• Broad-scale lake expansion and flooding inundates essential wood bison habitat

      Korosi, Jennifer; Thienpont, Joshua; Pisaric, Michael; deMontigny, Peter; Perreault, Joelle; McDonald, Jamylynn; Simpson, Myrna; Armstrong, Terry; Kokelj, Steven; Smol, John; et al. (Nature, 2017-02-23)
      Understanding the interaction between the response of a complex ecosystem to climate change and the protection of vulnerable wildlife species is essential for conservation efforts. In the Northwest Territories (Canada), the recent movement of the Mackenzie wood bison herd (Bison bison athabascae) out of their designated territory has been postulated as a response to the loss of essential habitat following regional lake expansion. We show that the proportion of this landscape occupied by water doubled since 1986 and the timing of lake expansion corresponds to bison movements out of the Mackenzie Bison Sanctuary. Historical reconstructions using proxy data in dated sediment cores show that the scale of recent lake expansion is unmatched over at least the last several hundred years. We conclude that recent lake expansion represents a fundamental alteration of the structure and function of this ecosystem and its use by Mackenzie wood bison, in response to climate change.
    • Forests, fire histories, and futures of Columbian and Rocky Mountain forests, western Canada

      Davis, Emma; Courtney Mustaphi, Colin; Pisaric, Michael (Western Division, Canadian Association of Geographers, 2018-10-17)
      Throughout the past few decades, shifting perspectives on fire management have led to the recognition that disturbance by fire is critical in maintaining ecological resilience in fire-adapted forests and grasslands. Long-term fire histories provide important information for land and resource managers seeking to understand the controls on wildfire dynamicsin western North America. In this paper we summarize fire history research that has recently been undertaken in the Canadian Cordillera. Using proxy records to reconstruct fire activity and vegetation change, these studies shared the overarching goal of identifying factors that control long-term fire regimes.A further aim was to identify how human activity has measurably altered various aspects of fire regimes. Looking to the future, these studies highlight the need to continue integrating information about local fire regimes and historical land-use activities when developing responsible fire and resource management strategies and identifying conservation priorities.
    • Have natural lake expansion and landscape inundationresulted in mercury increases in flooded lakes of the GreatSlave Lowlands (Northwest Territories, Canada)?

      Thienpont, Joshua; Perreault, Joelle; Korosi, Jennifer; Pisaric, Michael; Blais, Jules (Springer Netherlands, 2018-11-30)
      The inundation of terrestrial vegetation following landscape flooding is an important potential source of mercury to aquatic ecosystems, and may modify mercury cycling, such as through increased methylation. In the Great Slave Lowlands of Canada’s Northwest Territories, remarkable landscape flooding has occurred over the recent past, which is the most notable in at least the last several centuries. The potential for this flooding to increase inorganic mercury flux to the lakes of the region has not yet been explored. In this study we used sediment cores from five lakes experiencing a range of recently documented lake expansion to test whether inundation of terrestrial areas has increased the total mercury concentrations in sediments, and resulted in increased total mercury flux. Increases in sedimentary mercury concentrations and fluxes in sediment cores from the expanding lakes were relatively small and within the range of non-expanded systems, suggesting that, to date, flooding has not resulted in major total mercury enrichment, unlike in experimental and natural reservoir impoundments. The potential for increased methylation of existing inorganic mercury following expansion was not explored in this paper because methylmercury is dynamic in sediments and does not preserve well, but is an important consideration for future work.
    • Impacts of Road Dust on Small Subarctic Lake Systems

      Zhu, Liang; Anello, Rebecca; Ruhland, Kathleen; Pisaric, Michael; Kokelj, Steven; Prince, Tyler; Smol, John (Arctic, 2019-12-20)
      Arctic regions have been experiencing increasing pressures from multiple environmental stressors, most notably rapid climate change and human development. Previous research has demonstrated the impacts of calcareous dust from gravel roads on surrounding vegetation and permafrost, whereas aquatic systems have remained largely unstudied. Here, we explore whether 1) the chronic generation of dust from the 740 km long Dempster Highway has affected water chemistry and diatom assemblages in lakes in the Peel Plateau region of the Northwest Territories, and 2) accelerated regional warming has affected these lakes. A suite of 27 water chemistry variables was assessed from 28 lakes along a 40 m – 26 km distance from the highway. Paleolimnological analyses of biological proxies (diatoms, visible reflectance spectroscopy-derived chlorophyll-a, and an index of chrysophyte scales to diatoms [S:D]) were undertaken on dated sediment cores from two lakes near the highway and one lake situated far from the highway, outside the expected range of dust transport. Conductivity and calcium exhibited a wide range of measurements across our 28 sites; lakes within 1 km of the highway generally exhibited higher ions and related variables than more distant lakes. Analyses of diatom assemblages indicated that the two shallower sites near the highway underwent modest compositional changes over the past approximately 100 years, whereas changes recorded at the farther site were more pronounced. The diatom records, supported by chlorophyll-a and S:D indices, indicated that changes in both the near and far lakes were consistent with warming, with little discernable impact from road dust. Whilst chemical changes associated with the half-century old highway corridor appear clear, they are not yet of sufficient magnitude to elicit a directional biological response in algal assemblages.
    • Moisture-driven shift in the climate sensitivity of white spruce xylem anatomical traits is coupled to large-scale oscillation patterns across northern treeline in northwest North America

      Lange, Jelena; Carrer, Marco; Pisaric, Michael F.J.; Porter, Trevor J.; Seo, Jeong-Wook; Trouillier, Mario; Wilmking, Martin (Wiley Online, 2019-12-04)
      Tree growth at northern treelines is generally temperature‐limited due to cold and short growing seasons. However, temperature‐induced drought stress was repeatedly reported for certain regions of the boreal forest in northwestern North America, provoked by a significant increase in temperature and possibly reinforced by a regime shift of the Pacific decadal oscillation (PDO). The aim of this study is to better understand physiological growth reactions of white spruce, a dominant species of the North American boreal forest, to PDO regime shifts using quantitative wood anatomy and traditional tree‐ring width analysis. We investigated white spruce growth at latitudinal treeline across a > 1,000 km gradient in northwestern North America. Functionally important xylem anatomical traits (lumen area, cell‐wall thickness, cell number) and tree‐ring width were correlated with the drought‐sensitive standardized precipitation‐evapotranspiration index (SPEI) of the growing season. Correlations were computed separately for complete phases of the PDO in the 20th century, representing alternating warm/dry (1925–1946), cool/wet (1947–1976) and again warm/dry (1977–1998) climate regimes. Xylem anatomical traits revealed water‐limiting conditions in both warm/dry PDO regimes, while no or spatially contrasting associations were found for the cool/wet regime, indicating a moisture‐driven shift in growth‐limiting factors between PDO periods. Tree‐ring width reflected only the last shift of 1976/77, suggesting different climate thresholds and a higher sensitivity to moisture availability of xylem anatomical traits compared to tree‐ring width. This high sensitivity of xylem anatomical traits permits to identify first signs of moisture‐driven growth in treeline white spruce at an early stage, suggesting quantitative wood anatomy being a powerful tool to study climate change effects in the northwestern North American treeline ecotone. Projected temperature increase might challenge growth performance of white spruce as a key component of the North American boreal forest biome in the future, when drier conditions are likely to occur with higher frequency and intensity.
    • Moisture‐driven shift in the climate sensitivity of white spruce xylem anatomical traits is coupled to large‐scale oscillation patterns across northern treeline in northwest North America

      Lange, Jelena; Carrer, Marco; Pisaric, Michael; Porter, Trevor; Seo, Jeong‐Wook; Trouillier, Mario; Wilmking, Martin (Wiley, 2019-12-04)
      Tree growth at northern treelines is generally temperature-limited due to cold and short growing seasons. However, temperature-induced drought stress was repeatedly reported for certain regions of the boreal forest in northwestern North America, provoked by a significant increase in temperature and possibly reinforced by a regime shift of the Pacific decadal oscillation (PDO). The aim of this study is to better understand physiological growth reactions of white spruce, a dominant species of the North American boreal forest, to PDO regime shifts using quantitative wood anatomy and traditional tree-ring width analysis. We investigated white spruce growth at latitudinal treeline across a >1000 km gradient in northwestern North America. Functionally important xylem anatomical traits (lumen area, cellwall thickness, cell number) and tree-ring width were correlated with the drought-sensitive standardized precipitation-evapotranspiration index (SPEI) of the growing season. Correlations were computed separately for complete phases of the PDO in the 20th century, representing alternating warm/dry (1925-1946), cool/wet (1947-1976) and again warm/dry (1977-1998) climate regimes. Xylem anatomical traits revealed water-limiting conditions in both warm/dry PDO regimes, while no or spatially contrasting associations were found for the cool/wet regime, indicating a moisturedriven shift in growth-limiting factors between PDO periods. Tree-ring width reflected only the last shift of 1976/77, suggesting different climate thresholds and a higher sensitivity to moisture availability of xylem anatomical traits compared to tree-ring width. This high sensitivity of xylem anatomical traits permits to identify first signs of moisture-driven growth in treeline white spruce at an early stage, suggesting quantitative wood anatomy being a powerful tool to study climate change effects in the northwestern North American treeline ecotone. Projected temperature increase might challenge growth performance of white spruce as a key component of the North American boreal forest biome in the future, when drier conditions are likely to occur with higher frequency and intensity.
    • Postglacial Reconstruction of Fire History Using Sedimentary Charcoal and Pollen From a Small Lake in Southwest Yukon Territory, Canada

      Prince, Tyler; Pisaric, Michael; Turner, Kevin (Frontiers in Ecology and Evolution, 2018-12-19)
      Previous research suggests climate warming during the current century is likely to lead to an increase in the frequency and severity of wildfire. Recent wildfire seasons in northern Canada generally support these studies, with some of the worst fire seasons on record occurring during the past decade. While we can readily track the spatial and temporal distribution of these events during recent decades using satellite-derived data, these records of past fire activity are relatively short. Proxy records of past fire activity are needed to fully understand how fire regimes may be shifting in response to changing climatic conditions. A high-resolution fire record for the full Holocene was developed using a 539.5-cm sediment core collected from a small lake in southwest Yukon Territory, Canada. Macroscopic charcoal was counted throughout the core at contiguous 0.5-cm intervals. The core was also analyzed for loss-on-ignition and magnetic susceptibility. Fossil pollen preserved in the lake sediment was analyzed to determine vegetation change throughout the Holocene. Macroscopic charcoal analysis indicates an active fire history throughout the record, with 91 fires recorded during the Holocene. Results suggest the fire regime in this region responds to both top-down (climate) and bottom-up (vegetation) factors. Fire return intervals changed in response to shifts in precipitation and temperature as well as the expansion of lodgepole pine into the region. The shifts in precipitation and temperature were attributed to the oscillation of the Aleutian Low pressure system and fluctuations in climate associated with the Medieval Climate Anomaly and the Little Ice Age.
    • Road Construction, Mobility & Social Change in a Wakhi Village

      Butz, David; Cook, Nancy (2020)
      Throughout the global South road construction is a favoured mechanism of rural development, yet little attention has been given to the implications of new roads for everyday life in the communities to or through which they are routed. Road Construction, Mobility & Social Change offers an intimate glimpse of these implications for residents of Shimshal, a small agro-pastoral community in the Karakoram Mountains of Northern Pakistan, who in 2003 completed construction of a 60km jeep road linking the village to the regional road network. In 2011 and 2012 Shimshal residents were invited to create photos and provide accompanying verbal narratives that evoke the importance of the Shimshal road for their everyday lives. Fifty-seven community members submitted 402 photos with narratives. Approximately 130 of these photos are reproduced here (at least one from each photographer), each with a paragraph-length summary of its associated narrative in three languages: English, Wakhi, and Urdu. The photographs and captions are organized to express six main ways that Shimshalis understand their everyday lives to be affected by the road’s existence: spaces and social contexts; artifacts and visible traces; mobile activities and embodied practices; social relations; identities; and meanings and interpretive frames. Considered together, these photographic and textual materials provide a rare and richly-detailed insiders’ perspective on road construction, changing mobility practices, and daily life in Shimshal.