Category: HN publications

Arctic ecosystems are strongly influenced by herbivores, yet the role of herbivore diversity in shaping ecosystem structure and functioning has been overlooked.  As Arctic herbivore communities respond to rapid environmental changes, a better understanding of the consequences of changes in their diversity is urgently needed.  

We used a systematic review to synthesize available evidence on the effects of herbivore diversity on tundra ecosystems.  Greater herbivore diversity led to increased abundance of herbivory marks and soil temperature, and to reduced total abundance of plants, graminoids and forbs, plant leaf size, plant height, moss depth, and litter abundance. In some cases, the effects of different functional groups of herbivores added up or compensated each other, leading respectively to stronger or weaker responses than would be expected for each group separately, and were modulated by environmental conditions. 

Current knowledge on the role of herbivore diversity still remains limited and geographically biased towards well-established research locations, with a strong focus on impacts of vertebrate herbivores on vegetation.  Future studies should explicitly address the role of herbivore diversity targeting a broader range of ecosystem responses and explicitly including invertebrate herbivores, to refine predictions on whether and where these shifts could mitigate or further amplify the impact of environmental changes on Arctic ecosystems.

The article is open access and you can find it here. You can also see the database as an interactive map. Please feel free to reach out if you have ideas on future projects using this large database!

Reference: Barbero-Palacios, L., Barrio, I.C., García Criado, M. et al. Herbivore diversity effects on Arctic tundra ecosystems: a systematic review. Environ Evid 13, 6 (2024). https://doi.org/10.1186/s13750-024-00330-9

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

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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)

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.

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.

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.

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Photo: reindeer grazing (photo by Hannes Skarin)

Herbivores modify arctic vegetation and can counteract some of the climate-change driven increases in shrub cover and treeline advance induced by climate-change in the tundra. However, the effects of herbivores on plants and ecosystem structure and function vary across the Arctic and seem to depend on the environmental conditions under which herbivory takes place. Therefore, studies in one location can lead to different results than studies in another location, and generalizing the impacts of herbivores becomes difficult. Our systematic map assessed how well the existing literature of herbivore impacts on vegetation covers the environmental variation in the Arctic, to understand how robust are the conclusions that we can make about the effects of herbivores across the tundra biome. Our results show that herbivory research is concentrated in parts of the Arctic that are warmer, wetter, near the coast and that have experienced a moderate increase in temperature. The current evidence base might thus provide an incomplete picture of the effects of herbivores on Arctic vegetation throughout the region.

The database of studies of herbivore effects on arctic vegetation is available through an interactive visualization tool (Arctic Herbivory Systematic Map) that allows exploration of individual environmental variables and the coded data.

This systematic map has been a large effort led by Eeva Soininen. You can find the paper here.

Reference: Soininen, E.M., Barrio, I.C., Bjørkås, R., Björnsdóttir, K., Ehrich, D., Hopping, K.A., Kaarlejärvi, E., Kolstad, A.L., Abdulmanova, S., Björk, R.G.^,, Bueno, C.G., Eischeid, I.^,, Finger-Higgens, R., Forbey, J.S., Gignac, C., Gilg, O.^,, den Herder, M., Holm, H.S., Hwang, B.C., Jepsen, J.U., Kamenova, S.^,, Kater, I., Koltz, A.M.^,, Kristensen, J.A.^,, Little, C.J., Macek, P.^,, Mathisen, K.M., Metcalfe, D.B.^,, Mosbacher, J.B., Mörsdorf, M., Park, T.^,, Propster, J.R.^,, Roberts, A.J., Serrano, E., Spiegel, M.P., Tamayo, M., Tuomi, M.W., Verma, M., Vuorinen, K.E.M., Väisänen, M., van der Wal, R., Wilcots, M.E., Yoccoz, N.G., Speed, J. D. (2021). Location of studies and evidence of effects of herbivory on Arctic vegetation: a systematic map. Environmental Evidence, 10:25. https://doi.org/10.1186/s13750-021-00240-0

Ecological monitoring requires sustained, coordinated efforts.  We need to standardize what and how we measure so that data are comparable across sites and over time.  Further, if monitoring is to be carried out across vast and remote areas like the circumpolar North, it is critical that protocols for data collection are simple and repeatable by different observers. 

Say for example that we want to measure herbivory across the Arctic.  An additional challenge is that herbivores range from small invertebrates with relatively localized impacts to wide-ranging large mammals, so sampling protocols need to be developed at different spatial scales.  In a paper recently published in Arctic Science we applied and assessed standardized protocols to measure tundra herbivory at three spatial scales: plot, site (habitat), and study area (landscape).  The plot and site-level protocols build off earlier efforts of the Herbivory Network to design comparable protocols to measure herbivory across sites of the International Tundra Experiment (ITEX).  These protocols were tested in the field during summers 2014-2015 at eleven sites, nine of them comprising warming experimental plots included in the ITEX network.  The study area protocols are largely based on pellet counts and were assessed during 2014-2018 at 24 study areas across the Arctic, many of them belonging to the Interactions Working Group (IWG).

Our protocols provide comparable and easy-to-implement methods for assessing the intensity of invertebrate herbivory within smaller sampling plots and for characterizing vertebrate herbivore communities at larger spatial scales.  The aim of these protocols is that they can be readily used to obtain comparable estimates of herbivory, both at ITEX sites and at large landscape scales.  The application of these protocols across the tundra biome will allow characterizing and comparing herbivore communities across tundra sites and at ecologically relevant spatial scales, providing an important step towards a better understanding of tundra ecosystem responses to large-scale environmental change.

Reference: Barrio, I.C., Ehrich, D., Soininen, E.M., Ravolainen, V.T., Bueno, C.G., Gilg, O., Koltz, A.M., Speed, J.D.M., Hik, D.S., Mörsdorf, M., Alatalo, J.M., Angerbjörn, A., Bêty, J., Bollache, L., Boulanger-Lapointe, N., Brown, G.S., Eischeid, I., Giroux, M.A., Hájek, T., Hansen, B.B., Hofhuis, S.P., Lamarre, J.-F., Lang, J., Latty, C., Lecomte, N., Macek, P., McKinnon, L., Myers-Smith, I.H., Pedersen, Å.Ø., Prevéy, J.S., Roth, J.D., Saalfeld, S.T., Schmidt, N.M., Smith, P., Sokolov, A., Sokolova, N., Stolz, C., Van Bemmelen, R., Varpe, Ø., Woodard, P.F., Jónsdóttir, I.S. (2021) Developing common protocols to measure tundra herbivory across spatial scales. Arctic Science https://doi.org/10.1139/AS-2020-0020

Across the world, soils are impacted by disturbances caused by trampling of large animals and us, humans, as well as by the weight of our vehicles. Polar tundra ecosystems face these same pressures, as tundra is occupied by large grazers, such as reindeer and musk ox, but also experiences ever increasing human activities. Still today, the impacts of these disturbances on tundra soils remain largely unknown.

We carried out a literature review 1) to map how trampling affects soils across ecosystems and 2) to gather empirical evidence about trampling effects on polar tundra soils.

The reviewed literature revealed deteriorating effects of trampling on vegetation and, in polar tundra, trampling was particularly harmful for mosses. Since mosses play an important role in insulating tundra soils, the trampling-induced thinning and loss of the moss layer often leads to increasing soil temperatures that can further induce thawing of permafrost. Together, soil warming and permafrost thawing can, in turn, increase greenhouse gas emissions from polar tundra soils.

Our review also showed that trampling often induces soil compaction. This links with decreased soil pore space and reduced availability of oxygen and both of these changes have the potential to cascade down to soil biota. In line with this, trampling decreased the abundance of soil invertebrates and fungi, whereas bacteria were more resistant to trampling-induced changes in the soil environment.

We conclude that even though some of the trampling-induced impacts on soils are well documented and have received empirical evidence even from the polar tundra, the cascading effects and pathways leading to altered ecosystem services, such as soil biodiversity, nutrient availability and carbon balance, remain largely undocumented. The tundra-specific patterns reported in the paper highlight the urgent need for more empirical work to support informed efforts to manage and predict the functioning of polar tundra under global changes.

You can find the full article here.

Reference: Tuomi, M., Väisänen, M., Ylänne, H., Brearley, F.Q., Barrio, I.C., Bråthen, K.A., Eischeid, I., Forbes, B.C., Jónsdóttir, I.S., Kolstad, A.L., Macek, P., Petit Bon, M., Speed, J.D.M., Stark, S., Svavarsdóttir, K., Thórsson, J. and Bueno, C.G. Stomping in silence: Conceptualizing trampling effects on soils in polar tundra. Functional Ecology (in press)
https://doi.org/10.1111/1365-2435.13719

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Picture: Reindeer trampling bare soil in arctic Russia (photo credit: Bruce Forbes, University of Lapland)

In a paper recently published in Polar Biology, Sarah Rheubottom and collaborators investigate patterns of invertebrate herbivory across the tundra biome. Previous studies measuring invertebrate herbivory in tundra focused on a single host plant or a small group of species, but for the first time, in this study losses of plant tissue to invertebrate herbivores are assessed at the plant community level across a large number of tundra sites. The study also addressed how these patterns relate to long-term climatic conditions and the weather in the year of sampling, habitat characteristics, and aboveground biomass production.

Invertebrate herbivores depend on external temperature for growth and metabolism, so invertebrate herbivory is expected to increase as a result of continued warming in tundra ecosystems. The study found that invertebrate herbivory occurred low intensities but was present at all sites. On average <1% of the total plant community biomass was removed by invertebrate herbivores. The intensity of herbivory was influenced by mid-summer temperature, with warmer sites having greater leaf damage, but most of the variation in herbivory was associated with local ecological factors. More details about the local drivers of invertebrate herbivory are necessary to predict the consequences for rapidly changing tundra ecosystems.

Reference: Rheubottom, S.I., Barrio, I.C., Kozlov, M.V., Alatalo, J.M., Andersson, T., Asmus, A., Baubin, C., Brearley, F.Q., Egelkraut, D., Ehrich, D., Gauthier, G., Jónsdóttir, I.S., Konieczka, S., Lévesque, E., OLOFSSON, J., Prévey, J., Slevan-Tremblay, G., Sokolov, A., Sokolova, N., Sokovnina, S., Speed, J.D.M., Suominen, O., Zverev, V., Hik, D.S. (2019) Hiding in the background: community-level patterns in invertebrate herbivory across the tundra biome. Polar Biology (in press)

https://doi.org/10.1007/s00300-019-02568-3

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Picture: Damage by leaf miner on Betula nana (photo: Isabel C Barrio, Agricultural University of Iceland, 2017)

It is important to understand how biotic communities are organized, because that will determine how they respond to environmental changes. Beyond the number of species present in a community, two other aspects of diversity can provide useful information about the processes of community assembly. These aspects include how species are related to each other (phylogenetic diversity) and how similar they are in the ecological functions they perform (functional diversity).

In this study we investigate how different factors influence the phylogenetic and functional diversity of vertebrate herbivores across the Arctic tundra biome. We chose this group of organisms because herbivores play key ecological roles in tundra ecosystems. In turn, these ecosystems are likely to change substantially in response to the rapid environmental changes in this region. For example, ongoing warming and the northward expansion of boreal species could change the structure of herbivore communities in the Arctic. Further, Arctic vertebrate herbivore communities include species as functionally dissimilar as migratory, social grazers and solitary resident browsers, and as phylogenetically dissimilar as geese and ruminants.

We found that the functional and phylogenetic diversity of herbivore communities in the Arctic are driven by both bottom‐up and top‐down trophic interactions, as well as climatic severity. Under future warming and northward movement of predators, herbivore communities may become more phylogenetically and functionally diverse, with consequences to the functioning of tundra ecosystems.

Reference: Speed, J.D.M., Skjelbred, I.A., Barrio, I.C., Martin, M.D., Berteaux, D., Bueno, C.G., Christie, K.S., Forbes, B.F., Forbey, J., Fortin, D., Grytnes, J.A., Hoset, K.S., Lecomte, N., Marteinsdóttir, B., Mosbacher, J.B., Pedersen, A.O., Ravolainen, V., Rees, E.C., Skarin, A., Sokolova, N., Thornhill, A.H., Tombre, I., Soininen, E.M. (2019) Trophic interactions and abiotic factors drive functional and phylogenetic structure of vertebrate herbivore communities across the Arctic tundra biome. Ecography

https://doi.org/10.1111/ecog.04347

You can read the full article here.

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Picture: An example of a phylogenetically diverse herbivore assemblage, with a Svalbard reindeer and a rock ptarmigan (photo: N. Lecomte, University of Moncton, 2019)