Category: new publications

Arctic grazers are known to prevent the establishment of deciduous shrubs and, under certain conditions, promote the dominance of evergreen shrubs. As these shrubs associate with contrasting soil fungal communities, a grazer-induced shift in shrub abundance could alter the processes sustained by soil fungi – such as soil carbon sequestration. This role of grazers is of particular interest today now that both deciduous and evergreen shrubs are expanding their ranges, and arctic grazer could determine their relative success.

We assessed soil fungal community composition and its links to soil carbon storage in two contrasting long-term reindeer grazing regimes in the subarctic treeline ecotone at the border between Finland and Norway. We found that root-associated basidiomycetes and free-living moulds and yeasts were characteristic to the regime with only wintertime grazing, whereas few taxa of root-associated ascomycota dominated fungal communities on the open heaths in the year-round grazing regime. These patterns in fungal functional guild abundance were linked to organic soil carbon storage: root-associated ascomycetes were more abundant in plots with high soil carbon storage, whereas saprotrophic guilds were typical to plots with low soil carbon storage.

Overall, these findings suggest that when grazers promote the dominance of evergreen dwarf shrubs, they may induce shifts in soil fungal communities that, in the long term, increase soil carbon sequestration. This implies an overlooked role of grazers and grazing regimes in controlling soil carbon storage at the treeline ecotone.

Reference: Ylänne, H., Madsen, R.L., Castaño, C., Metcalfe, D.B. and Clemmensen, K.E. (2021) Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage. Global Change Biology, pp. 1– 15. https://doi.org/10.1111/gcb.15722

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Text by Henni Ylänne, Lund University

Pictures from the two grazing regimes by Henni Ylänne

In the Arctic, soil fungal communities may be intrinsically shaped by heavy grazing, which may locally induce an ecosystem change that couples with increased soil temperature and nutrients, and where climate change induced shrub encroachment is less likely to occur than in lightly grazed conditions. Due to these reasons, differences in grazing intensity may control the effects of climate change on fungal communities and thereby carbon and nutrient cycling.

We tested how contrasting long-term grazing intensities affect the responses of soil fungal communities to short-term warming and increased nutrient availability. We used a study design along a reindeer migration route, where 50-years history of an annually occurring pulse of heavy grazing during reindeer migration has shifted the subarctic tundra ecosystem towards increased graminoid dominance, higher soil temperature and nutrient availability. We found that heavy grazing had led to distinct shifts in soil fungal communities when compared to light grazing. Furthermore, the long-term grazing difference largely overrode the effects of short-term warming and fertilization, and the changes in the soil fungal communities caused by our experimental treatments were not unidirectional under different grazing intensities.

Our results demonstrate the determinant role of long-term difference in grazing intensity in shaping fungal communities and their responses to abiotic changes. Further, it reveals that if grazing shifts the fungal communities in Arctic ecosystems to a different state, this may dictate ecosystem responses to further abiotic changes. These results incline that the intensity of grazing cannot be left out when predicting future changes in fungi-driven processes in the tundra.

You can read the full article here: https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.17623

Reference: Ahonen, S.H., Ylänne, H., Väisänen, M., Ruotsalainen, A.L., Männistö, M.K., Markkola, A. and Stark, S. (2021) Reindeer grazing history determines the responses of subarctic soil fungal communities to warming and fertilization. New Phytologist.

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Text by Saija Ahonen, PhD student University of Oulu

Picture: Reindeer in Ráisduoddar (photo credit Sari Stark)

Decades of biogeographic theory suggests that a species geographic range is limited by abiotic conditions towards its high elevation limit and antagonistic biotic interactions towards its low elevation range limit. While many studies have supported the high-elevation range limit prediction, rigorous tests of the low-elevation and antagonistic interaction prediction have been limited. With this work, we tested if three alpine grass species are restricted to the top of the West Elk Mountains, Colorado, USA, in part by higher mammal herbivory rates towards and beyond their low-elevation range limit.

We transplanted individuals of our focal species (Elymus scribneri, Festuca brachyphylla, and Poa alpina) in the core of their range, at their range limit, and in a novel-beyond range limit site that reflected ~2 °C warming. At each site, we factorially excluded above and belowground mammal herbivore access to plants using fencing. Additionally, we collected demographic data from natural populations of the focal species and applied experimental treatment effect sizes to vital rates models (i.e., growth, survival, and reproduction) to project experimental effects on population growth. We found, generally, that herbivory increases from the core of the species’ range towards the limit and novel sites and that restricting above and belowground mammal access to plants increased their growth and reproduction more in limit and novel habitats than in their core range. Additionally, mammal exclusion increased population growth over controls most in limit and novel sites.

Our study suggested that higher herbivory below a species’ elevation range limit contributes to the plant’s exclusion from lower elevations. Importantly, the abiotic environment in novel habitats was hospitable for the individuals, but mammalian herbivory in range limit and novel habitats may drive focal species population growth rates below replacement. Results suggest that as mammals shift their foraging range upslope with further climate change, increased herbivory may drive the local extinction of these alpine restricted grass species.  

You can read the full article here: https://onlinelibrary.wiley.com/doi/epdf/10.1111/ele.13829

Reference: Lynn, J.S., Miller, T.E.X. and Rudgers, J.A. (2021) Mammalian herbivores restrict the altitudinal range limits of alpine plants. Ecology Letters.

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Text by Joshua S. Lynn, University of New Mexico.

Picture: View of an elevation transect used for the experiment in the West Elk Mountains, Colorado, USA. (Photo credit: Joshua S. Lynn).

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

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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)

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

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Text by Rebecca Finger-Higgens, Darmouth College.

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

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.

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Text written by Sari Stark.

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

Lemmings are key species in the arctic tundra. Yet, their whereabouts during the long winter is highly understudied. Luckily, we can use lemming winter nests as an indicator of habitat use by lemmings under the snow. Here we analyzed location data for more than 4200 collared lemming winter nests, collected each year since 1996 at Zackenberg in NE Greenland as part of Greenland Ecosystem Monitoring. We found that lemming select habitats where snow accumulates, but also showed that the strength of the habitat selection varies with lemming density. Moreover, by examining the winter nests for signs of breeding and predation by stoats, we found the larger lemming nests were found in the most preferred habitat (Salix snow beds), and that these were more likely to used for breeding, but also more likely to be depredated than smaller nests. These patterns suggest that the observed density-dependent habitat selection appeared to equalize fitness across the various habitat types.

You can read the full article here.

Reference: Schmidt, N.M., van Beest, F.M., Dupuch, A. et al. Long-term patterns in winter habitat selection, breeding and predation in a density-fluctuating, high Arctic lemming population. Oecologia (2021). https://doi.org/10.1007/s00442-021-04882-2

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Text written by Niels Martin Schmidt.

Picture: Collared lemming (photo credit: Lars Holst Hansen)

The high Arctic is changing rapidly: climate change means advancing springs, and more treacherous winters, with more frequent extreme weather events. On top of this, barnacle geese breeding in the Arctic have been on a diet. So many geese are now migrating to northern breeding grounds that in some places there’s less food to go around. The good news is that it doesn’t seem to restrict their population growth — yet.

This study of individuals’ physical condition, over almost 30 years, showed a 10% decline in average body condition. Especially for herbivores, reduced condition should lead to reduce reproduction and survival. Surprisingly, however, this decline didn’t translate into noticeable effects on population numbers. This is because it’s overridden by other important environmental effects, such as positive impacts of earlier springs and negative effects of Arctic foxes on reproduction. Nevertheless, there is obviously a limit to how skinny the geese can be, if their summer habitat continues to degrade, so it’s likely to restrict population growth at some point in the future.

You can find the full paper here.

Reference: Layton‐Matthews, K., Grøtan, V., Hansen, B.B., Loonen, M.J., Fuglei, E. and Childs, D.Z., 2020. Environmental change reduces body condition, but not population growth, in a high‐arctic herbivore. Ecology Letters. doi: 10.1111/ele.13634

Link to full article write up: https://norwegianscitechnews.com/2020/12/skinnier-but-resilient-geese-thriving-in-the-high-arctic/

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Text: Kate Layton-Matthews, Norwegian Institute for Nature Research

Photograph: Svalbard barnacle geese (Branta leucopsis) (photo credit Jasper Doest Photography)

In this article we describe for the first time the amount of C stored in the plant and soil compartments of extensively grazed highland grasslands of central Argentina under different grazing pressure, to understand their contribution to regional carbon storage.

We quantified C stocks of standing plant, litter, and roots biomass, and soil in three coexisting grassland types associated with different livestock use and analysed how those stocks vary across grassland types. Our main results showed that these mountain grasslands represent an important regional C reservoir, with total C stocks (plant plus soil) ranging from 110 to 472 Mg C ha−1, with more than 95% of C being stored in soils. Differences in soil C stocks up to 30 cm depth were not associated with grassland types. However, in patches associated with higher livestock use, belowground plant C increased, whereas aboveground plant C was reduced.

Our study shows that highland grasslands of central Argentina maintain huge soil C reservoirs. Livestock use could reduce surface C stocks by affecting the plant biomass compartments, which could have a long-term effect on soil C stocks, with direct implications for mountain grasslands management and conservation in the context of climate change mitigation.

You can find the full article here, or ask Georgina Conti for a copy 🙂

Reference: Vaieretti, M.V., Conti, G., Poca, M., Kowaljow, E., Gorné, L., Bertone, G., Cingolani, A.M. and Pérez‐Harguindeguy, N. (2021) Plant and soil carbon stocks in grassland patches maintained by extensive grazing in the highlands of central Argentina. Austral Ecology.
https://doi.org/10.1111/aec.12992

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Picture: Extensive grazing in the central highlands of Argentina (photo: Georgina Conti, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina)