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Effects of climate change on boreal wetland and riparian vegetation
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Models of climate change predict that temperature will increase during the 21th century and the largest warming will take place at high northern latitudes. In addition to warming, predictions for northern Europe include increased annual precipitation and a higher proportion of the precipitation during winter falling as rain instead of snow. These changes will substantially alter the hydrology of rivers and streams and change the conditions for riverine communities. The warming is also expected to result in species adjusting their geographic ranges to stay within their climatic tolerances. Riparian zones and wetlands are areas where excess water determines the community composition. It is therefore likely that these systems will be highly responsive to alterations in precipitation and temperature patterns.

In this thesis we have tested the predicted responses of riparian vegetation to climate-driven hydrologic change with a six year long transplant experiment (I). Turfs of vegetation were moved to a new elevation with shorter or longer flood durations. The results demonstrate that riparian species will respond to hydrologic changes, and that without rare events such as unusually large floods or droughts, full adjustment to the new hydrological regime may take at least 10 years.

Moreover, we quantified potential effects of a changed hydrology on riparian plant species richness (II) and individual species responses (III) under different climate scenarios along the Vindel River in northern Sweden. Despite relatively small changes in hydrology, the results imply that many species will become less frequent than today, with stochastic extinctions along some reaches. Climate change may threaten riparian vegetation along some of the last pristine or near-natural river ecosystems in Europe. More extensive loss of species than predicted for the Vindel River is expected along rivers in the southern boreal zone, where snow-melt fed hydrographs are expected to be largely replaced by rain-fed ones.

With a seed sowing experiment, we tested the differences in invasibility between open wetlands, forested wetlands and riparian zones (IV). All six species introduced were able to germinate and survive in all habitats and disturbance levels, indicating that the tested wetlands are generally invisible. Germination was highest in open wetlands and riparian zones. Increasing seed sowing density increased invasion success, but the disturbance treatments had little effect. The fact that seeds germinated and survived for 2 to 3 years in all wetland habitats indicates that wetland species with sufficiently high dispersal capacity and propagule pressure would be able to germinate and establish here in their respective wetland type.

Our results clearly demonstrate that a changed climate will result in substantial changes to functioning, structure and diversity of boreal wetland and riparian ecosystems. To preserve species rich habitats still unaffected by dams and other human stressors, additional protection and management actions may have to be considered.

Place, publisher, year, edition, pages
Institutionen för ekologi, miljö och geovetenskap, Department of Ecology and Environmental Sciences , 2011. , 30 p.
Keyword [en]
biomass, flooding, hydrologic niche, invasibility, riparian zone, riparian plant species, river margin, climate scenario, seed sowing experiment, species composition, species richness, transplant experiment
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-43811ISBN: 978-91-7459-184-2OAI: oai:DiVA.org:umu-43811DiVA: diva2:416090
Public defence
2011-06-10, Älgsalen, Uminova Science Park, Tvistevägen 48, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2011-05-13 Created: 2011-05-10 Last updated: 2014-12-22Bibliographically approved
List of papers
1. Hydrologic effects on riparian vegetation in a boreal river: an experiment testing climate change predictions
Open this publication in new window or tab >>Hydrologic effects on riparian vegetation in a boreal river: an experiment testing climate change predictions
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2011 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 17, no 1, 254-267 p.Article in journal (Refereed) Published
Abstract [en]

Climate change is expected to alter the magnitude and variation of flow in streams and rivers, hence providing new conditions for riverine communities. We evaluated plant ecological responses to climate change by transplanting turfs of riparian vegetation to new elevations in the riparian zone, thus simulating expected changes in water-level variation, and monitored the results over 6 years. Turfs moved to higher elevations decreased in biomass and increased in species richness, whereas turfs transplanted to lower elevations gained biomass but lost species. Transplanted plant communities responded slowly to the new hydrologic conditions. After 6 years, biomass of transplanted turfs was statistically indistinguishable from target level controls, but species richness and species composition of transplants were intermediate between original and target levels. By using projections of future stream flow according to IPCC climate change scenarios, we predict likely changes to riparian vegetation in boreal rivers. Climate-driven hydrologic changes are predicted to result in narrower riparian zones along the studied Vindel River in northern Sweden towards the end of the 21st century. Present riparian plant communities are projected to be replaced by terrestrial communities at high elevations as a result of lower-magnitude spring floods, and by amphibious or aquatic communities at low elevations as a result of higher autumn and winter flows. Changes to riparian vegetation may be larger in other boreal climate regions: snow melt fed spring floods are predicted to disappear in southern parts of the boreal zone, which would result in considerable loss of riparian habitat. Our study emphasizes the importance of long-term ecological field experiments given that plant communities often respond slowly and in a nonlinear fashion to external pressures.

Keyword
biomass, climate change, flooding, productivity, reciprocal transplant experiment, river banks, species composition, species richness, water table, wetlands
National Category
Natural Sciences
Identifiers
urn:nbn:se:umu:diva-38938 (URN)10.1111/j.1365-2486.2010.02230.x (DOI)000284851500022 ()
Available from: 2011-01-11 Created: 2011-01-11 Last updated: 2016-05-18Bibliographically approved
2. Projected changes in plant species richness and extent of riparian vegetation belts as a result of climate-driven hydrological change along the Vindel River in Sweden
Open this publication in new window or tab >>Projected changes in plant species richness and extent of riparian vegetation belts as a result of climate-driven hydrological change along the Vindel River in Sweden
2012 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 57, no 1, 49-60 p.Article in journal (Refereed) Published
Abstract [en]

1. Riparian plant communities are primarily structured by the hydrologic regime of the stream. Models of climate change predict increased temperatures and changed patterns of precipitation that will alter the flow of rivers and streams with consequences for riparian communities. In boreal regions of Europe, changes will result in stream flows with earlier spring flood peaks of lower magnitude, lower flows during the summer, and higher flows in autumn and winter. We quantified the effects of predicted hydrologic change on riparian plant species richness, using four different scenarios for the free-flowing Vindel River in northern Sweden.

2. We calculated the hydrologic niche of vegetation belts by relating the occurrence of species and vegetation belts to data on flood duration for 10 years preceding vegetation survey. We then used the flood duration predicted for 2071–2100 to estimate expected changes in the extent of each vegetation belt. Using species accumulation curves, we then predicted changes in plant species richness as a result of changes in extent.

3. The two most species-rich vegetation belts; the riparian forest and the willow shrub belts were predicted to decrease most in elevational extent, up to 39% and 32% respectively. The graminoid belt below the shrub belt will mainly shift upwards in elevation while the amphibious vegetation belt at the bottom of the riparian zone increases in size.

4. In the Vindel River, the riparian forest and willow shrub zone will lose most species, with reductions of 5–12% and 1–13%, respectively, depending scenario. The predicted loss from the entire riparian zone is lower, or 1–9% reduction, since many species occur in more than one vegetation belt. More extensive species losses are expected in the southern boreal zone, since much larger spring flood reductions are projected for these rivers.

5. With an expected reduction in area of the most species-rich belts, it becomes increasingly important to manage and protect riparian zones to alleviate other threats, thus minimizing the risk of species losses. Restoring river and stream reaches degraded by other impacts to gain riparian habitat is another option to avoid species losses.

Keyword
climate change, flooding, species accumulation curves, river banks, water table
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-43808 (URN)10.1111/j.1365-2427.2011.02694.x (DOI)
Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2014-03-11Bibliographically approved
3. Projected changes in hydrologic niches of riparian plants in response to climate change
Open this publication in new window or tab >>Projected changes in hydrologic niches of riparian plants in response to climate change
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Riparian zones are species-rich habitats also subject to wide-spread degradation and modification. The extensive habitat and biodiversity losses make conservation of riverine ecosystems a priority, especially in the few river systems that remain free-flowing. However, riparian ecosystems might also be threatened by ongoing and anticipated climate change. Models predict large changes in flow regime across the world, which is anticipated to alter riparian communities, but how is poorly known. In northern Europe, lower annual spring flood peaks and higher winter flows are expected, resulting in narrower riparian zones. To determine the impact on riparian plant species we surveyed five sites along the free-flowing Vindel River in northern Sweden. We calculated the probability of occurrence of plant species along gradients of flood frequency and duration. We then compared present and predicted future water-level fluctuations (based on climate models and IPCC emission scenarios) and thereby got an estimate of the future extent of the species based on their hydrologic requirements. The majority of the riparian species are predicted to decrease in elevational extent by on average 13−28 % until the end of the century, depending on scenario. Species growing in the upper, spring-flood controlled part of the riparian zone are predicted to decrease most, with largest reductions in species with narrow flood duration ranges (decreases of up to 54%). Many species would become less frequent than today, with stochastic extinctions expected along some reaches. Reductions may be more dramatic along rivers in the southern boreal zone where snowmelt-fed hydrographs are expected to be largely replaced by rain-fed ones. With few rivers remaining unaffected by dams and other human stressors, even moderate reductions in abundance can have grave consequences for regional conservation, calling for monitoring to detect declining species and management actions to minimize species losses. Management might include protection of more riverine ecosystems, reduction of negative impacts from land-use activities, implementation of more environmentally friendly flows, channel restoration, and more artificial management options such as mowing riparian meadows no longer maintained by recurrent floods.

Keyword
climate change, flooding, niche width, probability curves, river banks, water table, inundation duration
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-43809 (URN)
Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2011-05-11
4. Invasibility of boreal wetland plant communities
Open this publication in new window or tab >>Invasibility of boreal wetland plant communities
2014 (English)In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 25, no 4, 1078-1089 p.Article in journal (Refereed) Published
Abstract [en]

Question: How does germination and establishment of non-resident plant species differ among major types of wetland ecosystems in boreal forest landscapes? Location: A 250-km(2) large boreal forest landscape in northern Sweden. Methods: We performed a germination and establishment experiment to test for differences between three major wetland types: riparian zones, open wetlands and forested wetlands. These wetland types differ ecologically, hydrologically and in their distribution in the landscape. Six species of vascular plant native to the region but absent or rare in one or more of the three wetland types were sown separately in plots with two different levels of disturbance (complete vegetation removal and control) and were monitored for 3 yr. For two species, seed-sowing density was varied to test for effects of propagule pressure. Results: All six species were able to germinate and survive in all habitats and disturbance levels, suggesting that all three wetland types are invasible. There were positive correlations between germination or survival and species richness in resident vegetation for four out of six species, i.e. species-rich sites were more invasible. The germination frequency did not vary with seed-sowing density, indicating that density-dependent effects were small. All species had higher survival in their resident habitat, while the effect of disturbance was small. Conclusions: The results suggest that the low levels of plant invasion observed in boreal wetlands are better explained by low propagule pressure than high resistance to invasion. However, the habitat dependency of survival implies that population establishment is only expected in habitats to which the species are adapted. Nevertheless, levels of invasion might increase in the future, given that more species are being introduced as a result of increases in transport and trade.

Keyword
Climate change, Forested wetlands, Germination, Open wetlands, Riparian zones, Seeds, Sowing experiment
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-96773 (URN)10.1111/jvs.12157 (DOI)000340572000018 ()
Note

Originally included in thesis in manuscript form, with the title "Differences in plant invasibility among boreal wetland communities".

Available from: 2014-12-02 Created: 2014-12-02 Last updated: 2016-05-18Bibliographically approved

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