needle retention by 63%. When ethylene receptors were blocked by 1-MCP, needle retention increased by 147% despite the presence of ethylene and increased by 73% in the absence of ethylene when compared to the respective controls. When endogenous ethylene synthesis was inhibited by AVG, there was no improvement in needle retention in the presence of ethylene, but there was a 113% increase in needle retention in the absence of exogenous ethylene. Ethylene is strongly implicated as the signal triggering abscission in root-detached balsam fir. [ABSTRACT FROM AUTHOR]

ociations among the few tree species in the North American boreal landscape are the result of complex interactions between climate, biota, and historical disturbances during the Holocene. The closed-crown boreal forest of eastern North America is subdivided into two ecological regions having distinct tree species associations; the balsam fir zone and the black spruce zone, south and north of 49°N, respectively. Subalpine old-growth stands dominated by trees species typical of the balsam fir forest flora (either balsam fir or white spruce) are found on high plateaus, some of which are isolated within the black spruce zone. Here we identified the ecological processes responsible for the distinct forest associations in the subalpine belt across the eastern boreal landscape. Extensive radiocarbon dating, species composition, and size structure analyses indicated contrasted origin and dynamics of the subalpine forests between the two ecological regions. In the black spruce zone, the subalpine belt is a mosaic of post-fire white spruce or balsam fir stands coexisting at similar elevation on the high plateaus. With increasing time without wildfire, the subalpine forests become structurally similar to the balsam fir forest of the fir zone. These results concur with the hypothesis that the subalpine forests of this area are protected remnants of an historical northern expansion of the fir zone. Its replacement by the fire-prone black spruce forest flora was caused by recurrent fires. In the subalpine belt of the fir zone, no fire was recorded for several millennia. Harsh climate at high altitude is the primary factor explaining white spruce dominance over balsam fir forming a distinct subalpine white spruce belt above the balsam fir dominated forest. [ABSTRACT FROM AUTHOR]

The ability to model forest distributions in light of anthropogenic disturbance requires a thorough understanding of how trees respond to their physical and climatic environment. The primary objective of this study is to determine how four environmental variables (elevation, latitude, slope angle, and slope aspect) affect the distribution of seven common tree species (Acer saccharum, Betu!a alleghaniensis, Betula papyifera, Abies balsamea, Picea glauca, Thuja occidentalis, and Acer spicatum) using both regression tree analysis (RTA) and canonical correspondence analysis (CCA) techniques. In general, within the study area, Acer saccharum, Abies balsamea, and Thuja occidentalis abundance was controlled by elevation and latitude, whereas the other species showed limited response to the measured environmental variables. While CCA and RTA showed similar patterns, RTA allows for a more nuanced evaluation of species-environment interactions. Given that the study area encompasses Acer saccharum's northern limit, there were differences in the response of Abies balsamea to environmental conditions in the absence of Acer saccharum. [ABSTRACT FROM AUTHOR]

Abstract: The eastern Canadian boreal forest exhibits a specific disturbance regime where forest fires are less frequent than in the western part. This particularity may explain the abundance of irregular stands with distinct ecological features. To ensure sustainable forest management, these characteristics require the implementation of an adapted silviculture regime. In this context, two selection cutting methods were developed and compared with more conventional techniques, initially designed for cutting more regular stands of the boreal forest (cutting leaving small merchantable stems, careful logging preserving advance regeneration). The comparison focused on the capacity of treatments to maintain the primary attributes of irregular boreal forests, including complex vertical structure, abundant tree cover, species composition, and an abundance of dead wood. Mortality and regeneration processes were also compared. The experiment includes three sectors dominated by irregular black spruce (Picea mariana)-balsam fir (Abies balsamea) stands. Treatments were replicated in each sector in 0.25ha plots. Stand characteristics were sampled pre-harvest and monitored for 3 years after cutting. Initial results indicate an important treatment effect on residual structure. Selection cutting maintains an inverse (irregular) J-shaped structure, typical of natural stands. Also, selection cutting does not seem to produce a significant effect on tree species composition (no undesired balsam fir enrichment) and does not modify the abundance of coarse woody debris. From a sustainable forest management perspective, the selection methods tested appear efficient in maintaining the main attributes and processes of the boreal irregular stands over the short term. [Copyright &y& Elsevier]

When an herbivorous insect enters a new geographic area, it will select host plants based on short and long distance cues. A conifer-feeding bark beetle that has been recently introduced to North America, the Mediterranean pine engraver, Orthotomicus erosus (Wollaston), has a potentially wide host range, especially among members of the Pinaceae. The long-distance response of the beetles to tree odors may be a key feature of the mechanism of host recognition and selection. We used a laboratory olfactometer to study the walking response of 1,440 O. erosus to odor cues from the bark and phloem of six North American tree species. The beetle moved toward the angiosperm non-host Betula papyrifera more than would be expected by chance, but had a neutral response to odors of two tree species that support reproduction and three species that do not. These results suggest that tree odors alone may not be adequate for O. erosus to recognize novel hosts. [ABSTRACT FROM AUTHOR]

Copyright of Forestry Chronicle is the property of Canadian Institute of Forestry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article presents the study on the cost effectiveness of bacterial insecticide Bacillus thuringienses ssp. Kurstaki (Btk) on the defoliation of spruce budworm (SBW) Choristoneura fumiferana on balsam fir trees. The study has evaluated the growth loss and mortality to find out their contributions on the total losses in each tree treatment category. The result reveals that Btk is able to reduce growth loss impacts caused by SBW. It further concludes that Btk treatments has economic advantage.

Emulation of natural disturbance processes and their effects is important to maintain the structure and composition of managed forests. To examine whether logging and fire have different effects on natural regeneration, we studied the recruitment of six common boreal tree species ( Populus tremuloides, Betula papyrifera, Pinus banksiana, Picea mariana, Picea glauca, and Abies balsamea) after fire and clearcutting in northern Ontario. Regeneration densities of all studied species, except P. glauca and A. balsamea, were positively related to their respective pre-disturbance basal area. Post-disturbance regeneration densities of P. tremuloides and P. banksiana did not differ between disturbance types, whereas those of B. papyrifera were higher after fire, and those of P. mariana and A. balsamea were higher after clearcutting. Among tree species, the composition of P. tremuloides increased by approximately 35% after both disturbance types, that of B. papyrifera increased by 22% after fire and 11% after clearcutting, whereas those of P. banksiana, P. mariana, P. glauca, and A. balsamea decreased to various extents. Compared with fire, clearcutting significantly increased the post-disturbance presence of A. balsamea, which is attributed to surviving advance regeneration after logging. The natural regeneration process after fire appears to be emulated by clearcutting for P. tremuloides, P. banksiana, P. mariana, and P. glauca, but the increase in B. papyrifera after clearcutting is less pronounced than after fire, whereas the reduction of A. balsamea after clearcutting is less severe than after fire. [ABSTRACT FROM AUTHOR]

Landscape heterogeneity influences large herbivores by altering their feeding rates, but as herbivores attempt to maximize feeding rates they also create spatial heterogeneity by altering plant growth. Herbivore feeding rates thus provide a quantitative link between the causes and consequences of spatial heterogeneity in herbivore-dominated ecosystems. The fractal geometry of plant canopies determines both the density and mass of twigs available to foraging herbivores. These properties determine a threshold distance between plants (d*) that distinguishes the mechanisms regulating herbivore intake rates. When d* is greater than the actual distance between plants (d), intake is regulated by the rate of food processing in the mouth. But when d* < d, intake is regulated by the rate at which the herbivore encounters new plants. Alterations to plant geometry due to past browsing could change the rate at which herbivores encounter and process bites of plant tissue, modify d* relative to d, and thus change intake rates and the distribution of mechanisms regulating it across landscapes. We measured changes in the geometry of aspen (Populus tremuloides) and balsam fir (Abies balsamea) saplings along gradients of moose browsing from 2001 to 2005 at Isle Royale National Park, Michigan, USA. For aspen saplings, fractal dimension of bite density, bite mass and forage biomass responded quadratically to increasing moose browsing and were greatest at ~3-4 g.m-2.yr-1 consumption. For balsam fir, in contrast, these same measures declined steadily with increasing moose browsing. The different responses of plant canopies to increased browsing altered d* around plants. In summer, d* ≥ d for aspen saplings at all prior consumption levels. Food processing therefore regulated summer moose feeding rates across our landscapes. In winter, changes in bite mass due to past browsing were sufficient to cause d* < d for aspen and balsam fir. Therefore, travel velocity and food processing jointly regulated intake rate during winter. Browsing-induced changes in the small-scale geometry of plant canopies can determine intake rate at larger spatial scales by changing d* relative to d and, hence, which mechanisms determine intake rate, essentially altering how herbivores sense the distribution of their food resources. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of spruce budworm (Choristoneura fumiferana) on balsam fir (Abies balsamea) and white spruce (Picea glauca) at Itasca State Park in northwestern Minnesota. We studied the species composition, age structure, and radial growth patterns in tree rings along five belt transects at sites infested with spruce budworm. Our objectives were to: (1) discover when the latest spruce budworm outbreak started; (2) determine whether tree growth was similarly reduced in earlier decades, suggesting earlier spruce budworm outbreaks; and (3) test whether radial tree growth and the start of the outbreak(s) were correlated with climate. We used the computer program OUTBREAK to determine that the current spruce budworm infestation began to reduce tree growth in the 1 990s, before it was detected by park officials in 2001. The tree-ring record indicated that growth of the host-species trees was periodically reduced at all sites prior to the 1990s. We found no consistent relationship between temperature/ precipitation and the initiation of spruce budworm outbreaks, as reconstructed by the OUTBREAK program, at the southwestern edge of the distribution of balsam fir. The Palmer Drought Severity Index, however, was positive (i.e., wetter-than-normal conditions) before increased spruce budworm activity at all sites. Outbreaks are related to climatic conditions, but they also depend on other factors such as the availability of sufficient food for the spruce budworm. [ABSTRACT FROM AUTHOR]