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Stark, S., Egelkraut, D., Aronsson, K.-Å. & Olofsson, J. (2019). Contrasting vegetation states do not diverge in soil organic matter storage: evidence from historical sites in tundra. Ecology, 100(7), Article ID e02731.
Open this publication in new window or tab >>Contrasting vegetation states do not diverge in soil organic matter storage: evidence from historical sites in tundra
2019 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 100, no 7, article id e02731Article in journal (Refereed) Published
Abstract [en]

Ecosystems where severe disturbance has induced permanent shifts in vegetation and soil processes may represent alternative stable states. To date, little is known on how long-lasting changes in soil processes are following such disturbances, and how the changes in plant and soil processes between the alternative states eventually manifest themselves in soil organic matter (SOM) storage. Here, we analyzed plant density, the shrub : forb ratio, microbial respiration, extracellular enzyme activities and SOM stocks in soils of subarctic tundra and historical milking grounds, where reindeer herding induced a vegetation transition from deciduous shrubs to graminoids several centuries earlier but were abandoned a century ago. This provides the possibility to compare sites with similar topography, but highly contrasting vegetation for centuries. We found that enzymatic activities and N:P stoichiometry differed between control and disturbed sites, confirming that culturally induced vegetation shifts exert lasting impacts on tundra soil processes. Transition zones, where shrubs had encroached into the historical milking grounds during the past 50 yr, indicated that microbial activities for N and P acquisition changed more rapidly along a vegetation shift than those for microbial C acquisition. Although plant and soil processes differed between control and disturbed sites, we found no effect of historical vegetation transition on SOM stock. Across the study sites, soil SOM stocks were correlated with total plant density but not with the shrub : forb ratio. Our finding that SOM stock was insensitive to a centennial difference in plant community composition suggests that, as such, grazing-induced alternative vegetation states might not necessarily differ in SOM sequestration.

Keywords
cultural landscape, extracellular enzymes, historical ecology, reindeer, soil carbon stock, tundra
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-161833 (URN)10.1002/ecy.2731 (DOI)000474286800007 ()30991449 (PubMedID)
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-12Bibliographically approved
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(4), 1091-1102
Open this publication in new window or tab >>Consequences of grazer-induced vegetation transitions on ecosystem carbon storage in the tundra
2018 (English)In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 32, no 4, p. 1091-1102Article in journal (Refereed) Published
Abstract [en]

1. Large herbivores can control plant community composition and, under certain conditions, even induce vegetation shifts to alternative ecosystem states. As different plant assemblages maintain contrasting carbon (C) cycling patterns, herbivores have the potential to alter C sequestration at regional scales. Their influence is of particular interest in the Arctic tundra, where a large share of the world's soil C reservoir is stored.

2. We assessed the influence of grazing mammals on tundra vegetation and C stocks by resampling two sites located along pasture rotation fences in northern Norway. These fences have separated lightly grazed areas from heavily grazed areas (in close proximity to the fences) and moderately grazed areas (further away from the fences) for the past 50years. Fourteen years earlier, the lightly and moderately grazed areas were dominated by dwarf shrubs, whereas heavy grazing had promoted the establishment of graminoid-dominated vegetation. Since then, both reindeer densities and temperatures have increased, and more time has passed for transient dynamics to be expressed. We expected that the vegetation and C stocks would have changed under all grazing intensities, but not necessarily in the same way.

3. At the site where relative reindeer numbers and trampling intensity had increased the most, graminoid-dominated vegetation was now also found in the moderately grazed area. At the other site, the dominant vegetation types under all grazing intensities were the same as 14 years earlier.

4. We show that the heavily grazed, graminoid-dominated areas stored less C above-ground than the lightly grazed, shrub-dominated areas. Yet, the below-ground consequences of grazing-induced grassification varied between the sites: Grazing did not alter organic soil C stocks at the site where both evergreen and deciduous shrubs were abundant in the lightly grazed area, whereas heavy grazing increased organic soil C stocks at the site where the deciduous shrub Betula nana was dominant.

5. Our results indicate that, despite the negative impacts of grazers on above-ground C storage, their impact on below-ground C may even be positive. We suggest that the site-specific responses of organic soil C stocks to grazing could be explained by the differences in vegetation under light grazing. This would imply that the replacement of deciduous shrubs by graminoids, as a consequence of grazing could be beneficial for C sequestration in tundra soils.

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
Keywords
carbon stocks, grazing, herbivory, plant functional types, plant-soil interactions, Rangifer tarandus, reindeer, soil carbon
National Category
Ecology Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-147321 (URN)10.1111/1365-2435.13029 (DOI)000429323400023 ()
Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2018-08-17Bibliographically approved
Becher, M., Olofsson, J., Berglund, L. & Klaminder, J. (2018). Decreased cryogenic disturbance: one of the potential mechanisms behind the vegetation change in the Arctic. Polar Biology, 41(1), 101-110
Open this publication in new window or tab >>Decreased cryogenic disturbance: one of the potential mechanisms behind the vegetation change in the Arctic
2018 (English)In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 41, no 1, p. 101-110Article in journal (Other academic) Published
Abstract [en]

During the last few decades, the Arctic has experienced large-scale vegetation changes. Understanding the mechanisms behind this vegetation change is crucial for our ability to predict future changes. This study tested the hypothesis that decreased cryogenic disturbances cause vegetation change in patterned ground study fields (non-sorted circles) in Abisko, Sweden during the last few decades. The hypothesis was tested by surveying the composition of plant communities across a gradient in cryogenic disturbance and by reinvestigating plant communities previously surveyed in the 1980s to scrutinise how these communities changed in response to reduced cryogenic disturbance. Whereas the historical changes in species occurrence associated with decreased cryogenic disturbances were relatively consistent with the changes along the contemporary gradient of cryogenic disturbances, the species abundance revealed important transient changes highly dependent on the initial plant community composition. Our results suggest that altered cryogenic disturbances cause temporal changes in vegetation dynamics, but the net effects on vegetation communities depend on the composition of initial plant species.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Patterned ground, Plant abundance, Non-sorted circles, Freeze/thaw-index, Cryogenic disturbance, Differential heave
National Category
Other Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
urn:nbn:se:umu:diva-112507 (URN)10.1007/s00300-017-2173-5 (DOI)000418839500009 ()
Note

Originally included in thesis in manuscript form 2016 with title: Decreased cryogenic disturbance : one of the potential mechanisms behind the shrubification of non-sorted circles in subarctic Sweden.

Available from: 2015-12-15 Created: 2015-12-09 Last updated: 2019-08-12Bibliographically approved
Olofsson, J. & Post, E. (2018). Effects of large herbivores on tundra vegetation in a changing climate, and implications for rewilding. Philosophical Transactions of the Royal Society of London. Biological Sciences, 373(1761), Article ID 20170437.
Open this publication in new window or tab >>Effects of large herbivores on tundra vegetation in a changing climate, and implications for rewilding
2018 (English)In: Philosophical Transactions of the Royal Society of London. Biological Sciences, ISSN 0962-8436, E-ISSN 1471-2970, Vol. 373, no 1761, article id 20170437Article, review/survey (Refereed) Published
Abstract [en]

In contrast to that of the Pleistocene epoch, between approximately 2.6 million and 10 000 years before present, the extant community of large herbivores in Arctic tundra is species-poor predominantly due to human extinctions. We here discuss how this species-poor herbivore guild influences tundra ecosystems, especially in relation to the rapidly changing climate. We show that present herbivore assemblages have large effects on tundra ecosystem composition and function and suggest that the effect on thermophilic species expected to invade the tundra in a warmer climate is especially strong, and that herbivores slow ecosystem responses to climate change. We focus on the ability of herbivores to drive transitions between different vegetation states. One such transition is between tundra and forest. A second vegetation transition discussed is between grasslands and moss-and shrub-dominated tundra. Contemporary studies show that herbivores can drive such state shifts and that a more diverse herbivore assemblage would have even higher potential to do so. We conclude that even though many large herbivores, and especially the megaherbivores, are extinct, there is a potential to reintroduce large herbivores in many arctic locations, and that doing so would potentially reduce some of the unwanted effects of a warmer climate. This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.

Place, publisher, year, edition, pages
The Royal Society, 2018
Keywords
herbivory, climate change, state shifts, treeline shifts, mammoth steppe, rewilding
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-153631 (URN)10.1098/rstb.2017.0437 (DOI)000449344900005 ()30348880 (PubMedID)
Funder
Swedish Research Council, 2017-04515
Available from: 2018-11-27 Created: 2018-11-27 Last updated: 2018-11-27Bibliographically approved
Wackett, A. A., Yoo, K., Olofsson, J. & Klaminder, J. (2018). Human-mediated introduction of geoengineering earthworms in the Fennoscandian arctic. Biological Invasions, 20(6), 1377-1386
Open this publication in new window or tab >>Human-mediated introduction of geoengineering earthworms in the Fennoscandian arctic
2018 (English)In: Biological Invasions, ISSN 1387-3547, E-ISSN 1573-1464, Vol. 20, no 6, p. 1377-1386Article in journal (Refereed) Published
Abstract [en]

It is now well established that European earthworms are re-shaping formerly glaciated forests in North America with dramatic ecological consequences. However, few have considered the potential invasiveness of this species assemblage in the European arctic. Here we argue that some earthworm species (Lumbricus rubellus, Lumbricus terrestris and Aporrectodea sp.) with great geomorphological impact (geoengineering species) are non-native and invasive in the Fennoscandian arctic birch forests, where they have been introduced by agrarian settlers and most recently through recreational fishing and gardening. Our exploratory surveys indicate no obvious historical dispersal mechanism that can explain early arrival of these earthworms into the Fennoscandian arctic: that is, these species do not appear to establish naturally along coastlines mimicking conditions following deglaciation in Fennoscandia, nor were they spread by early native (Sami) cultures. The importance of anthropogenic sources and the invasive characteristics of L. rubellus and Aporrectodea sp. in the arctic is evident from their radiation outwards from abandoned farms and modern cabin lawns into adjacent arctic birch forests. They appear to outcompete previously established litter-dwelling earthworm species (i.e. Dendrobaena octaedra) that likely colonized the Fennoscandian landscape rapidly following deglaciation via hydrochory and/or dispersal by early Sami settlements. The high geoengineering earthworm biomasses, their recognized ecological impact in other formerly glaciated environments, and their persistence once established leads us to suggest that geoengineering earthworms may pose a potent threat to some of the most remote and protected arctic environments in northern Europe.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Earthworm invasion, Arctic, Lumbricidae, Land use, Hydrochory
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-148720 (URN)10.1007/s10530-017-1642-7 (DOI)000432717100003 ()2-s2.0-85037091124 (Scopus ID)
Available from: 2018-06-25 Created: 2018-06-25 Last updated: 2018-06-25Bibliographically approved
Egelkraut, D., Aronsson, K.-Å., Allard, A., Åkerholm, M., Stark, S. & Olofsson, J. (2018). Multiple feedbacks contribute to a centennial legacy of reindeer on tundra vegetation. Ecosystems (New York. Print), 21(8), 1545-1563
Open this publication in new window or tab >>Multiple feedbacks contribute to a centennial legacy of reindeer on tundra vegetation
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2018 (English)In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 21, no 8, p. 1545-1563Article in journal (Refereed) Published
Abstract [en]

Historical contingency is the impact of past events, like the timing and order of species arrival, on community assembly, and can sometimes result in alternative stable states of ecological communities. Large herbivores, wild and domestic, can cause profound changes in the structure and functioning of plant communities and therefore probably influence historical contingency; however, little empirical data on the stability of such shifts or subsequent drivers of stability are available. We studied the centennial legacy of reindeer (Rangifer tarandus) pressure on arctic tundra vegetation by considering historical milking grounds (HMGs): graminoid- and forb-dominated patches amid shrub-dominated tundra, formed by historical Sami reindeer herding practices that ended approximately 100 years ago. Our results show that the core areas of all studied HMGs remained strikingly stable, being hardly invaded by surrounding shrubs. Soil nitrogen concentrations were comparable to heavily grazed areas. However, the HMGs are slowly being reinvaded by vegetative growth of shrubs at the edges, and the rate of ingrowth increased with higher mineral N availability. Furthermore, our data indicate that several biotic feedbacks contribute to the stability of the HMGs: increased nutrient turnover supporting herbaceous vegetation, strong interspecific competition preventing invasion and herbivore damage to invading shrubs. In particular, voles and lemmings appear to be important, selectively damaging shrubs in the HMGs. We concluded that HMGs provide clear evidence for historical contingency of herbivore effects in arctic ecosystems. We showed that several biotic feedbacks can contribute to subsequent vegetation stability, but their relative importance will vary in time and space.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
alternative stable states, plant–herbivore interactions, historical contingency, land use legacy, plant–soil interactions, Rangifer tarandus, soil nutrients, vegetation composition
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-142126 (URN)10.1007/s10021-018-0239-z (DOI)000450919700005 ()
Funder
Swedish Research Council Formas, 2012-1039Swedish Research Council Formas, 2012-230Swedish Research Council Formas, 2015-1091
Note

Originnally included in thesis in manuscript form

Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2019-01-08Bibliographically approved
Bjorkman, A. D., Myers-Smith, I. H., Elmendorf, S. C., Normand, S., Rueger, N., Beck, P. S. A., . . . Weiher, E. (2018). Plant functional trait change across a warming tundra biome. Nature, 562(7725), 57-+
Open this publication in new window or tab >>Plant functional trait change across a warming tundra biome
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2018 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 562, no 7725, p. 57-+Article in journal (Refereed) Published
Abstract [en]

The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature-trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
Identifiers
urn:nbn:se:umu:diva-154596 (URN)10.1038/s41586-018-0563-7 (DOI)000446187900037 ()30258229 (PubMedID)
Funder
Carl Tryggers foundation Swedish Research Council, 2015-00465
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-01-14Bibliographically approved
Barrio, I. C., Lindén, E., te Beest, M., Olofsson, J., Rocha, A., Soininen, E. M., . . . Kozlov, M. V. (2018). Publisher Correction to: Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome (vol 40, pg 2265, 2017). Polar Biology, 41(8), 1653-1654
Open this publication in new window or tab >>Publisher Correction to: Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome (vol 40, pg 2265, 2017)
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2018 (English)In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 41, no 8, p. 1653-1654Article in journal (Refereed) Published
Abstract [en]

The above mentioned article was originally scheduled for publication in the special issue on Ecology of Tundra Arthropods with guest editors Toke T. Hoye . Lauren E. Culler. Erroneously, the article was published in Polar Biology, Volume 40, Issue 11, November, 2017. The publisher sincerely apologizes to the guest editors and the authors for the inconvenience caused.

Place, publisher, year, edition, pages
Springer, 2018
Identifiers
urn:nbn:se:umu:diva-154630 (URN)10.1007/s00300-018-2305-6 (DOI)000441514400012 ()
Note

Correction to: Barrio, Isabel C., Lindén, Elin, Te Beest, Mariska, Olofsson, Johan et al. Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome. Polar Biology, 40;11. DOI: 10.1007/s00300-017-2139-7

Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-01-15Bibliographically approved
Bognounou, F., Hulme, P. E., Oksanen, L., Suominen, O. & Olofsson, J. (2018). Role of climate and herbivory on native and alien conifer seedling recruitment at and above the Fennoscandian tree line. Journal of Vegetation Science, 29(4), 573-584
Open this publication in new window or tab >>Role of climate and herbivory on native and alien conifer seedling recruitment at and above the Fennoscandian tree line
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2018 (English)In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 29, no 4, p. 573-584Article in journal (Refereed) Published
Abstract [en]

Questions: We investigated the importance of climate and herbivory on native and alien conifer colonization of the birch-dominated Fennoscandian tree line by addressing the following questions: (a) are tree line and tundra habitats similarly suitable for conifer seedling recruitment; (b) do ungulate and rodent herbivores differentially impact seedling recruitment; and (c) how does the role of habitat and herbivory on seedling recruitment vary across a marked climate gradient?

Location: Northern Fennoscandia, Sweden (Vassijaure and Paddus), and Norway (Joatka and Seiland).

Methods: We conducted an experiment to assess the emergence rate, survival probability and height development of Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and Siberian larch (Larix sibirica) seedlings. Three experimental plots (i.e., open control, reindeer exclosure and complete vertebrate exclosure) were established in both tree line and tundra habitats at each of the four locations. Seeds of the three conifer species were sown in each plot in June 1999 during three consecutive years. The surviving seedlings were counted in August to September 1999, 2000, 2001, 2002 and 2007. The height of all seedlings was measured in 2007.

Results: Our study reveals that Norway spruce, Scots pine and Siberian larch can regenerate from seed at and above the current tree line in northern Fennoscandia. Their performance was generally higher above tree line in tundra than at tree line, but depended on species identity, climate aridity and mammal herbivory, particularly by rodents. These results suggest that the species composition and latitudinal limit of the tree line in the future might depend not only on direct effects of the future climate on the current tree line species, but also on the intensity of alien and native conifer introductions, as well as changes in herbivore populations.

Conclusion: If sufficient seeds of Norway spruce, Scots pine and Siberian larch should reach the current tree line, their performances will increase with a warmer and wetter climate, and this effect will be markedly modulated by herbivores (particularly rodents). Further work is required to extend these results to determine the ability of these conifers to become tree line-forming species in the future.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2018
Keywords
biological invasions, conifer, exclosures, lemmings, propagule pressure, reindeer, seedling cruitment, seedling survival, tundra, vole
National Category
Ecology Forest Science
Identifiers
urn:nbn:se:umu:diva-151796 (URN)10.1111/jvs.12637 (DOI)000443232400001 ()
Funder
Swedish Institute
Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2018-09-14Bibliographically approved
Egelkraut, D., Kardol, P., De Long, J. R. & Olofsson, J. (2018). The role of plant-soil feedbacks in stabilizing a reindeer-induced vegetation shift in subarctic tundra. Functional Ecology, 32(8), 1959-1971
Open this publication in new window or tab >>The role of plant-soil feedbacks in stabilizing a reindeer-induced vegetation shift in subarctic tundra
2018 (English)In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 32, no 8, p. 1959-1971Article in journal (Refereed) Published
Abstract [en]

1. Herbivory can drive vegetation into different states of productivity and community composition, and these changes may be stable over time due to historical contingency effects. Interactions with abiotic and biotic soil components can contribute to such long-term legacies in plant communities through stabilizing positive feedbacks.

2. We studied the role of plant-soil feedbacks in maintaining vegetation changes caused by historical (similar to 1350-1900 AD) reindeer herding in northern Sweden. These historical milking grounds (HMGs) consist of meadow plant communities formed in naturally nutrient-poor heath or naturally nutrient-rich shrub-dominated vegetation and are still clearly visible in the landscape, a century after active use ceased.

3. We selected two phytometer species: the forb Potentilla crantzii as representative of HMG vegetation, and the dwarf shrub Betula nana, as representative of control vegetation. We grew both species under glasshouse conditions on soils derived from replicated HMG and paired control plots, using live soils and sterilized (-radiation)-inoculated soils, to separate between biotic and abiotic soil effects.

4. A net negative plant-soil feedback for B.nana biomass in its home (i.e., control) soil and a net positive feedback for P.crantzii in its home (i.e., HMG) soil in heath habitat was partly driven by the soil biotic community. However, abiotic differences in mineral nitrogen (N) concentrations between control and HMG soils were a stronger driver of differences in plant growth. Positive feedbacks maintaining a high mineral nutrient availability are thus important, especially in nutrient-poor habitats.

5. The positive plant responses to higher soil mineral N concentrations, combined with positive biotic plant-soil feedbacks, might shift the competitive balance in favour of typical HMG plant species, thereby contributing to stability of HMG plant communities. Our data indicate that herbivore-driven changes in the interactions between plants and both biotic and abiotic components of the soil persist over long temporal scales.

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
Keywords
lternative state, herbivory, historical contingency, legacy effects, plant-soil feedback, Rangifer randus, reindeer husbandry, vegetation composition
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-142129 (URN)10.1111/1365-2435.13113 (DOI)000440651400006 ()
Funder
Swedish Research Council Formas, 2012-1039Swedish Research Council Formas, 2012-230Swedish Research Council Formas, 2015-1091
Note

Originally included in thesis in manuscript form.

Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2018-09-14Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6943-1218

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