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Grasslands in a changing climate: Summer drought and winter warming effects on grassland vegetation
Stockholm University, Faculty of Science, Department of Physical Geography.ORCID iD: 0000-0001-6469-3836
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Grasslands harbour a high biodiversity of both plants and animals, and they provide many ecosystem services such as fodder production, pollination, and carbon storage. Climate change is likely to alter grassland ecosystems, with the effects varying according to the exact nature and timing of changes. Hence, understanding of seasonal climate change effects on grasslands and how negative impacts can be reduced is important to maintain biodiversity and to ensure continued delivery of ecosystem services.

In this thesis I explored how seasonally specific aspects of climate change, i.e. summer drought and winter warming, affect aboveground plant biomass, plant community composition, and floral resources for pollinating insects. Moreover, I aimed to outline ways to mitigate potential negative climate change effects by adapting conventional grazing and mowing regimes and/or by applying soil amendments (i.e. compost) as a novel management method. Soil amendments have been suggested as a method to increase carbon sequestration and they might mitigate negative drought effects. However, there is no empirical evidence of how European grassland ecosystems would be affected should such measures be applied.

A literature review of climate change studies revealed that the terms ‘wetter’ and ‘drier’ can be defined by a variety of hydroclimatic variables, or are not defined at all, making it difficult to synthesise climate change effects on ecosystems and societies. In two in-situ experiments I investigated the effects of summer drought (using rain-out shelters), soil amendments and mowing on four Swedish grasslands, and the effects of winter warming (using open-top chambers) and sheep grazing on three British Upland grasslands. The experimental summer drought caused a non-significant decline in aboveground plant biomass (i.e. fodder production), plant species diversity, and floral resources. Applying soil amendments increased aboveground plant biomass and floral resources (in yearly mown plots), but these positive effects were reduced under drought. There were signs of negative soil amendment effects on legumes. Winter warming led to an increase in graminoid biomass and a decrease in bryophyte biomass. Sheep grazing buffered the growth of a competitive species under winter warming but had only minor effects overall.

My thesis emphasizes that it is important to clearly define terms like ‘wetter’ and ‘drier’ when studying effects of climate change on ecosystems, since clarifying the effects of climate across habitats and management interventions will require the synthesis of results across a range of experimental and observational systems. My field experiments indicate that even relatively small climatic changes affect grassland plant biomass and biodiversity, and that these effects depend on the season and grassland site in question. Furthermore, soil amendments have mainly positive effects on the grassland vegetation, indicating that they have potential for broad-scale application as a method to increase carbon sequestration. Given that my experiments were set up in-situ in grasslands and the treatments were rather mild and realistic in magnitude according to local climate change predictions, the observed vegetation changes within only three years are quite remarkable. They therefore highlight the need for detailed empirical and mechanistic understanding of how climate change processes are likely to affect grassland ecosystems.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University , 2023. , p. 35
Series
Dissertations in Physical Geography, ISSN 2003-2358 ; 33
Keywords [en]
biodiversity, climate change, compost, floral resources, grasslands, in-situ experiments, mowing, nectar, open-top chambers, plants, rain-out shelters, sheep grazing, soil amendments, summer drought, winter warming
National Category
Ecology Climate Research
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-223069ISBN: 978-91-8014-557-2 (print)ISBN: 978-91-8014-558-9 (electronic)OAI: oai:DiVA.org:su-223069DiVA, id: diva2:1805650
Public defence
2023-12-07, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14 and online via Zoom: https://stockholmuniversity.zoom.us/j/68534967825, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2023-11-14 Created: 2023-10-18 Last updated: 2023-11-06Bibliographically approved
List of papers
1. A call for consistency with the terms ‘wetter’ and ‘drier’ in climate change studies
Open this publication in new window or tab >>A call for consistency with the terms ‘wetter’ and ‘drier’ in climate change studies
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2021 (English)In: Environmental Evidence, E-ISSN 2047-2382, Vol. 10, article id 8Article, review/survey (Refereed) Published
Abstract [en]

Ongoing and future hydroclimatic changes have large environmental and societal impacts. In terrestrial ecosystems, these changes are usually described with the terms ‘wetter’ and ‘drier’, which refer to the change in the quantity and/or presence of water, either as water fluxes or stocks. We conducted a literature review of almost 500 recent climate change studies to quantitatively investigate the consistency of the use of these terms across disciplines, regarding the hydroclimatic variables they are related to. We found that although precipitation is prevalently used to describe ‘wetter’ and ‘drier’ conditions, many other variables are also used to refer to changes in water availability between research fields, pointing to a varied perspective on the use of these terms. Some studies do not define the terms at all. In order to facilitate meta-analyses across disciplines, we therefore highlight the need to explicitly state which hydroclimatic variables authors are referring to. In this way, we hope that the terms ‘wetter’ and ‘drier’ used in scientific studies are easier to relate to hydroclimatic processes, which should facilitate the application by authorities and policy makers.

Keywords
Definitions, Hydroclimatic variables, Multidisciplinary, Ecosystems
National Category
Earth and Related Environmental Sciences Other Social Sciences
Identifiers
urn:nbn:se:su:diva-213335 (URN)10.1186/s13750-021-00224-0 (DOI)000635905000001 ()2-s2.0-85103556012 (Scopus ID)
Available from: 2023-01-03 Created: 2023-01-03 Last updated: 2023-10-18Bibliographically approved
2. Soil amendments promote plant biomass in Swedish grasslands without impairing plant diversity, but they can only partly mitigate negative drought effects
Open this publication in new window or tab >>Soil amendments promote plant biomass in Swedish grasslands without impairing plant diversity, but they can only partly mitigate negative drought effects
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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-223066 (URN)
Available from: 2023-10-17 Created: 2023-10-17 Last updated: 2023-10-18
3. Floral resources in Swedish grasslands remain relatively stable under an experimental drought and are enhanced by soil amendments if regularly mown
Open this publication in new window or tab >>Floral resources in Swedish grasslands remain relatively stable under an experimental drought and are enhanced by soil amendments if regularly mown
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2023 (English)In: Ecological Solutions and Evidence, E-ISSN 2688-8319, Vol. 4, no 2, article id e12231Article in journal (Refereed) Published
Abstract [en]
  1. One of the main reasons why insect pollinators are declining is a lack of floral resources. In agricultural landscapes, remaining seminatural grasslands play a key role for providing such resources. However, droughts pose an increasing threat to the abundance and continuity of flowers. Soil amendments are a novel management tool for Swedish grasslands aiming to increase carbon sequestration and soil water holding capacity. In this study, we examined how drought is affecting floral resources (i.e. floral units, nectar quantity and nectar continuity) in grasslands with different mowing regimes, and if soil amendments could mitigate potential negative drought effects.
  2. In summer 2019, we set up an experiment combining rain-out shelters (‘drought’), soil amendments (‘compost’) and different mowing regimes (‘mown’ vs. ‘abandoned’) in four extensively managed Swedish grasslands (48 plots, size 2 m2). Between May and August 2021, we counted the floral units nine times in each plot. We derived values for the nectar sugar production per floral unit from an existing database.
  3. We observed a decrease in floral units under drought in the mown, but not in the abandoned plots. Nectar quantity and continuity over the season were not significantly affected by drought across both mowing regimes—in the abandoned plots the nectar provision even extended slightly in duration (towards late summer). The compost treatment had positive effects on the floral units, nectar quantity and continuity (extending it towards early summer) in the mown, but not in the abandoned plots. The plant species in our study reacted differently to the treatments. Most of the nectar was provided by only few species (mainly Lathyrus pratensis, Vicia cracca and Anthriscus sylvestris).
  4. The results are species specific, thus other plant communities might respond differently. However, our experiment shows that nectar provision (based on database values) in grasslands with a native plant community and natural soil conditions remains relatively stable under drought. We also found that soil amendments increase floral resources in managed grasslands.
Keywords
compost, drought, floral resources, grassland management, insect pollinators, mowing, nectar, soil amendments
National Category
Agricultural Science, Forestry and Fisheries Earth and Related Environmental Sciences Biological Sciences
Identifiers
urn:nbn:se:su:diva-216654 (URN)10.1002/2688-8319.12231 (DOI)000972714300001 ()
Available from: 2023-04-24 Created: 2023-04-24 Last updated: 2023-10-18Bibliographically approved
4. Experimental warming outside the growing season and exclusion of grazing has a mild effect on upland grassland plant communities in the short-term
Open this publication in new window or tab >>Experimental warming outside the growing season and exclusion of grazing has a mild effect on upland grassland plant communities in the short-term
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(English)Manuscript (preprint) (Other academic)
National Category
Environmental Sciences
Identifiers
urn:nbn:se:su:diva-223064 (URN)
Available from: 2023-10-17 Created: 2023-10-17 Last updated: 2023-10-19Bibliographically approved

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5678910118 of 31
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