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Abstract Arctic rodents influence tundra plant communities by altering species diversity, structure, and nutrient dynamics. These dynamics are intensified during rodent population peaks. Plants are known to induce defenses in response to rodent herbivory. However, changes in plant tissue digestibility may also play a role in deterring rodents or impacting their survival. This study presents a first look at the impacts of rodent herbivory on crude protein (CP) and acid detergent fiber (ADF) of two of the most common graminoid species (Carex nigraandDeschampsia cespitosa) and graminoid genus (Calamagrostisspp.) in the tundra meadows of the Varanger Peninsula, Norway. We selected 32 experimental plots representing both rodent-disturbed and adjacent, undisturbed control graminoid patches. In the summer of a rodent population peak, the disturbed plots had higher ADF (28.5%) values than less disturbed ones (26.6%), controlling for plant species. We also found differences between species, withCarex nigrahaving the lowest fiber content (24.3%, ADF) and highest protein content (18.2% CP)—making it the most palatable species. These results show that rodent activity can potentially alter plant food quality, suggesting that increasing fiber content may be a defensive response to herbivory. 

Abstract Arctic rodents influence tundra plant communities by altering species diversity, structure, and nutrient dynamics. These dynamics are intensified during rodent population peaks. Plants are known to induce defenses in response to rodent herbivory. However, changes in plant tissue digestibility may also play a role in deterring rodents or impacting their survival. This study presents a first look at the impacts of rodent herbivory on crude protein (CP) and acid detergent fiber (ADF) of three of the most common graminoid species (Calamagrostis sp.,Carex nigraandDeschampsia cespitosa) in the tundra meadows of the Varanger Peninsula, Norway. We selected 32 experimental plots representing both rodent-disturbed and adjacent, undisturbed control graminoid patches. During a rodent population peak, the disturbed plots had higher ADF (28.5%) values than less disturbed ones (26.6%), controlling for plant species. We also found differences between species, withCarex nigrahaving the lowest fiber content (24.3%, ADF) and highest protein content (18.2% CP) – making it the most palatable species. These results show that rodent activity can potentially alter plant food quality, suggesting that increased fiber content may be a defensive adaptation against herbivory. 

Grasslands, by definition, are dominated by graminoids. Nevertheless, forbs also make up a substantial part of vascular plant diversity in grasslands and are important resources of mammalian herbivores. However, forb recruitment is constrained by successful dominant graminoids, limiting access to safe sites for germination. Disturbances created by herbivores can reduce graminoid dominance and favor forb recruitment. Here we hypothesize that intense disturbance, such as that caused by megaherbivores, promotes safe sites for forbs in such graminoid‐dominated grasslands, whereas disturbance by today's herbivores, such as small rodents, may not be sufficiently intense. We selected a total of 80 plots with either of four successful graminoid species in tundra grasslands of the Varanger Peninsula, Norway. The graminoid species were silicon‐poor or rich, and of either mat‐ or bunch‐growth form. Plots were further selected in both rodent disturbed and undisturbed areas. We manually removed the dominant graminoid in half of the plots, mimicking megaherbivore disturbance by reducing both shading capabilities and belowground rhizome and root systems. Results show that forb recruitment was significantly enhanced one year following the manual removal of all four graminoids. This effect on forb recruitment was similar among the four graminoids even though they were associated with distinct plant communities. The rodent disturbance did not enhance forb recruitment. In plots with rodent‐disturbed graminoids, the manual removal enhanced forb recruitment only in plots with silicon‐rich graminoids. Forb recruitment was further enhanced by higher levels of initial species richness, initial forb abundance, and soil moisture. Our findings support the hypothesis that intense disturbance, simulating megaherbivore effects on dominant graminoids, significantly enhances forb recruitment. 

Abstract. Our understanding of how rapid Arctic warming and permafrost thaw affect global climate dynamics is restricted by limited spatio-temporal data coverage due to logistical challenges and the complex landscape of Arctic regions. It is therefore crucial to make best use of the available observations, including the integrated data analysis across disciplines and observational platforms. To alleviate the data compilation process for syntheses, cross-scale analyses, earth system models, and remote sensing applications, we introduce ARGO, a new meta-dataset comprised of greenhouse gas observations from various observational platforms across the Arctic and boreal biomes within the polar region of the northern hemisphere. ARGO provides a centralised repository for metadata on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) measurements linked with an interactive online tool (https://www.bgc-jena.mpg.de/argo/). This tool offers prompt metadata visualisation for the research community. Here, we present the structure and features of ARGO, underscoring its role as a valuable resource for advancing Arctic climate research and guiding synthesis efforts in the face of rapid environmental change in northern regions. The ARGO meta-dataset is openly available for download at Zenodo (https://doi.org/10.5281/zenodo.13870390) (Vogt et al., 2024). 

Wildfire activity is increasing in boreal forests as climate warms and dries, increasing risks to rural and urban communities. In black spruce forests of Interior Alaska, fuel reduction treatments are used to create a defensible space for fire suppression and slow fire spread. These treatments introduce novel disturbance characteristics, making longer-term outcomes on ecosystem structure and wildfire risk reduction uncertain. We remeasured a network of sites where fuels were reduced through hand thinning or mechanical shearblading in Interior Alaska to assess how successional trajectories of tree dominance, understory composition, and permafrost change over ∼ 20 years after treatment. We also assessed if these fuel reduction treatments reduce modeled surface rate of fire spread (ROS), flame length, and fireline intensity relative to an untreated black spruce stand, and if surface fire behavior changes over time. In thinned areas, soil organic layer (SOL) disturbance promoted tree seedling recruitment but did not change over time. In shearbladed sites, by contrast, both conifer and broad-leaved deciduous seedling density increased over time and deciduous seedlings were 20 times more abundant than spruce. Thaw depth increased over time in both treatments and was greatest in shearbladed sites with a thin SOL. Understory composition was not altered by thinning but in shearbladed treatments shifted from forbs and horsetail to tall deciduous shrubs and grasses over time. Modeled surface fire behavior was constant in shearbladed sites. This finding is inconsistent with expert opinion, highlighting the need for additional fuels-specific data to capture the changing vegetation structure. Treatment effectiveness at reducing modeled surface ROS, flame length, and fireline intensity depended on the fuel model used for an untreated black spruce stand, pointing to uncertainties about the efficacy of these treatments at mitigating surface fire behavior. Overall, we show that fuel reduction treatments can promote low flammability, deciduous tree dominated successional trajectories, and that shearblading has strong effects on understory composition and permafrost degradation that persist for nearly two decades after disturbance. Such factors need to be considered to enhance the design, management, and predictions of fire behavior in these treatments. 

Abstract Science, engineering, and society increasingly require integrative thinking about emerging problems in complex systems, a notion referred to as convergence science. Due to the concurrent pressures of two main stressors—rapid climate change and industrialization, Arctic research demands such a paradigm of scientific inquiry. This perspective represents a synthesis of a vision for its application in Arctic system studies, developed by a group of disciplinary experts consisting of social and earth system scientists, ecologists, and engineers. Our objective is to demonstrate how convergence research questions can be developed via a holistic view of system interactions that are then parsed into material links and concrete inquiries of disciplinary and interdisciplinary nature. We illustrate the application of the convergence science paradigm to several forms of Arctic stressors using the Yamal Peninsula of the Russian Arctic as a representative natural laboratory with a biogeographic gradient from the forest‐tundra ecotone to the high Arctic. 

Abstract. Large changes in the Arctic carbon balance are expectedas warming linked to climate change threatens to destabilize ancientpermafrost carbon stocks. The eddy covariance (EC) method is an establishedtechnique to quantify net losses and gains of carbon between the biosphereand atmosphere at high spatiotemporal resolution. Over the past decades, agrowing network of terrestrial EC tower sites has been established acrossthe Arctic, but a comprehensive assessment of the network'srepresentativeness within the heterogeneous Arctic region is still lacking.This creates additional uncertainties when integrating flux data acrosssites, for example when upscaling fluxes to constrain pan-Arctic carbonbudgets and changes therein. This study provides an inventory of Arctic (here > = 60∘ N)EC sites, which has also been made available online(https://cosima.nceas.ucsb.edu/carbon-flux-sites/, last access: 25 January 2022). Our database currentlycomprises 120 EC sites, but only 83 are listed as active, and just 25 ofthese active sites remain operational throughout the winter. To map therepresentativeness of this EC network, we evaluated the similarity betweenenvironmental conditions observed at the tower locations and those withinthe larger Arctic study domain based on 18 bioclimatic and edaphicvariables. This allows us to assess a general level of similarity betweenecosystem conditions within the domain, while not necessarily reflectingchanges in greenhouse gas flux rates directly. We define two metrics basedon this representativeness score: one that measures whether a location isrepresented by an EC tower with similar characteristics (ER1) and a secondfor which we assess if a minimum level of representation for statisticallyrigorous extrapolation is met (ER4). We find that while half of the domainis represented by at least one tower, only a third has enough towers insimilar locations to allow reliable extrapolation. When we consider methanemeasurements or year-round (including wintertime) measurements, the valuesdrop to about 1/5 and 1/10 of the domain, respectively. With themajority of sites located in Fennoscandia and Alaska, these regions wereassigned the highest level of network representativeness, while large partsof Siberia and patches of Canada were classified as underrepresented.Across the Arctic, mountainous regions were particularly poorly representedby the current EC observation network. We tested three different strategies to identify new site locations orupgrades of existing sites that optimally enhance the representativeness ofthe current EC network. While 15 new sites can improve therepresentativeness of the pan-Arctic network by 20 %, upgrading as fewas 10 existing sites to capture methane fluxes or remain active duringwintertime can improve their respective ER1 network coverage by 28 % to 33 %. This targeted network improvement could be shown to be clearlysuperior to an unguided selection of new sites, therefore leading tosubstantial improvements in network coverage based on relatively smallinvestments. 

Environmental observation networks, such as AmeriFlux, are foundational for monitoring ecosystem response to climate change, management practices, and natural disturbances; however, their effectiveness depends on their representativeness for the regions or continents. We proposed an empirical, time series approach to quantify the similarity of ecosystem fluxes across AmeriFlux sites. We extracted the diel and seasonal characteristics (i.e., amplitudes, phases) from carbon dioxide, water vapor, energy, and momentum fluxes, which reflect the effects of climate, plant phenology, and ecophysiology on the observations, and explored the potential aggregations of AmeriFlux sites through hierarchical clustering. While net radiation and temperature showed latitudinal clustering as expected, flux variables revealed a more uneven clustering with many small (number of sites < 5), unique groups and a few large (> 100) to intermediate (15–70) groups, highlighting the significant ecological regulations of ecosystem fluxes. Many identified unique groups were from under-sampled ecoregions and biome types of the International Geosphere-Biosphere Programme (IGBP), with distinct flux dynamics compared to the rest of the network. At the finer spatial scale, local topography, disturbance, management, edaphic, and hydrological regimes further enlarge the difference in flux dynamics within the groups. Nonetheless, our clustering approach is a data-driven method to interpret the AmeriFlux network, informing future cross-site syntheses, upscaling, and model-data benchmarking research. Finally, we highlighted the unique and underrepresented sites in the AmeriFlux network, which were found mainly in Hawaii and Latin America, mountains, and at under- sampled IGBP types (e.g., urban, open water), motivating the incorporation of new/unregistered sites from these groups.