Category: new publications

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Consequences of grazer‐induced vegetation transitions on ecosystem carbon storage in the tundra

In this paper published in Functional Ecology, Henni Ylänne and collaborators investigate the impact of reindeer on the carbon storage at two sub-arctic tundra sites in Northern Norway. The sites represent typical examples of herbivory-induced alternative ecosystem states, where high grazing pressure has led to a conversion of tundra shrublands or heaths to tundra meadows with higher rates of nutrient turnover. This study makes use of two 60-year-old reindeer fences that separate these alternative ecosystem states, and compares recent changes in above- and belowground carbon storage.

The paper reports that in the past 14 years, the increased reindeer numbers and higher trampling intensity have led to a larger areal extent of grass-dominated vegetation, leading also to higher soil nutrient availability. This demonstrates the capacity of tundra systems to adjust to changes in grazing pressure.

Further, the paper shows that the “grassification” of tundra shrublands, whether occurred recently or decades earlier, reduces carbon stored aboveground. However, the impacts of grazing belowground varied between the two study sites. At one site, the grass dominated, grazed area stored equal amounts of carbon compared to the tundra heath. At the other site, there was more carbon in the organic soil under the grass-dominated, grazed area compared to the shrub tundra. The consequences of grazing depend on the characteristics of the vegetation under light grazing.

Reference: Ylänne, H., Olofsson, J., Oksanen, L., Stark, S. (2018) Consequences of grazer‐induced vegetation transitions on ecosystem carbon storage in the tundra. Functional Ecology 32: 1091– 1102.

https://doi.org/10.1111/1365-2435.13029

Picture: Differences in vegetation across the reindeer fence in
Čearro (photo: Henni Ylänne, Lund University, 2018)

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Cervid exclusion alters boreal forest properties with little cascading impacts on soils

fence in boreal forest

This paper sheds new light on how moose affects forests. In a recently published article in the journal Ecosystems, Kolstad et al. showed the impact moose browsing has on boreal forest structure, tree species composition, and soil temperature and processes. Understanding the effect moose have on forest ecosystems is crucial for guiding how we manage their populations, as moose have no natural predators in most of Scandinavia. The article showed that chronic moose browsing has caused developing forest to become more open and considerably warmer. The researchers did not find any change in belowground parameters such as soil nutrient dynamics, in contrast to previous studies which showed that the conifer dominated forest associated with larger moose presence also comes with a reduction in soil fertility. This discrepancy may be a product of soils generally taking a long time to change in response to pressures, which makes way for exciting research in the future. We hope the large experimental infrastructure underpinning this study can continue for many more years so that we can increase our understanding of the functional role that moose has in the forest.

Reference: Kolstad, A.L., Austrheim, G., Solberg, E.J., Venete, A.M.A., Woodin, S.J., Speed, J.D.M. (2018) Cervid exclusion alters boreal forest properties with little cascading impacts on soils. Ecosystems 21(5):1027-1041

Picture: Moose exclosure 8 years after it was built on a recent boreal forest clear cut site in Trondheim, central Norway (Photo: Audun Hageskal)

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Multiple feedbacks contribute to a centennial legacy of reindeer on tundra vegetation

The article explores long-term stability of reindeer-induced vegetation shifts by addressing “Historical Milking Grounds” (HMGs): patches in the Scandinavian tundra that were subject to high reindeer concentrations until 100 years ago,but still show a striking similarity to actively grazed areas. Next to providing a detailed description in terms of vegetation, soil and reinvasion rate of the surrounding tundra, the study reveals that several ecological drivers, such as increased nutrient turnover rates and a preference of rodents to feed on shrubs inside the HMGs, contribute to the stability of this vegetation type.

You can access the full publication here. This paper is the first chapter of Dagmar’s PhD thesis to be published. She defended her PhD thesis, called ‘Long-Lasting Ecological Legacies of Reindeer on Tundra Vegetation’ recently. Please find here a link to the PhD thesis, or email Dagmar if you are interested in the full PDF or a paper copy.

Reference: Egelkraut, D., Aronsson, K.-A., Allard, A., Åkerholm, M., Stark, S., Olofsson, J. (2018) Multiple Feedbacks Contribute to a Centennial Legacy of Reindeer on Tundra Vegetation. Ecosystems 21: 1545–1563

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Wildlife species benefitting from a greener Arctic are most sensitive to shrub cover at leading range edges

Ground squirrel, reindeer and shrub encroachment

Through meta-analysis of existing literature we investigated the evidence for links between shrub cover and indicators of population performance in arctic and sub-arctic wildlife. Species from greener habitats (higher NDVI) were more likely to respond positively to shrub cover indicators demonstrating the potential for boreal species to expand northward.Populations at leading edges of species ranges with respect to greenness (low NDVI relative to species range) were more likely to respond positively to shrub cover, showing how shifts at leading edges of species ranges may be particularly rapid. To date, few studies assess how arctic specialists might respond to shrub change. The study also highlights the complexities of discriminating between herbivore responses to shrub and herbivore effects on vegetation and the need for further research to evaluate the relative influence of these two processes on shrub-wildlife associations.

Reference: Wheeler, H.C., Høye, T.T., Svenning, J-C. (2018) Wildlife species benefitting from a greener Arctic are most sensitive to shrub cover at leading range edges. Global Change Biology 24:212–223.

Link to publication

Picture: Different herbivores will respond differently to changes in shrub cover (photos: Helen Wheeler)

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Assessing the Ecological Impacts of Extensive Sheep Grazing in Iceland

Icelandic sheep

This paper compiles available information on the effects of sheep grazing on vegetation, soil properties and other organisms in the rangelands of Iceland. While the scarcity of studies prevented drawing general conclusions, there were some consistent trends. The extent of bare ground was significantly higher in grazed areas and grazing affected plant community structure. This indicates that sheep grazing increases the potential for soil erosion in Icelandic rangelands. A better understanding of the ecological impacts of sheep grazing is required to inform sustainable grazing practices adapted to the local conditions of this region. You can access the full publication here.

Reference: Marteinsdóttir, B., Barrio, I.C. and Jónsdóttir, I.S. (2017) Assessing the ecological impacts of extensive sheep grazing in Iceland. Icelandic Agricultural Sciences 30:57-72.

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Invertebrate herbivory in the tundra is prevalent and sensitive to climate change

Recent studies have shown that biotic interactions influence macroecological patterns and global dynamics, stressing the need to consider them outside local or regional scales. In the context of global changes affecting the dynamics and fate of whole biomes, we still know little about the role of key biotic interactions. In this study, the intensity of invertebrate background herbivory (low intensity but chronic herbivory) on one common tundra plant (Betula nana-glandulosa complex) is investigated across the tundra biome in relation to latitude and climate. Samples were collected from 56 locations across the tundra biome in the first coordinated effort to measure invertebrate herbivory in tundra, outside the well-studied effects of insect outbreaks. Background herbivory was detected at nearly all tundra sites. The intensity of background herbivory, although low, was mainly associated with higher temperatures. As such, invertebrate herbivory is likely to increase in a warmer Arctic. This paper represents the first coordinated effort combining two international research networks in the tundra: the Herbivory Network and the
Network for Arthropods of the Tundra (NeAT).

You can access the paper here.

Reference: Barrio, I.C., Lindén, E., TeBeest, M., Olofsson, J., Rocha, A., Soininen, E.M., Alatalo, J.M., Andersson,T., Asmus, A., Boike, J., Bråthen, K.A., Bryant, J.P., Buchwal, A., Bueno, C.G., Christie, K.S., Denisova, Y.V., Egelkraut, D., Ehrich, D., Fishback, L., Forbes, B.C., Gartzia, M., Grogan, P., Hallinger, M., Heijmans, M.M.P.D., Hik, D.S., Hofgaard, A., Holmgren, M., Høye, T.T., Huebner, D.C., Jónsdóttir, I.S., Kaarlejärvi, E., Kumpula, T., Lange, C.Y.M.J.G., Lange, J., Lévesque, E., Limpens, J., Macias-Fauria, M., Myers-Smith, I., van Nieukerken, E.J., Normand,S., Post, E.S., Schmidt, N.M., Sitters, J., Skoracka, A., Sokolov, A., Sokolova, N., Speed, J.D.M., Street, L.E., Sundqvist, M.K., Suominen, O., Tananaev, N., Tremblay, J.-P., Urbanowicz, C., Uvarov, S.A., Watts, D., Wilmking, M., Wookey, P.A., Zimmermann, H.H., Zverev, V., Kozlov, M.V. (2017) Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome. Polar Biology 40, 2265–2278

  

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Not only mosses: lemming winter diets as described by DNA metabarcoding

The temporal dynamics of most tundra food webs are shaped by the cyclic population dynamics of lemmings. While processes during winter may be behind the recent disruptions of lemming cycles, lemming winter ecology is poorly known. We present here the first DNA metabarcoding data on the winter diet of Norwegian lemmings (Lemmus lemmus), based on feces collected after a winter of population increase. Prostrate willows, mosses, and graminoids dominated the species winter diet, indicating that the conventional idea of lemmings as moss-specialists should be revised. The behavior of lemming-plant models in theoretical studies is conditional on the assumptions of mosses being their main winter food item. As shrubs have been excluded from the framework of these models, incorporating them in future modeling studies should nuance our understanding on how plants affect lemmings. We also sampled diet of a few individuals found dead on top of the snow. These individuals had relatively empty stomachs and had, prior to death, relied heavily on mosses. This apparent lack of abundant good quality indicates spatial heterogeneity in local food availability during the population increase phase.

Reference: Soininen, E.M., Zinger, L., G. Ludovic, Yoccoz, N.G., Henden, J-A., Ims, R.A. (2017) Not only mosses: lemming winter diets as described by DNA metabarcoding. Polar Biology 40(10):2097-103. DOI:10.1007/s00300-017-2114-3.

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Expansion of deciduous tall shrubs but not evergreen dwarf shrubs inhibited by reindeer in Scandes mountain range

exclosure

One of the most palpable effects of warming in Arctic ecosystems is shrub expansion above the tree line. However, previous studies have found that reindeer can influence plant community responses to warming and inhibit shrubification of the tundra.

 In this study, we revisited grazed (ambient) and ungrazed study plots (exclosures), at the southern as well as the northern limits of the Swedish alpine region, to study long-term grazing effects and vegetation changes in response to increasing temperatures between 1995 – 2011, in two vegetation types (shrub heath and mountain birch forest).

We found that shrub expansion is occurring rapidly in the Scandes mountain range, both above and below the tree line. But although tall, deciduous shrubs had benefitted significantly from grazing exclosure, both in terms of cover and height, which in turn lowered summer soil temperatures, the overriding vegetation shift across our sites was a striking increase in evergreen dwarf shrubs, which were not influenced by grazing. Since the effects of an increase in evergreen dwarf shrubs and more recalcitrant plant litter may to some degree counteract some of the effects of an increase in deciduous tall shrubs, herbivore influence on shrub interactions is potentially of great importance for shaping arctic shrub expansion and its associated ecosystem effects.

Reference: Vowles, T., Gunnarsson, B., Molau, U., Hickler, T., Klemedtsson, L., Björk, R.G. (2017) Expansion of deciduous tall shrubs but not evergreen dwarf shrubs inhibited by reindeer in Scandes mountain range. Journal of Ecology 105(6):1547-61. DOI: 10.1111/1365-2745.12753.

Picture: Reindeer exclosures in the Scandes mountains (photo: Tage Vowles, University of Gothenburg)

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Herbivory Network: An international, collaborative effort to study herbivory in Arctic and alpine ecosystems

This paper summarizes the need for herbivory studies and presents the protocols designed by the Herbivory Network.

Plant-herbivore interactions are central to the functioning of tundra ecosystems, but their outcomes vary over space and time. Accurate forecasting of ecosystem responses to ongoing environmental changes requires a better understanding of the processes responsible for this heterogeneity. To effectively address this complexity at a global scale, coordinated research efforts, including multi-site comparisons within and across disciplines, are needed. The Herbivory Network was established as a forum for researchers from Arctic and alpine regions to collaboratively investigate the multifunctional role of herbivores in these changing ecosystems. One of the priorities is to integrate sites, methodologies, and metrics used in previous work, to develop a set of common protocols and design long-term geographically-balanced, coordinated experiments. The implementation of these collaborative research efforts will also improve our understanding of traditional human-managed systems that encompass significant portions of the sub-Arctic and alpine areas worldwide. A deeper understanding of the role of herbivory in these systems under ongoing environmental changes will guide appropriate adaptive strategies to preserve their natural values and related ecosystem services.

Reference: Barrio, I.C., Hik, D.S., Jónsdóttir, I.S., Bueno, C.G., Mörsdorf, M.A., Ravolainen, V.T. (2016) Herbivory Network: An international, collaborative effort to study herbivory in Arctic and alpine ecosystems. Polar Science 10: 297-302.

Link to publication / request a copy

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Sea ice, rain-on-snow and tundra reindeer nomadism in Arctic Russia

frozen reindeer

According to oral histories collected among fully nomadic tundra Nenets on Yamal Peninsula in West Siberia, extreme weather (rain-on-snow) events resulting in significant mortality within tundra herds have occurred roughly once per decade during the past century.

The extreme weather events of November 2006 and 2013 caused mass reindeer starvation that we were able to track in detail using state-of-the-art satellite sensors. The most recent rain-on-snow event of November 2013 resulted in ca. 61,000 reindeer deaths, about 22% out of 275,000 reindeer on the Yamal Peninsula at the time. Empirical data and modelling efforts for the events in 2006 and 2013 found that the likely trigger was brief periods of significant Barents and Kara sea ice retreat during early November. Relatively warm, open water and fragmented ice allowed high levels of atmospheric humidity to develop, while onshore winds combined with anomalously high November air temperatures led to eventual rainfall over extensive continental areas in the Nenets and Yamal-Nenets Autonomous Okrugs.

Socio-economic and ecological implications of the 2013-14 event will play out for years to come. The herders who lost their reindeer through starvation have resorted to full-time fishing in situ, while also borrowing breeding stock to rebuild their herds. In the meantime, northern Yamal pastures that are normally subject to intense grazing pressure in summer will likely experience less grazing and trampling.

Reference: Forbes, B.C., Kumpula, T., Meschtyb, N., Laptander, R., Macias-Fauria, M., Zetterberg, P., Verdonen, M., Skarin, A., Kim, K.Y., Boisvert, L.N. and Stroeve, J.C. (2016) Sea ice, rain-on-snow and tundra reindeer nomadism in Arctic Russia. Biology Letters 12(11):20160466.

Link to publication

Picture: Reindeer frozen into the snowpack in Spring 2014 (photo: Roma Serotetto)

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