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Vegetation patterns in small boreal streams relate to ice and winter floods
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology Group)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology Group ; Arcum)
2015 (English)In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 103, no 2, 431-440 p.Article in journal (Refereed) Published
Abstract [en]

In-stream and riparian vegetation are species rich, productive and dynamic. Their patterns insmall boreal streams are largely driven by seasonal flow regimes. Traditionally, flow-related processes during the growing season, particularly the spring flood, have been seen as the most important, whereas vegetation has been viewed as being dormant and ‘less affected’ during winter.

Riparian and in-stream vegetation were inventoried during the summers 2011–2013 in eight reaches of northern Swedish streams. Along each reach, the ice formation was surveyed during winter by visual inspections and with permanently placed cameras. We then evaluated the potential effects of ice regimes and winter flooding on riparian and in-stream vegetation during 3 years by relating the abundance of winter floods caused by anchor ice to the cover, composition and biomass of vegetation.

We found that the numbers of winter floods were higher along reaches with anchor-ice formation than in reaches without. We also found that species diversity of riparian vegetation was higher inthe reaches with anchor ice. This resulted from a lower cover of riparian dwarf shrubs and a higher cover of graminoids and forbs along reaches with anchor ice. We also found a lower cover of instream algae but a higher cover of bryophytes in anchor-ice reaches. These patterns were consistent throughout the study period although there were interannual differences in temperature, water levels and ice cover.

During our study period, we encountered an average of 20 shifts per winter between freezing and thawing, while there was an average of 10 shifts per winter during 1960–1990. This indicates a warming climate in high latitudes. Higher temperatures and more shifts between freezing and thawing may initially increase ice dynamics. However, with further increases in mean temperature, ice production should eventually decrease.

Synthesis. Ice and winter floods caused by anchor ice appear to be important disturbance agents that allow less competitive species to establish along small boreal streams. If ice dynamics is reduced, the composition and production of riparian and in-stream vegetation may be changed, with possible consequences for the entire stream ecosystem.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2015. Vol. 103, no 2, 431-440 p.
Keyword [en]
anchor ice, bryophytes, climate change, determinants of plant community diversity and structure, disturbance, ice regime, riparian, vascular plants, vegetation, winter flooding
National Category
Research subject
Ecological Botany; Hydrology
URN: urn:nbn:se:umu:diva-98969DOI: 10.1111/1365-2745.12355ISI: 000350549000014OAI: diva2:785076
Swedish Research Council Formas
Available from: 2015-02-02 Created: 2015-01-30 Last updated: 2016-05-18Bibliographically approved
In thesis
1. Breaking the ice: effects of ice formation and winter floods on vegetation along streams
Open this publication in new window or tab >>Breaking the ice: effects of ice formation and winter floods on vegetation along streams
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Klimatförändringar och isbildning i vattendrag : effekter på biologisk mångfald
Abstract [en]

Streams in cold regions are characterized by unique hydrological processes that control flow regime and water levels. One of the most important processes is the formation, growth and melting of different types of ice in and around the stream channel during winter. River ice controls major hydrologic events such as winter floods with magnitudes and frequencies often greater than those created by open-water conditions. While river management in northern countries has already recognized high risk of ice damages, the focus of the risk assessment has been mostly aimed towards the local economy; the ecological role of river ice has been less acknowledged. Along rivers in boreal Sweden, riparian vegetation has developed specific zonation with height and age of the plants increasing the further away they are from the stream channel. On lower levels the vegetation is often comprised of short-lived plants, such as annuals and biennials whereas more permanent woody vegetation is found at higher levels. This zonation has most often been explained by the resilience of different growth forms to the inundation regimes, such as the spring flood in northern systems. Within this framework, I investigated which factors drive the ice formation and how ice and ice-induced floods affect riparian and in-stream vegetation. A 3-year survey was conducted of ice formation and vegetation along 25 stream reaches and a set of experiments were used to evaluate ice as a disturbance agent. Reaches far away from lake outlets which had a low input of groundwater and a high velocity and stream power were most prone to form anchor ice, but many other factors also influenced ice formation. Streams with anchor ice experienced more frequent flooding of the riparian vegetation during winter. Our findings suggests that ice and winter floods favour diversity and create habitat heterogeneity for riparian species. On a community level, woody plants such as evergreen dwarf shrubs are eliminated when flooded during winter, opening up patches for other species to colonize, creating a dynamic riparian understory community. Significant changes in river ice conditions could develop with projected changes in climate which would have important geomorphologic, ecological and socio-economic impacts. One implication of climate change could be less ice disturbance and consequently a riparian vegetation in cold regions that slowly changes from forb to dwarf-shrub dominated with a subsequent decrease in species richness. Changes in species diversity and abundance of groups of species related to changes in ice formation could potentially cascade into riparian and in-stream processes such as nutrient cycling, litter decomposition and organism dispersal.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2015. 25 p.
anchor ice, climate change, in-stream, riparian, river ice, streams, vegetation
National Category
urn:nbn:se:umu:diva-99008 (URN)978-91-7601-182-9 (ISBN)
Public defence
2015-02-27, Björken, Sveriges lantbruksuniversitet, Skogsmarksgränd 901 83, Umeå, 09:30 (English)
Swedish Research Council Formas
Available from: 2015-02-06 Created: 2015-02-02 Last updated: 2015-02-04Bibliographically approved

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Lind, LovisaNilsson, Christer
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