Author: isabel

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Does exclusion of large grazers matter to plant and soil nitrogen in oligotrophic boreal forests?

Oligotrophic boreal forests with lichen dominated field layer are important winter pastures for reindeer (Rangifer tarandus). In addition to the lichen dominated, drier sunlit habitats, these forests may also have moister shaded habitats with varying moss abundance. Mosses, in turn, control vascular plant-soil interactions, yet they all can also be altered by reindeer grazing.

We determined how two decades of reindeer exclusion affects feather moss (Pleurozium schreberi) depth, and the accompanying soil N dynamics, plant foliar N and stable isotopes of N and C in two contrasting habitats of an oligotrophic Scots pine forest. The study species were pine seedling (Pinus sylvestris), bilberry (Vaccinium myrtillus), lingonberry (V. vitis-idaea) and feather moss. We found that moss carpet was 80% deeper after excluding reindeer both in shaded and sunlit habitats. In the humus horizon, the proportion of heavy N isotope increased due to exclusion in the sunlit habitats and, in the mineral soil, exclusion also increased inorganic N in both habitats. These soil responses were correlated with moss depth. Foliar chemistry did not respond to reindeer exclusion and varied solely due to habitat but depending on species identity.

We conclude that despite strong reindeer grazing-induced shifts in mosses and subtler shifts in soil N, the N dynamics of vascular vegetation remain unchanged. These indicate that plant-soil interactions are resistant to shifts in grazing intensity, a pattern that appears to be common across boreal oligotrophic forests.

Reference: Väisänen M, Tuomi M, Bailey H, Welker JM. Plant and soil nitrogen in oligotrophic boreal forest habitats with varying moss depths: does exclusion of large grazers matter? Oecologia

https://doi.org/10.1007/s00442-021-04957-0

Text by Maria Väisänen, University of Oulu and University of Lapland.

Picture: Reindeer in an oligotrophic Scots pine forest in NE Finland (photo credit: Noora Kantola)

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HN fully endorsed as a UArctic TN

The UArctic TN on Herbivory was fully endorsed after a one year period with provisional status, at the meeting of the Assembly of UArctic!

During the year after the initial approval of the HN’s application to become a UArctic Thematic Network, things have been relatively slow due to the COVID pandemic. Still, HN remained active (see the annual report for 2020) and participated in (online) conferences, published several papers including an article in the UArctic Shared Voices magazine, and was able to secure funding for some of its activities.

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New TN institutional points of contact

During 2020 six new members were confirmed as institutional points of contact for the TN on Herbivory (Bruce Forbes at the University of Lapland, David Hik at Simon Fraser University, Ingibjörg Svala Jónsdóttir at the University of Iceland, Elina Kaarlejärvi at the University of Helsinki, Mikhail Kozlov at the University of Turku and Johan Olofsson at Umeå
University). The full list of institutional points of contact for the TN on Herbivory includes:

  • Isabel C. Barrio (Lead), Agricultural University of Iceland
  • Bruce Forbes (Member), University of Lapland
  • David Hik (Member), Simon Fraser University
  • Ingibjörg Svala Jónsdóttir (Member), University of Iceland
  • Elina Kaarlejärvi (Member), University of Helsinki
  • Mikhail Kozlov (Member), University of Turku
  • Johan Olofsson (Member), Umeå University
  • Eeva Soininen (Member), UiT The Arctic University of Norway
  • Maria Väisänen (Member), University of Oulu
  • Henni Ylänne (Member), Lund University

If you are working at a UArctic member institution and you want to become an institutional point of contact for the TN on Herbivory, please contact Isabel,

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Invertebrate herbivory on shrubs increases in warmer and drier tundra

Rapid warming is predicted to increase insect herbivory across the tundra biome, yet how this will impact the community and ecosystem dynamics remains poorly understood. More insect herbivory could reduce potential gains in Arctic plant growth, by serving as a top–down control on tundra vegetation. Additionally, many tundra ecosystems experience severe insect outbreaks, where large numbers of insects emerge and consume large amounts of leaves and other plant material, which can have leaf lasting damage to shrubs. To explore how tundra-insect herbivore systems respond to warming, we measured shrub traits and leaf herbivory damage at 16 sites along a landscape gradient in western Greenland. Here we show that shrub leaf insect herbivory damage on two dominant deciduous shrubs, grey willow (Salix glauca) and dwarf birch (Betula nana), was positively correlated with increasing temperatures throughout the first half of the 2017 growing season. We found that the majority of insect herbivory damage occurred in July, which was outside the period of rapid leaf expansion that occurred throughout most of June. Leaf-chewing insects caused the most leaf damage in both shrub species. Additionally, insect herbivores removed a larger proportion of dwarf birch leaf biomass in warmer sites, which is due to a combination of increased herbivory with a coinciding decline in leaf biomass. These results suggest that the effects of rising temperatures on both insect herbivores and plants are important to consider when predicting the trajectory of Arctic tundra shrub expansion.  

Reference: Finger-Higgens, R., DeSiervo, M., Ayres, M.P. and Virginia, R.A., 2021. Increasing shrub damage by invertebrate herbivores in the warming and drying tundra of West Greenland. Oecologia, pp.1-11.
https://doi.org/10.1007/s00442-021-04899-7

Text by Rebecca Finger-Higgens, Darmouth College.

Picture: Fieldwork in Kangerlussuaq (photo credit: Rebecca Finger Higgens)

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Katariina Vuorinen’s PhD thesis defence!

Save the date! Next April 16, 2021, Katariina Vuorinen will defend her thesis titled “When do ungulates override the climate? Defining the interplay of two key drivers of northern vegetation dynamics“. Kata’s thesis has been carried out at the Faculty of Natural Sciences, Norwegian University of Science and Technology (NTNU), under the supervision of James Speed, Gunnar Austrheim, Allison Hester and Jean-Pierre Tremblay. 

As a requirement of Norwegian universities, Katariina will have first a trial lecture on a topic related to her thesis work, followed by the public defence of her thesis.

  • The trial lecture will be at 10:15 Norwegian time. The topic of her trial lecture will be: Looking back in time and space: how and where did Pleistocene megaherbivores affect vegetation? The Zoom link for the presentation will be announced here closer to the date.
  • The public defence will be at 13:15 Norwegian time. The Zoom link for the presentation will be announced here closer to the date.

Summary of the thesis

Climate change is expected to transform the vegetation of the Earth, and thus cascade through ecosystems from bottom-up. However, ecological processes rarely work like a one-way street. Top-down effects of herbivores can change vegetation, and thus modify and even counteract the effects of warming. In northern ecosystems, ungulate herbivores such as deer, moose, reindeer, muskox, and sheep may decrease tree growth, prevent shrub expansion and shape vegetation communities.
From the viewpoint of forestry and forest restoration, increasing mean temperatures may bring desired boost for tree growth, whereas ungulates cause undesired growth decrease by browsing the trees. In contrast, in arctic and alpine environments, warming may drive shrub advancement and closing-up of the vegetation with detrimental effects to tundra species and ecosystem functioning, and thus the counteracting force of ungulates can be seen as a positive management tool that may be used to mitigate the impacts of warming. To adapt ungulate management to the prevailing and future climatic conditions for preserving and achieving desired vegetation states, knowledge on the combined effects of climate and ungulates is urgently needed.
In this thesis, I studied the interplay of climate and ungulates in affecting the vegetation of tundra and boreal forests within multiple different ecological contexts. I identified conditions under which ungulates are likely to counteract climatic effects on tree growth, shrub growth and functional structure of plant communities. With this approach, I aimed at answering the question: When do ungulates override the climate?
The results showed that climate and ungulate effects on plants may depend on each other, and that their effects vary between different ecological contexts across northern biomes. Deer were shown to counteract the effect of temperature on pine growth in the Scottish Highlands, and the effect of browsing intensity increased at high temperatures. Similarly, moose counteracted the effects of warming on boreal tree growth in Norway and Canada, but only for preferred forage species. Reindeer, muskox and sheep had a weak negative effect on tundra shrub growth, and this effect was only detected at intermediate temperatures but not at the coldest and the warmest parts of the Arctic. The functional composition of alpine plant communities in Norway showed high resistance to changing sheep densities, but there was evidence for a moderate climate-driven increase in plant size. These results may be useful for management purposes, and help us to achieve and retain desired vegetation states under changing climatic conditions.

You can access the full thesis here.

The thesis has already resulted in two publications:

  • Vuorinen, K.E., Rao, S.J., Hester, A.J. and Speed, J.D., 2020. Herbivory and climate as drivers of woody plant growth: Do deer decrease the impacts of warming?. Ecological Applications, 30(6): e02119 link to publisher
  • Vuorinen, K.E., Kolstad, A.L., De Vriendt, L., Austrheim, G., Tremblay, J.P., Solberg, E.J. and Speed, J.D., 2020. Cool as a moose: How can browsing counteract climate warming effects across boreal forest ecosystems?. Ecology, 101(11): e03159 link to publisher
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Measuring herbivory across the tundra from plots to landscapes

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

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Two master projects in Arctic terrestrial ecology at the University of Iceland

We are looking for two motivated and enthusiastic students to work on master project in Arctic terrestrial ecology at the Faculty of Life and Environmental Sciences, University of Iceland.

One of the MS projects is a part of the research project „Trapped in a degraded state?  Tundra ecosystem responses of grazing cessation – TRAPP“, funded by the Icelandic Research Fund. Through field and laboratory experiments the student will study the mechanisms that keep tundra ecosystems in the Icelandic highlands trapped in a degraded state for a long time after grazing protection. Supervisors will be Ingibjörg Svala Jónsdóttir, University of Iceland and Kari Anne Bråthen, the Arctic University of Norway, Tromsø.

The second MS project will be linked to the research network International Tundra Experiment – ITEX, which aims at studying effects of climate change on tundra vegetation and ecosystems. The master project is partly funded by the Svalbard Environmental Protection Fund and will be based on long-term warming experiments in the Icelandic highlands and Svalbard. The aim of the master project will be to compare responses of individual bryophyte and vascular plant species and functional groups to long-term warming. The plan is to do vegetation analyses and data collection in Svalbard by the end of July, but it is possible that this part of the project will be postponed to the summer 2022 due to the covid pandemic. In that case all project work will be in Iceland in 2021.  

In both cases, the students need to be prepared to do fieldwork in harsh conditions (the Icelandic highlands, the high Arctic Svalbard) and to work in a team (good communication skills).  Good skills in plant identification are desirable as well as skills and/or interest in data analysis (R) and in English.

Even though the master programme does not formally start until in the fall semester we want both students to start working within their projects this summer and assist in setting up field experiments, collecting data and material to work with in the lab, etc.

For further information, please contact Ingibjörg Svala Jónsdóttir isj@hi.is

Application deadline is April 6, 2021

Submit your application by e-mail to isj@hi.is  with MASTER PROJECT as subject. Attach the following documents:

  • An short introduction letter where you explain your motivation for master studies
  • Names and full contact information for two referees
  • CV
  • Transcripts of grades during your Bachelor studies

It is expected that the applicants that will be selected then formally apply for the master programme at the Faculty of Life and Environmental Sciences before the deadline April 15. Further information on the master programme is provided here: https://english.hi.is/biology

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MSc project at the University of Iceland

MS research project – Sheep farmers’ perspectives of the impact of wild herbivores in the Icelandic highlands

We are seeking a motivated Master student to join our interdisciplinary team of social and natural scientists working on the impact of wild and domesticated herbivores on the vegetation of the Icelandic highlands. This project will involve the use of social research methods to gather farmers’ perspectives on the impact of reindeer and wild geese on summer pastures.

Management of Arctic rangelands needs to consider the pressure from various herbivores. Wild birds and mammals (e.g. geese, ptarmigan, reindeer) as well as farmed animals (e.g. sheep) are vital parts of these ecosystems. In recent years, the increase in the number of migratory geese and reindeer has raised concerns by sheep farmers in parts of Iceland, as they are thought to reduce forage availability to sheep. While the regulation of sheep numbers is based on the conditions of the grazing commons, wild herbivore species management and hunting quotas are largely disconnected from habitat conditions. Moreover, farmers can document damages caused by wild herbivores on farmed lands, but little is known about their impact on summer pastures in the highlands.

The student will be based in the Department of Geography of the University of Iceland and co-supervised by Karl Benediktsson and Noémie Boulanger-Lapointe (Department of Biology). Since the project will involve active engagement with farmers, candidates are required to be fluent in Icelandic. You can contact Noémie (nbl@hi.is) for further information regarding this project. The deadline to apply for a master program at the University of Iceland is April 15th.

Sheep and pink footed geese in Iceland (photo: Maite Gartzia)
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Timing of reindeer grazing drives changes in mountain birch forest structure and understory vegetation

Subarctic mountain birch (Betula pubescens ssp. czerepanovii) forests with an understorey vegetation of dwarf shrubs, lichens and mosses form an important habitat for semi-domestic reindeer (Rangifer tarandus). In the summer ranges, reindeer browse mountain birches, whereas in the winter ranges, reindeer leave mountain birches intact and feed on lichens and evergreen dwarf shrubs. Here, we re-analyzed forest structure and understorey vegetation after 12 years in northern Finnish reindeer herding co-operatives where winter and summer ranges had been separated since the 1980’s. We found that the number of mountain birches and the biomass of evergreen and deciduous dwarf shrubs had increased substantially. Yet, the increases in many plant groups varied with seasonal range and habitat, revealing that the seasonal use of reindeer ranges was a major driver for the ongoing subarctic ecosystem change. For example, tall mountain birch seedlings had increased twice as fast in winter than summer ranges. Evergreen dwarf shrub mountain crowberry (Empetrum nigrum ssp. hermaphroditum) had increased to a greater extent in winter ranges in a semidry habitat, but to a greater extent in summer ranges in a dry habitat.

These vegetation trends revealed the cumulative effect of climate warming and grazing regimes, which gave insights into the vegetation we may expect to see in the future. This information helps predicting forage availability for the reindeer under warming climate.

You can read the full article here.

Reference: Stark, S., Ylänne, H. and Kumpula, J., Recent changes in mountain birch forest structure and understory vegetation depend on the seasonal timing of reindeer grazing. Journal of Applied Ecology.

Text written by Sari Stark.

Picture: Subarctic forest‐tundra ecotones dominated by mountain birch (Betula pubescens ssp. czerepanovii) (photo credit: Sari Stark)

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MSc position at the Agricultural University of Iceland

Deadline for applications: March 26, 2021

We are looking for an enthusiastic MSc student to join the project “Herbivores in the tundra: linking diversity and function (TUNDRAsalad)” funded by the Icelandic Research Fund.

TUNDRAsalad will explore the role of herbivore diversity in tundra ecosystems, and how different assemblages of herbivores influence ecosystem functions in high latitude ecosystems. The MSc project will use a systematic review to synthesize existing knowledge to assess the effects of herbivore diversity on the functioning of tundra ecosystems. Using a peer-reviewed protocol, the student will conduct a systematic literature search and compile all relevant studies investigating the effects of herbivore diversity on the functioning of tundra ecosystems. The results of different studies will be synthesized using meta-regression.

Ptarmigan in Bylot Island (photo credit: Eeva Soininen)

The MSc student will be based at the Reykjavík campus of the Agricultural University of Iceland, and will be co-supervised by Isabel C Barrio (Agricultural University of Iceland), Eeva Soininen (UiT The Arctic University of Norway) and James Speed (Norwegian University of Science and Technology).

The deadline for applications is March 26, 2021 and the position will start on June 1, 2021. The student will be hired for 12 months for the development of the project.

Applications are welcome from candidates with a BSc degree in ecology, environmental sciences or related fields. Applicants should ideally enjoy reading scientific papers, have good organizational skills and the ability to work as part of a team and independently. Previous experience conducting literature reviews and meta-analysis are desirable skills.

In your application you should include:

  • Cover letter that explains how your research interests and experience align with the position
  • CV or resume, including your overall grade and relevant experience
  • List of two professional references and their contact information

Please send your application and any questions to Isabel C Barrio (isabel@lbhi.is). For more details see the ad on the website of the Agricultural University of Iceland.

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