Search

The identification of climate anomalies associated with large-scale stand disturbances can help inform climate-focused forest management. In the spring and summer of 2018, an unusual spike in balsam fir (Abies balsamea) mortality was reported in multiple areas across its southern distribution range limit, from Wisconsin, United States, to New Brunswick, Canada. Such an event was previously reported in 1986 in the study region and referred to as Stillwell's Syndrome. To identify the role of climate anomalies in the 2018 event, we used monthly climate anomalies as explanatory variables in a Random Forest model predicting the presence of mortality from air and field-based surveys across the Maritimes region of eastern Canada. Results were validated by (1) comparing common climate predictors of mortality from this model and a separate Random Forest model fitted on the 1986 event, and (2) using the 2018 model to predict areas of mortality in 1986. Both the 1986 and 2018 models identified multiple common climate anomalies. Areas with unusually high water deficit and temperatures in the previous growing season, followed by thick April snowpack and high May temperatures the same year, were associated with balsam fir mortality. Such climate anomalies have been previously associated with water stress and desiccation in trees. When using the 2018 model to map the occurrence of mortality in 1986 using historical climate data, we report a 95% accuracy in prediction (kappa = 0.88). The approach used here in conjunction with mapped records of past stand disturbances could help with understanding the impacts of future climate anomalies and adaptive management strategies to deal with these events. [ABSTRACT FROM AUTHOR]

The identification of climate anomalies associated with large-scale stand disturbances can help inform climate-focused forest management. In the spring and summer of 2018, an unusual spike in balsam fir (Abies balsamea) mortality was reported in multiple areas across its southern distribution range limit, from Wisconsin, United States, to New Brunswick, Canada. Such an event was previously reported in 1986 in the study region and referred to as Stillwell’s Syndrome. To identify the role of climate anomalies in the 2018 event, we used monthly climate anomalies as explanatory variables in a Random Forest model predicting the presence of mortality from air and field-based surveys across the Maritimes region of eastern Canada. Results were validated by (1) comparing common climate predictors of mortality from this model and a separate Random Forest model fitted on the 1986 event, and (2) using the 2018 model to predict areas of mortality in 1986. Both the 1986 and 2018 models identified multiple common climate anomalies. Areas with unusually high water deficit and temperatures in the previous growing season, followed by thick April snowpack and high May temperatures the same year, were associated with balsam fir mortality. Such climate anomalies have been previously associated with water stress and desiccation in trees. When using the 2018 model to map the occurrence of mortality in 1986 using historical climate data, we report a 95% accuracy in prediction (kappa = 0.88). The approach used here in conjunction with mapped records of past stand disturbances could help with understanding the impacts of future climate anomalies and adaptive management strategies to deal with these events.

Aim: Seedling recruitment is a vital process for forest regeneration and is influenced by various factors such as stand composition, climate, and soil disturbance. We conducted a long‐term field experiment (18 years) to study the effects of these factors and their interactions on seedling recruitment. Location: Our study focused on five main species in boreal mixed woods of eastern Canada: trembling aspen (Populus tremuloides), paper birch (Betula papyrifera), white spruce (Picea glauca), balsam fir (Abies balsamea), and white cedar (Thuja occidentalis). Methods: Sixteen 1‐m2 seedling monitoring subplots were set up in each of seven stands originating from different wildfires (fire years ranging from 1760 to 1944), with a soil scarification treatment applied to every other subplot. Annual new seedling counts were related to growing‐season climate (mean temperature, growing degree days and drought code), scarification, and stand effects via a Bayesian generalized linear mixed model. Results: Soil scarification had a large positive effect on seedling recruitment for three species (aspen, birch and spruce). As expected, high mean temperatures during the seed production period (two years prior to seedling emergence) increased seedling recruitment for all species but aspen. Contrary to other studies, we did not find a positive effect of dry conditions during the seed production period. Furthermore, high values of growing degree days suppressed conifer seedling recruitment. Except for white cedar, basal area was weakly correlated with seedling abundance, suggesting a small number of reproductive individuals is sufficient to saturate seedling recruitment. Conclusion: Our findings underscore the importance of considering multiple factors, such as soil disturbance, climate, and stand composition, as well as their effects on different life stages when developing effective forest management strategies to promote regeneration in boreal mixed‐wood ecosystems. [ABSTRACT FROM AUTHOR]

In this investigation, the effects of exogenous indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), and 1-aminocyclopropane-1-carboxylic acid (ACC) on anatomical development within cultured segments of Abies balsamea (L.) Mill. were compared, using debudded and defoliated leaders produced in the preceding year as bioassay material. In stem apical regions, IAA promoted radial enlargement of pre-existing cortical resin ducts and attending parenchyma enlargement, whereas IBA promoted cell division and expansion of parenchyma on the outer edge of phloem without altering cortical duct shape. Cortical woody ducts, each partially surrounded by cambium, were observed as a novel but infrequent feature. A single cortical woody duct was spatially associated with each mature leaf as its vascular trace, and they were not encountered elsewhere in the cortex, nor were they induced to form in response to any hormone application. An unknown leaf factor induces the development of cortical woody ducts. Both IAA and IBA promoted cell division in the vascular cambium. The common cellular response at the interface between the latewood boundary and cambial zone was the radial expansion of primary-walled fusiform cambial cell derivatives with little if any ensuing tracheary element (TE) differentiation. Enhanced TE production at basal stem positions occurred when ACC was provided with IAA and/or IBA, and an IAA + IBA + ACC combination produced a basal stem response similar to that in untreated segments having intact leaves. The data support the conclusion that IAA, IBA, and ACC have distinct but complementary roles in the overall regulation of the types of cellular differentiation that contribute to cortex histogenesis and diameter growth of balsam-fir leaders.

In boreal old-growth forests, advance regeneration typically attains canopy dominance through growth release events following partial disturbances. We sampled competing Picea mariana (Mill.) and Abies balsamea (L.) in disturbed old-growth stands in Quebec, Canada, to understand the intra- and interspecific size hierarchy development. We reconstructed tree size development and examined the role of initial size difference, time between germination and a disturbance, and the strength of response to the disturbance in determining tree size hierarchies. Trees that regenerated first generally dominated their intraspecific competitors also following a disturbance event. However, prolonged time between germination and disturbance resulted in a less deterministic outcome. Tree size difference prior to disturbance also influenced the development of size hierarchies. In interspecific competition between individuals of the same diameter, A. balsamea had a 61% probability of gaining dominance over P. mariana, the probability being 50% if P. mariana was 5 mm larger than A. balsamea. Dominant trees generally had the strongest response to the disturbance, reinforcing the existing size hierarchies. The largest trees typically gain dominance after a partial disturbance. However, interspecific competition is less predictable than intraspecific competition, small initial size difference, and prolonged time in suppression potentially changing tree size hierarchies. [ABSTRACT FROM AUTHOR]

Needle abscission in balsam fir has been linked to both cold acclimation and changes in lipid composition. The overall objective of this research is to uncover lipid changes in balsam fir during cold acclimation and link those changes with postharvest abscission. Branches were collected monthly from September to December and were assessed for cold tolerance via membrane leakage and chlorophyll fluorescence changes at −5, −15, −25, −35, and −45 °C. Lipids were extracted and analyzed using mass spectrometry while postharvest needle abscission was determined gravimetrically. Cold tolerance and needle retention each significantly (p < 0.001) improved throughout autumn in balsam fir. There were concurrent increases in DGDG, PC, PG, PE, and PA throughout autumn as well as a decrease in MGDG. Those same lipids were strongly related to cold tolerance, though MGDG had the strongest relationship (R2 = 55.0% and 42.7% from membrane injury and chlorophyll fluorescence, respectively). There was a similar, albeit weaker, relationship between MGDG:DGDG and needle retention (R2 = 24.3%). Generally, a decrease in MGDG:DGDG ratio resulted in better cold tolerance and higher needle retention in balsam fir, possibly due to increased membrane stability. This study confirms the degree of cold acclimation in Nova Scotian balsam fir and presents practical significance to industry by identifying the timing of peak needle retention. It is suggested that MGDG:DGDG might be a beneficial tool for screening balsam fir genotypes with higher needle retention characteristics. [ABSTRACT FROM AUTHOR]

A study was conducted to identify balsam fir (Abies balsamea) for use in Christmas tree breeding programs in Northeastern North America. A total of sixty-four phenotypically good trees were identified from a provincial clonal seed orchard in New Brunswick, a multi-aged natural seed production area in Nova Scotia, and an operational plantation in Quebec, Canada. Trees were selected for good growth and form, numbers, and vigour of internodal branches, acceptable crown taper, needle colour, age class, branch angle, needle configuration, and freedom from insects and diseases or deformities, all traits deemed desirable in a Christmas tree. Three branches from each tree were collected at two harvest dates each year, one early and one late during the normal harvesting season in 2020, 2021, and 2022. Qualitative assessments of colour and branch pliability were performed weekly in conjunction with needle loss rub tests. A quantitative assessment of moisture loss was conducted weekly by measuring branch weights. The combination of qualitative and quantitative assessments was used to identify 7 of the 64 trees for which one or more tested branches consistently remained green and pliable, retained the majority of their needles, and lost moisture at a significantly reduced rate in all six testing periods. Grafts of the seven 'Select' trees are currently being integrated into seed orchards in the three participating provinces. These second-generation seed orchards are part of breeding programs designed to develop Christmas trees that will perform well under warm fall conditions, an outcome of climate change. The results from this study combined with the progeny testing of the 'Select' trees will be used to test for the heritability of needle retention, a key trait for the next generation of Christmas trees in the Northeast. [ABSTRACT FROM AUTHOR]

Natural root grafts (anastomoses) are morphological unions formed between roots of different trees. Common root systems allow translocation of water, nutrients and photosynthesis products between grafted trees, affecting their growth and their physiology. As carbohydrates are redistributed among grafted trees, the formation of a common root system could reduce the negative effect of intraspecific competition for light or soil resources within stands. The aim of this study was to investigate the role of root grafting on intraspecific competition and growth of balsam fir Abies balsamea. We studied inter‐tree relationships in three natural balsam fir stands of the boreal forest of Quebec (Canada) that contained an average 36% of grafted trees. At each stand, ring width and basal area of trees were measured using dendrochronology techniques. We used mixed linear models to test the effect of root grafting and intraspecific competition on annual basal area increment of trees. Trees before grafting had higher growth rates than trees once grafted. Thus, root grafting did not improve tree growth. Growth of grafted trees was more negatively affected by intraspecific competition than growth of non‐grafted trees. Thus, grafted trees cannot be considered as better competitors than non‐grafted trees. Under high intraspecific competition, growth of larger grafted trees was less affected than that of smaller trees suggesting that they were able to divert resources at their advantage within a union. Our study demonstrated that grafted trees acted on each other's growth and provides support for the idea that grafted trees respond to competition for resources more as a community rather than as individual trees. [ABSTRACT FROM AUTHOR]

Background and Aims Upscaling carbon allocation requires knowledge of the variability at the scales at which data are collected and applied. Trees exhibit different growth rates and timings of wood formation. However, the factors explaining these differences remain undetermined, making samplings and estimations of the growth dynamics a complicated task, habitually based on technical rather than statistical reasons. This study explored the variability in xylem phenology among 159 balsam firs [ Abies balsamea (L.) Mill.]. Methods Wood microcores were collected weekly from April to October 2018 in a natural stand in Quebec, Canada, to detect cambial activity and wood formation timings. We tested spatial autocorrelation, tree size and cell production rates as explanatory variables of xylem phenology. We assessed sample size and margin of error for wood phenology assessment at different confidence levels. Key Results Xylem formation lasted between 40 and 110 d, producing between 12 and 93 cells. No effect of spatial proximity or size of individuals was detected on the timings of xylem phenology. Trees with larger cell production rates showed a longer growing season, starting xylem differentiation earlier and ending later. A sample size of 23 trees produced estimates of xylem phenology at a confidence level of 95 % with a margin of error of 1 week. Conclusions This study highlighted the high variability in the timings of wood formation among trees within an area of 1 km2. The correlation between the number of new xylem cells and the growing season length suggests a close connection between the processes of wood formation and carbon sequestration. However, the causes of the observed differences in xylem phenology remain partially unresolved. We point out the need to carefully consider sample size when assessing xylem phenology to explore the reasons underlying this variability and to allow reliable upscaling of carbon allocation in forests. [ABSTRACT FROM AUTHOR]

Eastern spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), is a major pest of eastern North American forests. Outbreaks of spruce budworm occur every 30–40 years, causing high tree mortality.Researchers have established that higher proportions of hardwood trees within stands (higher hardwood content) may reduce the defoliation and mortality of balsam fir and spruces during spruce budworm outbreaks. One mechanism posited to explain these patterns is that hardwood trees positively impact the parasitoids of spruce budworm. Indeed, parasitism of spruce budworm by parasitoids has been found to be impacted by hardwood content. However, more research is needed to understand how hardwood content impacts the parasitoid community as a whole.In this study, we trialled the use of two analyses, phylogenetic community structure and stable isotope analysis, to examine how hardwood content influenced the parasitoid community associated with spruce budworm.We found that phylogenetic community structure differed between forest stands with different hardwood content. Furthermore, the trophic relationships between several parasitoids and caterpillars on balsam fir or hardwood trees changed within and between years.Our study highlights the potential of these two analyses for understanding how hardwood content influences the parasitoid community associated with spruce budworm. [ABSTRACT FROM AUTHOR]

Needle abscission in balsam fir has been linked to both cold acclimation and changes in lipid composition. The overall objective of this research is to uncover lipid changes in balsam fir during cold acclimation and link those changes with postharvest abscission. Branches were collected monthly from September to December and were assessed for cold tolerance via membrane leakage and chlorophyll fluorescence changes at −5, −15, −25, −35, and −45 °C. Lipids were extracted and analyzed using mass spectrometry while postharvest needle abscission was determined gravimetrically. Cold tolerance and needle retention each significantly (p < 0.001) improved throughout autumn in balsam fir. There were concurrent increases in DGDG, PC, PG, PE, and PA throughout autumn as well as a decrease in MGDG. Those same lipids were strongly related to cold tolerance, though MGDG had the strongest relationship (R2 = 55.0% and 42.7% from membrane injury and chlorophyll fluorescence, respectively). There was a similar, albeit weaker, relationship between MGDG:DGDG and needle retention (R2 = 24.3%). Generally, a decrease in MGDG:DGDG ratio resulted in better cold tolerance and higher needle retention in balsam fir, possibly due to increased membrane stability. This study confirms the degree of cold acclimation in Nova Scotian balsam fir and presents practical significance to industry by identifying the timing of peak needle retention. It is suggested that MGDG:DGDG might be a beneficial tool for screening balsam fir genotypes with higher needle retention characteristics.

A study was conducted to identify balsam fir (Abies balsamea) for use in Christmas tree breeding programs in Northeastern North America. A total of sixty-four phenotypically good trees were identified from a provincial clonal seed orchard in New Brunswick, a multi-aged natural seed production area in Nova Scotia, and an operational plantation in Quebec, Canada. Trees were selected for good growth and form, numbers, and vigour of internodal branches, acceptable crown taper, needle colour, age class, branch angle, needle configuration, and freedom from insects and diseases or deformities, all traits deemed desirable in a Christmas tree. Three branches from each tree were collected at two harvest dates each year, one early and one late during the normal harvesting season in 2020, 2021, and 2022. Qualitative assessments of colour and branch pliability were performed weekly in conjunction with needle loss rub tests. A quantitative assessment of moisture loss was conducted weekly by measuring branch weights. The combination of qualitative and quantitative assessments was used to identify 7 of the 64 trees for which one or more tested branches consistently remained green and pliable, retained the majority of their needles, and lost moisture at a significantly reduced rate in all six testing periods. Grafts of the seven ‘Select’ trees are currently being integrated into seed orchards in the three participating provinces. These second-generation seed orchards are part of breeding programs designed to develop Christmas trees that will perform well under warm fall conditions, an outcome of climate change. The results from this study combined with the progeny testing of the ‘Select’ trees will be used to test for the heritability of needle retention, a key trait for the next generation of Christmas trees in the Northeast.

Plants under water stress alter their normal morphological and physiological processes. However, biomass allocation and nutrient use efficiency remain largely unknown under the interactive effect of irrigation and fertilization for many economically important conifer species. In this study, we compared biomass allocation and resources use efficiency of two-year-old (plug+1) containerized balsam fir [Abies balsamea (L) Mill.] 'Cooks' and concolor fir [Abies concolor (Gord. & Glend.) Lindl. Ex Hildebr.] 'Cibola', and one-year-old bare-root white pine [Pinus strobus L.] transplants grown under variable watering and fertilization conditions. In a controlled greenhouse setting, transplants were submitted to three irrigation levels and two fertilization rates in a factorial experimental design. Fir species, mainly concolor fir, had a greater capacity to utilize water resulting in decreased stem water potential than white pine, leading to increased aboveground growth and shoot-to-root (S/R) ratio. White pine transplants had a higher assimilatory nutrient efficiency, nutrient use efficiency (NUE), root weight ratio, and a lower nitrogen availability index than the two fir species, suggesting a better ability to tolerate water stress. The high rates of fertilization increased nutrient concentration more than growth, suggesting luxury consumption. These results indicate that white pine responds to drought stress by closing their stomata and decreasing their S/R ratio to limit physiological activities, while the two fir species exhibit increased water uptake via expanded fine root networks, increasing the NUE and S/R ratio. However, there was no clear trend for the irrigation and fertilization interaction for NUE for three species, making it difficult to generalize responses. [ABSTRACT FROM AUTHOR]

Lowland northern white-cedar (Thuja occidentalis) forests are increasingly exposed to extreme droughts and floods that cause tree mortality. However, it is not clear the extent to which these events may differentially affect regeneration of cedar and its increasingly common associate, balsam fir (Abies balsamea). To test this, we measured how seedlings of cedar and fir were able to avoid, resist, and recover from experimental drought and flood treatments of different lengths (8-66 days). Overall, we found that cedar exhibited a strategy of stress resistance and growth recovery (resilience) from moderate drought and flood stress. Fir, on the other hand, appears to be adapted to avoid drought and flood stress and exhibited overall lower growth resilience. In drought treatments, we found evidence of different stomatal behaviors. Cedar used available water quickly and therefore experienced more drought stress than fir but cedar was able to survive at water potentials > 3 MPa below key hydraulic thresholds. On the other hand, fir employed a more conservative water use strategy and therefore avoided extremely low water potential. In response to flood treatments, cedar survival was higher and only reached 50% if exposed to 23.1 days of flooding in contrast to only 7.4 days to reach 50% mortality for fir. In both droughts and floods, many stressed cedar were able to maintain partially brown canopies and often survived the stress, albeit with reduced growth, suggesting a strategy of resistance and resilience. In contrast, fir that experienced drought or flood stress had a threshold-type responses and they either had full live canopies with little effect on growth or they died suggesting reliance on a strategy of drought avoidance. Combined with increasingly variable precipitation regimes, seasonal flooding, and complex microtopography that can provide safe sites in these forests, these results inform conservation and management of lowland cedar stands., (Published by Oxford University Press 2024.)

Balsam fir needle retention and fatty acid profile changes due to cold acclimation throughout autumn, but little is known about the relationship between these two phenomena. The objective was to examine differences in FAs in contrasting needle abscission resistant balsam fir genotypes throughout autumn and early winter. Branches from genotypes with low and high needle abscission resistance (NAR) were collected from September to January and analyzed for FA composition. High NAR genotypes retained needles 120–130% longer than low NAR genotypes and NAR increased through autumn in both genotypes. There was approximately a 3:1 ratio of unsaturated: saturated FAs, which increased by 4% in favor of unsaturated fatty acids through autumn. Palmitic, palmitoleic, and linolenic acid content was significantly higher in high NAR versus low NAR genotypes; arachidic, oleic, linoleic, pinolenic, coniferonic, icosadienoic, and sciadonic acids were lower in high NAR genotypes versus low. Linolenic acid was of particular interest because it tended to decrease throughout autumn, to the point that high NAR genotypes were significantly lower in linolenic acid than low NAR genotypes in January. These changes may be linked to an increase in abscisic acid and/or jasmonic acid synthesis depleting linolenic acid stores and promoting postharvest needle abscission resistance. [ABSTRACT FROM AUTHOR]

Spruce–fir (Picea–Abies) forests of the North American Acadian Forest Region are at risk of disappearing from the northeastern United States and Canada due to climate change. Species distribution models (SDMs) have been used to predict changes in this critical transitional ecosystem in the past, but none have addressed how seasonal patterns of temperature and precipitation interact to influence tree species abundance. Inferences have also been limited by contemporary inventory data that could not fully characterize species ranges because they either, (1) only sampled species occurrence after large‐scale human disturbance and settlement, or (2) did not span critical geopolitical boundaries (e.g., the US–Canadian border) that intersect the focal species' range(s). Here, we built new SDM models to better assess the bioclimatic distribution of four spruce–fir species and to test the importance of seasonal climate interactions. We compiled an extensive database of tree occurrence and abundance from recent (~1955–2012) and historical time periods (1623–1869) to model current species distributions and to predict how these might change under future climate. We found that including historical tree data in our SDMs revealed previously unrecognized suitable habitat along the southern edge of species' contemporary ranges. Random forest models predicted occurrence with high accuracy (area under receiver operator curve >0.98), and the seasonal climate variables that emerged as most important for these cold‐adapted species all included interactions that reflected sensitivity to colder temperatures, and preferences for wet weather concentrated in the winter months. Under moderate climate warming (representative concentration pathway 6.0), the northeastern United States retained additional suitable habitat when historical data were included through 2060 for three of the four species: red spruce (Picea rubens), black spruce (Picea mariana), and balsam fir (Abies balsamea), while white spruce (Picea glauca) habitat contracted into Canada. In contrast, future predictions from models that used contemporary data alone forecast extirpation for all four species from the northeastern United States. Overall, these findings highlight that prediction of species ranges in transitional ecosystems that span geopolitical boundaries and gradients of intense land use are improved when historical data and seasonal climate interactions of both temperature and precipitation variables are incorporated. [ABSTRACT FROM AUTHOR]

Abstract Spruce–fir (Picea–Abies) forests of the North American Acadian Forest Region are at risk of disappearing from the northeastern United States and Canada due to climate change. Species distribution models (SDMs) have been used to predict changes in this critical transitional ecosystem in the past, but none have addressed how seasonal patterns of temperature and precipitation interact to influence tree species abundance. Inferences have also been limited by contemporary inventory data that could not fully characterize species ranges because they either, (1) only sampled species occurrence after large‐scale human disturbance and settlement, or (2) did not span critical geopolitical boundaries (e.g., the US–Canadian border) that intersect the focal species' range(s). Here, we built new SDM models to better assess the bioclimatic distribution of four spruce–fir species and to test the importance of seasonal climate interactions. We compiled an extensive database of tree occurrence and abundance from recent (~1955–2012) and historical time periods (1623–1869) to model current species distributions and to predict how these might change under future climate. We found that including historical tree data in our SDMs revealed previously unrecognized suitable habitat along the southern edge of species' contemporary ranges. Random forest models predicted occurrence with high accuracy (area under receiver operator curve >0.98), and the seasonal climate variables that emerged as most important for these cold‐adapted species all included interactions that reflected sensitivity to colder temperatures, and preferences for wet weather concentrated in the winter months. Under moderate climate warming (representative concentration pathway 6.0), the northeastern United States retained additional suitable habitat when historical data were included through 2060 for three of the four species: red spruce (Picea rubens), black spruce (Picea mariana), and balsam fir (Abies balsamea), while white spruce (Picea glauca) habitat contracted into Canada. In contrast, future predictions from models that used contemporary data alone forecast extirpation for all four species from the northeastern United States. Overall, these findings highlight that prediction of species ranges in transitional ecosystems that span geopolitical boundaries and gradients of intense land use are improved when historical data and seasonal climate interactions of both temperature and precipitation variables are incorporated.

In the long term, defoliation strongly decreases tree growth and survival. Insect outbreaks are a typical cause of severe defoliation. Eastern spruce budworm (Choristoneura fumiferana Clem.) outbreaks are one of the most significant disturbances of Picea and Abies boreal forests. Nevertheless, in boreal conifers, a 2-year defoliation has been shown to quickly improve tree water status, protect the foliage and decrease growth loss. It suggests that defoliation effects are time-dependent and could switch from favorable in the short term to unfavorable when defoliation duration exceeds 5–10 years. A better understanding of the effect of defoliation on stem radius variation during the needle flushing time-window could help to elucidate the relationships between water use and tree growth during an outbreak in the medium term. This study aims to assess the effects of eastern spruce budworm (Choristoneura fumiferana Clem.) defoliation and bud phenology on stem radius variation in black spruce [Picea mariana (Mill.) B.S.P.] and balsam fir [Abies balsamea (L.) Mill.] in a natural stand in Quebec, Canada. We monitored host and insect phenology, new shoot defoliation, seasonal stem radius variation and daytime radius phases (contraction and expansion) from 2016 to 2019. We found that defoliation significantly increased stem growth at the beginning of needle flushing. Needles flushing influenced the amplitude and duration of daily stem expansion and contraction, except the amplitude of stem contraction. Over the whole growing season, defoliation increased the duration of stem contraction, which in turn decreased the duration of stem expansion. However, the change (increase/decrease) of the duration of contraction/expansion reflects a reduced ability of the potential recovery from defoliation. Black spruce showed significantly larger 24-h cycles of stem amplitude compared to balsam fir. However, both species showed similar physiological adjustments during mild stress, preventing water loss from stem storage zones to support the remaining needles’ transpiration. Finally, conifers react to defoliation during a 4-year period, modulating stem radius variation phases according to the severity of the defoliation.

1. The spruce budworm, Choristoneura fumiferana Clem., is an important outbreaking pest of balsam fir, Abies balsamea (L.) Mill, and black spruce, Picea mariana (Mill.) Britton, Sterns & Poggenb., throughout the boreal forests of North America. 2. Despite several studies reporting higher performance for larvae on balsam fir versus those on black spruce, many females still lay eggs on spruce. In this 2‐year study, we explored possible tri‐trophic trade‐offs associated with host selection taking into account both larval overwintering and feeding periods. 3. Based on field surveys, parasitism rates were significantly higher for overwintering larvae on balsam fir than on black spruce in 2017. 4. Field bioassays confirmed past studies showing 21% higher larval survival on balsam fir versus black spruce, especially when larval emergence was synchronized with host budburst. 5. Considering both overwintering and feeding survival, overall spruce budworm performance was nearly equal between hosts, though larvae gained some advantage on balsam fir if larval feeding was synchronized with budburst. 6. These results suggest that female egg lay on both hosts may be a 'bet‐hedging' strategy that balances trade‐offs between higher parasitism and higher foliage quality on different potential host species. [ABSTRACT FROM AUTHOR]

Phenological shifts, induced by global warming, can lead to mismatch between closely interacting species. The eastern spruce budworm, Choristoneura fumiferana, an important outbreaking insect defoliator in North America, mainly feeds on balsam fir, Abies balsamea, which has historically been well synchronized with the insect. But as climate change pushes the northern range limit of the budworm further north into the boreal forest, the highly valuable black spruce, Picea mariana, historically protected against the budworm by its late budburst phenology, is suffering increased defoliation during the current outbreak. We tested the hypothesis that rising temperatures can lead, not to a mismatch, but to an improved match between the budworm and black spruce through differential phenological advancement. For 3 years, eastern spruce budworm larvae were reared from instar 2 to pupae, on both black spruce and balsam fir, in a temperature free‐air controlled enhancement experiment (T‐FACE) consisting in 24 field plots, half of which were heated at +2°C from March to October. Our results show that every year, larval development was faster on heated trees and pupation was earlier than on unheated trees. Bud development was also accelerated in heated trees of both species. However, there was no difference in mass between pupae that developed at +2°C and controls at the end of the season. Finally, we found no difference either in development rate or pupal mass between larvae reared on black spruce and those reared on balsam fir. This suggests that under higher temperature regimes, eastern spruce budworm will be as successful on black spruce as on balsam fir, as black spruce budburst becomes better synchronized with the insect's emergence from diapause. This could lead to critical changes in outbreak dynamics and severity with important ecological state shifts at the landscape level. [ABSTRACT FROM AUTHOR]

Balsam fir needle retention and fatty acid profile changes due to cold acclimation throughout autumn, but little is known about the relationship between these two phenomena. The objective was to examine differences in FAs in contrasting needle abscission resistant balsam fir genotypes throughout autumn and early winter. Branches from genotypes with low and high needle abscission resistance (NAR) were collected from September to January and analyzed for FA composition. High NAR genotypes retained needles 120–130% longer than low NAR genotypes and NAR increased through autumn in both genotypes. There was approximately a 3:1 ratio of unsaturated: saturated FAs, which increased by 4% in favor of unsaturated fatty acids through autumn. Palmitic, palmitoleic, and linolenic acid content was significantly higher in high NAR versus low NAR genotypes; arachidic, oleic, linoleic, pinolenic, coniferonic, icosadienoic, and sciadonic acids were lower in high NAR genotypes versus low. Linolenic acid was of particular interest because it tended to decrease throughout autumn, to the point that high NAR genotypes were significantly lower in linolenic acid than low NAR genotypes in January. These changes may be linked to an increase in abscisic acid and/or jasmonic acid synthesis depleting linolenic acid stores and promoting postharvest needle abscission resistance.

Aims: In temperate forests, small increases in winter temperature can lead to substantial decreases in snow accumulation, which may alter plant–consumer interactions such as seed predation. However, seed predation by small mammals may also be affected by local habitat structure (e.g., downed woody debris). We tested whether the effect of snow depth on seed predation by small mammals depends on habitat structure (woody debris) that may influence small-mammal foraging behavior. Location: Northern temperate forests in Wisconsin, USA. Methods: We performed a factorial manipulation of snow depth and woody debris presence at 10 sites that differed in site-level ambient woody debris. At these sites, we monitored seed removal of four temperate tree species (Abies balsamea, Acer rubrum, Acer saccharum, Pinus resinosa). Results: Mean rates of winter seed removal varied among species, as did the effects of snow depth and woody debris. The presence of woody debris decreased Abies balsamea seed removal in plots with snow removed. Regardless of woody debris, snow removal increased Acer saccharum seed removal. Acer rubrum seed removal was lowest at sites with high site-level woody debris volume, especially in plots with snow removed. Conclusions: Warming winter temperatures may amplify seed removal for some tree species, but local-scale heterogeneity in woody debris may modify these effects. Because the effects of woody debris and snow removal were much stronger for some tree species than others, changes in seed removal associated with reduced future snow cover or changes in forest management may accelerate regional changes in forest composition. [ABSTRACT FROM AUTHOR]

Aims: When deciding whether or not to eat a plant, herbivores are influenced by the nutritional value of potential foods, but also indirectly by neighbouring plants (associational effects). We aimed to investigate how the abundance and nutritional quality of neighbours of balsam firs (Abies balsamea) affects browsing on balsam firs by white‐tailed deer. We sought to distinguish the effects of conspecific and heterospecific neighbour abundance, and to evaluate whether intraspecific variation in nutritional traits produces associational effects. Location: Anticosti Island, QC, Canada. Methods: We measured the abundance of stems in 4‐m2 plots centred on a focal balsam fir and evaluated nutritional value (nitrogen content and digestibility) of focal firs and neighbouring plants. We used generalized linear models to explain browsing on firs as a function of the neighbouring stem abundance (conspecific and heterospecific), and of the nutritional value of firs and neighbouring stems. Results: Fir abundance only affected browsing of firs after accounting for fir nutritional value, e.g., browsing in plots of low fir digestibility decreased as the number of fir stems increased (resource dilution effect). The associational effects of heterospecific neighbour abundance, especially birch stem and shoot abundance, were also contingent on neighbour nutritional value. For example, at low birch digestibility, browsing on the focal fir increased with the number of neighbouring birches. Browsing on fir also increased as the number of spruce stems of high nutritional value increased. Conclusions: By taking into account the abundance of all species, we could discriminate between conspecific effects and associational effects caused by heterospecifics. Our study suggests that the strength of associational effects varies in a continuous fashion in response to relative nutritional value. We propose that future studies should not only consider the identity of neighbours but also the nutritional traits of plant communities. [ABSTRACT FROM AUTHOR]

Herbivory alters plant chemistry thereby affecting subsequent palatability for the same or different herbivore species. Balsam fir is an important food for various insect and mammalian herbivores that consume tissues at different times of year. In eastern Canada, intense selective browsing of this tree species by ungulates has impeded natural regeneration of fir-dominated forests. Our objective was to determine whether late-season (simulated) browsing of apical and lateral branches affected the defense chemistry of emerging foliage of balsam fir saplings in the following season. At each of five locations in the vicinity of Gros Morne National Park, western Newfoundland, four browsing treatments were imposed in the late growing season on healthy fir saplings; apical, lateral, apical + lateral, and no browsing. In the following season, newly expanded and previous-year needles were collected shortly after bud break and analyzed for total phenols and condensed tannins. Browsing treatments had no effect on levels of these defense chemicals in either needle age class indicating the lack of an induced chemical response or preferential defense of the apical versus lateral shoots. New foliage appeared to be better defended than previous-year foliage. Neither phenol nor tannin levels were related to canopy closure or height and diameter of saplings; however, foliar phenol concentration was positively related to soil pH for both age classes of fir needle indicating a possible relationship between soil characteristics and plant secondary metabolites. Levels of both phenols and tannins in current-year needles were positively related to those of previous-year needles, whereas the concentration of phenols and tannins were negatively related for previous-year needles only. Our results support the premise that the main antiherbivore strategy of balsam fir is tolerance of intense browsing. [ABSTRACT FROM AUTHOR]

The Green River precommercial thinning (PCT) trial was established between 1959–1961 in New Brunswick (Canada) within natural balsam fir (Abies balsamea (L.) Mill.)-dominated stands. Three silviculture scenarios differing only by the increasing nominal spacings of PCT treatments (1.2 m, 1.8 m, 2.4 m) were compared to an unthinned control within randomized replicates that were clearcut harvested in 2008 and treated with herbicide in 2011. During the fourth post-harvest growing season, we assessed regeneration, competing vegetation and coarse woody debris (CWD; differentiated between large woody debris and slash) to assess the legacy effects of PCT on regeneration of next rotation stands. Our results confirmed that silviculture scenarios including PCT significantly increased conifer stocking in treated plots compared to control conditions, but only in the 1.8 m nominal spacing. Considering that treated and untreated stands were fully stocked, we conclude that PCT using the spacing gradient tested has no legacy effect on the regeneration of next rotation natural balsam fir stands. Given the known sensitivity of balsam fir to future climate conditions in this region, we suggest that future treatments should promote tree species diversity to support ecosystem resilience to climate change by favouring more warm-adapted species, such as some hardwoods.

Acid rain in eastern North America contributed to the widespread decline of red spruce in high-elevation spruce-fir forests. With recent reductions in acid deposition and a warming climate, resurgence of red spruce growth has been reported in some mountain areas. Based on an extensive tree-ring sampling network established across elevations (600 to 1,200 m above sea level) in spruce-fir forests on 10 mountains in the northeastern US (New York, Vermont, New Hampshire, and Maine), we investigated whether this resurgence was specific only to red spruce or if it occurred also in the co-dominant balsam fir. Furthermore, we tested if tree growth changes for both species were related to recent trends in acidic deposition and climate. Sharply increasing growth rates of red spruce were evident at all elevations and most closely correlated with increasing rainwater pH. Although climate of the previous year (cool July and warm November) explained higher spruce growth in certain years, recent trends in climate did not drive observed increases in spruce growth. In contrast, balsam fir exhibited no regional growth surge during the period of spruce recovery. Thus, spruce growth resurgence appears to be mediated primarily by declining acid deposition and not climatic changes or stand dynamics that would also impact fir growth. Although high-elevation forests may ultimately be at risk for future warming-related heat and drought stress, the observed recent dramatic resurgence of spruce growth illustrates the benefits of policy-driven reductions in acidic deposition for the health and productivity of northeastern US forests.

Succession is generally well described above-ground in the boreal forest, and several studies have demonstrated the role of interspecific facilitation in tree species establishment. However, the role of mycorrhizal communities for tree establishment and interspecific facilitation, has been little explored. At the ecotone between the mixed boreal forest, dominated by balsam fir and hardwood species, and the boreal forest, dominated by black spruce, several stands of trembling aspen can be found, surrounded by black spruce forest. Regeneration of balsam fir seems to have increased in the recent decades within the boreal forest, and it seems better adapted to grow in trembling aspen stands than in black spruce stands, even when located in similar abiotic conditions. As black spruce stands are also covered by ericaceous shrubs, we investigated if differences in soil fungal communities and ericaceous shrubs abundance could explain the differences observed in balsam fir growth and nutrition. We conducted a study centered on individual saplings to link growth and foliar nutrient concentrations to local vegetation cover, mycorrhization rate, and mycorrhizal communities associated with balsam fir roots. We found that foliar nutrient concentrations and ramification indices (colonization by mycorrhiza per length of root) were greater in trembling aspen stands and were positively correlated to apical and lateral growth of balsam fir saplings. In black spruce stands, the presence of ericaceous shrubs near balsam fir saplings affected ectomycorrhizal communities associated with tree roots which in turn negatively correlated with N foliar concentrations. Our results reveal that fungal communities observed under aspen are drivers of balsam fir early growth and nutrition in boreal forest stands and may facilitate ecotone migration in a context of climate change.

Balsam fir the principal tree species of the Christmas tree industry, is a major export commodity of Atlantic Canada region. However, postharvest needle abscission poses a main concern leading to low consumer satisfaction and a shift in preference towards artificial trees. The search for diverse balsam fir lines with high needle retention is very crucial for quality improvement programmes. In this regard, a panel of 75 balsam fir genotypes exhibiting diversity for needle retention traits were randomly selected from a set of 220 genotypes evaluated for needle retention characteristics for two consecutive years (2012 and 2013) and genotyped with 41 bi‐allelic single nucleotide polymorphism (SNP)/insertion/deletion markers. The cluster analysis and population structure identified four and seven subpopulations. We observed an SNP marker with significant association (p < 0.05) with the needle retention/abscission trait by using general linear model and mixed linear model approaches. The present study lays the foundation for analysing the genetic mechanisms underlying needle retention/abscission, as well as the use of molecular markers to target specific traits in balsam fir. [ABSTRACT FROM AUTHOR]

• Mortality was high in previously unmanaged Picea mariana - Abies balsamea stands. • Total mortality increased with harvesting intensity when such stands were treated. • Mortality was dominated by similar amounts of standing dead and overturned trees. • Total mortality was best explained by a mixture of variables from different scales. • The type of mortality was best explained by tree-level variables. Mortality is an important process to include when modelling forest stand development. Previous attempts to model mortality after partial cutting mostly focused on overturning and stem breakage. However, in old irregular and unmanaged stands, many processes may be acting at the same time, portions of the stands being at different developmental stages. In order to better understand the mortality processes in such stands, mortality after 5 years was analyzed in old-growth black spruce (Picea mariana) and balsam fir (Abies balsamea) stands subjected to a wide range of harvesting intensities. The study comprises three sites where five treatments were applied at two scales. Mixed logistic regressions explaining total mortality and its distribution across mortality types were developed. Results show that the effects of partial cutting in these stands are complex. Mortality in uncut stands was rather high and many trees died standing. Stem breakage was of minor importance, regardless of treatment. Mortality increased with DBH and harvesting intensity and was higher for balsam fir in comparison with black spruce. Mortality was influenced not only by the locally applied treatment (2500 m2) but also by the treatment applied over a larger area (10–20 ha). Critical wind speeds derived form an adaptation of the ForestGales model were not successful in explaining total mortality or mortality type, although critical wind speeds were generally lower for dead trees in comparison with living trees. The increased mortality was directly related to an increase in the relative importance of uprooting. The type of mortality was more difficult to predict than total mortality and was related to individual tree variables. Results show an influence of crown width, with overturning being more prevalent for trees with wider crowns. Our study indicates that, until there is a better understanding of the factors leading to trees that die standing, it will continue to be difficult to predict mortality in these types of stand. [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.)

Highlights • Rings formed during the defoliation had a significant and progressive loss of biomass. • Defoliation significantly reduced latewood density for black spruce and balsam fir. • Average ring density was reduced only in black spruce. • The changes in growth and density were associated with changes in anatomical features. • Significant reductions occurred in cell-wall thickness after 3rd year of defoliation. Abstract Spruce budworm (SBW – Choristoneura fumiferana Clem.) is one of the most damaging defoliating insects in the coniferous forests of eastern North America. In Canada, the widely distributed balsam fir (Abies balsamea L. (Mill)) and black spruce (Picea mariana B.S.P. (Mill)) are its most important hosts. Defoliation by SBW reduces growth in the host trees and can lead to host mortality. Although SBW impacts on growth are well documented, much less is known about changes in wood properties resulting from defoliation. To address this knowledge gap, we sampled 36 SBW-infested stands located in the boreal forest of Quebec (Canada) to determine whether defoliation modifies the wood quality of affected trees. The selected stands had been subjected to one to four years of SBW defoliation. For both species, we assessed ring growth, wood density, and the anatomical characteristics of stem wood formed during the outbreak years. We determined that rings formed during the SBW outbreak had a significant and progressive loss of biomass production with a longer duration of defoliation. SBW significantly reduced latewood density in the second and third year of defoliation for black spruce and the third and fourth year for balsam fir. Average ring density was reduced only in black spruce and only after four years of defoliation. The observed changes in growth and density were associated with changes in anatomical features. While the cellular characteristics of the earlywood remained fairly constant, significant reductions occurred in latewood cell-wall thickness after three years of defoliation. Our study shows that not only do SBW outbreaks reduce annual radial growth, but the cellular characteristics in latewood cells are also modified momentarily. Thus, SBW outbreaks affect wood density and quality in both black spruce and balsam fir. [ABSTRACT FROM AUTHOR]

Aims: Bryophytes can cover three quarters of the ground surface, play key ecological functions, and increase biodiversity in mesic high‐elevation conifer forests of the temperate zone. Forest gaps affect species coexistence (and ecosystem functions) as suggested by the gap and gap‐size partitioning hypotheses (GPH, GSPH). Here we test these hypotheses in the context of high‐elevation forest bryophyte communities and their functional attributes. Study Site: Spruce–fir forests on Whiteface Mountain, NY, USA. Methods: We characterized canopy openness, microclimate, forest floor substrates, vascular vegetation cover, and moss layer (cover, common species, and functional attributes) in three canopy openness environments (gap, gap edge, forest canopy) across 20 gaps (fir waves) (n = 60); the functional attributes were based on 16 morphologic, reproductive, and ecological bryophyte plant functional traits (PFTs). We tested GPH and GSPH relative to bryophyte community metrics (cover, composition), traits, and trait functional sensitivity (functional dispersion; FDis) using indicator species analysis, ordination, and regression. Results: Canopy openness drove gradients in ground‐level temperature, substrate abundance and heterogeneity (beta diversity), and understory vascular vegetation cover. The GPH was consistent with (a) the abundance patterns of forest canopy indicator species (Dicranum fuscescens, Hypnum imponens, and Tetraphis pellucida), and (b) FDis based on three PFTs (growth form, fertility, and acidity), both increasing with canopy cover. We did not find support for GPH in the remaining species or traits, or for GSPH in general; gap width (12–44 m) was not related to environmental or bryophyte community gradients. Conclusions: The observed lack of variation in most bryophyte metrics across canopy environments suggests high resistance of the bryophyte layer to natural canopy gaps in high‐elevation forests. However, responses of forest canopy indicator species suggest that canopy mortality, potentially increased by changing climate or insect pests, may cause declines in some forest canopy species and consequently in the functional diversity of bryophyte communities. Forest regeneration effects on the ground‐level bryophytes were assessed by testing gap partitioning hypothesis predictions. A survey of bryophytes and forest structure, analyzed with functional, species, and community metrics, identified: indicator species for forest canopy; an increase of functional dispersion and some species abundance from canopy gap to forest canopy; and no change in moss cover among canopy environments. [ABSTRACT FROM AUTHOR]

Highlights • Charcoal buried in the mineral soil is a method to reconstruct fire history at the stand scale. • Soils reveal an accurate fire history if the number of charcoals dated is sufficiently large. • It is difficult to reconstruct the oldest fires due to repeated burning of charcoals. • Adjacent peatland may be used as a complement to establish the record of the oldest fire events. Abstract Analysis and 14C dating of charcoal fragments ≥2 mm buried in mineral soils make it possible to obtain a stand-scale portrait of Holocene fires that occurred in well-drained, fire-prone environments, as well as changes in forest stand composition over time, based on botanical identification of charcoals. However, it is not always possible to reconstruct all fire events, due to disturbances that altered soil stratigraphy. In order to evaluate the efficacy of this approach, we conducted a comparative analysis with a proximal environment that presents an a priori continuous stratigraphy of charcoal fragments. For two sites in the coniferous boreal forest of eastern North America, the charcoal record of a forest soil was compared with that of an adjacent peatland margin situated at a distance of 20 m. For both types of sedimentary environments, a similar fire history was reconstructed for a large part of the Holocene. The greatest differences were for the early Holocene period, for which a smaller number of fires was detected in the forest soil compared to the peatland soil. Retracing the oldest fires using mineral soils in a fire prone environment is more difficult, due to charcoal decay that results from repeated fire events. However, forest soils reveal a relatively accurate fire history for subsequent millennia if the number of charcoals dated is sufficiently large. Any accurate reconstruction of the fire history of proximal peatland environments is strongly dependent on continuous stratigraphic units of peat and charcoal. Indeed, the age of charcoal fragments in peat may be different from that of the sedimentary layer in which they are buried due to allogenic disturbances like erosion events caused by deep burning of the organic horizon and other mass wasting events. Despite the large number of 14C dates it requires, analysis of soil macrocharcoal yields a realistic picture of the fire history at the stand scale. The concurrent analysis of macrocharcoal from adjacent peatland deposits may be used as a complement to more accurately record the oldest fire events. [ABSTRACT FROM AUTHOR]

Christmas trees produced in Quebec, Canada, mostly include balsam fir (Abies balsamea), which is a species susceptible to Delphinella shoot blight. Over the past decade, the Canadian forests and Christmas tree industry have encountered an increase in Delphinella shoot blight, and only a few studies have assessed and quantified the damage caused by this disease. The different developmental stages of the disease were studied and the presumed causal pathogenic agent was isolated from infected needles in this work. Delphinella balsameae was isolated less frequently than its phylogenetically closely related pathogen Sydowia polyspora. Furthermore, species-specific PCR protocols to detect both D. balsameae and S. polyspora were developed and the occurrence of these species in infected and symptomless needles sampled in Christmas tree plantations was evaluated. While D. balsameae was detected only in diseased needles, S. polyspora was frequently found in both asymptomatic needles and in needles displaying shoot blight. Experiments showed that D. balsameae is the more prevalent agent associated with fir tree shoot blight in Quebec. [ABSTRACT FROM AUTHOR]

Premise of the Study: Extreme weather events can injure plants, causing decreased survival. However, we may underestimate the ecological importance of extreme events if they have strong sublethal effects that manifest after several months. We tested the hypothesis that late‐winter extreme‐cold events decrease the ability of woody plants to grow and tolerate stem removal in summer. Methods: Seedlings from four temperate tree species (Abies balsamea, Pinus resinosa, P. strobus, Quercus rubra) were acclimated to winter conditions in growth chambers, and experienced 1 week of warm temperatures before being exposed to one of three 24‐h extreme‐cold events (minimum temperature: 8°C control, −8°C, or −16°C). Seedlings were then transferred to a greenhouse where we monitored survival and growth. Three months after the extreme‐cold event, we mimicked an herbivore attack by removing either 25% or 75% of new stem growth from seedlings of two species (P. resinosa, Q. rubra). Key Results: While extreme cold had no immediate effect on seedling survival, the coldest temperature treatment reduced stem growth 51% relative to controls. Stem removal decreased P. resinosa survival in the −16°C treatment, but stem removal treatment had no effect on P. resinosa survival in the intermediate −8°C treatment or 8°C control. Stem removal did not alter Q. rubra survival. Conclusions: Ephemeral late‐winter cold temperatures can have unappreciated effects on growing‐season seedling dynamics, including growth and herbivory. For predicting how extreme‐cold events might alter large‐scale patterns of tree distribution, seedlings should be monitored throughout the growing season following extreme late‐winter frosts. [ABSTRACT FROM AUTHOR]

Abies balsamea is native to the mountains of North America and often used as Christmas Trees. In this study, we reported the complete chloroplast genome of A. balsamea. The complete chloroplast genome is 121,574 bp in length, comprising a large single copy (LSC) region of 67,211 bp, a small single copy (SSC) region of 53,835 bp, and two inverted repeat regions (IRa and IRb) of 264 bp each. The genome contains 114 genes and they were 68 peptide-encoding genes, 35 tRNA genes, 4 rRNA genes, 6 open reading frames and one pseudogene. Loss of ndh genes and inverted repeat sequences were identified in this genome. The phylogenetic analysis confirms that the Abies species are supported as monophyletic, with high bootstrap values.

Herpotrichia needle browning (HNB) is a disease that affects several species of fir trees in Europe and North America. HNB was first described by Hartig in 1884, who isolated a fungal pathogenic agent identified as responsible for the disease. This fungus was later named Herpotrichia parasitica but is currently named Nematostoma parasiticum . However, the identity of the pathogens causing HNB is regularly questioned and, to date, the true causal agent of this disease has not been definitely established. The present study aimed to identify the fungal populations present in needles of Christmas fir trees ( Abies balsamea ) and to correlate them with needle health status using robust molecular methods. PCR primers specific to N. parasiticum allowed detection of the presence of this fungus in DNA samples from symptomatic needles. Furthermore, high-throughput sequencing (Illumina MiSeq) clearly showed that N. parasiticum was associated with symptomatic needles. However, high-throughput sequencing results revealed that the presence of other species such as Sydowia polyspora and Rhizoctonia sp. may also correlate with the development of HNB. A diagnostic tool, based on quantitative PCR using a probe, was then developed to detect and quantify N. parasiticum in DNA samples. The efficacy of this molecular approach was validated through the detection of the pathogenic agent in symptomatic needle samples as well as in nonsymptomatic needles collected in trees affected by HNB. In contrast, N. parasiticum could not be found in needles from healthy trees. The present study argues for the importance of N. parasiticum in causing HNB symptoms., Competing Interests: The author(s) declare no conflict of interest.

Marginal stands of balsam fir (Abies balsamea [L.] Mill.) and eastern white cedar (Thuja occidentalis L.) are found north of their limits of continuous distribution in eastern North America. Regional-scale paleoecological studies have suggested that fir and cedar populations could have had larger extents in the past. This study aimed at verifying this hypothesis at the local scale. Wood charcoal fragments were collected from the soils of two marginal fir and cedar stands as well as from 15 sites in the surrounding forest matrix where the species are absent currently. Anatomical identification and radiocarbon-dating showed that fir was more extensive in the study area until about 680 cal. BP, representing up to 31% of the charcoal assemblages at sites where it is currently absent. The evidence is less conclusive for cedar, however, although some of the charcoal fragments from the matrix sites could have been either fir or cedar (undistinguishable). Most of the dated fir/cedar charcoal in the matrix were from the ‘Medieval Warm Period’ (ca. 1000 cal. BP), suggesting contraction may have occurred at that time. Marginal fir – and possibly cedar – stands are thus relics of once more extensive populations. Fire is likely the main factor having contributed to the contraction of the species’ distributions. Fir and cedar are now relegated to areas where fires are less frequent and severe, such as the shores of lakes and rivers. [ABSTRACT FROM AUTHOR]

Aims Given the importance of resorption in nutrient conservations, nutrient resorption should change with leaf age if resorption depends on nutrient content, and if nutrient content changes with leaf age. However, no study has addressed this issue. Methods Here, we measured N and P concentrations of needles of different ages in two woody evergreen conifer species—white spruce (Picea glauca Voss.) and balsam fir (Abies balsamea Mill.)—to determine the effects of needle aging on nutrient resorption. Important Findings For both species, N and P concentrations were higher in newer needles than in older needles. Nutrient resorption efficiency, i.e. percentage of nutrients resorbed during senescence, also declined significantly with needle age from 73 to 22% in these two evergreen conifer species. The difference in nutrient resorption between old and young needles may be attributed to the size of N and P sink tissues, which is likely to decrease with needle age. These results suggest that needle age affects the extent of N and P resorption in these two evergreen conifer species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Defoliation by spruce budworm(Choristoneura fumiferana Clem.) on balsamfir (Abies balsamea (L.) Mill.) is more severe in fir than in mixed fir-hardwood stands. Previous studies assumed that defoliation in fir-hardwood stands was reduced in proportion to percent hardwood regardless of outbreak severity. We tested the influence of stand composition on defoliation during the first 5 years of a spruce budworm outbreak near Amqui, Quebec, by sampling 27 fir-hardwood plots selected to represent three percent hardwood basal area classes (0%-25%, 40%-65%, and 75%-95%). Balsam fir defoliation was significantly lower (p < 0.001) as hardwood content increased, but the relationship varied with overall defoliation severity each year. Annual plot defoliation in fir-hardwood plots, estimated using: (1) defoliation in pure fir plots and the assumption that defoliation in fir-hardwood plots was reduced in proportion to percent hardwood; (2) a generalized linear mixed-effects model with defoliation in pure fir plots, percent hardwood, and interaction as fixed-effects; and (3) Random Forests prediction incorporating 11 predictor variables, resulted in r = 0.77, 0.87, and 0.92 versus measured defoliation, respectively. Average defoliation severity in softwood plots and percent hardwood content were the most important variables in Random Forests analysis. Data on average defoliation level in softwood stands, as an indicator of overall outbreak severity, improves prediction of balsam fir defoliation in mixed stands. [ABSTRACT FROM AUTHOR]

Abstract: Diapause‐mediated dormancy in overwintering insect eggs has rarely been studied with regard to the ecological factors controlling postdiapause development. In insects of temperate latitudes, water availability at the end of winter, in interaction with temperature, could control the resumption of development for insect stages in postdiapause quiescence. The balsam twig aphid, Mindarus abietinus Koch (Hemiptera: Aphididae), overwinters as eggs in southern Québec, Canada, on balsam fir, Abies balsamea (L.) Miller (Pinaceae), in Christmas tree plantations, where it is known as a pest. Previous work has shown that eggs of this aphid maintain low water content during winter, presumably to survive sub‐zero temperatures. Conversely, in late winter and early spring, they passively or actively absorb surrounding moisture, which is accompanied by notable changes in size, shape, and fresh mass. The primary objective here was to determine the embryonic stage at which winter diapause starts and is maintained in M. abietinus, a relatively primitive aphid. Secondly, we tested the hypothesis that free water availability to postdiapause eggs, in combination with temperatures above developmental threshold, is essential for embryonic development and hatching, by experimentally soaking field‐collected eggs in water at controlled frequencies. We observed that embryogenesis starts at the time of egg laying and stops after a few days, before the anatrepsis stage of blastokinesis is complete, when the germ band has not yet entirely immersed itself into the yolk. We also found that water surrounding overwintered eggs on fir shoots, in interaction with temperature regime, significantly increases M. abietinus egg hatching rates. Potential impacts of environmental factors such as precipitation are discussed in relation to M. abietinus egg hatching rates and potential for population growth in spring. [ABSTRACT FROM AUTHOR]

Postharvest needle abscission in balsam fir varies based on time of harvest, but little is known about the effect of soil and tree nutrition on postharvest needle abscission. From April to November, 18 balsam fir samples were obtained each month and evaluated for postharvest needle abscission characteristics. Soil samples were collected simultaneously and evaluated for moisture, pH, organic matter, cation exchange capacity, and mineral nutrition. Needle tissue samples were also evaluated for mineral nutrition. Many parameters were found to vary based on month throughout the study, but not all were associated with needle abscission. Soil organic matter, cation exchange capacity, Ca, and Mn all had a significant (P < .01) positive relationship with needle retention; soil Al had a significant (P < .01) negative relationship with needle retention. Needle N, Ca, and Fe were also associated with needle abscission. The strongest positive relationship was found between needle Ca and needle retention (R2 > .50), suggesting that higher concentrations of tissue Ca were linked to superior needle retention in balsam fir. Overall, this study provides evidence that changes to soil management, such as the inclusion of organic matter and certain minerals, may improve needle retention in balsam fir. [ABSTRACT FROM AUTHOR]