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Papers in this Special Feature were presented at a symposium on the biology of Glaucomys sabrinus convened at the 86th Annual Meeting of the American Society of Mammalogists in June 2006. Because G. sabrinus is an arboreal species that relies on several attributes of older forests, it is an ideal model organism for studying impacts of broad-scale habitat loss and alteration from logging, clearing, and natural disturbances. The objective of the symposium was to integrate knowledge of mammalogists from multiple disciplines to achieve a more complete biological portrait to gain insights about how forest communities are being impacted by dramatic changes in forest composition and distribution following European settlement of North America, and to identify gaps in knowledge and information needs that can guide future research. The symposium included 5 papers that encompass a diversity of biological information, including the evolutionary origin and systematics of Glaucomys, the anatomy and evolution of G. sabrinus, its biogeography, genetic variation within and among regional populations, its ecology, functional morphology, kinetics, and issues and challenges of conservation. [ABSTRACT FROM AUTHOR]

Incomplete knowledge of carbon (C) allocation dynamics in trees hinders accurate modeling and future predictions of tree growth. We studied C allocation dynamics in a mature Pinus sylvestris L. dominated forest with a novel analytical approach, allowing the first comparison of: (i) magnitude and δ13C of shoot, stem and soil CO2 fluxes (A shoot, R stem and R soil), (ii) concentration and δ13C of compound-specific and/or bulk non-structural carbohydrates (NSCs) in phloem and roots and (iii) growth of stem and fine roots. Results showed a significant effect of phloem NSC concentrations on tracheid growth, and both variables significantly impacted R stem. Also, concentrations of root NSCs, especially starch, had a significant effect on fine root growth, although no effect of root NSC concentrations or root growth was detected on R soil. Time series analysis between δ13C of A shoot and δ13C of R stem or δ13C of R soil revealed strengthened C allocation to stem or roots under high C demands. Furthermore, we detected a significant correlation between δ13C of R stem and δ13C of phloem sucrose and glucose, but not for starch or water-soluble carbohydrates. Our results indicate the need to include C allocation dynamics into tree growth models. We recommend using compound-specific concentration and δ13C analysis to reveal C allocation processes that may not be detected by the conventional approach that utilizes bulk organic matter. [ABSTRACT FROM AUTHOR]

Copyright of Ornithological Applications is the property of Oxford University Press / USA 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.)

Research on cambium phenology in trees and its limiting factors in natural conditions is still at an early stage of development, restricting our capacity to precisely evaluate the effect of growing season length and climate fluctuations on tracheid production. The first objective of this paper was to describe cambial tracheid production phenology of black spruce (Picea mariana (Mills.) BSP). Repeated tree ring sampling was performed from 2002 to 2006 on four sites (48°13.78′ N, 71°15.18′ W; 48°51.92′ N, 70°20.57′ W; 49°43.92′ N, 71°56.88′ W; and 50°41.78′ N, 72°11.03′ W) representative of closed black spruce forest in Quebec, Canada. The timing of cambial initiation and cambial cessation in black spruce differs from year to year, the first occurring on 4 June on average, whereas the second occurs on 15 August. During a single year, these events do not vary significantly in space within the study area. The duration of cambial tracheid production does not vary significantly in either time or space. The second objective of this study was to identify the climatic factors that explain variations in initiation and cessation. Air temperature and humidity, soil temperature and water content, rain precipitations, snow cover as well as photosynthetically active radiation were monitored at each studied site. These were then used to create sets of candidate regressors to explain timing of phenological events. Timing of cambial initiation is primarily dependent on mean temperature between mid-March and initiation itself. Vapor pressure during this period is also important but in a negative way. A significant effect of the previous year’s August soil and air temperature conditions suggests a link with spring bud activity resumption, an interpretation that is supported by an analysis significantly linking measured timing of bud break to cambial initiation. Cessation of cambial tracheid production is influenced by factors linked to photosynthesis during the period from mid-July to cessation. Those related to water status, namely saturation vapor pressure, soil water content and vapor pressure are particularly influential, but light intensity and soil temperature also have an effect. Also, because mid-July corresponds to the timing of bud set and because the previous late summer’s soil temperature has a significant effect, a clear link is established with apical cessation. [ABSTRACT FROM PUBLISHER]

Background and Aims Carbon reserves are a critical source of energy and substrates that allow trees to cope with periods of minimal carbon gain and/or high carbon demands, conditions which are prevalent in high-latitude forests. However, we have a poor understanding of carbon reserve dynamics at the whole-tree level in mature boreal trees. We therefore sought to quantify the seasonal changes in whole-tree and organ-level carbon reserve pools in mature boreal Betula papyrifera. Methods Non-structural carbohydrate (NSC; soluble sugars and starch) tissue concentrations were measured at key phenological stages throughout a calendar year in the roots, stem (inner bark and xylem), branches and leaves, and scaled up to estimate changes in organ and whole-tree NSC pool sizes. Fine root and stem growth were also measured to compare the timing of growth processes with changes in NSC pools. Key Results The whole-tree NSC pool increased from its spring minimum to its maximum at bud set, producing an average seasonal fluctuation of 0.96 kg per tree. This fluctuation represents a 72 % change in the whole-tree NSC pool, which greatly exceeds the relative change reported for more temperate conspecifics. At the organ level, branches accounted for roughly 48–60 % of the whole-tree NSC pool throughout the year, and their seasonal fluctuation was four to eight times greater than that observed in the stemwood, coarse roots and inner bark. Conclusions Branches in boreal B. papyrifera were the largest and most dynamic storage pool, suggesting that storage changes at the branch level largely drive whole-tree storage dynamics in these trees. The greater whole-tree seasonal NSC fluctuation in boreal vs. temperate B. papyrifera may result from (1) higher soluble sugar concentration requirements in branches for frost protection, and/or (2) a larger reliance on reserves to fuel new leaf and shoot growth in the spring. [ABSTRACT FROM AUTHOR]

Aims Intraspecific variation in plant traits has important consequences for individual fitness and herbivore foraging. For plants, trait variability across spatial dimensions is well documented. However, temporal dimensions of trait variability are less well known, and may be influenced by seasonal differences in growing degree days (GDD), temperature and precipitation. Here, we aim to quantify intraspecific temporal variation in traits and the underlying drivers for four commonly occurring boreal plant species. Methods We sampled the elemental and stoichiometric traits (%C, %N, %P, C:N, C:P, N:P) of four common browse species' foliage across 2 years. Using a two-step approach, we first fitted generalized linear models (GzLM, n = 24) to the species' elemental and stoichiometric traits, and tested if they varied across years. When we observed evidence for temporal variability, we fitted a second set of GzLMs (n = 8) with temperature, productivity and moisture as explanatory variables. Important Findings We found no evidence of temporal variation for most of the elemental and stoichiometric traits of our four boreal plants, with two exceptions. Year was an important predictor for percent carbon across all four species (R 2 = 0.47–0.67) and for multiple elemental and stoichiometric traits in balsam fir (5/8, R 2 = 0.29–0.67). Thus, variation in percent carbon was related to interannual differences, more so than nitrogen and phosphorus, which are limiting nutrients in the boreal forest. These results also indicate that year may explain more variation in conifers' stoichiometry than for deciduous plants due to life history differences. GDD was the most frequently occurring variable in the second round of models (8/8 times, R 2 = 0.21–0.41), suggesting that temperature is an important driver of temporal variation in these traits. [ABSTRACT FROM AUTHOR]

Human-caused habitat disturbances and climate change are leading threats to biodiversity. Studying the impacts of human activities on wildlife from a behavioral perspective is a relevant starting point to understand the mechanisms underlying population and species resistance and resilience to disturbances. In this study, we assessed the effects of weather (temperature and precipitation), habitat disturbances (roads and clearcuts), and natural habitat types on the space use patterns of a threatened boreal population of woodland caribou (Rangifer tarandus caribou). An extensive data set of 288,665 relocations from 50 adult females outfitted with GPS collars over 7 years in the boreal forest of Québec, Canada was used to evaluate residency time in natural and disturbed habitats for five distinct biologically defined periods. The most parsimonious linear mixed-effects model for each period showed that individuals stayed longer in more natural habitat types. During calving and summer, residency time decreased with increasing road density, whereas residency time decreased with increasing temperature during winter and spring. We found no evidence of a synergistic effect between daily weather and human disturbances on movement behavior of caribou, but consider their respective influence as additive. We also showed large individual variation in residency time, except during the calving period. Lower individual variation in residency time during calving may be explained by strong evolutionary constraints on behavior faced by females to ensure protection and survival of their offspring. Based on our results, we suggest keeping large patches of suitable and roadless habitat for caribou to favor the spacing-out antipredator strategy exhibited by females during calving. By tracking individuals over several complete annual cycles, we showed variation in the effects of daily weather and human disturbances on residency time across biological periods. Our study highlights that the inclusion of daily weather variables helps better understand space-use patterns of a threatened species. [ABSTRACT FROM AUTHOR]

Wildlife species exhibit changes in behavior, population dynamics, and abundance after disturbances to forests. In western North America, large swathes of dead trees have resulted from unusually large outbreaks of bark beetles (Dendroctonus spp.) over recent decades. For bats, these tree mortality events could be either negative or positive, depending on whether cavities and crevices for roosting increase in response to beetle outbreaks and how the food supply is affected. It is therefore important to determine bat presence and activity in areas with many beetle-killed trees. We examined bat species richness in the southern interior of British Columbia, Canada, in areas with light and severe beetle-kill. We identified six bat species from acoustic recorders; the federally endangered little brown myotis (Myotis lucifugus) had the most detections. Although we surveyed stand-level vegetation, we found no systematic difference between areas identified from government aerial surveys as having had high or low beetle-kill within the previous decade. Neither beetle-kill severity nor the fine-scale vegetation that we measured correlated with bat presence or activity. We conclude that bats in this region use beetle-killed forests and that the severity of beetle-killed trees is neither adversely affecting bat presence or activity, nor enabling increased use by bats of affected forest stands in comparison to activity levels found in other high elevation forests. [ABSTRACT FROM AUTHOR]

We quantified seasonal CO2 assimilation capacities for seven dominant vascular species in a wet boreal forest peatland then applied data to a land surface model parametrized to the site (ELM-SPRUCE) to test if seasonality in photosynthetic parameters results in differences in simulated plant responses to elevated CO2 and temperature. We collected seasonal leaf-level gas exchange, nutrient content and stand allometric data from the field-layer community (i.e. Maianthemum trifolium (L.) Sloboda), understory shrubs (Rhododendron groenlandicum (Oeder) Kron and Judd, Chamaedaphne calyculata (L.) Moench. Kalmia polifolia Wangenh. and Vaccinium angustifolium Alton.) and overstory trees (Picea mariana (Mill.) B.S.P. and Larix laricina (Du Roi) K. Koch). We found significant interspecific seasonal differences in specific leaf area, nitrogen content (by area; Na) and photosynthetic parameters (i.e. maximum rates of Rubisco carboxylation (V cmax25°C), electron transport (J max25°C) and dark respiration (R d25°C)), but minimal correlation between foliar Na and V cmax25°C, J max25°C or R d25°C, which illustrates that nitrogen alone is not a good correlate for physiological processes such as Rubisco activity that can change seasonally in this system. ELM-SPRUCE was sensitive to the introduction of observed interspecific seasonality in V cmax25°C, J max25°C and R d25°C, leading to simulated enhancement of net primary production (NPP) using seasonally dynamic parameters as compared with use of static parameters. This pattern was particularly pronounced under simulations with higher temperature and elevated CO2, suggesting a key hypothesis to address with future empirical or observational studies as climate changes. Inclusion of species-specific seasonal photosynthetic parameters should improve estimates of boreal ecosystem-level NPP, especially if impacts of seasonal physiological ontogeny can be separated from seasonal thermal acclimation. [ABSTRACT FROM AUTHOR]

Aims The impact of global warming on belowground processes, especially on fine root production, is poorly understood in comparison with its aboveground counterpart. Methods Here, we compiled 227 measurements to assess the influence of temperature and precipitation on fine root biomass of Norway spruce (Picea abies [L.] Karst) forest ecosystems in the Eurasia boreal region. Important Findings We found that fine root biomass decreased significantly with latitudes. There was a biomass increase of 0.63 Mg ha-1 and 0.32 Mg ha-1 for fine roots <2 and <1 mm in diameter, respectively, with 1°C increase of mean annual temperature. There was an increase of 0.5 and 0.1 Mg ha-1 per 100 mm year-1 precipitation for the two size classes of fine roots. If the adaption of root production can match the pace of global warming and water is not a limiting factor for plant growth, fine root biomass would be expected to increase by 40-140% in response to the predicted increase in temperature (3-10°C) over the next century. Our analyses highlighted the strongly positive influences of temperature and precipitation on belowground function, suggesting that predicted future climate change could substantially enhance belowground biomass in the boreal region where the greatest warming is anticipated. This potential increase of belowground biomass, coupled with aboveground biomass, may provide a better understanding of climate-ecosystem feedbacks. [ABSTRACT FROM AUTHOR]

Water stress has been identified as a key mechanism of the contemporary increase in tree mortality rates in northwestern North America. However, a detailed analysis of boreal tree hydrodynamics and their interspecific differences is still lacking. Here we examine the hydraulic behaviour of co-occurring larch (Larix laricina) and black spruce (Picea mariana), two characteristic boreal tree species, near the southern limit of the boreal ecozone in central Canada. Sap flux density (Js), concurrently recorded stem radius fluctuations and meteorological conditions are used to quantify tree hydraulic functioning and to scrutinize tree water-use strategies. Our analysis revealed asynchrony in the diel hydrodynamics of the two species with the initial rise in Js occurring 2 h earlier in larch than in black spruce. Interspecific differences in larch and black spruce crown architecture explained the observed asynchrony in their hydraulic functioning. Furthermore, the two species exhibited diverging stomatal regulation strategies with larch and black spruce employing relatively isohydric and anisohydric behaviour, respectively. Such asynchronous and diverging tree-level hydrodynamics provide new insights into the ecosystem-level complementarity in tree form and function, with implications for understanding boreal forests' water and carbon dynamics and their resilience to environmental stress. [ABSTRACT FROM AUTHOR]

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

The reduction of competition through thinning increases radial growth in the stem and roots of many conifer species. However, not much is known about the effect of thinning on the dynamics of wood formation and intra-annual development of the growth ring, especially in the roots, which are an essential part of the tree for stability and resource acquisition. The aim of this study was to evaluate the effect of an experimental thinning on the dynamics and phenology of xylogenesis in the stem and roots of black spruce and balsam fir. Experimental and control trees were selected in two mature even-aged stands, one black spruce (Picea mariana (Mill.) BSP) and one balsam fir (Abies balsamea (L.) Mill.). Wood microcores were collected weekly in the stem and roots from May to October for a period of 4 years. The onset and ending of each cell differentiation phase were computed, as well as growth rate and total cell production. Results show that thinning increased the cell production rate of stem and roots of black spruce and balsam fir. This higher daily growth rate caused an increase in the total number of cells produced by the cambium. The intensity of the treatment was sufficient to significantly increase light availability for residual trees, but insufficient to modify soil temperature and water content to a point at which a significant change in the timing or duration of xylogenesis would be induced. Thus, thinning increased cell production rate and total number of cells produced in both stem and roots, but did not result in a change in the phenology of wood formation that could lead to increased risks of frost damage in the spring or autumn. [ABSTRACT FROM AUTHOR]

Copyright of Condor: Ornithological Applications is the property of Oxford University Press / USA 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.)

Copyright of Condor: Ornithological Applications is the property of Oxford University Press / USA 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.)

Within the managed boreal forest of Quebec (Canada), there is a need to ensure the maintenance of age diversity across the forest resource, and, as a result, forest age has become an important variable in forest management plans. Forest age is a major driver of stand height, with site factors such as climate, water, and light availability, modifying height based on local conditions. The link between stand age and height is used to evaluate the site index, a commonly used measure of productivity, which is the basis of many forest management decisions. Stand age is extremely costly and laborious to measure in situ and, as a result, new technologies are required to provide added predictive power, such as light detection and ranging (LiDAR) which can provide insights into forest structure and site characteristics. In this article, we examined the utility of airborne LiDAR data to estimate stand age across 158 sample plots within a naturally regenerated boreal forest in Quebec, Eastern Canada. A suite of forest structure (height, first return penetration rate, and corresponding Weibull distribution parameters) and site attributes (elevation, slope, aspect, solar radiation, wetness index, catchment area, and flow path length) was derived from the LiDAR data. The /(-nearest neighbor approach allowed imputation of stand age across the forest area, as well as providing key information on the predictive power of LiDAR metrics for estimating age in this forest region. Results indicate that LiDAR-derived predictors can estimate age well (R2 = 0.83, root mean square error [RMSE] = 19%) with a predicted error of less than 10 years. Estimations using only forest structure variables were lower (R2 = 0.74, RMSE = 22%). The most important forest structural predictors were stand height and Weibull crown shape parameters. Site predictors, in contrast, which had less predictive power, included elevation, slope, and catchment area with low to moderate importance [ABSTRACT FROM AUTHOR]

In the Nordic countries, growth of Norway spruce (Picea abies (L.) Karst.) is generally limited by low availability of nutrients, especially nitrogen. Optimizing forest management requires better insight on how growth responds to the environmental conditions and their manipulation. The aim of this study was to analyse the effects of nutrient optimization on timing and the rate of tracheid formation of Norway spruce and to follow the differentiation of newly formed tracheids. The study was performed during two growing seasons in a long-term nutrient optimization experiment in northern Sweden, where all essential macro- and micronutrients were supplied in irrigation water every second day from mid-June to mid-August. The control plots were without additional nutrients and water. Tracheid formation in the stem was monitored throughout the growing season by weekly sampling of microcores at breast height. The onset of xylogenesis occurred in early June, but in early summer there were no significant between-treatment differences in the onset and relative rate of tracheid formation. In both treatments, the onset of secondary cell wall formation occurred in mid-June. The maximum rate of tracheid formation occurred close to the summer solstice and 50% of the tracheids had been accumulated in early July. Optimized nutrition resulted in the formation of ∼50% more tracheids and delayed the cessation of tracheid formation, which extended the tracheid formation period by 20–50%, compared with control trees. The increased growth was mainly an effect of enhanced tracheid formation rate during the mid- and later-part of the growing season. In the second year, the increased growth rate also resulted in 11% wider tracheids. We conclude that the onset and rate of tracheid formation and differentiation during summer is primarily controlled by photoperiod, temperature and availability of nutrients, rather than supply of carbohydrates. [ABSTRACT FROM AUTHOR]

Accumulated carbon uptake, apparent quantum yield (AQY) and light-saturated net CO2 assimilation (Asat) were used to assess the responses of photosynthesis to environmental conditions during spring for three consecutive years. Whole-tree chambers were used to expose 40-year-old field-grown Norway spruce trees in northern Sweden to an elevated atmospheric CO2 concentration, [CO2], of 700 μmol CO2 mol−1 (CE) and an air temperature (T) between 2.8 and 5.6 °C above ambient T (TE), during summer and winter. Net shoot CO2 exchange (Anet) was measured continuously on 1-year-old shoots and was used to calculate the accumulated carbon uptake and daily Asat and AQY. The accumulated carbon uptake, from 1 March to 30 June, was stimulated by 33, 44 and 61% when trees were exposed to CE, TE, and CE and TE combined, respectively. Air temperature strongly influenced the timing and extent of photosynthetic recovery expressed as AQY and Asat during the spring. Under elevated T (TE), the recovery of AQY and Asat commenced ∼10 days earlier and the activity of these parameters was significantly higher throughout the recovery period. In the absence of frost events, the photosynthetic recovery period was less than a week. However, frost events during spring slowed recovery so that full recovery could take up to 60 days to complete. Elevated [CO2] stimulated AQY and Asat on average by ∼10 and ∼50%, respectively, throughout the recovery period, but had minimal or no effect on the onset and length of the photosynthetic recovery period during the spring. However, AQY, Asat and Anet all recovered at significantly higher T (average +2.2 °C) in TE than in TA, possibly caused by acclimation or by shorter days and lower light levels during the early part of the recovery in TE compared with TA. The results suggest that predicted future climate changes will cause prominent stimulation of photosynthetic CO2 uptake in boreal Norway spruce forest during spring, mainly caused by elevated T, but also elevated [CO2]. However, the effects of elevated T may not be linearly extrapolated to future warmer climates. [ABSTRACT FROM AUTHOR]

The effects of the past century's increase in atmospheric CO2 concentration ([CO2]) have been recorded in the stable carbon isotope composition (δ13C) of the annual growth rings of trees. The isotope record frequently shows increases in photosynthetic CO2 uptake relative to stomatal conductance, which estimates the CO2 concentration gradient across the stomata (ca − ci). This variable, which is one control over the net photosynthetic rate, has been suggested as a homeostatic gas-exchange set point that is easy to estimate from δ13C and [CO2]. However, in high-latitude conifer forests, the literature is mixed; some studies show increases in (ca − ci) and others show homeostasis. Here we present leaf and tree-ring δ13C data from a controlled experiment that tested factorial combinations of elevated [CO2] (365 and 700 ∝mol mol−1) and fertilization on mature Norway spruce (Picea abies (L.) Karst.) trees in northern Sweden. We found first that the leaf carbon pool was contaminated by the current photosynthate in the older leaf cohorts. This is the reverse of the common observation that older photosynthate reserves can be used to produce new tissue; here the older tissue contains recent photosynthate. We found that the tree-ring data lack such contamination and in any case they better integrate over the canopy and the growing season than do leaves. In the second and third years of treatment, elevated [CO2] alone increased (ca − ci) by 38%; when combined with fertilization, it increased (ca − ci) by 60%. The results of this study support the idea that annual rings provide a clearer isotopic signal than do foliage age-classes. The tree-ring data show that inferred (ca − ci) depends not only on [CO2], but also on mineral-nutrient status. The differences in (ca − ci) are sufficiently large to account for the treatment-induced increase in wood-volume production in these stands. [ABSTRACT FROM AUTHOR]

The growth responses of mature Norway spruce (Picea abies (L.) Karst.) trees exposed to elevated [CO2] (CE; 670–700 ppm) and long-term optimized nutrient availability or elevated air temperature (TE; ±3.9 °C) were studied in situ in northern Sweden in two 3 year field experiments using 12 whole-tree chambers in ca. 40-year-old forest. The first experiment (Exp. I) studied the interactions between CE and nutrient availability and the second (Exp. II) between CE and TE. It should be noted that only air temperature was elevated in Exp. II, while soil temperature was maintained close to ambient. In Exp. I, CE significantly increased the mean annual height increment, stem volume and biomass increment during the treatment period (25, 28, and 22%, respectively) when nutrients were supplied. There was, however, no significant positive CE effect found at the low natural nutrient availability. In Exp. II, which was conducted at the natural site fertility, neither CE nor TE significantly affected height or stem increment. It is concluded that the low nutrient availability (mainly nitrogen) in the boreal forests is likely to restrict their response to the continuous rise in [CO2] and/or TE. [ABSTRACT FROM AUTHOR]

Forests typically experience a mix of anthropogenic, natural and climate-induced stressors of different intensities, creating a mosaic of stressor combinations across the landscape. When multiple stressors co-occur, their combined impact on plant growth is often greater than expected based on single-factor studies (i.e., synergistic), potentially causing catastrophic dysfunction of physiological processes from an otherwise recoverable situation. Drought and herbivory are two stressors that commonly co-occur in forested ecosystems, and have the potential to ‘overlap’ in their impacts on various plant traits and processes. However, the combined impacts from these two stressors may not be predictable based on additive models from single-stressor studies. Moreover, the impacts and subsequent recovery may be strongly influenced by the relative intensities of each stressor. Here, we applied drought stress and simulated bark-feeding herbivory at three levels of intensity (control, moderate and severe) in a full factorial design on young Pinus sylvestris L. seedlings. We assessed if the combined effects from two stressors were additive (responses were equal to the sum of the single-factor effects), synergistic (greater than expected) or antagonistic (less than expected) on a suite of morphological and physiological traits at the leaf-, tissue- and whole-plant level. We additionally investigated whether recovery from herbivory was dependent on relief from drought. The two stressors had synergistic impacts on specific leaf area and water-use efficiency, additive effects on height and root-to-shoot ratios, but antagonistic effects on photosynthesis, conductance and, most notably, on root, shoot and whole-plant biomass. Nevertheless, the magnitude and direction of the combined impacts were often dependent on the relative intensities of each stressor, leading to many additive or synergistic responses from specific stressor combinations. Also, seedling recovery was far more dependent on the previous year's drought compared with the previous year's herbivory, demonstrating the influence of one stressor over another during recovery. Our study reveals for the first time, the importance of not only the presence or absence of drought and herbivory stressors, but also shows that their relative intensities are critical in determining the direction and magnitude of their impacts on establishing seedlings. [ABSTRACT FROM PUBLISHER]

Vegetation biomass is the ideal variable to estimate vegetation abundance and productivity and is necessary for studies of community structure. However, biomass data are difficult and destructive to collect, unlike areal cover data. To date, equations to predict biomass from percent cover have been developed for upland ground flora; however, these equations are lacking for riparian forests. We quantified relationships between aboveground biomass and percent cover of eight ground floristic growth forms (short forbs, tall forbs, ferns, clubmosses, horsetails, graminoids, dwarf shrubs, and bryoids) in riparian forests of the Canadian Boreal Plain and tested whether relationships differ for ground plants growing in two different successful stages (early and late). Without exception, linear relationships were identified with percent cover (P < 0.001) that explained 61-93% of the variation in biomass. Slopes of these lines depended on growth form but not on successional stage. When direct biomass measurements are not appropriate or possible, the relationships presented can be used to rapidly and nondestructively estimate biomass in the Boreal Plain riparian forests. [ABSTRACT FROM AUTHOR]

In boreal ecosystems, an increase in soil temperature can stimulate plant growth. However, cambium phenology in trees was better explained by air than soil temperature, which suggested that soil temperature is not the main limiting factor affecting xylogenesis. Since soil temperature and snowmelt are correlated to air temperature, the question whether soil temperature directly limits xylogenesis in the stem will remain unresolved without experiments disentangling air and soil temperatures. This study investigated the effects of an increase of 4 °C in soil temperature and a consequent 1-week earlier snowmelt on growth of black spruce [Picea mariana (Mill.) BSP] in the boreal forest of Quebec, Canada. The soil of two natural stands at different altitudes was warmed up with heating cables during 2008–2010 and cambial phenology and xylem production were monitored weekly from April to October. The results showed no significant effect of the treatment on the phenological phases of cell enlargement and wall thickening and lignification. The number of cells produced in the xylem also did not differ between control and heated trees. These findings allowed the hypothesis of a direct influence of soil temperature on stem growth to be rejected and supported the evidence that, in the short term, air temperature is the main limiting factor for xylogenesis in trees of these environments. [ABSTRACT FROM PUBLISHER]

The article presents the study conducted regarding the success of breeding the migratory songbirds in the harvested boreal forests in northwestern Newfoundland and Labrador. The study aims to determine the impact of forest harvest on the success pf passerines breeding and the natural harvesting on the harvesting consequences. The result from a series of nests and banded hatch-year birds monitoring shows that spatial and temporal heterogeneity have complex interactions in the forest harvest and the daily survival of nests are significantly associated to the harvest proportion.

Variations in fine root biomass of trees and understory in 16 stands throughout Finland were examined and relationships to site and stand characteristics determined. Norway spruce fine root biomass varied between 184 and 370 g m-2, and that of Scots pine ranged between 149 and 386 g m-2. In northern Finland, understory roots and rhizomes (< 2mm diameter) accounted for up to 50% of the stand total fine root biomass. Therefore, the fine root biomass of trees plus understory was larger in northern Finland in stands of both tree species, resulting in a negative relationship between fine root biomass and the temperature sum and a positive relationship between fine root biomass and the carbon:nitrogen ratio of the soil organic layer. The foliage:fine root ratio varied between 2.1 and 6.4 for Norway spruce and between 0.8 and 2.2 for Scots pine. The ratio decreased for both Norway spruce and Scots pine from south to north, as well as from fertile to more infertile site types. The foliage:fine root ratio of Norway spruce was related to basal area and stem surface area. The strong positive correlations of these three parameters with fine root nitrogen concentration implies that more fine roots are needed to maintain a certain amount of foliage when nutrient availability is low. No significant relationships were found between stand parameters and fine root biomass at the stand level, but the relationships considerably improved when both fine root biomass and stand parameters were calculated for the mean tree in the stand. When the northern and southern sites were analyzed separately, fine root biomass per tree of both species was significantly correlated with basal area and stem surface area per tree. Basal area, stem surface area and stand density can be estimated accurately and easily. Thus, our results may have value in predicting fine root biomass at the tree and stand level in boreal Norway spruce and Scots pine forests. [ABSTRACT FROM AUTHOR]

Carbon (C) availability to ectomycorrhizal fungi is likely to increase at elevated atmospheric CO2. To determine whether there are any broad patterns in species' responses that relate to their ecology, we compared growth, respiration, N uptake and C exudation of 17 fungal isolates in liquid culture. As a surrogate for increased C availability we used three different C:N ratios (10:1, 20:1 and 40:1), moving from conditions of C limitation to conditions of N limitation. Responses were species-specific, and suilloid fungi were the most responsive in terms of growth and respiration. In contrast, a group of eight isolates showed no growth increase above C:N 20:1. This inability to respond was not due to N limitation, although there were marked differences in N uptake between isolates. At higher C availability isolates generally became more efficient in converting C into biomass. Six isolates showed net release of exudates into the culture medium (up to 40% of the C in biomass and respiration). We conclude that the findings were in agreement with field observations, and suggest that pure culture observations can yield ecologically relevant information on how ectomycorrhizal fungi may respond under conditions of elevated CO2. [ABSTRACT FROM AUTHOR]

I summarize our current understanding of the evolutionary origin and biogeographic history of the New World flying squirrels (Glaucomys). The emerging synthesis of flying squirrel systematics supports a monophyletic origin for the group in the early Miocene followed by a divergence of New World and Eurasian flying squirrels in the late Miocene. Today, the New World flying squirrels consist of 2 recognized species, G. sabrinus and G. volans. These 2 species are closely associated with the northern coniferous and deciduous hardwood forest biomes of North America, respectively, making them especially useful as biogeographic indicator species for these 2 forest types. Molecular systematic studies have revealed the presence of 2 distinct evolutionary lineages within G. sabrinus (a widespread Continental lineage and a more geographically restricted Pacific Coastal lineage). Bacular morphology and data from nuclear loci suggest recent or ongoing gene flow between these 2 lineages where they meet in the Pacific Northwest of North America. Populations of G. volans from eastern North America represent a 3rd distinct lineage within the genus. Mesoamerican flying squirrels (traditionally considered to be southern forms of G. volans) have not been examined with molecular data and may represent 1 or more additional lineages. From a biogeographic perspective, Quaternary climatic fluctuations and associated changes in the location and extent of forest habitats appear to have been important factors in promoting early evolutionary diversification within the genus; structuring of intraspecific patterns of genetic variation; and producing geographically isolated peripheral populations in high-elevation habitats at the southern extremes of each species' range, several of which are now of conservation concern. These results have broad implications for understanding the Quaternary biogeography of the coniferous and deciduous forest biomes of North America. [ABSTRACT FROM AUTHOR]

Forested wetlands and peatlands are important in boreal and terrestrial biogeochemical cycling, but most general-purpose forest process models are designed and parameterized for upland systems. We describe changes made to Biome-BGC, an ecophysiological process model, that improve its ability to simulate poorly drained forests. Model changes allowed for: (1) lateral water inflow from a surrounding watershed, and variable surface and subsurface drainage; (2) adverse effects of anoxic soil on decomposition and nutrient mineralization; (3) closure of leaf stomata in flooded soils; and (4) growth of nonvascular plants (i.e., bryophytes). Bryophytes were treated as ectohydric broadleaf evergreen plants with zero stomatal conductance, whose cuticular conductance to CO2 was dependent on plant water content. Individual model changes were parameterized with published data, and ecosystem- level model performance was assessed by comparing simulated output to field data from the northern BOREAS site in Manitoba, Canada. The simulation of the poorly drained forest model exhibited reduced decomposition and vascular plant growth (-90%) compared with that of the well-drained forest model; the integrated bryophyte photosynthetic response accorded well with published data. Simulated net primary production, biomass and soil carbon accumulation broadly agreed with field measurements, although simulated net primary production was higher than observed data in well-drained stands. Simulated net primary production in the poorly drained forest was most sensitive to oxygen restriction on soil processes, and secondarily to stomatal closure in flooded conditions. The modified Biome-BGC remains unable to simulate true wetlands that are subject to prolonged flooding, because it does not track organic soil formation, water table changes, soil redox potential or anaerobic processes. [ABSTRACT FROM AUTHOR]

Examination of temperature variations over the past century for Europe and the Arctic from northern Norway to Siberia suggests that variations in the North Atlantic Oscillation are associated with an increase in oceanicity in certain maritime regions. A southward depression of the treeline in favour of wet heaths, bogs and wetland tundra communities is also observed in northern oceanic environments. The physiological basis for this change in ecological succession from forest to bog is discussed in relation to the long‐term effects of flooding on tree survival. The heightened values currently detected in the North Atlantic Oscillation Index, together with rising winter temperatures, and increased rainfall in many areas in northern Europe, presents an increasing risk of paludification with adverse consequences for forest regeneration, particularly in areas with oceanic climates. Climatic warming in oceanic areas may increase the area covered by bogs and, contrary to general expectations, lead to a retreat rather than an advance in the northern limit of the boreal forest. High water‐table levels are not automatically detrimental to forest survival as can be seen in swamp, bottomland and mangrove forests. Consequently, the inhibitory effects of flooding on tree survival and regeneration in northern regions should not be uncritically accepted as merely due to high water levels. Evidence is discussed which suggests that physiological and ecological factors may interact to inhibit forest regeneration in habitats where there is a risk of prolonged winter‐flooding combined with warmer winters and cool moist summers. [ABSTRACT FROM PUBLISHER]

Specific leaf area (SLA) and leaf area index (LAI) were estimated using site-specific allometric equations for a boreal black spruce (Picea mariana (Mill.) BSP) fire chronosequence in northern Manitoba, Canada. Stands ranged from 3 to 131 years in age and had soils that were categorized as well or poorly drained. The goals of the study were to: (i) measure SLA for the dominant tree and understory species of boreal black spruce-dominated stands, and examine the effect of various biophysical conditions on SLA; and (ii) examine leaf area dynamics of both understory and overstory for well- and poorly drained stands in the chronosequence. Overall, average SLA values for black spruce (n = 215), jack pine (Pinus banksiana Lamb., n = 72) and trembling aspen (Populus tremuloides Michx., n = 27) were 5.82 ± 1.91, 5.76 ± 1.91 and 17.42 ± 2.21 m2 kg−1, respectively. Foliage age, stand age, vertical position in the canopy and soil drainage had significant effects on SLA. Black spruce dominated overstory LAI in the older stands. Well-drained stands had significantly higher overstory LAI (P < 0.001), but lower understory LAI (P = 0.022), than poorly drained stands. Overstory LAI was negligible in the recent (3–12 years old) burn sites and highest in the 70-year-old burn site (6.8 and 3.0 in the well- and poorly drained stands, respectively), declining significantly (by 30–50%) from this peak in the oldest stands. Understory leaf area represented a significant portion (> 40%) of total leaf area in all stands except the oldest. [ABSTRACT FROM PUBLISHER]

One-year-old seedlings of Abies balsamea (L.) Mill, Picea glauca (Moench) Voss, Pinus contortaLoudon, Betula papyrifera Marsh., Populus tremuloides Michx. and Populus balsamifera L. were transplanted in the spring, in pots, to the understory of a mixed P. tremuloides–P. balsamifera stand or to an adjacent open site. Growth and leaf characteristics were measured and photosynthetic light response curves determined in mid-August. Overall, the coniferous seedlings showed less photosynthetic plasticity in response to growth conditions than the deciduous species. Abies balsamea, P. glauca and B. papyrifera responded to the understory environment with higher leaf area ratios, and lower photosynthetic light saturation points and area-based leaf respiration relative to values for open-grown seedlings, while they matched or exceeded the height growth of open-grown seedlings. In contrast, seedlings of Pinus contorta, P. tremuloides and P. balsamifera displayed characteristics that were not conducive to survival in the understory. These characteristics included a high light saturation point and leaf dark respiration rate in P. contorta, and lower leaf area variables combined with higher carbon allocation to roots in P. tremuloides and P. balsamifera. By the second growing season, all seedlings of P. tremuloides and P. balsamifera growing in the understory had died. [ABSTRACT FROM PUBLISHER]

We used an automated, multiplexing gas-exchange system to measure the net exchange of CO2 at the surfaces of three shady feather moss and three exposed sphagnum moss sites in a black spruce forest during 35 days at the end of the 1995 growing season. Midday gross photosynthesis was 0.5 to 1.0 μmol m−2 s−1 by feather moss and 0.5 to 2.5 μmol m−2 s−1 by sphagnum moss. Photosynthesis by sphagnum moss was reduced by approximately 70% at 0 °C, and reached a maximum rate at 8 °C. Nighttime CO2 efflux, the sum of soil and moss respiration was 1 to 2.5 μmol m−2 s−1 above feather moss and 0.5 to 1.5 μmol m−2 s−1 above sphagnum moss at moss temperatures of 0 to 15 °C. The higher rates of respiration at the feather moss sites probably reflected a greater belowground input of carbon from black spruce, and the lower rates of photosynthesis were probably associated with shading by the black spruce canopy. Photosynthesis by moss accounted for 10 to 50% of whole-forest gross CO2 uptake measured simultaneously by eddy covariance. Respiration at the moss surface was 50 to 90% of whole-forest respiration, with a decreasing fraction on warm nights apparently because of a disproportionate rise in aboveground respiration. [ABSTRACT FROM AUTHOR]

A process-based, general ecosystem model (BIOME–BGC) was used to simulate daily gross primary production, maintenance and heterotrophic respiration, net primary production and net ecosystem carbon exchange of boreal aspen, jack pine and black spruce stands. Model simulations of daily net carbon exchange of the ecosystem (NEE) explained 51.7% (SE = 1.32 g C m−2 day−1) of the variance in daily NEE derived from stand eddy flux measurements of CO2 during 1994. Differences between measured and simulated results were attributed to several factors including difficulties associated with measuring nighttime CO2 fluxes and model assumptions of site homogeneity. However, comparisons between simulations and field data improved markedly at coarser time-scales. Model simulations explained 66.1% (SE = 0.97 g C m−2 day−1) of the variance in measured NEE when 5-day means of daily results were compared. Annual simulations of aboveground net primary production ranged from 0.6–2.4 Mg C ha−1 year−1 and were concurrent with results derived from tree increment core measurements and allometric equations.Model simulations showed that all of the sites were net sinks (0.1–4.1 Mg C ha−1 year−1) of atmospheric carbon for 1994. Older conifer stands showed narrow margins between uptake of carbon by net photosynthesis and carbon release through respiration. Younger stands were more productive than older stands, primarily because of lower maintenance respiration costs. However, all sites appeared to be less productive than temperate forests. Productivity simulations were strongly linked to stand morphology and site conditions. Old jack pine and aspen stands showed decreased productivity in response to simulated low soil water contents near the end of the 1994 growing season. Compared with the aspen stand, the jack pine stand appeared better adapted to conserve soil water through lower daily evapotranspiration losses but also exhibited a narrower margin between daily net photosynthesis and respiration. Stands subjected to water stress during the growing season may exist on the edge between being annual sources or sinks for atmospheric carbon. [ABSTRACT FROM AUTHOR]