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Herbivores affect plants via direct consumption, but also indirectly via changes in the vegetation. These indirect effects may only manifest after decades of exposure and, as a result, their impact is rarely accounted for. To better understand the direct and indirect impacts of a large herbivore, moose (Alces alces), on forests, we measured tree growth in areas that were both subjected to and excluded from herbivory for over 80 years. Growth data were gathered from five tree species, ranging from low to high palatability. We found that at small sizes, Betula papyrifera, a preferred species, benefited from herbivore exclusion. However, larger individuals grew more when exposed to herbivory, a response we attribute to lower competition in heavily browsed conditions. Populus tremuloides, a highly preferred tree, did not show any differences between levels of herbivory. Abies balsamea, a preferred winter browsed, was only marginally affected by browsing at smaller sizes. The two non-preferred species, Picea glauca and Picea mariana, did not show differential growth between herbivory levels. We conclude that herbivores can impact forests through both direct and indirect effects, that these effects are size specific, and that effects vary among species in ways not always predicted by consumption patterns. [ABSTRACT FROM AUTHOR]

Aim: Altitudinal and latitudinal treeline ecotones have not consistently responded to climate warming in the direction and/or magnitude predicted by climate alone, suggesting that non‐climatic mechanisms (e.g. biotic interactions) also mediate treeline range dynamics. Through a collaborative research approach, we assessed environmental conditions associated with pre‐dispersal insect cone granivory and how this biotic interaction may govern the reproductive potential, and therefore range dynamics, of spruce‐dominated treelines across northern Canada. Location: In all, 10 boreal forest treelines, tundra and alpine, from Yukon to Newfoundland and Labrador, Canada. Taxa: White spruce (Picea glauca [Moench] Voss), Black spruce (Picea mariana [Mill.] B.S.P.), Strobilomyia spp., Megastigmus spp. Methods: Treeline sites were assessed for presence and magnitude of pre‐dispersal seed granivory by insects along with viable seed availability. We quantified stand density metrics, organic layer depth and understorey vegetation composition at each location and, subsequently, incorporated those variables into generalized linear mixed models to establish predictors of granivory magnitude and viability of available seed. Results: Insect granivory was widespread across sites; however, site‐specific patterns of granivory were associated with increased moss cover and decreased shrub cover and stand density. While all black spruce‐dominated sites exhibited seed viability rates > 50%, the number of seeds produced per cone varied, suggesting that within‐site abiotic conditions and biotic interaction pressures limit successful colonization of novel environments in advance of seed dispersal. Main Conclusions: The modelled relationships between granivory, seed viability and environmental conditions represent an essential step towards generalizing how and when biotic interactions across subarctic treelines influence boreal tree range dynamics before seed dispersal. Connections between granivory magnitude and site‐level treeline characteristics (e.g. stand density, understorey vegetation) will provide a more comprehensive understanding of treeline range dynamics under continued climate change. [ABSTRACT FROM AUTHOR]

1. Boreal forest soils contain large stocks of soil carbon (C) that may be sensitive to changes in climate and disturbance. Destablization of boreal forest soil C through changes in C inputs, belowground C pools and/or wildfire could feedback to accelerate rising atmospheric CO2 concentration. Additionally, increasing frequency of severe fires may be changing the dominant forest types and reshaping aboveground C stocks. 2. Although controls on ecosystem C pools have received considerable attention, many studies have been limited to locations near the road system, leading to uncertainty in current and future C stocks across boreal Alaska. Here, we leveraged 545 randomly selected and spatially balanced Forest Inventory and Analysis (FIA) plots across ~13.5 million hectares in interior Alaska to examine the factors governing soil and live tree C pools. 3. Forest type mediated the effects of mean summer air temperature and the probability of near-surface permafrost on soil C. Meanwhile, forest type, stand age and aspect were the primary drivers of live tree C. Overall, plots with a known history of wildfire during the past 70 years did not have significantly different soil C stocks than plots without a known history of fire, likely due to the historical predominance of low severity fires. 4. Where wildfire likely initiated a transition to deciduous trees (19% of plots), live tree and soil C pools were reduced by 16% and 20%, respectively. Ecosystem C likely recovered over time, as maturing deciduous stands rapidly gained C in live trees. Deciduous stands without a known fire had comparatively very large live tree C stocks, suggesting a significant change in the distribution of ecosystem C following severe fire. 5. Synthesis. Our results highlight the nuanced interactions among wildfire, landscape position and forest type that will play important roles in shaping future boreal ecosystem C stocks. [ABSTRACT FROM AUTHOR]

• May minimum temperature is the primary driver of budburst in boreal conifers. • P. mariana showed the highest response to warmer springs and P. glauca the lowest. • Precipitation's effect on budburst is limited when compared to temperature. • Changes in bud phenology may disrupt host-insect interactions. • Budburst timing correlates with latitude and ecological provinces. Budburst is a pivotal event in plant life, representing a crucial response to seasonal meteorological shifts. Boreal tree species exhibit species-specific phenologies, and the rate of phenological changes under warming conditions may differ among these species. In this study we aim to investigate the timing of budburst in three coniferous species [Balsam fir (Abies balsamea), black spruce (Picea mariana) and white spruce (Picea glauca) (Pinaceae)]; identify the main drivers of budburst, its rate of advance and the spatiotemporal patterns of budburst in relation to climate across Canada using a time period of 1980–2021. The timing of budburst was observed at 2839 locations stretching from Alberta to Newfoundland. We developed response functions between budburst and climate (air temperature, precipitation and solar radiation) and used the strongest correlations to test their effect on budburst using species, time and the ecoclimatic framework of Canadian ecoprovinces. We applied spatially constrained multivariate clustering and identified natural budburst clustering across Canada. We found a baseline difference of 17 days in the budburst of black spruce relative to that of balsam fir and white spruce. Mean minimum temperature of May was negatively correlated with budburst date. Black spruce advanced budburst at a rate of change per degree of temperature (−3.33 days °C−1), twice that of balsam fir and white spruce (−1.53 and −1.27 days °C−1, respectively). Cluster distribution of budburst timing matched well with the distribution of Canadian ecoprovinces. Budburst within the clusters followed clinal patterns in temperature across Canada. Mean minimum temperature in May is the main factor driving budburst in northern tree species. Under a warmer spring, we project an earlier budburst, with black spruce being the species expected to show the greatest rate of change. The identified clustering patterns did not vary with precipitation, which represents the primary longitudinal gradient across Canada. [ABSTRACT FROM AUTHOR]

As northern latitudes experience rapid winter warming, there is an urgent need to assess the effect of varying winter conditions on tree growth and forest carbon sequestration potential. We examined tree growth responses to variability in cold-season (November–- April) frequency of freeze days (FFD) over 1951 to 2018 using tree-ring data from 35,217 trees and 57 species at 4,375 sites distributed across Canada. We found that annual radial growth responses to FFD varied by species, with some commonalities across genera and clades. The growth of gymnosperms with late spring leaf-out strategies was negatively related to FFD; years with high FFD were most detrimental to the annual growth of Pinus banksiana, Pinus contorta, Larix lyalli, Abies amabilis, and Abies lasiocarpa. In contrast, the growth of angiosperms with early leaf-out strategies, namely, Populus tremuloides and Betula papyrifera, was better in the coldest years, and gymnosperms with intermediate leaf-out timing, such as widespread Picea mariana and Picea glauca, had no consistent relationship to FFD. Tree growth responses to FFD were further modulated by tree size, tree age, regional climate (i.e., mean cold-season temperature), and local site conditions. Overall, our results suggest that moderately warming winters may temporarily improve the growth of widespread pines and some high-elevation conifers in western Canada, whereas warming winters may be detrimental to the growth of widespread boreal angiosperms. Our findings also highlight the value of using species-specific climate-growth relationships to refine predictions of forest carbon dynamics. [ABSTRACT FROM AUTHOR]

The representation of snow processes in forest growth models is necessary to accurately predict the hydrological cycle in boreal ecosystems and the isotopic signature of soil water extracted by trees, photosynthates and tree-ring cellulose. Yet, most process-based models do not include a snow module; consequently, their simulations may be biased in cold environments. Here, we modified the MAIDENiso model to incorporate a new snow module that simulates snow accumulation, melting and sublimation, as well as thermal exchanges driving freezing and thawing of the snow and the soil. We tested these implementations in two sites in eastern and western Canada for black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss) forests, respectively. The new snow module improves the skills of the model to predict components of the hydrological cycle. The MAIDENiso model is now able to reproduce the spring discharge peak and to simulate stable oxygen isotopes in tree-ring cellulose more realistically than in the original snow-free version of the model. The new implementation also results in simulations with a higher contribution from the source water on the oxygen isotopic composition of the simulated cellulose, leading to more accurate estimates of cellulose isotopic composition. Future work may include the development of inverse modelling with this new version of MAIDENiso to produce robust reconstructions of the hydrological cycle and isotope processes in cold environments. [ABSTRACT FROM AUTHOR]

Merging robust statistical methods with complex simulation models is a frontier for improving ecological inference and forecasting. However, bringing these tools together is not always straightforward. Matching data with model output, determining starting conditions, and addressing high dimensionality are some of the complexities that arise when attempting to incorporate ecological field data with mechanistic models directly using sophisticated statistical methods. To illustrate these complexities and pragmatic paths forward, we present an analysis using tree‐ring basal area reconstructions in Denali National Park (DNPP) to constrain successional trajectories of two spruce species (Picea mariana and Picea glauca) simulated by a forest gap model, University of Virginia Forest Model Enhanced—UVAFME. Through this process, we provide preliminary ecological inference about the long‐term competitive dynamics between slow‐growing P. mariana and relatively faster‐growing P. glauca. Incorporating tree‐ring data into UVAFME allowed us to estimate a bias correction for stand age with improved parameter estimates. We found that higher parameter values for P. mariana minimum growth under stress and P. glauca maximum growth rate were key to improving simulations of coexistence, agreeing with recent research that faster‐growing P. glauca may outcompete P. mariana under climate change scenarios. The implementation challenges we highlight are a crucial part of the conversation for how to bring models together with data to improve ecological inference and forecasting. [ABSTRACT FROM AUTHOR]

The representation of snow processes in forest growth models is necessary to accurately predict the hydrological cycle in boreal ecosystems and the isotopic signature of soil water extracted by trees, photosynthates and tree-ring cellulose. Yet, most process-based models do not include a snow module, consequently their simulations may be biased in cold environments. Here, we modified the MAIDENiso model to incorporate a new snow module that simulates snow accumulation, melting and sublimation, as well as thermal exchanges driving freezing and thawing of the snow and the soil. We tested these implementations in two sites in East and West Canada for black spruce (Picea mariana) and white spruce (Picea glauca) forests, respectively. The new snow module improves the skills of the model to predict components of the hydrological cycle. The model is now able to reproduce the spring discharge peak and to simulate stable oxygen isotopes in tree-ring cellulose more realistically than in the original, snow-free version of the model. The new implementation also results in simulations with a higher contribution from the source water on the oxygen isotopic composition of the simulated cellulose, leading to more accurate estimates. Future work may include the development of inverse modelling with the new version of MAIDENiso to produce robust reconstructions of the hydrological cycle and isotope processes in cold environments. [ABSTRACT FROM AUTHOR]

Defoliation level and site type are thought to influence tree response during spruce budworm (Choristoneura fumiferana (Clemens)) outbreaks. We determined the effects of four manual defoliation treatments (0%, 50%, 100%, and 100% + bud removal of current foliage) for 3 years on foliage production of balsam fir (Abies balsamea (L.) Mill.), black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.), and white spruce (Picea glauca (Moench) Voss) trees on four site-quality classes. After 3 years of defoliation and 2 years of recovery, foliage biomass was reduced by 34%–98%. During defoliation, the number of shoots generally increased and shoot length of spruce generally decreased, especially on rich sites. During recovery, the number of shoots increased substantially, shoot length decreased, and bud destruction reduced the number of shoots by about 50% compared with that of trees that received the 100% defoliation treatment. Defoliation did not substantially affect needle length. Trees on rich sites had two- to fourfold greater foliage production than trees on poor sites. Effects of site and defoliation differed among species, but site quality, especially nutrition, played an important role in production of shoots and needles and the tree's ability to withstand defoliation. Black spruce had more limited ability to recover foliage biomass, only producing more shoots, whereas balsam fir and white spruce had stronger ability to recover needle and shoot length, respectively. [ABSTRACT FROM AUTHOR]

Conifer winter damage results primarily from loss of cold hardiness during unseasonably warm days in late winter and early spring, and such damage may increase in frequency and severity under a warming climate. In this study, the dehardening dynamics of lodgepole pine ( Pinus contorta Dougl. ex. Loud), jack pine ( Pinus banksiana Lamb.), white spruce ( Picea glauca (Moench) Voss), and black spruce ( Picea mariana (Mill.) B.S.P.) were examined in relation to thermal accumulation during artificial dehardening in winter (December) and spring (March) using relative electrolyte leakage and visual assessment of pine needles and spruce shoots. Results indicated that all four species dehardened at a similar rate and to a similar extent, despite considerably different thermal accumulation requirements. Spring dehardening was comparatively faster, with black spruce slightly hardier than the other conifers at the late stage of spring dehardening. The difference, however, was relatively small and did not afford black spruce significant protection during seedling freezing tests prior to budbreak in late March and early May. The dehardening curves and models developed in this study may serve as a tool to predict cold hardiness by temperature and to understand the potential risks of conifer cold injury during warming-freezing events prior to budbreak. [ABSTRACT FROM AUTHOR]

A two-stage modelling approach was used for developing ingrowth models for four major tree species in Alberta: aspen, lodgepole pine, black spruce and white spruce. The probability of ingrowth presence was modelled first, followed by the modelling of annual amount of ingrowth conditional on ingrowth being present. To handle variable measurement intervals and plot sizes typical of repeatedly measured forestry data, two generalized logistic models were evaluated at the first stage: a traditional model with measurement interval length and plot size factor incorporated as an exponent of a standard logistic function and an alternative model with measurement interval length and plot size factor incorporated as a denominator. Two criteria were evaluated for defining optimal threshold values for plot classification: criterion 1 to maximize the summation of sensitivity and specificity and criterion 2 to maximize the overall rate of correct plot classification. It was found that criterion 1 was superior to criterion 2 for providing better plot classifications. The two ingrowth probability models behaved similarly based on model fitting and model validation results. Annual amount of ingrowth was modelled at the second stage by exponential functions. [ABSTRACT FROM AUTHOR]

The late-Holocene shift from Picea glauca (white spruce) to Picea mariana (black spruce) forests marked the establishment of modern boreal forests in Alaska. To understand the patterns and drivers of this vegetational change and the associated late-Holocene environmental dynamics, we analyzed radiocarbon-dated sediments from Grizzly Lake for chironomids, diatoms, pollen, macrofossils, charcoal, element composition, particle size, and magnetic properties for the period 4100–1800 cal BP. Chironomid assemblages reveal two episodes of decreased July temperature, at ca. 3300–3150 (ca −1 °C) and 2900–2550 cal BP (ca −2 °C). These episodes coincided with climate change elsewhere in the Northern Hemisphere, atmospheric reorganization, and low solar activity. Diatom-inferred lake levels dropped by ca. 5 m at 3200 cal BP, suggesting dry conditions during the period 3200–1800 cal BP. P. glauca declined and P. mariana expanded at ca. 3200 cal BP; this vegetational change was linked to diatom-inferred low lake levels and thus decreased moisture availability. Forest cover declined at 3300–3100, 2800–2500 and 2300–2100 cal BP and soil erosion as inferred from increased values of Al, K, Si, Ti, and Ca intensified, when solar irradiance was low. Plant taxa adapted to disturbance and cold climate (e.g. Alnus viridis , shrub Betula , Epilobium ) expanded during these periods of reduced forest cover. This open vegetation type was associated with high fire activity that peaked at 2800 cal BP, when climatic conditions were particularly cold and dry. Forest recovery lagged behind subsequent climate warming (≤+3 °C) by ca. 75–225 years. Our multiproxy data set suggests that P. glauca was dominant under warm-moist climatic conditions, whereas P. mariana prevailed under cold-dry and warm-dry conditions. This pattern implies that climatic warming, as anticipated for this century, may promote P. glauca expansions, if moisture availability will be sufficiently high, while P. mariana may expand under dry conditions, possibly exacerbating climate impacts on the fire regime. [ABSTRACT FROM AUTHOR]

Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki ( Btk) against spruce budworm Choristoneura fumiferana in black spruce ( Picea mariana (Mill.) BSP), white spruce ( P. glauca (Moench) Voss) and balsam fir ( Abies balsamea (L.) Mill.) was investigated in Québec's Côte-Nord region. As expected, larval mortality was higher in Btk-treated plots (80.26 ± 2.34 %) than in control plots (66.32 ± 2.80 %). There were no differences in larval mortality among the three host tree species tested. Btk was most efficient in reducing spruce budworm defoliation when applied to black spruce and white spruce trees. Black spruce and white spruce exhibited lower final defoliation in Btk-treated plots than balsam fir. Btk applications produced a reduction in defoliation of 36 % in balsam fir, 44 % in white spruce and 41 % in black spruce. Control plots exhibited about 35 % higher amount of current-year foliage destroyed (AFD) and 56 % lower amount of current-year foliage remaining (ARF) than Btk-treated plots, whereas no differences in the amount of current-year foliage produced (AFP) were observed among host tree species. Black spruce trees showed the lowest AFD. Although not statistically significant, black spruce also showed the highest ARF. Our results suggest that Btk application is more efficient in protecting against spruce budworm damage when it is applied to spruce species than it is to balsam fir. It appears that the observed inter-specific differences in host tree foliage protection might be related to interactions between Btk, host tree foliage, and larval feeding behaviour. [ABSTRACT FROM AUTHOR]

Leaf life span is an important plant trait associated with interspecific variation in leaf, organismal, and ecosystem processes. We hypothesized that intraspecific variation in gymnosperm needle traits with latitude reflects both selection and acclimation for traits adaptive to the associated temperature and moisture gradient. This hypothesis was supported, because across 127 sites along a 2,160-km gradient in North America individuals of Picea glauca Picea mariana, Pinus banksiana, and Abies balsamea had longer needle life span and lower tissue nitrogen concentration with decreasing mean annual temperature. Similar patterns were noted for Pinus syivestris across a north-south gradient in Europe. These differences highlight needle longevity as an adaptive feature important to ecological success of boreal conifers across broad climatic ranges. Additionally, differences in leaf life span directly affect annual foliage turnover rate, which along with needle physiology partially regulates carbon cycling through effects on gross primary production and net canopy carbon export. However, most, if not all, global land surface models parameterize needle longevity of boreal evergreen forests as if it were a constant. We incorporated temperature-dependent needle longevity and %nitrogen, and bio-mass allocation, into a land surface model. Community Atmosphere Biosphere Land Exchange, to assess their impacts on carbon cycling processes. Incorporating realistic parameterization of these variables improved predictions of canopy leaf area index and gross primary production compared with observations from flux sites. Finally, increasingly low foliage turnover and biomass fraction toward the cold far north indicate that a surprisingly small fraction of new biomass is allocated to foliage under such conditions. [ABSTRACT FROM AUTHOR]

Background EST (expressed sequence tag) sequences and their annotation provide a highly valuable resource for gene discovery, genome sequence annotation, and other genomics studies that can be applied in genetics, breeding and conservation programs for non-model organisms. Conifers are long-lived plants that are ecologically and economically important globally, and have a large genome size. Black spruce (Picea mariana), is a transcontinental species of the North American boreal and temperate forests. However, there are limited transcriptomic and genomic resources for this species. The primary objective of our study was to develop a black spruce transcriptomic resource to facilitate on-going functional genomics projects related to growth and adaptation to climate change. Results We conducted bidirectional sequencing of cDNA clones from a standard cDNA library constructed from black spruce needle tissues. We obtained 4,594 high quality (2,455 5' end and 2,139 3' end) sequence reads, with an average read-length of 532 bp. Clustering and assembly of ESTs resulted in 2,731 unique sequences, consisting of 2,234 singletons and 497 contigs. Approximately two-thirds (63%) of unique sequences were functionally annotated. Genes involved in 36 molecular functions and 90 biological processes were discovered, including 24 putative transcription factors and 232 genes involved in photosynthesis. Most abundantly expressed transcripts were associated with photosynthesis, growth factors, stress and disease response, and transcription factors. A total of 216 full-length genes were identified. About 18% (493) of the transcripts were novel, representing an important addition to the Genbank EST database (dbEST). Fifty-seven di-, tri-, tetra- and penta-nucleotide simple sequence repeats were identified. Conclusions We have developed the first high quality EST resource for black spruce and identified 493 novel transcripts, which may be species-specific related to life history and ecological traits. We have also identified full-length genes and microsatellite-containing ESTs. Based on EST sequence similarities, black spruce showed close evolutionary relationships with conspecific Picea glauca and Picea sitchensis compared to other Pinaceae members and angiosperms. The EST sequences reported here provide an important resource for genome annotation, functional and comparative genomics, molecular breeding, conservation and management studies and applications in black spruce and related conifer species. [ABSTRACT FROM AUTHOR]

We use two types of age-structured population models to study how the distribution of toxins among segments of the twigs of woody plants, by affecting the feeding behavior of snowshoe hares, might affect snowshoe hare population dynamics. In the first model a twig has N discrete toxin containing segments joined end to end. Depending on species these segments vary tremendously in length. Preferred browse species such as the deciduous shrub birch Betula glandulosa have a small number of long twig segments and defend only the youngest segments near the twig tip. Hares counter this defense by biting off a twig at an older segment, eating only the older segments and rejecting younger, more toxic attached segments. Twigs of less preferred foods, such as the juvenile developmental stages of the evergreen spruces Picea glauca and P. mariana, have an arrangement of toxin producing resin ducts along their twig's long axis that is best modeled using a large number of short segments. We also propose a continuous model as an alternative to the N-segment model in the case when N is large. For each model we determine completely the conditions for linear stability of the hare-extinct equilibrium. An important implication is that the most effective defense against hares is to defend twig segments of all diameters that a hare can eat, as does spruce. Numerical simulations of both models confirm and enhance our understanding of the dynamics of the interaction between woody plants and snowshoe hares. [ABSTRACT FROM AUTHOR]

Pollen is among the most ubiquitous of terrestrial fossils, preserving an extended record of vegetation change. However, this temporal continuity comes with a taxonomic tradeoff. Analytical methods that improve the taxonomic precision of pollen identifications would expand the research questions that could be addressed by pollen, in fields such as paleoecology, paleoclimatology, biostratigraphy, melissopalynology, and forensics., We developed a supervised, layered, instance-based machine-learning classification system that uses leave-one-out bias optimization and discriminates among small variations in pollen shape, size, and texture. We tested our system on black and white spruce, two paleoclimatically significant taxa in the North American Quaternary., We achieved > 93% grain-to-grain classification accuracies in a series of experiments with both fossil and reference material. More significantly, when applied to Quaternary samples, the learning system was able to replicate the count proportions of a human expert ( R 2 = 0.78, P = 0.007), with one key difference - the machine achieved these ratios by including larger numbers of grains with low-confidence identifications., Our results demonstrate the capability of machine-learning systems to solve the most challenging palynological classification problem, the discrimination of congeneric species, extending the capabilities of the pollen analyst and improving the taxonomic resolution of the palynological record. [ABSTRACT FROM AUTHOR]

Black spruce ( Picea mariana (Mill.) Britton, Sterns & Poggenb.) and white spruce ( Picea glauca (Moench) Voss) are phylogenetically proximal species that differ in productivity. Crown characteristics of these two species have not been extensively studied, in spite of the importance of these two species to the Canadian boreal forest and the importance of tree crowns for understanding and modelling tree growth. In this paper, we characterize and compare the crown lengths, crown profiles (i.e., radii), shapes, and surface areas of these two species using 65 white spruce and 57 black spruce trees destructively sampled in the provinces of Alberta, Ontario, and Quebec, Canada. Crown length was measured on every sample tree, while crown profile was obtained by reconstructing crowns from branch measurements. Our results showed that crown lengths did not differ between these two species given the same tree size and growth conditions. However, these two species establish under different growth conditions resulting in crown length differences. Further, differences in crown radii and profiles were found even under the same growth conditions. White spruce trees had wider crown radii and profiles changed from a parabola to a cone shape under increased density. As a result, differences in crown surface areas were found. [ABSTRACT FROM AUTHOR]

The effect of host nutritional quality on spruce budworm (Choristoneura fumiferana (Clemens)) parental and offspring performance was studied using field and laboratory rearing experiments, and foliar chemical analyses. Foliage of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss) and black spruce (P. mariana (Mill.) BSP) was used to rear the parental generation in the field, whereas an artificial diet was used to rear the progeny under laboratory conditions. Important differences in the food quality were provided by the three hosts. Black spruce foliage had higher concentrations of certain monoterpene deterrents and total phenolics, together with stronger seasonal declines in nutrients such as N, P and Mg, compared with the other hosts. We hypothesise that this trend may be related to poor performance and survival of the progeny. Laboratory rearing showed that progeny of parents that fed on black spruce exhibited longer developmental times and greater mortality, and had lower pupal mass than progeny of parents fed on the other hosts. Further, artificial food-fed progeny of insects reared on black spruce reached sixth-instar later, with lower mass, and exhibited higher relative growth rate (RGR) than progeny of parents fed on the other hosts. These results suggest nutritionally-based parental effects. These results also confirmed that the quality of food consumed by the parents can influence the fitness of the next generation. [ABSTRACT FROM PUBLISHER]

The effects of climate on radial growth of Larix laricina (Du Roi) K. Koch, Picea glauca (Moench) Voss, and Picea mariana (Mill) BSP were investigated in the Hudson Bay Lowlands of northern Manitoba. The objective was to characterize spatial and temporal variations in growth of trees across the forest-tundra ecotone. Along a 250 km transect, 299 trees were sampled in three zones: northern forest, central tundra, and southern forest. Ring-width indices were compared with climate through correlation- and response-function analyses. Numerous years of suppressed growth at the three locales resulted from cooling that followed major volcanic eruptions at much lower latitudes. Temperatures during July of the current year and autumn of the previous year were most limiting, particularly for L. laricina, which was temperature-sensitive across the region. A weakened growth response to temperature during the 1940-60 period was likely due to atmospheric circulation shifts. Most chronologies were intercorrelated, which suggests common environmental forcing, though environmental influences differed in the southern forest (particularly for P. mariana). The source of this disparity has yet to be determined. [ABSTRACT FROM AUTHOR]

In many situations, information on stem diameters inside bark (dib) are more desirable than on diameters outside bark (dob). However, obtaining dib measurements is usually expensive, time-consuming, and prone to significant measurement errors when done on standing trees. Many bark thickness equations have been proposed to estimate the dibs of standing trees. In this study, we compared several commonly used bark thickness equations for seven conifer species in the Acadian Region of North America. Mixed-effects modeling techniques were employed to fit linear and non-linear bark thickness equations. We found the equation proposed by Cao and Pepper (South J Appl Forestry 10:220-224, 1986; Eq. 5) performed significantly better than other equations for most of our study species. The Cao and Pepper (South J Appl Forestry 10:220-224, ) equation is a function of dob, relative height in the stem, tree height, and the ratio of dib to dob at breast height. The mean absolute bias was found to be reduced up to 74% compared with using a fixed ratio approach employed in the widely used Northeastern variant of the Forest Vegetation Simulator (FVS-NE) growth and yield model. Leave-one-out cross validation was further performed to determine the location of suitable prior measurements in the prediction process for three of the most well-behaved equations. Results show that no unified prior measurement can provide best predictive abilities across all species as the choice of prior dib measurements depends on both species and bark thickness equations. [ABSTRACT FROM AUTHOR]

Mineral soils exposed by fire are often covered by a layer of ash due to complete consumption of the forest floor (litter and duff). To assess the possible effects of ash on seed germination and viability of jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) Britton, Sterns, Poggenb.), white spruce (Picea glauca (Moench) Voss), and balsam fir (Abies balsamea (L.) Mill.), a laboratory experiment was conducted using ash derived from three types of forest floor samples. The samples represented areas of high conifer concentration, high aspen concentration, and mixed aspen and conifer and were collected from five mature aspen (Populus tremuloides Michx.) – conifer mixedwood stands in southeastern Manitoba. Ash derived from each forest floor type neither prohibited nor delayed conifer germination, except that of balsam fir. Balsam fir had significantly less germination on ash derived from forest floor samples with high aspen concentration. When corrected for seed viability, balsam fir had significantly less germination on all three ash types compared with jack pine, black spruce, and white spruce. However, the impact of ash on balsam fir is unlikely to have meaningful ecological implications, as balsam fir is a climax species and will establish in undisturbed mature forests. Le sol minéral exposé par le feu est souvent recouvert d’une couche de cendre due à la combustion de la couverture morte (litière et humus). Les effets de la cendre sur la viabilité et la germination des graines de pin gris (Pinus banksiana Lamb.), d’épinette noire (Picea mariana (Mill.) Britton, Sterns, Poggenb.), d’épinette blanche (Picea glauca (Moench) Voss) et de sapin baumier (Abies balsamea (L.) Mill.) ont été évalués. Une expérience en laboratoire a été réalisée en utilisant de la cendre provenant de trois types d’échantillons de couverture morte, représentatifs de zones avec une concentration élevée de conifères (HC), de peupliers (LC) et d’un mélange de peupliers et de conifères (MC) prélevés dans cinq peuplements mixtes matures de peuplier faux-tremble (Populus tremuloides Michx.) dans le sud-est du Manitoba. La cendre provenant de chacun des types de couverture morte n’a ni inhibé ni retardé la germination des conifères à l’exception du sapin baumier. Les graines de sapin baumier germaient significativement moins bien sur la cendre provenant du type de couverture morte LC. Lorsqu’elle était corrigée pour la viabilité des graines, la germination du sapin baumier était significativement plus faible sur les trois types de cendre comparativement au pin gris, à l’épinette noire et à l’épinette blanche. L’impact de la cendre sur le sapin baumier a peu de chances d’avoir des implications écologiques significatives étant donné que le sapin baumier est une espèce climacique qui s’établira dans les forêts matures non perturbées. [ABSTRACT FROM AUTHOR]

Height and diameter distributions between improved and unimproved (checklot) seedlots for white spruce [Picea glauca (Moench) Voss] and black spruce [Picea mariana (Mill.) BSP] were compared using the two-parameter Weibull function. Individual tree height at age 5-15 years and diameter at breast height at age 15 years that were collected from two series of large-plot realized gain tests were used for this purpose. For both species, improved seedlots did not significantly (α=0.05) change the shape parameter of the distributions relative to their checklots, suggesting that an overall shape value will be adequate to predict tree size distributions of various improved seedlots. The most important finding was that seedlot influenced the scale parameter (related to the range of the distribution) significantly, but from a practical viewpoint, only those scale values of the higher rated seedlots (i.e. seedlots collected from a rogued seed orchard or superior families) were significantly higher (α=0.05) than those of the respective unimproved seedlot. The changes in scale value of the alternative improved seedlots relative to the checklot (ΔScale) were comparable in magnitude to the respective realized genetic gains, suggesting that tree improvement effects on the scale value can be adjusted by realized genetic gains. The results also suggest that site and age significantly affected the scale value; in general, ΔScale became larger at earlier ages or on better sites. The findings reported here will be used in the development of yield functions for genetically improved white and black spruce in New Brunswick. [ABSTRACT FROM AUTHOR]

Interactions between vegetation and fire have the potential to overshadow direct effects of climate change on fire regimes in boreal forests of North America. We develop methods to compare sediment-charcoal records with fire regimes simulated by an ecological model, ALFRESCO (Alaskan Frame-based Ecosystem Code) and apply these methods to evaluate potential causes of a mid-Holocene fire-regime shift in boreal forests of the south-central Brooks Range, Alaska, USA. Fire-return intervals (FRIs, number of years between fires) are estimated over the past 7000 calibrated 14C years (7-0 kyr BP [before present]) from short-term variations in charcoal accumulation rates (CHARs) at three lakes, and an index of area burned is inferred from long-term CHARs at these sites. ALFRESCO simulations of FRIs and annual area burned are based on prescribed vegetation and climate for 7-5 kyr BP and 5-0 kyr BP, inferred from pollen and stomata records and qualitative paleoclimate proxies. Two sets of experiments examine potential causes of increased burning between 7-5 and 5-0 kyr BP. (I) Static-vegetation scenarios: white spruce dominates with static mean temperature and total precipitation of the growing season for 7-0 kyr BP or with decreased temperature and/or increased precipitation for 5-0 kyr BP. (2) Changed-vegetation scenarios: black spruce dominates 5-0 kyr BP, with static temperature and precipitation or decreased temperature and/or increased precipitation. Median FRIs decreased between 7-5 and 5-0 kyr BP in empirical data and changed-vegetation scenarios but remained relatively constant in static-vegetation scenarios. Median empirical and simulated FRIs are not statistically different for 7-5 kyr BP and for two changed-vegetation scenarios (temperature decrease, precipitation increase) for 5-0 kyr BP. In these scenarios, cooler temperatures or increased precipitation dampened the effect of increased landscape flammability resulting from the increase in black spruce. CHAR records and all changed-vegetation scenarios indicate long-term increases in area burned between 7-5 and 5-0 kyr BP. The similarity of CHAR and ALFRESCO results demonstrates the compatibility of these independent data sets for investigating ecological mechanisms causing past fire-regime changes. The finding that vegetation flammability was a major driver of Holocene fire regimes is consistent with other investigations that suggest that landscape fuel characteristics will mediate the direct effects of future climate change on boreal fire regimes. [ABSTRACT FROM AUTHOR]

CO2–light interactions can influence the competition among boreal plants, but are poorly understood. We investigated the effect of such interactions on the growth and biomass of 1-year-old black spruce (Sb) (Picea mariana (Mill.) BSP) and white spruce (Sw) (Picea glauca (Moench) Voss) grown with CO2 concentrations ([CO2]) of 360 and 720 µmol·mol–1 under 30%, 50%, and 100% light, in greenhouses. There were significant two-way and three-way interactions. Root collar diameter (RCD) of Sw decreased with decreasing light, while in Sb, there was no significant difference in RCD for plants grown under 50% or 30% light. Height was greater for plants grown under 100% light than if the plants were shaded. Elevated [CO2] increased RCD by 33% and enhanced stem volume by 67%, 98%, and 84% under 100%, 50%, and 30% light, respectively. The CO2 enhancement of total biomass was relatively higher under lower light, and greater for Sb than Sw. Elevated [CO2] decreased specific leaf area under 50% light only. Root mass was generally higher under 100% light than when shaded. Elevated [CO2] increased the root mass of Sb under 100% light, but decreased it under 30% light. Elevated [CO2] decreased the shoot/root ratio under 100% light, but increased it under 30% light. Our data suggest that raising [CO2] will likely increase species competitiveness under low light conditions, and that the increase will be greater in species that are relatively shade tolerant. [ABSTRACT FROM AUTHOR]

Symbiotic fungi’s role in providing nitrogen to host plants is well-studied in tundra at Toolik Lake, Alaska, but little-studied in the adjoining boreal forest ecosystem. Along a 570 km north-south transect from the Yukon River to the North Slope of Alaska, the 15N content was strongly reduced in ectomycorrhizal and ericoid mycorrhizal plants including Betula, Salix, Picea mariana (P. Mill.) B.S.P., Picea glauca Moench (Voss), and ericaceous plants. Compared with the 15N content of soil, the foliage of nonmycorrhizal plants (Carex and Eriophorum) was unchanged, whereas content of the ectomycorrhizal fungi was very much higher (e.g., Boletaceae, Leccinum and Cortinarius). It is hypothesized that similar processes operate in tundra and boreal forest, both nitrogen-limited ecosystems: (i) mycorrhizal fungi break down soil polymers and take up amino acids or other nitrogen compounds; (ii) mycorrhizal fungi fractionate against 15N during production of transfer compounds; (iii) host plants are accordingly depleted in 15N; and (iv) mycorrhizal fungi are enriched in 15N. Increased N availability for plant roots or decreased light availability to understory plants may have decreased N allocation to mycorrhizal partners and increased δ15N by 3‰-4‰ for southern populations of Vaccinium vitis-idaea L. and Salix. Fungal biomass, measured as ergosterol, correlated strongly with soil organic matter and attained amounts similar to those in temperate forest soils. [ABSTRACT FROM AUTHOR]

Black spruce ( Picea mariana), white spruce ( Picea glauca) and jack pine ( Pinus banksiana) were inoculated with Suillus tomentosus and subjected to potassium fluoride (1 m M KF and 5 m M KF) in the presence and absence of 60 m M NaCl. The NaCl and KF treatments reduced total dry weights in jack pine and black spruce seedlings, but they did not affect total dry weights in white spruce seedlings. The addition of 60 m M NaCl to KF treatment solutions alleviated fluoride-induced needle injury in ectomycorrhizal (ECM) black spruce and white spruce, but had little effect in jack pine seedlings. Both KF and 60 m M NaCl treatments reduced E values compared with non-treated control seedlings. However, with the exception of small reductions of Kr by NaCl treatments in black spruce, the applied KF and NaCl treatments had little effect on Kr in ECM plants. Chloride tissue concentrations in NaCl-treated plants were not affected by the presence of KF in treatment solutions. However, shoot F concentrations in ECM black spruce and white spruce treated with 5 m M KF + 60 m M NaCl were significantly reduced compared with the 5 m M KF treatment. The results point to a possible competitive inhibition of F transport by Cl. We also suggest that the possibility that aquaporins may be involved in the transmembrane transport of F should be further investigated. [ABSTRACT FROM AUTHOR]

Local distributions of black spruce (Picea mariana) and white spruce (Picea glauca) are largely determined by edaphic and topographic factors in the interior of Alaska, with black spruce dominant on moist permafrost sites and white spruce dominant on drier upland sites. Given the recent evidence for climate warming and permafrost degradation, the distribution of white spruce is expected to expand, but the transition from black to white spruce may be dispersal limited: unlike the semi-serotinous black spruce, postfire regeneration of white spruce relies on seed dispersal from unburned areas. To determine the relative roles of dispersal, establishment, and growth in recruitment of white and black spruce, we studied postfire spruce regeneration in a 21-year-old burn across a white spruce-black spruce transition in the interior of Alaska. Although prefire spatial distributions of adults of the two species were well separated along the topographic sequence from upland to floodplain sites, the spatial distributions of recruits overlapped considerably. Even >700 m away from its seed source, white spruce sapling density on typical black spruce sites was high enough to form fully stocked stands. In contrast, black spruce regeneration was sparse on typical white spruce upland sites. Establishment rates of both species, estimated from a statistical model, were highest in mossy, wet depressions, which tended to have a thick residual postfire organic layer (∼10 cm). On all site types, height growth rates inferred from age-height relationships were comparable for recruits of both species. On typical black spruce sites ⩾300 m into the burn, white spruce was younger (and, therefore, shorter) than black spruce due to the timing of masting events following the fire. There was no indication that dispersal, establishment, or edaphic constraints on juvenile growth limit white spruce's capacity to invade typical black spruce stands during the recruitment stage in our study area. It is unlikely that white spruce recruits would persist to the adult stage if the permafrost returned to the original prefire levels during future postfire succession. However, if permafrost continues to degrade under climate warming, transition to a white spruce-dominated landscape could be rapid. [ABSTRACT FROM AUTHOR]

Thirty-five stands of mature, closed canopy black spruce (Picea mariana), white spruce (Picea glauca) and balsam fir (Abies balsamea) in Prince Albert National Park, Saskatchewan, were assessed for cumulative defoliation caused by eastern spruce budworm (Choristoneura fumiferana). Multitemporal Landsat 5 TM images (15 June 1992 and 18 July 2004) and a single-date SPOT 4 HRVIR (high resolution visible and infrared) image (19 August 2004) were obtained over these stands. Correlation analysis suggested that the strength of the relationship between the defoliation and various vegetation indices was generally moderate. The SPOT HRVIR indices were more highly correlated to cumulative defoliation than the Landsat indices, and the multitemporal Landsat TM index outperformed the single-date Landsat TM index. These results may help in the design of defoliation assessment procedures that integrate satellite remotely-sensed data and aerial sketch mapping techniques. [ABSTRACT FROM AUTHOR]

The reproductive potentials of balsam fir and white spruce (co-dominants in mixedwood forests) and black spruce (dominant in coniferous forests) were studied to explain the location of the ecotone between the two forest types in the boreal zone of Quebec. Four sites were selected along a latitudinal gradient crossing the ecotone. Cone crop, number of seeds per cone, percentage filled seeds, and percentage germination were measured for each species. Balsam fir and white spruce cone crops were significantly lower in the coniferous than in the mixedwood forest, while black spruce had greater crop constancy and regularity between both forest types. Mast years were more frequent for black spruce than for balsam fir in both forest types (mast year data not available for white spruce). The number of seeds per cone was more related to cone size than to forest type for all species. Black spruce produced more filled seeds in the coniferous forest than balsam fir or white spruce. The sum of growing degree-days and the maximum temperature of the warmest month (both for the year prior to cone production) significantly affected balsam fir cone production. The climate-related northward decrease in reproductive potential of balsam fir and white spruce could partly explain the position of the northern limit of the mixedwood forest. This could change drastically, however, as the ongoing climate warming might cancel this competitive advantage of black spruce. [ABSTRACT FROM AUTHOR]

Abstract: Picea is an important taxon in late-glacial pollen records from eastern North America, but little is known about which species of Picea were present. We apply a recently developed palynological method for discriminating the three Picea species in eastern North America to three records from New England. Picea glauca was dominant at ∼14,500–14,000 cal yr BP, followed by a transition to Picea mariana between ∼14,000 and 13,500 cal yr BP. Comparison of the pollen data with hydrogen isotope data shows clearly that this transition began before the beginning of the Younger Dryas Chronozone. The ecological changes of the late-glacial interval were not a simple oscillation in the position of a single species'' range, but rather major changes in vegetation structure and composition occurring during an interval of variations in several environmental factors, including climate, edaphic conditions, and atmospheric CO2 levels. [Copyright &y& Elsevier]

New radiocarbon-dated plant macrofossils provide evidence for black spruce (Picea mariana) and white spruce (Picea glauca) within the unglaciated Yukon Territory at the onset of glacial conditions during the Marine Isotope Stage 3/2 transition, between about 26 000 and 24500 14C yr BP. These data indicate that spruce trees were able to reproduce sexually and grow to maturity within a glacial environment characterized by widespread steppe-tundra vegetation, loess aggradation, and icewedge formation. These trees may have been restricted to rare valley-bottom habitats that provided adequate shelter and moisture similar to those at the present latitudinal tree line. Previously published hypotheses suggest that low Picea frequencies in regional Beringian pollen data point to the local persistence of spruce trees through the last glaciation. Although our data provide evidence for local spruce trees at the onset of the last glaciation, the available macrofossil record is inconclusive regarding the survival of spruce through the Last Glacial Maximum in Eastern Beringia. These new plant macrofossil data require palynologists to reexamine the relationship between Picea pollen frequency and local trees and highlight the importance of integrated pollen- and macrofossil-based paleoecological reconstructions. [ABSTRACT FROM AUTHOR]

We examined jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) BSP), and white spruce (Picea glauca (Moench) Voss) seed germination and seedling recruitment in aspen (Populus tremuloides Michx.) and conifer mixedwood stands following the 1999 Black River fire in southeastern Manitoba, Canada. Three postfire seedbed types were tested: scorched (surface litter only partially consumed), lightly burned (surface litter consumed with little or no duff consumption), and severely burned (complete consumption of litter and duff exposing mineral soil). Seeds were sown in 1999, 2000, and 2001, and each cohort was monitored for 3 years. In 1999, severely burned seedbeds had poor germination, while scorched seedbeds had the highest germination. The reverse was true in 2001. After the first growing season, continued survival of seedlings was greater on severely burned seedbeds for all three cohorts. However, better survival on severely burned seedbeds was not sufficient to overcome poor germination in 1999 and 2000. When using artificial seeding to promote conifer regeneration, we recommend a delay of one full year after a severe spring fire for jack pine and two full years for black spruce and white spruce on boreal aspen and conifer mixedwood sites. [ABSTRACT FROM AUTHOR]

Picea glauca (white spruce) and P. engelmannii (Engelmann spruce) are so similar and integrated that it is impossible to distinguish between them and their hybrids using morphological characteristics. Although natural hybrids between P. glauca and P. mariana (black spruce) do not generally occur, even though the 2 species are sympatric in North America, a first-generation hybrid, called the Rosendahl spruce, has been reported in the literature. In this study, several inter-simple sequence repeat (ISSR) markers were developed, as were randomly amplified polymorphic DNA (RAPD) markers, to certify spruce trees and their hybrids. ISSR fingerprinting was more efficient than RAPD assay; it detected 70% polymorphic DNA markers among the spruce species analyzed, whereas RAPD fingerprinting detected only 53%. Species-diagnostic ISSR and RAPD markers differentiating P. glauca from P. engelmannii and P. mariana were cloned and sequenced. Molecular certification of the spruce samples analyzed confirmed that all the seeds from interior spruce populations were true hybrids of P. glauca and P. engelmannii. But the analysis of seeds derived from the putative Rosendahl spruce indicated that this tree is likely a pure P. glauca genotype, rather than a hybrid of P. glauca and P. mariana. These data were confirmed by cytological analyses. Further analysis, using a more sensitive DNA amplification method with designed primers flanking the species-diagnostic ISSR and RAPD markers, revealed that such sequences are not generally species-specific because they are present in other spruce species. [ABSTRACT FROM AUTHOR]

An aging American population may be less willing than a younger population to install and remove a live, fresh-cut evergreen tree in their home for Christmas celebrations. An alternative to using traditional, large, fresh-cut or potted Christmas trees could be forcing these evergreen species in a small (≈1-L) container that could be displayed on a tabletop. We initiated this study to determine consumer preferences and marketability for six evergreen tree species produced for tabletop display and used three decoration themes and three price points. We constructed a web-based survey in which 331 participants were compensated with a $5 e-coupon for viewing 27 photographs of tabletop trees and providing preference and use information. The conjoint model accounted for 91.2% of the variance and showed that consumers valued tree species as the most important attribute (61% of the tree value), with decoration color/theme the second most important feature (27%) and, last, price (12%). Black Hills spruce (Picea glauca var. densata (Moench) Voss) was the most preferred species overall, and red was the most preferred decoration theme. Logically, the lowest price point was the most preferred. However, price was the most important attribute for participants younger than 25 years. The importance of price decreased as participant age increased until age 60, when price became a more important component. With a cost of production of $5.45 and decoration and shipping estimated at an additional $4.00, the product could be a profit generator priced at any of the tested price points ($14.95 and above). [ABSTRACT FROM AUTHOR]

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO[sub 2] uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage. [ABSTRACT FROM AUTHOR]

The present study was conducted to understand the role of sucrose in the medium on the maturation of black spruce and white spruce somatic embryos. A maturation medium containing 6% sucrose, which hydrolyzed into glucose and fructose, gave significantly more embryos than a medium containing 3.16% of each glucose and fructose. Preventing the complete sucrose hydrolysis by a daily transfer of the tissues onto fresh medium significantly decreased the yield of somatic embryos compared to when sucrose was allowed to complete its hydrolysis. This reduction was not due to the manipulation of the tissues during the transfer, since a daily in situ transfer did not affect embryo production. To verify if the better embryo production observed on a medium containing 6% sucrose was due to the increasing osmotic pressure of the medium, this increasing osmotic pressure was simulated with a sequence of media containing different concentrations of glucose and fructose. Unexpectedly and for both species, this simulation did not improve somatic embryo production, which stayed similar to the one obtained on constant osmotic pressure. To understand these results, embryos produced on the different treatments were analyzed in terms of sucrose, glucose, fructose and starch levels and protein contents. The embryo carbohydrate content was independent from the carbohydrate used in the maturation medium. However, embryos matured on 6% sucrose allowed to hydrolyze during the maturation period contained significantly more soluble and insoluble proteins than embryos matured on any other treatment. Furthermore, embryos with a higher protein content also exhibited a higher epicotyl appearance frequency. The role of sucrose as a regulatory factor during the maturation of spruce somatic embryos is discussed. [ABSTRACT FROM AUTHOR]

Whole root systems of 2-yr-old containerized white spruce [Picea glauca (Moench) Voss], black spruce [Picea mariana (Mill.) B.S.P.] and jack pine (Pinus banksiana Lamb.) seedlings, with intact root plugs, were exposed to various frost temperatures, which a preliminary test indicated would induce approximately 0 (control), 20, 40, 60, 80 and nearly 100% frost damage. Damage to root systems was evaluated using: (1) two measures of electrolyte leakage (relative conductivity and total tissue leakage after autoclaving); (2) water loss after pressurization; (3) chlorophyll fluorescence (F[sub v]/[sub Fm], maximal PSII photochemical efficiency) measured 4, 21 and 30 days after the beginning of seedling regrowth and (4) live root dry mass measured 21 days after the artificial frost and 60 days after the beginning of regrowth. Seedling survival and growth after the artificial frost were evaluated using live root dry mass measured after 60 days of regrowth and new shoot length, stem diameter, and root and shoot dry mass. Live root dry mass, dead tissue leakage, jack pine root water loss and fluorescence measurements were all significantly correlated with one or more of the growth variables and the number of significant correlations varied with species. Dead tissue leakage measurements appear to be the most promising method for evaluating root damage to 2-yr-old well-developed root systems of these species. [ABSTRACT FROM AUTHOR]

The treeline in Alaska is usually mapped as the limit of white spruce Picea glauca (Moench) Voss along the south slope of the Brooks Range and in western Alaska and as the limit of Sitka spruce Picea sitchensis (Bong.) Can. on Kodiak Island and in the Alaska Peninsula. In some localities black spruce Picea mariana (Mill.) B.S.P. and paper birch Bemia papyrifera Marsh, fonn components of the treeline community with white spruce. Of special interest are the groves of balsam poplar Populus balsamifera L. occurring on the north slope of the Brooks Range and to the west and southwest of the spruce treeline. There is some question as to whether trees survived in unglaciated portions of Alaska during the last glacial period. Spruce trees became prevalent about 10000 yr ago and may still be expanding to their climatic limits. In some areas of Alaska the treeline was more expanded during the Hypsithermal period than it is at present, but in other regions evidence for such an expansion is lacking. Treetine in some areas seems to have been stable for the last several centuries, but is has been expanding rapidly for the last 40 yr in entral and western Alaska and for a longer period on Kodiak Island. [ABSTRACT FROM AUTHOR]

An index of tree growth based on the mean growth curve of black spruce shows that tree growth in the boreal forest of central Canada decreases linearly as the forest-tundra boundary is approached. A theoretical tree line is defined by black spruce growth data. The distribution of tree growth and the theoretical tree line indicate that the forest-tundra boundary is the mean summer position of the arctic front. The growth of white spruce is briefly considered, but because of a small sample size, no conclusions are drawn. [ABSTRACT FROM AUTHOR]

Prior to the Mount Allison Dendrochronology (MAD Lab) sampling in the summer of 2007, little tree ring work was conducted in Labrador, with the most studies coming from the eastern coast and from one species. Given this, the information is still quite spotty, as the cost of transportation and limited tree availability has limited a systematic sampling across the landscape. Over this backdrop, the MAD Lab initiated a more region-wide study breaking Labrador into three zones (east, west, and north). Within each zone a consistent grid was used that will link the entire region together, while at the same time highlight the major zones of homogenous tree cover currently found. This talk will illustrate some of the early results of areas in southeastern Labrador, while at the same time discuss some of the difficulties in sampling the more northern locations. Three species will be discussed (white spruce (Picea glauca), black spruce (Picea mariana) and balsam fir (Abies balsamea)). Preliminary results from chronologies of black spruce and balsam fir developed from the southeastern region will be compared to the other chronologies in adjacent areas in Labrador, highlighting some of the similarities and differences in growing conditions that are already being seen. [ABSTRACT FROM AUTHOR]