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Hair lichens (Alectoria, Bryoria, Usnea) dominate old coniferous forest canopies across the boreal biome. These lichens play key roles in element cycling, hydrology, canopy microclimate and provide critical forage for reindeer/caribou and habitat for invertebrates. Clear-cutting has caused large-scale declines of hair lichens, highlighting the need for continuous cover forestry. We examined the long-term (2008–2019) effects of partial cutting on hair lichens in an old Picea abies-dominated forest using an experiment with three levels of basal area (BA) removal (0%, 33%, 67%). We compared pale Alectoria and dark Bryoria to understand how light-screening cortical pigments and other functional traits drive their responses to partial cutting. Forest structure, canopy profiles (using LiDAR data) and microclimate were monitored, and hair lichen mass was quantified at two heights (3−4 m and 6−7 m) on P. abies. Light intensity increased up to 2.6 times and radial growth of P. abies up to two times in partial cuts. Lichen mass per tree depended on lichen genus, height, level of BA removal and time. Alectoria dominated both heights, but Bryoria increased with height. Both genera declined in the first year after logging but thereafter increased 1.5−4.3 times the baseline over 10 years. Bryoria increased faster than Alectoria, except at 6−7 m after five years. The long-term changes in mass of Alectoria and Bryoria were positively correlated with canopy openness, showing that light is the major driver of hair lichen mass accumulation. The stand-level lichen mass after 10 years exceeded the baseline with 32−40% in the 33% BA removal but declined in the 67% removal. Our findings demonstrate that partial cutting, by altering canopy structure and microclimate, can significantly increase hair lichen mass and thus maintain their ecosystem functions in managed boreal forests.

Arctic deltas are highly dynamic environments at the land-ocean interface that have acted as long-term sinks of sediment, carbon (C), and nitrogen (N). Climate impacts Arctic deltas and their upstream catchments through sea-level rise, altered river discharge, increased sediment fluxes, intensified biogeochemical cycling, and permafrost thaw. As a result, soil C and N in Arctic delta deposits are becoming more bioavailable. Here, we present a C and N inventory for Arctic delta compiled from over 1600 soil samples spanning 17 river deltas. We estimate that Arctic delta deposits store 57.5 (+ 9.2/−8.2) Pg C and 3.8 (+ 0.8/−0.7) Pg N across a combined area of nearly 100,000 km², representing large and potentially vulnerable biogeochemical pools. Our findings underscore the potentially pivotal role of Arctic deltas in the pan-Arctic carbon cycle and highlight their importance as dynamic zones of both C and N storage and release in a rapidly changing Arctic.

Land cover data are commonly used to model the terrestrial carbon (C) sink, yet these data have wide margins of error that significantly alter estimates of global C storage. Here we demonstrate this data vulnerability in grasslands, which are critical to C cycling but whose estimated distribution has varied by >50 million km2 (3.5-42% of the Earth's terrestrial surface). Comparing multiple high-resolution land cover products with expertly annotated grassland data from six continents, we show sources of mapping error and discuss C implications based on 2023 United Nations (UN) FAO estimates. Past misidentification arose from inconsistent definitions on grassland identity and classification flaws especially relating to woody plant cover. Correcting these errors adjusted grassland coverage to 22.8% of the terrestrial land base (30.1 million km2), elevating UN projections of soil C stocks to 155.02 Pg (0-30 cm depth). These findings underscore the challenges of biome mapping for ecosystem accounting and policy, when lacking field-validated remotely sensed data.

Herbivores are an integral part of Arctic terrestrial ecosystems, driving ecosystem functioning and sustaining local livelihoods. In the context of accelerated climate warming and land use changes, understanding how herbivores contribute to the resilience of Arctic socio-ecological systems is essential to guide sound decision-making and mitigation strategies. While research on Arctic herbivory has a long tradition, recent literature syntheses highlight important geographical, taxonomic, and environmental knowledge gaps on the impacts of herbivores across the region. At the same time, climate change and limited resources impose an urgent need to prioritize research and management efforts. We conducted a horizon scan within the Arctic herbivory research community to identify emerging scientific and management priorities for the next decade. From 288 responses received from 85 participants in two online surveys and an in-person workshop, we identified 8 scientific and 8 management priorities centred on (a) understanding and integrating fundamental ecological processes across multiple scales from individual herbivore-plant interactions up to regional and decadal scale vegetation and animal population effects; (b) evaluating climate change feedbacks; and (c) developing new research methods. Our analysis provides a strategic framework for broad, inclusive, interdisciplinary collaborations to optimise terrestrial herbivory research and sustainable management practices in a rapidly changing Arctic.

The Arctic is warming faster than anywhere else on Earth, placing tundra ecosystems at the forefront of global climate change. Plant biomass is a fundamental ecosystem attribute that is sensitive to changes in climate, closely tied to ecological function, and crucial for constraining ecosystem carbon dynamics. However, the amount, functional composition, and distribution of plant biomass are only coarsely quantified across the Arctic. Therefore, we developed the first moderate resolution (30 m) maps of live aboveground plant biomass (g m−2) and woody plant dominance (%) for the Arctic tundra biome, including the mountainous Oro Arctic. We modeled biomass for the year 2020 using a new synthesis dataset of field biomass harvest measurements, Landsat satellite seasonal synthetic composites, ancillary geospatial data, and machine learning models. Additionally, we quantified pixel-wise uncertainty in biomass predictions using Monte Carlo simulations and validated the models using a robust, spatially blocked and nested cross-validation procedure. Observed plant and woody plant biomass values ranged from 0 to ∼6000 g m−2 (mean ≈ 350 g m−2), while predicted values ranged from 0 to ∼4000 g m−2 (mean ≈ 275 g m−2), resulting in model validation root-mean-squared-error (RMSE) ≈ 400 g m−2 and R2 ≈ 0.6. Our maps not only capture large-scale patterns of plant biomass and woody plant dominance across the Arctic that are linked to climatic variation (e.g., thawing degree days), but also illustrate how fine-scale patterns are shaped by local surface hydrology, topography, and past disturbance. By providing data on plant biomass across Arctic tundra ecosystems at the highest resolution to date, our maps can significantly advance research and inform decision-making on topics ranging from Arctic vegetation monitoring and wildlife conservation to carbon accounting and land surface modeling.

Herbivory may offset climate change-driven treeline expansion into the tundra, but the strength of this effect is rarely quantified. This study leverages a unique semi-natural experiment involving Malla Strict Nature Reserve in northernmost Finland, where the reindeer herding regime shifted from being nearly ungrazed for several decades to being heavily grazed for the past two decades. This is contrasted by low grazing pressure in the adjacent herding district in Norway, which is separated by the border fence preventing free reindeer movement between the two countries. We aimed to quantify the effects of reindeer browsing and grazing on mountain birch treeline position and structure on both sides. We measured seedling numbers and the allometry of trees, vegetation composition, nutrient concentrations in soils and birch leaves, and radial tree growth. We found higher numbers of seedlings and saplings in the area with lower reindeer density, indicating that the treeline may be responding to climatic forcing by expanding into the tundra. Contrastingly, we observed almost no recruitment and treeline expansion in the area with high reindeer density. Furthermore, while birch leaves showed signs of nitrogen enrichment under high reindeer density, we found no differences in soil chemical composition or birch tree growth rates. Our results suggest that the high density of reindeer in Malla Strict Nature Reserve keeps the treeline in a browsing trap, thereby preventing climate change-driven forest expansion. These results are highly relevant for land management decisions that aim to preserve mountain tundra.

High-resolution unoccupied aerial vehicle (UAVs) data have alleviated the mismatch between the scale of ecological processes and the scale of remotely sensed data, while machine learning and deep learning methods allow new avenues for quantification in ecology. Ant nests play key roles in ecosystem functioning, yet their distribution and effects on entire landscapes remain poorly understood, in part because they and their mounds are too small for satellite remote sensing. This research maps the distribution and impact of ant mounds in a 20 ha treeline ecotone. We evaluate the detectability from UAV imagery using a deep learning model for object detection and different combinations of RGB, thermal and multispectral sensor data. We were able to detect ant mounds in all imagery using manual detection and deep learning. However, the highest precision rates were achieved by deep learning using RGB data which has the highest spatial resolution (1.9 cm) at comparable UAV flight height. While multispectral data were outperformed for detection, it allows for novel insights into the ecology of ants and their spatial impact on vegetation productivity using the normalized difference vegetation index. Scaling up, this suggests that ant mounds quantifiably impact vegetation productivity for up to 4% of our study area and up to 8% of the Betula nana vegetation communities, the vegetation type with the highest abundance of ant mounds. Therefore, they could have an overlooked role in nutrient-limited tundra vegetation, and on the shrubification of this habitat. Further, we show the powerful combination UAV multi-sensor data and deep learning for efficient ecological tracking and monitoring of mound-building ants and their spatial impact.

We perform a first permafrost higher education curriculum survey in Norden. Permafrost is part of the education within both bio- and geosciences and engineering, and the variation in educational activities reflect this. Five permafrost-specific geoscience and engineering permafrost courses exist, whereas there are 23 bachelor and 25 master courses with a permafrost content ranging from 1% to 50 %. The is large potential and clear needs for closer permafrost teaching collaboration. This could focus on permafrost course development, teaching methods, sharing practical experiences including fieldwork and further developing the educational offer. Such collaboration could establish: 1) An online, joint Nordic specific course on permafrost, sharing the special permafrost competences existing across the universities using digital teaching tools, 2) Nordic collaboration on developing joint, both general but also specific, PhD courses on permafrost, 3) Lifelong education in permafrost, and 4) Internships a part of active permafrost education to better meet the future employers and society’s needs. The Nordic region might also gain largely from establishing an overview-providing interdisciplinary joint Nordic course aiming to characterize the region and its diversity broadly including both natural and social sciences, and naturally covering different topics including permafrost and seasonally frozen ground. The mapping done for this paper will function as a first overall roadmap catalogue providing an overview of all offered courses on permafrost. The overall outcome of our survey shows large potential for increased and deeper inter-university collaboration for further developing joint permafrost higher education both in the form of courses and other educational activities between institutions across Norden, and potentially with ambitions for joint permafrost degrees between several institutions. Based on the presented results and the mapped different future plans for permafrost education across Norden, we discuss the implications of our results, specifically concerning the potential for increased collaboration in Nordic permafrost education. These focus on permafrost course development, teaching methods, sharing practical experiences including fieldwork and further developing the educational offer. In more detail increased collaboration could establish: 1) An online, joint Nordic-specific course on permafrost, sharing the special permafrost competences existing across the universities using digital teaching tools, 2) Nordic collaboration on developing joint PhD courses on permafrost, 3) Lifelong education in permafrost, and 4) Internships as part of active permafrost education to better meet the needs of future employers and society. The Nordic region might also gain largely from establishing an interdisciplinary joint Nordic course, aiming to characterize the region and its diversity broadly and including both natural and social sciences, and naturally covering different topics including permafrost and seasonally frozen ground.

1. The term “applied ecology of fear” was recently introduced to describe the growing research field that applies the theory of the ecology of fear to manage wildlife behaviour. The management goal is to drive targeted species spatially and temporally away from areas of human interest by inducing cues from real or simulated predators to reduce human-wildlife conflict.

2. We aimed to quantify, through a meta-analysis, if prey anti-predator response would vary among field trials versus pen-based studies, predator cue types, predator hunting style and prey feeding type, and be stronger in response to larger predators relative to the prey's size. We also explored what studies found in terms of wildlife habituation to cues.

3. We used species belonging to the Cervidae family as a case study since deer are among the group of species with the highest degree of human-wildlife conflict. We retrieved 114 studies from online databases and collected information from 39 of those studies that fitted our research scope.

4. We found that acoustic cues more frequently led to an anti-predator response in deer than olfactory or visual cues. Neither predator hunting strategy nor deer feeding strategy or type of study (free-ranging or pen-based animals) influenced the extent to which deer responded to cues. Deer more frequently responded to cues that belonged to a larger predator relative to their size. Habituation was reported in less than one-third of the studies, with a study period ranging from 1 to 90 days, and occurred as soon as 7 days after the start of the study on average.

5. Our meta-analysis suggested that acoustic cues hold most potential as a tool to manage deer behaviour. These findings support the development of applied ecology of fear tools that introduce predator cues to reduce human-wildlife conflicts. Major knowledge gaps remain that limit the effective use of such tools in wildlife management and future research should focus on improving our understanding of habituation to cues, on comparing the effectiveness of different types of cues, on simultaneously using a combination of cue types, and on testing cues at spatial–temporal scales of actual land-uses.

Climate warming is degrading palsa peatlands across the circumpolar permafrost region. Permafrost degradation may lead to ecosystem collapse and potentially strong climate feedbacks, as this ecosystem is an important carbon store and can transition to being a strong greenhouse gas emitter. Landscape-level measurement of permafrost degradation is needed to monitor this impact of warming. Surface subsidence is a useful metric of change in palsa degradation and can be monitored using interferometric synthetic-aperture radar (InSAR) satellite technology. We combined InSAR data, processed using the ASPIS algorithm to monitor ground motion between 2017 and 2021, with airborne optical and lidar data to investigate the rate of subsidence across palsa peatlands in northern Sweden. We show that 55% of Sweden's eight largest palsa peatlands are currently subsiding, which can be attributed to the underlying permafrost landforms and their degradation. The most rapid degradation has occurred in the largest palsa complexes in the most northern part of the region of study, also corresponding to the areas with the highest percentage of palsa cover within the overall mapped wetland area. Further, higher degradation rates have been found in areas where winter precipitation has increased substantially. The roughness index calculated from a lidar-derived digital elevation model (DEM), used as a proxy for degradation, increases alongside subsidence rates and may be used as a complementary proxy for palsa degradation. We show that combining datasets captured using remote sensing enables regional-scale estimation of ongoing permafrost degradation, an important step towards estimating the future impact of climate change on permafrost-dependent ecosystems.