Category: new publications

While typically thought of as having top-down roles in ecosystems, small mammal herbivores bottom-up roles are often underappreciated. As structure builders, small mammals can impact ecosystem function through alterations of soil nutrient cycling. We examined the effects of small mammal-built structure types (hay piles, runways, latrines) on soil and plant biogeochemical cycling across three tundra ecosystems in northern Alaska.

We found that structures play important roles in regulating soil nitrogen levels, regardless of tundra ecosystem. However, different structures influence soil nutrients in different ways. Hay piles increased soil N and plant P, while latrines influenced soil C, N, and P, and runways mainly affected soil N. We also found strong changes in the cover of structures on tundra during different phases of the small mammal population cycle.

Structures built by small mammals have the ability to increase or decrease biogeochemical cycling rates and arctic ecosystem function. Additionally, changes in the abundance of these structures may create pulses of resource availability during the high phase of the population cycle or may aid in maintaining ecosystem function when animals are rare on the landscape. Our work highlights the roles that small mammals play in the bottom-up regulation of tundra ecosystems and the need to include small mammals in our understanding of ecosystem function.   

You can read the full paper here: https://doi.org/10.1111/1365-2435.14127

Reference: Roy, A., Gough, L., Boelman, N.T., Rowe, R.J., Griffin, K.L. and McLaren, J.R., 2022. Small but mighty: Impacts of rodent‐herbivore structures on carbon and nutrient cycling in arctic tundra. Functional Ecology.

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Text: Austin Roy, University of Texas at El Paso. This paper is a contribution of Team Vole, a group of collaborative scientists seeking to understand the impacts of small herbivores on carbon and nutrient cycling in tundra ecosystems.

Photo credit: Luke Johnson

Northern rangelands are changing fast, and these changes can have profound consequences to species coexistence and management.

In their recent paper, Noémie Boulanger-Lapointe and collaborators compiled occurrence data for the main vertebrate herbivore species present in the highlands of Iceland (sheep, reindeer, pink-footed goose and rock ptarmigan). They used an ensemble model workflow to analyse their distribution and its drivers and produced the first high-resolution national open-source and open-access models for Iceland.

The analyses show that vegetation productivity and soil type were the main drivers of herbivore species diversity across Iceland. The overlapping distributions of sheep and geese point out the potential for wildlife-livestock conflicts and for continued ecosystem degradation at higher elevations even under declining livestock abundance.

Compiling data on herbivore occurrence across Iceland was not a trivial task. Data sources ranged from GPS collar data to citizen science observations and span a long period of time (1861-2021). The data compilation provides the most extensive database on herbivore distribution in Iceland. Together with the open-access modelling workflow, such dataset provides a framework for transparent and repeatable science-based management decisions.

You can read the full paper here: https://www.sciencedirect.com/science/article/pii/S0048969722042371

Reference: Boulanger-Lapointe, N., Ágústsdóttir, K., Barrio, I.C., Defourneaux, M., Finnsdóttir, R., Jónsdóttir, I.S., Marteinsdóttir, B., Mitchell, C., Möller, M., Nielsen, Ó.K. and Sigfússon, A.Þ., 2022. Herbivore species coexistence in changing rangeland ecosystems: First high resolution national open-source and open-access ensemble models for Iceland. Science of The Total Environment, p.157140.

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This paper was part of Noémie’s postdoc project funded by the University of Iceland and is a contribution to the TUNDRAsalad project

Photograph: Sheep and pink-footed geese in Iceland (photo: Maite Gartzia)

To what extent herbivores concomitantly alter silicon-based defence and nutrient levels in tundra grasses will ultimately determine changes in the quality of their pastures. In this study, we asked to what extent keystone tundra herbivores, small rodents and reindeer, affect silicon content and silicon:nutrient ratios of grasses found in tundra-grasslands.

Herbivores did not promote a net silicon accumulation in grasses, but rather enhanced their quality by increasing leaf nitrogen and phosphorus levels, thus decreasing silicon:nutrient ratios. Yet, the magnitude of these quality increments varied depending on the herbivore(s) involved and differed between inherently silicon-rich and silicon-poor grasses, ultimately leading to the formation of a fine-scale mosaic of tundra-patches with different nutrient values. In tundra-patches utilised by both herbivores, the quality of inherently silicon-rich grasses was further decreased relative to that of the already more palatable silicon-poor grasses. This could provide an advantage against herbivory, potentially being one of the pathways through which tundra-grassland vegetation states dominated by silicon-rich grasses are generally maintained by herbivores.

Reference: Petit Bon, M., Inga, K.G., Utsi, T.A., Jónsdóttir, I.S. and Bråthen, K.A. (2022), Forage quality in tundra grasslands under herbivory: Silicon-based defences, nutrients, and their ratios in grasses. Journal of Ecology 110(1): 129-143. https://doi.org/10.1111/1365-2745.13790

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Text: Matteo Petit Bon, Czech Academy of Sciences.

Picture: The fence built in the 1950s at Ifjordfjellet, Finnmark, separates spring/fall migratory and summer pasture ranges for semi-domesticated reindeer (Photo: Matteo Petit-Bon).

As vegetation and soil jointly regulate whole-ecosystem processes, differential sensitivity and magnitude of their carbon and nitrogen responses to environmental perturbations may have implications for the functioning of tundra ecosystems. In this study, we addressed sensitivity and magnitude of short-term carbon and nitrogen responses of vascular plants, mosses, and soil to simulated goose disturbance and warming across three habitats that differ in soil moisture in a high-Arctic ecosystem in Svalbard.

Though the system’s total carbon and nitrogen contents were relatively resistant to both perturbations, the three studied ecosystem compartments still differed in their chemical responses (vascular plants > soil > mosses), and such differential sensitivity was further exacerbated by their different responses across habitats (mesic > moist > wet).

These findings highlight the potential for environmental perturbations to have small, yet differential short-term impacts on the carbon and nitrogen contents of vascular plants, mosses, and soil, both within and between tundra-habitats. They also imply that assessments of a single ecosystem compartment in a given context cannot be extrapolated to the whole ecosystem, suggesting that addressing vegetation and soil chemical responses in different habitats can advance our predictive capability of how the biogeochemistry of tundra ecosystems respond to environmental changes.

Reference: Petit Bon, M., Böhner, H., Bråthen, K. A., Ravolainen, V. T., and Jónsdóttir, I. S.. 2021. Variable responses of carbon and nitrogen contents in vegetation and soil to herbivory and warming in high-Arctic tundra. Ecosphere 12( 9):e03746. https://doi.org/10.1002/ecs2.3746

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Text: Matteo Petit Bon, Czech Academy of Sciences.

Picture: Pink-footed geese after their arrival in Svalbard (Photo: Matteo Petit-Bon).

Insect herbivory is a significant source of plant stress and, due to climate change, the herbivory stress is continuously increasing. In the Arctic, where climate warming proceeds with the rate twice of the global average, insect herbivory stress to vegetation is expected to become more severe. In response to herbivory, plants produce specialized metabolites to fulfil physiological and ecological functions, which include volatile organic compounds (VOCs). VOCs are highly reactive and play an important role in biosphere-atmosphere interactions. Various biotic and abiotic stressors, including insect herbivory, can enhance and/or induce the production of many VOCs and alter the composition of the overall VOC blend emitted from the plants.

Due to lack of the empirical studies in the Arctic, it is unclear how the effects of insect herbivory and changing climate such as warming and increased cloudiness, which are both predicted conditions for the future Arctic, will affect VOC emissions in the changing Arctic.

Therefore, in this study we assessed how experimental manipulations of temperature and light availability in subarctic tundra, that had been maintained for 30 years at the time of the measurements, affect the VOC emissions from a widespread dwarf birch when subjected to herbivory by local geometrid moth larvae, the autumnal moth and the winter moth.

Our study showed that whether the future subarctic tundra in Northern Fennoscandia experiences rising temperatures or increasing cloudiness, and therefore milder temperature increases, matter very little for herbivory-related VOC emissions. Under both conditions, we showed strong interactions with herbivory effects on VOC emissions with potentially positive feedbacks on cloud formation. We also show that acclimation of plants to long-term climate treatments, which has resulted in changes in anatomical traits, might strongly interact with volatile responses to insect herbivory. This finding further complicates predictions of how climate change, together with interacting biotic stresses, affects VOC emissions in the Arctic.

Full article here:  https://doi.org/10.1111/gcb.15773

Reference: Rieksta, J., Li, T., Michelsen, A., & Rinnan, R. (2021). Synergistic effects of insect herbivory and changing climate on plant volatile emissions in the subarctic tundra. Global Change Biology, 27(20), 5030-5042.

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Text: Jolanta Rieksta, University of Copenhagen.

Picture: Measuring volatile organic compound (VOC) emissions from dwarf birch in the field using branch enclosure method where VOC are collected using custom built pull-push systems. (Photo: Jolanta Rieksta).

Have you ever been puzzled by the fact that we as ecologists often lump a range of plant species into a single functional category? In this paper the focus is to the most species rich functional grouping we often apply in grasslands, the herbaceous plants with colorful flowers, the forbs. We lump them because each single species often make up a very small abundance, yet why are there so many forb species with small abundances? And why are they in sum often inferior in abundance to the grasses? If looking at forbs in a paleoecological perspective, in the cold Mammoth steppe and in which DNA-based evidence indicates the forbs flourished, we may rethink the importance of forbs and why they often do not seem to thrive in grasslands today.

You can access the paper here: https://esajournals.onlinelibrary.wiley.com/doi/10.1002/fee.2405

Reference: Bråthen, K.A., Pugnaire, F.I. and Bardgett, R.D., 2021. The paradox of forbs in grasslands and the legacy of the mammoth steppe. Frontiers in Ecology and the Environment.

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Text: Kari Anne Bråthen, Professor, UiT The Arctic University of Norway.
Illustration: Ernst Asbjørn Høgtun