Katariina Elsa Maria Vuorinen

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.

Protected areas are one of the main strategic means for conserving biodiversity. Yet, the design of protected areas usually neglects phylogenetic diversity, an important diversity measure. In this paper we assess the phylogenetic diversity and species richness of vascular plants in Fennoscandian protected areas. We evaluate how much species richness and phylogenetic diversity is found within and outside protected areas, and the differences in plant diversity between different categories of protected areas. We also assess the differences in the diversity-area relationship of the different protected area categories in terms of both species richness and phylogenetic diversity. We build a multi-locus phylogeny of 1,519 native vascular plants of Norway, Sweden, and Finland. We estimate the phylogenetic diversity and species richness by combining the phylogeny with publicly available occurrence data and the currently protected area system of Fennoscandia. Our results indicate that protected areas in Fennoscandia hold more plant diversity when larger, and that phylogenetic diversity increases faster with area than species richness. We found evidence for more plant diversity outside of protected areas of the different countries of Fennoscandia than inside of protected areas, but no evidence for plant diversity differences between areas with different protection status. Hence, our results indicate that the current protected area system in Fennoscandia is no more effective in conserving phylogenetic diversity and species richness of vascular plants than a random selection of localities. Our results also indicate that planning conservation strategies around phylogenetic diversity, rather than species richness, might be a first step to protect vascular plant diversity more effectively.

The searching efficiency of predators depends on the balance between the adaptations of the predator and the counter‐adaptations of the prey. In this evolutionary race, the prey should normally have the upper hand, as it can perform tradeoffs between efficiency in resource use and ability to avoid predators. In terrestrial predator–herbivore systems, however, the huge difference in food quality between prey and predators seems to give predators an advantage. In productive terrestrial ecosystems, predators thus chronically overexploit herbivores, i.e. regulate them at densities far below the point of maximum sustainable yield. Assuming type II functional response, this should result in violent limit cycle dynamics. In reality, however, such cycles are only common at high latitudes, whereas the herbivory‐based food webs of species‐rich ecosystems at middle and low latitudes are characterized by asymptotic dynamics, where numerical changes only occur in response to external forcing. One way or another, diversity thus seems to beget stability in terrestrial grazing webs. We propose that strong, donor‐controlled energy flows from the detritus web and directly from plants to predators are the key for the prevalence of asymptotic dynamics at middle and low latitudes. These flows support generalists with type III functional response and, therefore, a capacity to curb budding outbreaks at an early stage. The ongoing extinction wave could critically weaken these stabilizing interactions, which could destabilize currently stable food webs. and result in violent limit cycle dynamics in ecosystems, where the dominating species have evolved under asymptotic dynamics. This could cause secondary extinctions and inflict large economic losses. Keywords: extinction, food webs, limit cycles, overexploitation, searching efficiency, stability

Climate change-related biological research concentrates on studying the relations of increasing mean temperatures and different organisms and ecosystems. Yet, the biology of the species most crucial for climate change mitigation is often ignored – namely, the behavioural biology of our own species. In their comment article, Jenny & Betsch (2022) open discussion on this important topic, highlighting the need for large-scale behavioural data for designing effective climate policy actions. For along time, a lot of emphasis has been placed on voluntary behavioural change of individual people, even though empirical evidence suggests that such changes fall short of achieving the required emission reductions. Instead, we need large-scale system-level changes that regulate, nudge and incentivize individual behaviour. Jenny & Betsch (2022) sketch a potential data observatory system through which the effects of such large-scale policies could be evaluated, inspired by equivalent research infrastructure for handling the COVID-19 pandemic. Thus, this paper should be of high interest for policymakers, as well as for scientific community that should increase its focus on behavioural aspects of human species in solving ecocrises.

Traditionally, biogeography has described the distribution of species. But as plant functional traits and functional diversity underpin ecosystem dynamics, understanding drivers of functional diversity at biogeographical scales is essential to understand spatial variation in ecosystem characteristics, particularly in light of ongoing environmental changes. Here we investigate geographic patterns of functional diversity and ‐traits of the Norwegian flora. We explore whether climate, land‐use or glacial history are important drivers of functional diversity. We combine species occurrence records and assemblage‐means of functional traits to assess the spatial distribution of functional traits and ‐diversity of native vascular plants in Norway in a 20 × 20 km grid. We use multiple‐model inference to identify which environmental factors contribute the most in explaining the spatial patterns of trait distributions and functional diversity. Additionally, we use the constructed models to predict potential changes in distributions of traits and functional diversity given different climate change scenarios. Both individual traits and functional diversity display clear geographic patterns, predictable by climate, landscape and glacial history. Traits related to plant size and growth peak in warmer areas and are predicted to increase in the future, as is functional richness and dispersion. In contrast, functional evenness peaks in northern regions and is predicted to decrease in the future. The different environmental drivers vary in degree of importance, effect sizes and ‐directions on the assemblage‐averaged functional traits and ‐diversity. This underlines the importance of multiple drivers in determining plant assemblage functionality. In the face of climate‐ and land‐use change, Norway is expected to become warmer, wetter and experience a substantial increase in anthropogenic land‐uses, such as increased urbanisation. In turn, the functional composition of the Norwegian flora is predicted to shift towards tall, woody, fast‐growing species.

Global warming has pronounced effects on tundra vegetation, and rising mean temperatures increase plant growth potential across the Arctic biome. Herbivores may counteract the warming impacts by reducing plant growth, but the strength of this effect may depend on prevailing regional climatic conditions. To study how ungulates interact with temperature to influence growth of tundra shrubs across the Arctic tundra biome, we assembled dendroecological data from 20 sites, comprising 1,153 individual shrubs and 22,363 annual growth rings. Evidence for ungulates suppressing shrub radial growth was only observed at intermediate summer temperatures (6.5-9°C), and even at these temperatures the effect was not strong. Multiple factors, including forage preferences and landscape use by the ungulates, and favourable climatic conditions enabling effective compensatory growth of shrubs, may weaken the effects of ungulates on shrubs, possibly explaining the weakness of observed ungulate effects. Earlier local studies have shown that ungulates may counteract the impacts of warming on tundra shrub growth, but we demonstrate that ungulates’ potential to suppress shrub radial growth is not always evident, and may be limited to certain climatic conditions.

There is a solid base of studies on trophic cascades of terrestrial megafauna and how they are affected by climatic changes, but the same aspects of aquatic megafauna remain highly understudied. Cabrera et al. (2022) made a substantial contribution to fill this gap by looking into the long-term demographic responses to post-Last Glacial Maximum (LGM) warming in baleen whales and their prey. They used intra-specific genetic variation (based on DNA sequences from over 7000 specimens) to gain insights into the responses of whales to climate oscillation, and found highly synchronized and exponential increases in abundance in both baleen whales and their prey in the Southern Atlantic Ocean where the food web is based mostly on Antarctic krill. However, in the Northern Atlantic Ocean, where the food web basis comprises a diverse zooplankton community and environmental conditions are more variable, the synchrony was lacking. They also suggest that the current global warming may already have set processes in motion that will result in long-term and wide-ranging rearrangements in marine ecosystems. Although Cabrera et al. (2022) suggest that their results show the Southern Atlantic Ocean being a bottom-up system, it is an interesting question whether this bottom-up stage is just transient, potentially eventually being replaced by top-down control.

Herbivores shape vegetation by suppressing certain plant species while benefitting others. By thus modifying plant species functional composition, herbivores affect carbon cycling, albedo, vegetation structure and species' interactions. These effects have been suggested to be able to counteract the effects of increasing temperatures on vegetation in alpine environments. Managing the dominant large ungulates in these ecosystems could thus provide a tool to mitigate climate change effects. However, it is possible that legacy effects of past grazing will dampen ungulate impacts on vegetation. We shed a light on this topic by investigating the short‐ and long‐term effects of varying sheep densities on the plant trait composition in the Norwegian alpine tundra with centuries‐long of intensive grazing history. In the first part of our study, we quantified the effects of sheep on the plant community functional trait composition at different elevations and under moderate and low productivity in. We combined data from two long‐term (14 and 19 yr) sheep fence experiments and showed that differences in sheep densities did not affect plant trait composition, irrespective of productivity. However, in the second part of our study, we showed that the plant trait composition in mainland (that has been grazed for centuries) differed from vegetation on islands which have been herbivore‐free. Taken together, these results suggest that sheep have an effect on the alpine plant communities on historical time scales covering centuries, but that the resulting sheep grazing resistant/tolerant communities may not respond to shorter‐term (14 and 19 yr) changes in sheep densities, that is, at temporal scales relevant for ecosystem management. Furthermore, we showed that the plant trait composition at the site with low productivity had gone through a temporal trait change independent of sheep treatment, potentially due to increased temperatures and precipitation, suggesting that sheep may not be able to counteract climatic impacts in the areas with centuries‐long grazing history.