Author: isabel

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Growth rings show limited evidence for ungulates’ potential to suppress shrubs across the Arctic

Herbivores may counteract climate warming impacts on tundra by reducing plant growth. However, the strength of this effect may depend on prevailing 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.

Interestingly, evidence for ungulates suppressing shrub growth was only observed at intermediate summer temperatures, and even at these temperatures the effect was minor. Forage preferences and landscape use of the ungulates may explain these results, as well as favorable climatic conditions that may enable effective compensatory growth of shrubs. Earlier local studies have shown that ungulates may counteract the impacts of warming on tundra shrub growth, but we demonstrated that ungulates’ potential to suppress shrub growth is not always evident and may be limited to certain temperature and precipitation conditions.

Reference: Vuorinen, K., Austrheim, G., Tremblay, J.-P., Myers-Smith, I.H., Hortman, H.I., Frank, P., Barrio, I.C., Dalerum, F., Björkman, M.P., Björk, R.G., Ehrich, D., Sokolov, A., Sokolova, N., Ropars, P., Boudreau, S., Normand, S., Prendin, A.L., Schmidt, N.M., Pacheco, A., Post, E., John, C., Kerby, J.T., Sullivan, P.F., Le Moullec, M., Hansen, B.B., Van der Wal, R., Pedersen, Å.Ø., Sandal, L., Gough, L., Young, A., Li, B., Magnússon, R.Í., Sass-Klaassen, U., Buchwal, A., Welker, J.M., Grogan, P., Andruko, R., Morrissette-Boileau, C., Volkovitskiy, A., Terekhina, A., Speed, J.D.M., 2022. Growth rings show limited evidence for ungulates’ potential to suppress shrubs across the Arctic. Environmental Research Letters. https://iopscience.iop.org/article/10.1088/1748-9326/ac5207/meta

This paper is a contribution to the DISENTANGLE project and was included as one of the chapters of Katariina’s PhD at the Norwegian University of Science and Technology.

Photograph: Muskoxen (Ovibos moschatus) in a willow patch (photo: Katariina Vuorinen)

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Call for help with microhistological analyses of reindeer diet

photo: Eeva Soininen

Stefaniya Kamenova and collaborators are currently trying to elucidate possible methodological biases in the assessment of diet in large herbivores. This is motivated by our recent observation that considerable discrepancies occur in the estimation of dietary proportions in the Svalbard reindeer according to the method used (i.e. DNA metabarcoding, microhistology, stable isotope analysis…). Consequently, we aim at comparing these three methods using samples from the very same individuals, collected at the same time.

While we have a rather good grasp of the DNA metabarcoding and stable isotope methods, microhistology remains a technique requiring very specific training. Therefore, our call is for collaborators trained in the microhistological analysis of herbivore diets, to help us with the screening of 96 rumen and faecal Svalbard reindeer samples.

If you have the expertise and certain interest for this iconic Arctic herbivore, please get in touch with Stefaniya.

Photo: Svalbard reindeer (Eeva Soininen)

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A protocol for conducting a systematic review on the effects of herbivore diversity on tundra ecosystems

How do the effects of different herbivores combine to affect tundra ecosystem? This is the question we want to address with a new systematic review. This project builds on earlier work by Herbivory Network members where we compiled available evidence on effects of herbivores on tundra vegetation using a systematic map (Soininen et al, 2021). The systematic review will expand this effort beyond tundra vegetation to include other ecosystem components as well, and will focus on studies that compare areas with different herbivore diversity.

Following the guidelines of the Collaboration for Environmental Evidence (CEE), the process of the systematic review involves two steps: developing a systematic review protocol (that is then peer-reviewed and published), and using that protocol to conduct the actual systematic review. A smaller group of authors has been developing the protocol, that has now been published in Environmental Evidence. We have also started to work on the systematic review. There is still time if you want to get involved in this project! See here the call for collaboration, and contact Laura Barbero-Palacios for more information.

You can access the full text here.

Reference: Barrio, I.C., Barbero-Palacios, L., Kaarlejärvi, E., Speed, J.D.M., Heiðmarsson, S., Hik, D.S., Soininen, E.M. (2022) What are the effects of herbivore diversity on tundra ecosystems? A systematic review protocol. Environmental Evidence 11:1. https://doi.org/10.1186/s13750-022-00257-z

This project is a contribution to the TUNDRAsalad and CHARTER projects.

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Will borealization of Arctic tundra herbivore communities be driven by climate warming or vegetation change?

Arctic ecosystems are changing fast, and these changes involve both plant and herbivore communities. Poleward shifts of species distributions, termed borealization when referring to northward movements of boreal species into tundra, have been observed and are expected to continue. Increasing greenness, shrubification and treeline advance in Arctic ecosystems have been associated with warming trends. Vertebrate herbivores have the potential to limit greening and shrub advance and expansion on the tundra, posing the question of whether changes in herbivore communities could partly mediate the impacts of climate warming on Arctic tundra. Therefore, future changes in the herbivore community in the Arctic tundra will depend on whether the community tracks the changing climates directly (i.e. occurs in response to temperature) or indirectly, in response to vegetation changes (which can be modified by trophic interactions).

We used biogeographic and remotely sensed data to quantify spatial variation in vertebrate herbivore communities across the boreal forest and Arctic tundra biomes and assess whether borealization of vertebrate herbivore communities is a direct response to warming temperatures, or an indirect response through changing vegetation. We then tested whether present-day herbivore community structure is determined primarily by temperature or vegetation.

The composition of herbivore communities across the biome boundary between the boreal forest and the tundra is mainly driven by temperature, rather than vegetation productivity and woody plant cover.

We found that vertebrate herbivore communities are significantly more diverse in the boreal forest than in the Arctic tundra in terms of species richness, phylogenetic diversity and functional diversity. A clear shift in community structure was observed at the biome boundary, with stronger northward declines in diversity in the Arctic tundra. Interestingly, important functional traits characterizing the role of herbivores in limiting tundra vegetation change, such as body mass and woody plant feeding, did not show threshold changes across the biome boundary. The composition of herbivore communities was mainly driven by temperature rather than by vegetation productivity or woody plant cover. Thus, our study does not support the premise that herbivore-driven limitation of Arctic tundra shrubification or greening would limit herbivore community change in the tundra. Instead, borealization of tundra herbivore communities is likely to result from the direct effect of climate warming.

You can access the full text here.

Reference: Speed, J.D., Chimal‐Ballesteros, J.A., Martin, M.D., Barrio, I.C., Vuorinen, K.E. and Soininen, E.M., 2021. Will borealization of Arctic tundra herbivore communities be driven by climate warming or vegetation change?. Global Change Biology, 27(24):6568-6577.

Photo: reindeer grazing (photo by Hannes Skarin)

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Silicon-based defence and nutrient levels in tundra grasses under herbivory

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

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).

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Vegetation and soil C/N chemistry is differentially affected by perturbations like goose grubbing and warming in the high-Arctic

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

Text: Matteo Petit Bon, Czech Academy of Sciences.

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

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An assessment of the functional and phylogenetic diversity of herbivore assemblages across the Arctic and boreal biomes

Following up earlier HN work on the patterns and drivers of herbivore diversity across the Arctic (Barrio et al. 2016, Speed et al. 2019), James Speed and MSc student Jesus Adrian Chimal Ballesteros assessed phylogenetic and functional diversity of both Arctic and boreal herbivore species. Their work examined the presence of clusters of herbivore communities in functional and phylogenetic space, and tested whether these relate to biome transitions or biogeographic transitions. This work helps understand the likely implications of northward movement of herbivore species from the boreal to Arctic biomes.

Adrian successfully defended his MSc thesis in 2019, and the full text is available here. The results of this work were published in Global Change Biology:

SPEED, J.D., CHIMAL-BALLESTEROS, J.A., MARTIN, M.D., BARRIO, I.C., VUORINEN, K.E., SOININEN, E.M. (2021) Will borealization of Arctic tundra herbivore communities be driven by climate warming or vegetation change?. Global Change Biology, 27(24):6568-6577 link to publisher

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Call for collaboration: teabags and grazing!

Interested in burying teabags into your grazing experiment plots?

Do you work in cold ecosystems, tundra or taiga, where you manipulate the intensity of herbivory with exclosures? If the answer is yes, you might be interested in participating in a newly launched research initiative entitled “Impacts of grazers on litter decay rates across northern hemisphere revealed using peer-sourced research network and standardized protocols”.

This research initiative aims at studying the effects of varying herbivory on the initial stages of organic matter decomposition and its underlying drivers across the North. This will be accomplished by the use of green and rooibos tea, following the established teabag index, accompanied by microclimate and vegetation measurements.

This initiative was started by researchers representing the different partner institutes of the UArctic Thematic Network on Herbivory in Spring 2021. The project will provide the protocols and supplies (teabags, microclimate sensors) for collaborating researchers.  

If you are interested to join, please contact Maria Väisänen (maria.vaisanen@oulu.fi). To facilitate communication, please, write “TBI” in the subject field.

You can find the call for collaboration here.

Contact info:
Maria Väisänen
Ecology and genetics research unit, University of Oulu, Finland
maria.vaisanen@oulu.fi


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University of Iceland Post-doc grants

Would you be interested in developing a postdoc in Iceland? The University of Iceland offers 3-year post-doc grants for researchers who have obtained their PhD within the last seven years. It is open now for applications until December 2, 2021.

More information and how to apply here.

If interested in developing a project, you can get in touch with Ingibjörg Svala Jónsdóttir.

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Synergistic effects of insect herbivory and changing climate on plant volatile emissions in the subarctic tundra

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.

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).

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