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Northwest North America has unique high elevation Picea–Abies forests and parkland classified in British Columbia as the Engelmann Spruce–Subalpine–fir (ESSF) Biogeoclimatic zone. These ecosystems occur on a topographically and climatically complex landscape, juxtaposed with diverse vegetation types including alpine tundra, inland rain forest, dry conifer forest, and grasslands. Spatio-temporal ecosystem disturbance is varied, driven by factors such as climate variation, wildfire, volcanic eruptions, and insect herbivory. A pollen and charcoal record derived from a lake sediment core from the ESSF reveals a unique late-glacial to modern vegetation history progressing from alpine steppe through dry open conifer forest to moist spruce–fir ecosystems, the latter arising only 4600 years ago, late by comparison to other ESSF sites in the region. Repeated disturbance in the mid Holocene by wildfire coupled with volcanic ash deposition and increased climatic variation resulted in recurring Pinus contorta-dominated seral forest stands before cooling and moistening in the late Holocene led to stable Picea–Abies forest. With rapid climate change, changing disturbance regimes, and timber harvest, the management of dry ESSF forests needs to consider that this forest-type could transform into parkland or open seral pine stands, with a high frequency disturbance regime. [ABSTRACT FROM AUTHOR]

Dissolved black carbon (DBC) is the remobilized soluble fraction of black carbon (BC). DBC, present in all aquatic environments, is a heterogeneous mixture of various pyrogenic aromatics. For a long time, oceans were solely considered to be the largest pool of DBC. However, recent research indicates that lakes might also contain significant concentrations of DBC. Anthropogenic BC emissions and seasonal changes driven by climate change could increase DBC flux to glacial and fluvial lacustrine systems with unique effects. In this article, current knowledge concerning the formation, sources, transportation, fate, and environmental implications of DBC in lacustrine networks is presented. Furthermore, ambiguities pertaining to terminology and methodologies used in the separation and quantification of DBC are also reviewed, and research gaps that should be addressed in future studies are highlighted. Constraining DBC dynamics and residence times in lacustrine systems could provide valuable insights into anthropogenic perturbations of the global carbon cycle. [ABSTRACT FROM AUTHOR]

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Biotic disturbance agents are important factors influencing forest dynamics; incorporating them into management planning requires a detailed understanding of their distribution, prevalence, and effects on stand dynamics. However, this information can be difficult to collect in remote forest systems, such as lowland black spruce (Picea mariana (Mill.) B.S.P.) forests affected by eastern spruce dwarf mistletoe (Arceuthobium pusillum Peck, hereafter ESDM). In such cases, predictive modeling is often needed to inform management decisions and address forest health questions. Here, we used two publicly available datasets to predict areas where black spruce is more likely to be infested with ESDM in northeastern Minnesota, USA. Using random forest modeling and logistic regression, we found location, stand age, basal area, site index, average diameter, and metrics of species composition to be among the most important predictors of ESDM occurrence. Predictions showed two regions of greater likelihood of infestation with distinct ecological characteristics and ownership patterns. By understanding how stand structural characteristics relate to ESDM infestations, managers can improve monitoring and management of ESDM at the stand and landscape scales. Additionally, our approach of using multiple datasets and modeling methods can serve as a framework for decision-making on other forest health concerns. [ABSTRACT FROM AUTHOR]

Minimizing tillage has been promoted as an agricultural practice that may mitigate greenhouse gas emissions through carbon sequestration. However, there is some ambiguity regarding the effect of minimum tillage (MT) on emissions of other greenhouse gases, in particular soil nitrous oxide (N2O) emissions. To determine how effective MT could be in helping Canada mitigate greenhouse gas emissions, we used a meta-analysis to compare growing season N2O emissions from MT versus conventional tillage (CT). Overall, MT had 12% lower N2O emissions compared to CT (P = 0.03). However, there was high variability due to soil texture and growing season precipitation (GSP), with MT tending to emit more N2O than CT in climates where GSP exceeded 600 mm, particularly for soils with sand content less than 60%. Therefore, unless long-term tillage trials, which are urgently needed in eastern Canada, show a reduction in N2O emissions over time, MT should be used as a greenhouse gas mitigation measure only in dry climates or on sandy soils. [ABSTRACT FROM AUTHOR]

As one of the most widely used dwarf bamboos, Pleioblastus viridistriatus has well-developed rhizome and root systems, which can rapidly expand into forest stands. However, little is known about the influence of P. viridistriatus expansion on the undergrowth diversity in subtropical forests of China and its association with the diversity of soil bacterial microbiota. The species diversity and soil bacterial community structure were investigated in a forest where P. viridistriatus was expanding into coniferous and broad-leaved mixed forest. We found that P. viridistriatus expansion reduced species diversity in the shrub and herbaceous layers and had significant effects on major soil physicochemical properties. In addition, the alpha diversity indexes were significantly increased and the abundance of Actinobacteria and Candidatus Saccharibacteria increased, while the abundance of Nitrospirae and Deinococcus-Thermus decreased with the increasing expansion. At the genus level, a total of 25 genera of soil bacteria showed significant difference in abundance. Overall, expansion of P. viridistriatus reduced forest species diversity, while increased soil nutrient accumulation and specific bacterial abundance to improve nutrient acquisition. Our results can provide guidance for controlling dwarf bamboo expansion and help the sustainable forest management. [ABSTRACT FROM AUTHOR]

Arctic warming is occurring at a much faster rate than in other parts of the globe, with potentially devastating consequences for the diverse array of species within ecologically and biologically sensitive areas in the Arctic marine region. However, climate change research in this region is sparse compared to other biomes, hindering conservation efforts. In this article, we review and synthesize the available literature to understand the observed and potential impacts of climate change on different species and ecosystems in the Arctic marine region. We reviewed 253 articles reporting changes in species and ecosystems in the Arctic marine region in response to climate change (225 studies documenting observed impacts and 28 reporting predicted impacts). The review revealed that most research effort has been concentrated in only a subset of Arctic Large Marine Ecosystems (LMEs) (5/18 LMEs), with the majority of Arctic LMEs being poorly studied. The majority of the reviewed papers focused on marine mammals (19%) followed by microalgae (17%). A number of studies documented variability in planktonic communities (microalgae, macroalgae, zooplankton), resulting in alteration in ecosystem structure and function. Reproductive failure, decline in populations, and changes in diet composition, behavior, and breeding biology were reported for sea birds and mammals. Further, shifts in spatial distribution of fishes were observed by several studies. This review provides persuasive evidence that multiple climate change indices in the Arctic region are changing, with impacts on almost all components of marine biotic ecosystems (from plankton to top predators). We identify a number of gaps (such as limited inventory of biota, robustness of data supporting climate change indices on an Arctic Ocean scale, and climate suitability assessment for all species) in climate change research in Arctic marine ecosystems where future studies can help to quantify the impacts of climate change on species and ecosystems and advance understanding for their adaptive management. [ABSTRACT FROM AUTHOR]

This study reveals the thermal control mechanism of a ventilated–closed block layer composite embankment structure by analyzing the heat transfer and temperature change based on the measured data of the high-grade highway experimental engineering in the Beiluhe area of the Qinghai–Tibet Plateau. During the cold season, natural convection occurred in the block layer when the upper boundary temperature was approximately 2 °C lower than that of the bottom boundary. In addition, heat from the foundation was transferred upwards through the block layer via heat convection. During the warm season, air inside the block layer was almost static, and external heat was transferred downwards through the block layer via heat conduction. The equivalent thermal conductivity of the block layer in the cold season was approximately 17.4 times that of the warm season, and heat release through the block layer was 9.65 times that of heat absorption, exhibiting a thermal semiconductor effect. The results show that the frozen soil foundation was in net exothermic state, the permafrost table continuously rose, and the mean annual soil temperature continuously decreased above 14 m depth. This research can contribute to thermal control technology development and construction scheme selection of expressway in permafrost regions. [ABSTRACT FROM AUTHOR]

Although relatively infrequent, invasions by non-native plants at high latitudes are increasingly recognized as an emerging problem. Churchill, MB, Canada is unusual as over 100 non-native species have been found in human-disturbed areas, making it an outlier amongst subarctic habitats. Although these non-native species have persisted almost exclusively within town, some occur in isolated locations throughout the local road network. Most of these non-native species have been observed in areas with a history of soil movement (e.g., for construction or road repairs), suggesting that they have been moved within the soil, likely either germinating from seeds or growing clonally from root and rhizome fragments. Using a greenhouse experiment, we found evidence that soils from human-disturbed sites can contain a substantial non-native seed bank. In particular, we grew a significantly higher number of non-native seedlings from translocated soils compared with uninvaded soils. These germinated non-native species are native to Europe but have widely invaded temperate regions. This study provides the first direct evidence that movement of seed-contaminated soil is a significant source of local non-native species spread. Future warming in Arctic regions may increase seed production of these species, leading to increased spread and persistence via contaminated soil. [ABSTRACT FROM AUTHOR]

Willow (Salix viminalis spp.) shrubs are being planted along riverbanks, on erodible and marginal farmland. Wood chips made from the woody biomass could improve the properties of light-textured soils with low organic matter content in potato-based systems. Willow chips were applied at 0, 20, 40, and 60mgha?1 (fresh weight) as a soil amendment. Soil health parameters were evaluated after 12months, followed by C and N contents in whole soil, particulate, and mineral-associated organic matter fractions after 18months. Willow chip application increased soil aggregation, respiration, C and N contents in whole soil, and plant-available K. On plante l'osier blanc (Salix viminalis spp.) le long des berges ainsi que sur les terres agricoles sujettes à l'érosion ou peu rentables. Des copeaux de bois tirés de la biomasse ligneuse pourraient améliorer les propriétés des sols à texture légère pauvres en matière organique, comme ceux servant à la culture de la pomme de terre. Les auteurs ont appliqué un amendement correspondant à 0, 20, 40 ou 60 Mg (poids frais) de copeaux d'osier par hectare. Douze mois plus tard, ils ont évalué la vitalité du sol puis, au bout de dix-huit mois, la teneur en C et en N du sol complet ainsi que les fractions de matière organique associées aux particules et aux minéraux. Les copeaux d'osier améliorent l'agrégation et la respiration du sol, la concentration de C et de N dans le sol complet, de même que le K assimilable par les plantes. [Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing 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.)

As Arctic ecosystems become increasingly vulnerable to climate- and human-induced stressors, effective marine management will rely on the characterization of fish movements. Over a six-year study period, the movements of 65 Greenland sharks (Somniosus microcephalus) (41 males, 24 females; mean LT = 2.48 ± 0.50 m) were monitored using static acoustic telemetry. Shark presence in a typical deep-water fjord was restricted to the summer open-water period. Residency duration varied based on age class (juvenile, n = 17; subadult, n = 48); however, activity space size and extent were comparable. A quarter of tagged sharks (n = 16) returned to the system in subsequent years after tagging, with individuals redetected for a maximum of 4 years. Movements between coastal and offshore waters occurred primarily via a deep-water channel with sharks detected along the channel banks. These multiyear data depict how a potentially vulnerable Arctic predator utilizes a deep-water fjord in the context of the regional development of community inshore and offshore commercial fisheries. [ABSTRACT FROM AUTHOR]

The main objective of this study was to compare the effects of two densities (278 stems·ha−1 with two spacings of 6 m × 6 m or 4.5 m × 8 m, 400 stems·ha−1 with two spacings of 5 m × 5 m or 3 m × 8 m) and three poplar clones (NL95, NL895, and NL797) on productivity and carbon (C) sequestration of poplar ecosystems. The results showed that planting density significantly affected the biomass of a single tree. The mean tree biomass of clone NL95 was higher in all spacings than that of the other clones, with a significant difference for the 6 m × 6 m spacing. The biomass of poplar trees ranged from 78.9 to 110.3 Mg·ha−1, with the highest tree biomass observed in the square configuration. Soil C concentration (0–100 cm) increased after 12 years of management. Soil C storage ranged from 138.1 to 164.3 Mg C·ha−1, and the highest soil C storage was in the NL797 poplar plantation with 6 m × 6 m spacing. Our results suggested that clones NL95 and NL797 should be chosen for planting, with a planting density of 278 stems·ha−1 and spacing of 6 m × 6 m. [ABSTRACT FROM AUTHOR]

The stylonurid eurypterid Leiopterella tetliei Lamsdell, Braddy, Loeffler, and Dineley, 2010 (Chelicerata: Eurypterida: Rhenopteridae) from the Early Devonian (Lochkovian) of Nunavut in Arctic Canada is redescribed. Restudy of the holotype under polarized light revealed a labrum, epistomal sutures, prosomal appendage III, and deltoid plates anterior to the genital appendage. An additional new specimen preserves the distal podomeres of appendage VI and gradually tapering opisthosomal tergites. The characters resolved here support the hypothesis that L. tetliei was relatively basal within the wider Stylonurina clade, with its tapering postabdomen supporting a more basal position within Rhenopteridae than previously suggested. [ABSTRACT FROM AUTHOR]

The warming trends observed in the temperature nodes (thermistors, SAAs) in the embankment fill and foundation soil are attributedto twofactors:(i)warmerandlonger summermonths recorded from the AWS led to deeper thaw penetration in the slopesandfoundationsoiland(ii)heatextractionduringthewintermonths was attenuatedbecause of snow accumulation at the embankmentslopes. Key words: highway embankments, permafrost, winter construction, frozen fill compaction, reinforced slopes, wicking geotextiles. These geotextiles have an overhang of 0.5 m (Fig.5b)toallowwatertoflowoutoftheembankment.The length of the geotextile installed in the embankment is 8.4 m, to intercept the potential failure surface when the embankment thaws and if sloughing occurs. Although the permafrost aggraded to the natural ground surface for the 1.8 m embankment, best practice design is to have the permafrost aggradeintotheembankment. [Extracted from the article]

Northwestern Canada's boreal forest has experienced rapid warming, drying, and changes to permafrost, yet the growth responses and mechanisms driving productivity have been under-studied at broad scales. Forest responses are largely driven by black spruce (Picea mariana (Mill.) B.S.P.) — the region's most widespread and dominant tree. We collected tree ring samples from four black spruce-dominated sites across 15° of latitude, spanning gradients in climate and permafrost. We investigated (i) differences in growth patterns, (ii) variations in climatic drivers of growth, and (iii) trends in water use efficiency (WUE) through 13C isotope analysis from 1945 to 2006. We found positive growth trends at all sites except those at mid-latitude, where rapid permafrost thaw drove declines. Annual growth was lowest at the tree limit site and highest at the tree line. Climatic drivers of these growth patterns varied; positive growth responses at the northerly sites were associated with warmer winters, whereas Δ13C trends and climate-growth responses at mid-latitude sites indicated that growth was limited by moisture availability. Δ13C signatures indicated increased WUE at the southernmost site, with no significant trends at northern sites. These results suggest that warming will increase the growth of trees at the northern extent of black spruce, but southerly areas may face drought stress if precipitation does not balance evapotranspiration. [ABSTRACT FROM AUTHOR]

This study investigated differences in forest structure, organic layer thickness, soil organic carbon, and permafrost depth between late-successional (LS) and postfire (PF; 90–120 years since burn) plots under black spruce (Picea mariana (Mill.) B.S.P.) growing on fine-textured, poorly drained lacustrine sediments in the Copper River Basin, Alaska. Although live stem and seedling density and organic layer thickness were not significantly different between PF and LS plots (28 ± 7 cm and 31 ± 10 cm, respectively), we did find a significant difference in soil organic carbon (SOC) stocks (30 ± 10 kg·m−2 and 46 ± 12 kg·m−2, respectively) permafrost depth (90 ± 28 cm and 56 ± 12 cm, respectively). OLT was linearly related to 1 m SOC stocks for LS plots but not for PF plots, and LS plots had a greater proportion of highly decomposed (humic) material in the organic layer. The soil properties of PF plots appear to be on a trajectory of recovery toward those of LS plots with respect to SOC stocks, permafrost depth, and organic layer composition. However, PF plots remain different despite nearly 100 years since fire disturbance and thus they are potentially more sensitive to changes in future fire frequency or climate. [ABSTRACT FROM AUTHOR]

The relationship between littoral macroinvertebrate communities and environmental gradients in Arctic lakes is poorly understood, making it difficult to predict whether these important components of lake ecosystems will be affected by emerging stressors such as permafrost thaw and road development. To better understand how littoral macroinvertebrates are related to environmental gradients, we characterized macroinvertebrate communities and environmental variables for 32 Arctic lakes across the boreal–tundra transition in the Northwest Territories. Our analysis showed that a small selection of variables had strong relationships with community structure: calcium, conductivity, latitude, surface area, catchment area, percent fine sediment, chlorophyll a, and whitefish (Coregonus clupeaformis or Coregonus nasus) presence. Many of these variables, including calcium, conductivity, and chlorophyll a levels, are affected by permafrost thaw and road dust contamination. Based on the direction and magnitude of these relationships, we hypothesize that macroinvertebrate abundance might decline in response to permafrost thaw and road dust contamination, while taxon diversity may rise. While correlative in nature, our results and hypotheses may be valuable as future studies evaluate ongoing changes in Canada's Arctic lakes. [ABSTRACT FROM AUTHOR]

Analyses of marine and terrestrial palynomorphs of Ocean Drilling Program (ODP) Site 645 in Baffin Bay led us to define a new biostratigraphical scheme covering the late Miocene to Pleistocene based on dinocyst and acritarch assemblages. Four biozones were defined. The first one, from 438.6 m below sea floor (mbsf) to 388 mbsf, can be assigned a late Miocene to early Pliocene age (>4.5 Ma), based on the common occurrence of Cristadinium diminutivum and Selenopemphix brevispinosa. Biozone 2, spanning from an erosional unconformity to a recovery hiatus, is marked by the highest occurrences (HOs) of Veriplicidium franklinii and Cristadinium diminutivum, which suggest an early Pliocene age >3.6 Ma (∼4.5 to ∼3.6 Ma). Biozone 3, above the recovery hiatus and up to 220.94 mbsf, corresponds to a late Pliocene or early Pleistocene age based on occurrences of Bitectatodinium readwaldii, Cymatiosphaera? icenorum, and Lavradosphaera canalis. Finally, between 266.4 and 120.56 mbsf, Biozone 4, marked by the HO of Filisphaera filifera, Filisphaera microornata, and Habibacysta tectata, has an early Pleistocene age (>1.4 Ma). Our biostratigraphy implies that horizon b1 of the Baffin Bay seismic stratigraphy corresponds to the recovery hiatus at ODP Site 645, which suggests a very thick Pliocene sequence along the Baffin Island slope. Dinocyst assemblages and terrestrial palynomorphs in our records indicate that the late Miocene and (or) early Pliocene were characterized by relatively warm coastal surface waters and boreal forest or forested tundra vegetation over adjacent lands. In contrast, the early Pleistocene dinocyst assemblages above the recovery hiatus indicate cold surface waters, while pollen data suggest reduced vegetation cover on adjacent lands. [ABSTRACT FROM AUTHOR]

Only two species of boreal Holarctic frogs (genus Rana Linnaeus, 1758) can survive freezing and overwinter on land; they are found in the subarctic and cold regions of North America (Wood Frog, Rana sylvatica LeConte, 1825) and Eurasia (Moor Frog, Rana arvalis Nilsson, 1842) and are an example of an unusual adaptive strategy of overwintering. Freeze tolerance (down to –16 °C) of R. sylvatica has been thoroughly studied; however, little is known about cold resistance of R. arvalis in cold regions. We found that R.arvalis from European Russia and from West Siberia tolerate freezing down to –12 or –16 °C, whereas frogs from the Danish population survived freezing only to –4 °C (Y. Voituron et al. 2009b; J. Comp. Physiol. B, 179: 223–230). All of these populations, according to mitochondrial DNA markers, are closely related. We suggest that the observed differences in cold tolerance (–4 °C vs. –12 or –16 °C) could be caused either by adaptations to climatic factors or by differences in experimental protocols. The northeastern boundary of the geographic range of R. arvalis in Yakutia coincides with the transitional area between discontinuous and continuous permafrost; beyond this area, winter soil temperature sharply declines. The lower lethal temperature and overwintering ecology of R. arvalis in Siberia are similar to those of the North American R.sylvatica. [ABSTRACT FROM AUTHOR]

The article focuses on greenhouse gas emissions from peatlands under manipulated warming, nitrogen addition, and vegetation composition change. Topics include the carbon dioxide in the atmosphere has absorbed by the vegetation through photosynthesis, the decomposition is another essential factor in carbon accumulation, and the waterlogged peat and low temperature are two limiting factors for the decomposition.

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing 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.)

We describe a new fossil wood species of pine, Pinuxylon selmeierianum sp. nov., for a piece of petrified wood encased within a concretion that was recovered in marine, fine-grained sandstones of the Paleogene Eureka Sound Group on Wootton Peninsula, Ellesmere Island. The fossil wood is allochthonous, having drifted in from a nearby landmass. Within the fossil wood genus Pinuxylon Gothan, 1905, Pinuxylon selmeierianum sp. nov. shares anatomical characteristics with the haploxylon sections Parrya Mayr, 1890 and Strobus Little and Critchfield, 1969. The new species is most closely related to the extant Pinus lambertiana Douglas, 1827, a species belonging to section Strobus. Our study provides the first evidence for a fossil Pinus Linné, 1753 on Wootton Peninsula, supporting the idea that Pinus was an "Arctic conifer", and providing insights into Paleogene vegetation at high latitudes. [ABSTRACT FROM AUTHOR]

Tree roots comprise a huge carbon pool. Their dynamics are driven by environmental factors and thereby affected by climate change. We studied the effects of soil temperature on root and shoot phenology and their linkages in Norway spruce (Picea abies (L.) Karst.). Saplings were grown in controlled-environment rooms for three simulated growing seasons (GS1, GS2, and GS3). Soil-temperature treatments of 9, 13, 18, and 21 °C were applied during GS2. Root growth was monitored with minirhizotrons and commenced in all treatments simultaneously. Temporal growth patterns of short and long roots were usually bimodal. Root growth was very low during the coldest treatment of GS2 but increased during GS3 as an aftereffect. During GS3, growth of short roots continued later after colder treatments than warmer treatments. Reduced sink strength of roots and increased carbohydrate accumulation into needles at 9 °C during GS2 probably enabled compensatory root growth under restored temperatures during GS3. Soil temperature did not affect shoot phenology, and root and shoot phenology varied between growing seasons; thus, the linkage of root and shoot phenology was inconsistent. In warmer soil, root longevity was shorter and turnover rate was higher than in colder soil. This can further affect soil carbon dynamics and ecosystem carbon cycling in boreal forest ecosystems. [ABSTRACT FROM AUTHOR]

Arid areas have a comparatively narrow range of habitat types, with restricted variation in environmental parameters, leaving narrow boundaries for phenotypic variation to correlate with ecological variables. To test this presumption, we explored variation in size and shape of the mandible in the dwarf fat-tailed jerboa (Pygeretmus pumilio (Kerr, 1792)) under the constraints of a rigorous desert environment. Size varied significantly and predictably with geographic position and demonstrated a strong, nonlinear longitudinal pattern. Moreover, size was associated with several other climatic variables but not with soil properties or with proxies for primary productivity. Our results suggest that for rodents exposed to rapid and extreme changes, larger size may have multiple advantages, notably in maintaining euthermia during cold nights and efficient water metabolism under aridity stress, in accumulating fat reserves for hibernation, and in digging deeper burrows, better protected from surface extremes. Shape varied clinally along the longitudinal transect, and the pattern was affected more by temperature than by precipitation. We conclude that the success of dwarf fat-tailed jerboa in occupying an extensive geographic range relies on their ability to meet environmental heterogeneity through cohesive and diverse responses, including physiology, behaviour, life-history traits, and morphological plasticity. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing 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.)

Intensified warming in the Arctic and Subarctic is resulting in a wide range of changes in the extent, productivity, and composition of aquatic and terrestrial ecosystems. Analysis of remote sensing imagery has documented regional changes in the number and area of ponds and lakes as well as expanding cover of shrubs and small trees in uplands. To better understand long-term changes across the edaphic gradient, we compared the number and area of water bodies and dry barrens (>100 m2) between 1956 (aerial photographs) and 2008-2011 (high-resolution satellite images) for eight ∼25 km2 sites near Nejanilini Lake, Manitoba (59.559°N, 97.715°W). In the modern landscape, the number of water bodies and barrens were similar (1162 versus 1297, respectively), but water bodies were larger (mean 3.1 × 104 versus 681 m2, respectively) and represented 17% of surface area compared with 0.4% for barrens. Over the past 60 years, total surface area of water did not change significantly (16.7%-17.1%) despite a ∼30% decrease in numbers of small (<1000 m2) water bodies. However, the number and area of barrens decreased (55% and 67%, respectively) across all size classes. These changes are consistent with Arctic greening in response to increasing temperature and precipitation. Loss of small water bodies suggests that wet tundra areas may be drying, which, if true, may have important implications for carbon balance. Our observations may be the result of changes in winter conditions in combination with low permafrost ice content in the region, in part explaining regional variations in responses to climate change. [ABSTRACT FROM AUTHOR]

Assimilation and exchange of carbon for arctic ecosystems depend strongly on leaf area index (LAI) and total foliar nitrogen (TFN). For dry–mesic tundras, the seasonality of these characteristics is unexplored. We addressed this knowledge gap by measuring variations of LAI and TFN at five contrasting subarctic heaths during the growing season 2007, from about 2 weeks after bud burst until about 2 weeks before senescence. The communities generally showed an early season LAI and TFN increase, owing to leaf development of deciduous shrubs, and limited variations later on, owing to concurrent leaf growth and mortality of evergreen shrubs. For most of the communities, the TFN:LAI ratio was constant along the entire sampling period, indicating that leaf growth and mortality, triggers for both LAI and TFN, are more important than leaf N retranslocation, which only affects TFN. A constant TFN:LAI ratio facilitates the determination of TFN from LAI, which is easier to measure or simulate. However, a sheltered community showed an increment in the LAI of the deciduous canopy in mid–late season, paralleled by a decreased TFN:LAI ratio. [ABSTRACT FROM AUTHOR]

This study presents Last Interglacial and Holocene vegetation and climate changes at Fog Lake (67°11′N, 63°15′W) on eastern Baffin Island, Arctic Canada. The vegetation cover is reported as vegetation structural types (or biomes). July air temperature and sunshine during the growing season (June–July–August–September) were reconstructed from pollen assemblages using the modern analogue technique. The vegetation of the Last Interglacial period evolved from a prostrate dwarf-shrub tundra to a low- and high-shrub tundra vegetation. The succession of four Arctic biomes was distinguished from the Last Interglacial sediments, whereas only one Arctic biome was recorded in the Holocene sediments. From ca. 8300 cal. years BP to present, hemiprostrate dwarf-shrub tundra occupied the soils around Fog Lake. During the Last Interglacial, growing season sunshine was higher than during the Holocene and July air temperature was 4 to 5 °C warmer than present. A principal component analysis helped in assessing relationship between floristic gradients and climate. The major vegetation changes through the Last Interglacial and Holocene were driven by July air temperature variations, whereas the minor, or subtle, vegetation changes seem rather correlated to September sunshine. This study demonstrates that growing season sunshine conditions can be reconstructed from Arctic pollen assemblages, thus providing information on feedbacks associated with cloud cover and summer temperatures, and therefore growing season length. Cette étude présente les changements climatiques et de végétation survenus au cours du dernier interglaciaire et de l’Holocène au lac Fog (67°11′N, 63°15′O), sur la côte est de la Terre de Baffin, dans l’Arctique canadien. La couverture végétale est décrite sous forme de biomes, c.-à-d. de structures de végétation. La température de l’air en juillet et l’ensoleillement lors de la saison de croissance (juin, juillet, août, septembre) ont été reconstitués à partir d’assemblages polliniques selon la méthode des analogues modernes. La végétation de la dernière période interglaciaire a évolué d’une toundra arbustive naine, prostrée à une toundra arbustive basse et haute. Une succession de quatre biomes est visible dans les sédiments du dernier interglaciaire, alors qu’un seul biome est observé dans les sédiments de l’Holocène. Une toundra arbustive hémiprostrée colonize les sols des environs du lac Fog depuis environ 8300 années. Au cours du dernier interglaciaire, l’ensoleillement durant de la saison de croissance était plus élevé que lors de l’Holocène et la température de juillet était de 4 à 5 °C plus chaude qu’actuellement. Une analyse en composantes principales a permis d’évaluer la relation entre les gradients floristiques et le climat. Les changements majeurs de végétation lors du dernier interglaciaire et de l’Holocène découlent principalement des variations de la température de juillet, alors que les changements de végétation plus subtils sont plutôt liés à l’ensoleillement en septembre. Cette étude démontre que les conditions d’ensoleillement lors de la saison de croissance peuvent être déduites à partir des assemblages polliniques des sédiments de l’Arctique, fournissant ainsi de l’information pertinente sur les rétroactions associées au couvert nuageux et aux températures estivales et donc sur la durée de la saison de croissance. [ABSTRACT FROM AUTHOR]

Climatic variations during the past 10 000 and 1 000 years in the Canadian Arctic are recorded in a variety of proxy-climate records. Paleoclimates of the past 1000 years are interpreted from ice cores, lake sediments, and primarily tree rings. The past 500 years, between A.D. 1500 and A.D. 1850 were relatively cool, with coolest temperatures in the 1600s and 1800s. In the 1700s temperatures were slightly warmer, but still not as warm as the latter half of the 20th Century. Warming in the 20th century is also apparent in most records. Paleoclimates of the past 10 000 years can be interpreted from ice cores, pollen diagrams, and the analysis of frequency distributions of fossils. During the past 10 000 years, the Arctic experienced maximum temperatures in the early Holocene, although there are also regional variations. [ABSTRACT FROM AUTHOR]

Lakes, of average size 33 ha, occupy a quarter of the surface area of Richards Island, Northwest Territories. Most of the lakes have a central pool deeper than the thickness of winter ice, and many have prominent, shallow, littoral terraces. The relatively warm lake bottoms cause considerable disturbance to the surrounding continuous permafrost. Water and lake-bottom temperatures, the configuration of permafrost, and active-layer thickness were measured at a tundra lake between 1992 and 1997. The lake is oval, 1.6 km long, 800 m wide, and as deep as 13 m. Sandy terraces, covered by less than 1 m of water, extend over 100 m from the shore. The terraces are underlain by permafrost, which terminates almost vertically at their edge. The annual mean temperature measured at lake bottom in the central pool ranged between 1.5°C and 4.8°C, depending on depth, and between –0.2°C and –5°C on the terraces, due to differences in snow cover and proximity to the central pool. In consequence, the temperature of permafrost at 7 m depth in the terraces also varied, from –2°C near shore to –5°C in mid-terrace. The active layer in the terraces was uniformly 1.4 m deep. Geothermal modelling of talik configuration indicates that there is no permafrost beneath the central pool of the lake. The modelling indicates that, under equilibrium conditions, about one quarter of the lakes on Richards Island have taliks that penetrate permafrost, and at least 10–15% of the island is underlain by talik. Short-term climatic changes predicted for the region imply a small increase in summer lake-water temperature and an extension of the open-water season, accompanied by thicker snow cover in winter. Following such changes, with longer freeze-up and warmer terrace temperatures in winter, permafrost may not be sustainable in the lake terraces.Le quart de la superficie de l'île Richards, dans les Territoires du Nord-Ouest, est occupé par des lacs, dont la superficie moyenne est de 33 ha. La plupart des lacs ont un bassin central plus profond que l'épaisseur de la glace en hiver et plusieurs ont des terrasses littorales, proéminentes et peu profondes. Le fond relativement chaud des lacs perturbe considérablement le pergélisol avoisinant. Les températures de l'eau et du fond du lac, la configuration du pergélisol et l'épaisseur de la couche active ont été mesurées dans un lac de toundra entre 1992 et 1997. Le lac est de forme ovale, il a une longueur de 1,6 km, une largeur de 800 m et sa profondeur atteint 13 m. Des terrasses de sable, recouvertes de moins d'un mètre d'eau s'étendent à plus de 100 m de la berge. Le pergélisol se retrouve sous les terrasses et il se termine presque verticalement au bord de ces terrasses. La température moyenne annuelle mesurée au fond du lac dans le bassin central varie entre 1,5 et 4,8 ºC et elle varie entre –0,2 et –5,0 ºC sur les terrasses; ces différences sont fonction du couvert de neige et de la proximité au bassin central. En conséquence, la température du pergélisol, à une profondeur de 7 m, varie également, de –2 près de la berge à –5 ºC au milieu de la terrasse. La couche active des terrasses a une profondeur uniforme de 1,4 m. Une modélisation géothermique de la configuration du talik indique qu'il n'y a pas de pergélisol sous le bassin central du lac. La modélisation indique aussi que, sous des conditions d'équilibre, environ le quart des lacs sur l'île Richards ont des taliks qui pénètrent le pergélisol et qu'il y a des taliks sous environ 10 à 15 % de l'île. Les changements climatiques à court terme prévus pour la région impliquent une faible augmentation de la température des eaux des lacs en été et une extension de la saison des eaux libres, accompagné d'un couvert de neige plus épais en hiver. Après de tels changements, accompagnés, en hiver, de périodes de gel plus longues et de températures plus chaudes pour les terrasses, il se pourrait que le pergélisol ne subsiste pas dans les terrasses des lacs.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

A correction to the article "Seasonal Variation in Plant Nutritive Quality for Greater Snow Goose Goslings in Mesic Tundra," that appeared in the 2013 issue is presented.