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The role of herbivores in mediating responses of tundra ecosystems to climate change
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Arctic areas are warming more rapidly than other parts of the world. Increasing temperatures are predicted to result in shrubification, higher productivity, declining species diversity and new species invasions to the tundra. Changes in species diversity and plant community composition are likely to alter ecosystem functions with potential consequences for human population also at lower latitudes. Thus, in order to better predict the effects of the rapid arctic warming, we need knowledge on how plant communities respond to a warmer climate. Here, I investigate the effects of climate warming on tundra plant communities and focus on the role of mammalian herbivores in mediating these responses. I examined the role of herbivores by incorporating herbivore manipulations to short- and long-term warming experiments as well as along altitudinal gradients. I measured how individual plants and plant communities respond to warming with and without herbivores.

Results of my PhD Thesis illustrate several ways how herbivores modify the responses of plants to warming. I found that herbivores (reindeer, hare, voles, lemmings) may prevent lowland forbs from invading open tundra.  Herbivores might also protect small tundra forbs from being outcompeted by taller and denser vegetation under climate warming. Thus, different herbivore pressures may lead to differing plant abundances and distribution shifts in different areas. Furthermore, my results show that high herbivore pressure can reverse the effects of long-term climate warming very rapidly, even in one year. This finding suggests that well-planned targeted reindeer grazing episodes could potentially be used as a conservation tool to keep selected tundra habitats open. Sudden cessation of grazing may initiate rapid changes in plant community, especially if it coincides with warm temperatures. Taken together, I show that herbivores counteract the effects of climate warming by slowing down or preventing vegetation changes in tundra. Therefore, it is important to consider mammalian herbivores when predicting tundra plant community responses to changing climate.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2014. , 23 p.
Keyword [en]
Climate change, warming, grazer, Rangifer, Lemmus lemmus, species distribution, biotic interactions, altitude
National Category
Ecology
Research subject
biology, Environmental Science
Identifiers
URN: urn:nbn:se:umu:diva-85208ISBN: 978-91-7459-782-0 (print)OAI: oai:DiVA.org:umu-85208DiVA: diva2:692137
Public defence
2014-02-21, KBC-huset, Stora hörsalen, KB3B1, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2014-01-31 Created: 2014-01-30 Last updated: 2016-11-10Bibliographically approved
List of papers
1. Effects of warming on shrub abundance and chemistry drive ecosystem-level changes in a forest-tundra ecotone
Open this publication in new window or tab >>Effects of warming on shrub abundance and chemistry drive ecosystem-level changes in a forest-tundra ecotone
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2012 (English)In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 15, no 8, 1219-1233 p.Article in journal (Refereed) Published
Abstract [en]

Tundra vegetation is responding rapidly to on-going climate warming. The changes in plant abundance and chemistry might have cascading effects on tundra food webs, but an integrated understanding of how the responses vary between habitats and across environmental gradients is lacking. We assessed responses in plant abundance and plant chemistry to warmer climate, both at species and community levels, in two different habitats. We used a long-term and multisite warming (OTC) experiment in the Scandinavian forest-tundra ecotone to investigate (i) changes in plant community composition and (ii) responses in foliar nitrogen, phosphorus, and carbon-based secondary compound concentrations in two dominant evergreen dwarf-shrubs (Empetrum hermaphroditum and Vaccinium vitis-idaea) and two deciduous shrubs (Vaccinium myrtillus and Betula nana). We found that initial plant community composition, and the functional traits of these plants, will determine the responsiveness of the community composition, and thus community traits, to experimental warming. Although changes in plant chemistry within species were minor, alterations in plant community composition drive changes in community-level nutrient concentrations. In view of projected climate change, our results suggest that plant abundance will increase in the future, but nutrient concentrations in the tundra field layer vegetation will decrease. These effects are large enough to have knock-on consequences for major ecosystem processes like herbivory and nutrient cycling. The reduced food quality could lead to weaker trophic cascades and weaker top down control of plant community biomass and composition in the future. However, the opposite effects in forest indicate that these changes might be obscured by advancing treeline forests. © 2012 Springer Science+Business Media, LLC.

Keyword
CBSC, global warming, grazing, N, P, reindeer, secondary plant metabolite, shrub, treeline
National Category
Climate Research Ecology
Identifiers
urn:nbn:se:umu:diva-63640 (URN)10.1007/s10021-012-9580-9 (DOI)
Available from: 2013-01-04 Created: 2013-01-03 Last updated: 2017-12-06Bibliographically approved
2. Herbivory prevents positive responses of lowland plants to warmer and more fertile conditions at high altitudes
Open this publication in new window or tab >>Herbivory prevents positive responses of lowland plants to warmer and more fertile conditions at high altitudes
2013 (English)In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 27, no 5, 1244-1253 p.Article in journal (Refereed) Published
Abstract [en]

Warm-adapted low elevation plants are expected to exhibit considerable range shifts to higher altitudes and latitudes as a result of climate warming and increased nutrient loads. However, empirical studies show that the magnitude and direction of plant responses are highly species- and site-specific, suggesting that several additional drivers interact with warmer climate.

We experimentally tested the interactive effects of climate warming, mammalian herbivory and soil fertility on low elevation plants. Seedlings of three warm-adapted lowland forbs (Epilobium angustifolium, Silene dioica and Solidago virgaurea) were transplanted to an open tundra site with native mountain tundra vegetation, and the effects of full factorial combinations of herbivore exclosures, warming and fertilization on transplant survival, growth and flowering were studied for two growing seasons. We also investigated the response of native vegetation biomass to the same treatments and compared it with the responses of transplanted lowland forbs.

Effects of both warming and fertilization on the transplanted lowland forbs strongly hinged on herbivore exclusion, resulting in 2–13-fold increase in biomass in warmed and fertilized plots without herbivores compared with warmed and fertilized plots with herbivores present, the magnitude depending on the species. While warm-adapted transplants benefited from warming, the native tundra plant community biomass did not respond to warming treatment.

Our results show that grazing limits the growth of transplants under warmer and more productive conditions, indicating that the expansion of lowland plant species to higher altitudes with warming may be hampered by mammalian herbivory. Furthermore, our results also suggest that migration of warm-adapted species into lightly grazed high-altitude tundra ecosystems might transform these communities to be more responsive to warmer climate and nutrient loads. Studies that do not consider species' upward shifts from lower altitudes might thus have underestimated vegetation responses to global warming, as well as the potential of herbivory to influence these responses.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2013
Keyword
consumer control, global warming, grazing, range shift, reindeer, thermophilic plant, tundra, upward migration
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-79786 (URN)10.1111/1365-2435.12113 (DOI)000325366500016 ()
Available from: 2013-09-02 Created: 2013-09-02 Last updated: 2017-12-06Bibliographically approved
3. Concurrent biotic interactions influence plant performance at their altitudinal distribution margins
Open this publication in new window or tab >>Concurrent biotic interactions influence plant performance at their altitudinal distribution margins
2014 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 123, no 8, 943-952 p.Article in journal (Refereed) Published
Abstract [en]

Recent studies have shown that biotic interactions can shape species’ distributions, but empirical data on multiple biotic interactions are scarce. Therefore, we examined effects of plant-plant and plant-herbivore interactions on plant survival, growth and reproduction at different altitudes. For these purposes we conducted a factorial neighbor removal and large herbivore exclusion experiment with six transplant species (three tall forbs with their main distribution at low altitudes and three small forbs with their main distribution at high altitudes) on Låktačohkka Mountain, northern Sweden, replicated at two altitudes (ca. 600 and 900 m a.s.l.) and consequently a 2.1 °C difference in summer air temperatures. Overall transplant survival was 93%. Two out of three tall forbs grew better at low than at high altitudes, while no significant differences in growth between altitudes were found for any of the three small forbs. Since the main difference in abiotic conditions between the altitudes was most likely in temperature (as the sites were topographically and edaphically matched as closely as possible), this result indicates that climatic warming could induce upward migration of tall low-altitude forbs. Negative plant-plant interactions prevailed at both altitudes, and we found indications that competition may set the lower altitudinal limits of some small tundra forbs. Thus, increased competition in response to climate warming may potentially shift the lower margins of high-altitude forbs’ distributions upward. Large mammalian grazers reduced the growth of tall forbs and enhanced the flowering of small forbs, and grazers could thus at least partly counteract the anticipated warming-induced distribution shifts.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
National Category
Ecology Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-85206 (URN)10.1111/oik.01261 (DOI)000340664700006 ()
Available from: 2014-01-30 Created: 2014-01-30 Last updated: 2017-12-06Bibliographically approved
4. Short-term herbivory overweighs effects of long-term warming on plant community
Open this publication in new window or tab >>Short-term herbivory overweighs effects of long-term warming on plant community
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-85207 (URN)
Available from: 2014-01-30 Created: 2014-01-30 Last updated: 2014-01-30Bibliographically approved

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