Arctic warming is causing widespread “greening” of tundra ecosystems. What this means for plant–herbivore relations, including the grazing pressure herbivores exert on increasingly productive tundra ecosystems, is poorly understood. Svalbard is one of the fastest warming places on Earth, with concomitant increases in both forage biomass and reindeer numbers. In 11 years between 1998 and 2023, we measured grass biomass and the proportion of shoots grazed in mesic grass-dominated tundra to evaluate whether increased forage biomass of grass absorbed the grazing pressure of more reindeer. Also, we used GPS data from adult female reindeer (2009–2023) to identify if grazing pressure was relieved by spillover into other habitats. During the study period, reindeer abundance, estimated by annual capture-mark-recapture, tripled, while grass biomass only doubled. Grazing pressure increased from 4% to 8%, which was lower than expected from the increased reindeer density. This discrepancy was not caused by spillover into other habitats, but rather by increased grazing in higher-biomass patches that have emerged with summer warming. Our findings support the notion that increased summer forage has contributed to Svalbard reindeer population growth, notably by making available higher biomass grass swards that allow for greater food offtake.

The composition of vegetation cover in Arctic environments is evolving due to climate change. This study focused on estimating carbon and nitrogen stocks in vegetation and soil for different Arctic habitats (i.e., sub-ecosystem environments) with contrasted plant communities and soil profiles, to better understand the spatial variation of these stocks and the relationships between aboveground vegetation and soil characteristics in these environments. Vegetation composition and soil characteristics were measured in different habitats in a mire and a heathland ecosystem in northern Sweden. Multivariate analyses were used to define dominant vegetation and soil profile types, and carbon and nitrogen stocks were computed and compared across these types. Shrub-dominated and graminoid-dominated vegetation types presented similar carbon stocks but different nitrogen stocks, and shrub-dominated environments presented significantly higher proportions of their stocks distributed in the long-lived (i.e., woody) compartment. Soil stocks varied considerably between ecosystems. However, no clear relationships could be established between current vegetation community composition and soil carbon and nitrogen stocks across environments. The increase in shrub or graminoid abundance may affect carbon and nitrogen cycles most through biomass distribution between plant compartments rather than through the absolute stocks they represent. Ultimately, in Arctic and subarctic ecosystems experiencing climate change, the interactions between plant biomass composition and soil characteristics could have contrasted consequences for ecological functioning and C and N cycles.

A scenario-based approach was used to test air and ground response to warming with and without changes to inverted surface lapse rates in four Yukon valleys. Generally, climate warming coupled with weakening of temperature inversions resulted in the greatest increase in air temperature at low elevations. However, ground temperatures at high elevations showed the greatest response to warming and variability between scenarios due to increased connectivity between air and ground. Low elevations showed less of a response to warming and permafrost was largely preserved in these locations. Local models also predicted higher permafrost occurrence compared to a regional permafrost probability model, due to the inclusion of differential surface and thermal offsets. Results show that the spatial warming patterns in these mountains may not follow those predicted in other mountain environments following elevation-dependent warming (EDW). As a result, the concept of EDW should be expanded to become more inclusive of a wider range of possible spatial warming distributions. The purpose of this paper is not to provide exact estimations of warming, but rather to provide hypothetical spatial warming patterns, based on logical predictions of changes to temperature inversion strength, which may not directly follow the distribution projected through EDW.

Seasonal migrations allow access to temporally varying resources and individuals may show fidelity to specific locations, particularly for important life processes such as reproduction. Polar bears ( Ursus maritimus) are a sea ice-dependent species that migrate between marine and terrestrial habitats, the latter being important for parturition and early cub rearing. However, fidelity to maternity dens is poorly understood. Using capture and telemetry data collected between 1979 and 2018, we assessed site fidelity of female polar bears in the Western Hudson Bay subpopulation in Manitoba, Canada. We compared within-individual inter-year distances between dens to between-individual distances via non-parametric bootstrapping, and used generalized additive models to assess how maternal age, years between denning events, and sea ice conditions affected fidelity. Within-individual distances were smaller than between-individual distances by approximately 18.7 km, indicating some evidence of fidelity. Inter-den distances increased with time between denning events, but no other variables significantly affected fidelity. Our findings suggest that western Hudson Bay polar bears may exhibit fidelity to areas within the larger denning region, but not to specific dens. Understanding the site fidelity of maternal polar bears has important implications for population dynamics, on-land spatial distributions, and conservation efforts aimed at preserving important habitat for reproduction.

Sediment cores were collected from Wrong (WL) and Lenore (LL) lakes in boreal central Yukon Territory, Canada, spanning circa 6000 years. Analyses of pollen, charcoal, magnetic susceptibility, levoglucosan, and down-scaled paleoclimatic data reveal the vegetation history and character/drivers of Holocene fire disturbance. Boreal forest has persisted in the region for millennia, with a regional mid-Holocene expansion of Picea mariana (Mill.) Britton, Sterns & Poggenb. followed by expansion of Pinus contorta var. latifolia Douglas ex Loudon Engelm. ex S. Watson in the latest Holocene. The shortest reconstructed fire return intervals (FRIs; ca. 110–125 years) occurred in the mid-Holocene, coincident with the development of highly flammable Picea-dominated forest and warm, dry summers that were characterized by elevated June-August 500 hPa geopotential height anomalies (JJA Z500) and associated with an eastward/intense Aleutian Low. In the late-Holocene, FRI increased to ca. 240 years at WL and 280 years LL. Drivers of this change include regional cooling and increased precipitation, with a westward/weaker Aleutian Low position delivering more moisture to interior Yukon. Longer FRIs allowed for greater fuel accumulation between fires, enhancing fire size/severity. While higher fire frequency is noted in the mid-Holocene and increased fire size/severity in the late-Holocene, recent changes in Yukon fire disturbance suggest that the fire regime may soon lie outside the natural range of mid- and late-Holocene variability.

The North Water Polynya is one of the most productive Arctic regions on Earth, sustaining the world's northernmost Inuit communities for millennia. The polynya is a large and persistent region of open water surrounded by sea ice and exhibits high primary productivity, is a biodiversity hotspot, and is a key habitat and migration corridor for Arctic species. Many aspects of the ecosystem structure and the role of resident species in the North Water Polynya remain uncertain. To shed light on these, we developed the first representation of the North Water Polynya food web using the Ecopath modelling framework. Modelled trophic flows indicated that pelagic and benthic communities were primarily connected by Age 1+ Arctic cod ( Boreogadus saida), walrus ( Odobenus rosmarus), and ringed seal ( Pusa hispida). Large copepods, Age 1+ Arctic cod, and bivalves were key prey species. Overall productivity in the North Water Polynya was higher compared to Western Baffin Bay and Western Greenland, corroborating expectations of relatively high productivity within the polynya. This model provides a baseline description of the North Water Polynya ecosystem structure and function prior to future climate-driven food web changes and the emergence of large-scale commercial fisheries.

The Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut (74°55′N, 109°34′W) was established in 2003 to examine Arctic ecosystem processes that would be impacted by climate warming and permafrost degradation. This paper provides a synthesis of how remote sensing has contributed to biogeophysical modelling and monitoring at the CBAWO from 2003 to 2023. Given the location and isolated nature of the CBAWO in the Canadian High Arctic, remote sensing data and derivatives have been instrumental for studies examining ecosystem structure and function at local and landscape scales. In combination with field measurements, remote sensing data facilitated mapping and modelling of vegetation types, % vegetation cover and aboveground phytomass, soil moisture, carbon exchange rates, and permafrost degradation and disturbance. It has been demonstrated that even in an environment with limited vegetation cover and phytomass, spectral vegetation indices (e.g., the normalized difference vegetation index) are able to model various biogeophysical variables. These applications are feasible for research sites such as the CBAWO using high spatial resolution remote sensing data across the visible, infrared, and microwave regions of the electromagnetic spectrum. Furthermore, as the satellite record continues to expand, we will gain a greater understanding of the impacts arising from the expected continued warming at northern latitudes. Although the logistics for research in the Arctic remain challenging, today's technologies (e.g., high spatial resolution satellite remote sensing, automated in situ sensors and data loggers, and wireless communication systems) can support a host of scientific endeavours in the Arctic (and other remote sites) through modelling and monitoring of biogeophysical variables and Earth surface processes with limited but critical field campaigns. The research synthesized here for the CBAWO highlights the essential role of remote sensing of terrestrial ecosystems in the Canadian Arctic.

Arctic cod (Boreogadus saida) is the most abundant forage fish species in Arctic seas and plays a pivotal role in the transfer of energy between zooplankton and top predators. Arctic cod's dominance, together with the Arctic's relatively low biodiversity, interact such that changing population dynamics of Arctic cod have cascading effects on whole Arctic marine ecosystems. Over the last decades, warming in the Arctic has led to a decline in Arctic cod populations in the Barents Sea, but in the Canadian Arctic these conditions have been correlated with up to a ten-fold higher biomass of age-0 Arctic cod at the end of summer. However, it is unknown whether this enhanced larval survival with warmer waters endures through age-1+ populations. A better understanding of spatial variation in the responses of Arctic cod populations to environmental conditions is critical to forecast future changes in Arctic ecosystems. Here, we rely on a 17-year time series of acoustic-trawl surveys (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019) to test whether ice breakup date, sea surface temperature, zooplankton density, and Arctic climate indices during early life stages affect the subsequent recruitment of age-1+ Arctic cod in the Beaufort Sea and Baffin Bay. In the Beaufort Sea, the biomass of age-1+ Arctic cod was correlated with the previous year's Arctic Oscillation indices and age-0 biomass. In Baffin Bay, the biomass of age-1+ Arctic cod was correlated with the previous year's North Atlantic Oscillation indices and the timing of ice breakup.

This Indigenous-led project aims to better understand historical and contemporary ways in which Alaska Native Peoples steward salmon and the values connected to salmon stewardship. Indigenous Peoples have stewarded Alaska lands and waters for thousands of years yet have been largely excluded from western science and management systems. In this project, we utilize a participatory approach that allows for the equitable valuing of ideas and knowledges to document the breadth and depth of Yup'ik and Athabascan knowledge and governance systems in southwestern Alaska. We reshape research methodologies by centering Indigenous frameworks and methodologies, including circle dialogues and multi-generational interviews led by Indigenous scholars and students in their home communities and regions. In this paper, we share the Yup'ik and Athabascan values, knowledge, management, and governance mechanisms that can improve the long-term sustainability and equity of Alaska salmon systems. This research elevates the voices of Alaska Native salmon stewards and experts from the Kuskokwim Bay and the Kuskokwim River. We elaborate on five key themes that emerged from this research, including traditional Indigenous ways of life, Indigenous stewardship, self-determination, food and livelihood sovereignty, and ecosystem changes, and identify a more equitable and sustainable path forward for salmon and people in Alaska.

As sea-ice cover is shrinking, polar bears ( Ursus maritimus, Phipps, 1774) face decreased access to seals, their primary prey, resulting in a greater dependence on terrestrial food sources. Whether polar bears can benefit from these terrestrial food sources, however, depends on their ability to find and capture prey items without expending more energy than is acquired. Here, we report one of the northernmost observations of polar bear predation on adult birds. The bear used a dive-hunting technique, which consisted of submerging itself, approaching underwater, and catching flightless greater snow geese ( Anser caerulescens caerulescens (Linnaeus, 1758)) from beneath the surface of a tundra pond. After evaluating energy expenditures during swimming and energy intakes from consuming geese, we estimated that this rarely documented dive-hunting technique could be energetically profitable for a certain range of pursuit durations. This observation highlights the behavioral plasticity that polar bears can deploy to punctually exploit land-based food sources.