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Effects of river restoration on riparian biodiversity in secondary channels of the Pite River, Sweden
Department of Environmental Science, Huxley College of the Environment, Western Washington University, Bellingham, Washington 98225-9181 USA.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology Group)
Department of Environmental Science, Huxley College of the Environment, Western Washington University, Bellingham, Washington 98225-9181 USA.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology Group ; Arcum)
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2012 (English)In: Environmental Management, ISSN 0364-152X, E-ISSN 1432-1009, Vol. 49, no 1, 130-141 p.Article in journal (Other academic) Published
Abstract [en]

Between 1850 and 1970, rivers throughout Sweden were channelized to facilitate timber floating.  Floatway structures were installed to streamline banks and disconnect flow to secondary channels, resulting in simplified channel morphologies and more homogenous flow regimes.  In recent years, local authorities have begun to restore channelized rivers.  In this study, we examined the effects of restoration on riparian plant communities at previously disconnected secondary channels of the Pite River.  We detected no increase in riparian diversity at restored sites relative to unrestored (i.e., disconnected) sites, but we did observe significant differences in species composition of both vascular plant and bryophyte communities.  At disconnected sites, plots closest to the stream featured greater representation of mesic-hydric floodplain species, whereas plots farthest from the stream featured greater representation of mesic-xeric species characteristic of the surrounding upland forest.  In contrast, restored sites were most strongly represented by upland species at all distances relative to the stream.  These patterns suggest that restoration has resulted in increased water levels in reconnected channels, but that the restored fluvial regime has not influenced the development of characteristic flood-adapted plant communities.  This may be due to the short time interval (ca. 5 years) since restoration.  Previous studies have demonstrated relatively quick responses to similar restoration in single-channel tributaries, but secondary channels may respond differently due to the more buffered hydrologic regimes typically seen in anabranching systems.  These findings illustrate how restoration outcomes can vary according to hydrologic, climatic and ecological factors, reinforcing the need for site-specific restoration strategies.

Place, publisher, year, edition, pages
2012. Vol. 49, no 1, 130-141 p.
Keyword [en]
biodiversity, boreal, bryophyte, off-channel habitat, restoration, riparian, river, secondary channel, vegetation
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-37825DOI: 10.1007/s00267-011-9773-6OAI: oai:DiVA.org:umu-37825DiVA: diva2:370241
Available from: 2010-11-16 Created: 2010-11-16 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Ice, wood and rocks: regulating elements in riverine ecosystems
Open this publication in new window or tab >>Ice, wood and rocks: regulating elements in riverine ecosystems
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Riparian ecosystems are of great importance in the landscape, connecting landscape elements longitudinally and laterally and often encompassing sharp environmental gradients in ecological processes and communities. They are influenced by fluvial disturbances such as flooding, erosion and sediment deposition, which create dynamic and spatially heterogeneous habitats that support a high diversity of species. Riverine ecosystems belong among the world’s most threatened systems. In rivers throughout the world, human alterations to fluvial disturbance regimes have resulted in degraded ecosystems and species loss. For example, in Sweden, watercourses of all sizes have been channelized to facilitate timber floating, but in the last 10–20 years the impacts in some of the affected rivers have been reduced by restoration actions. The objectives of this thesis are to evaluate how riverine ecosystems in general, with specific focus on riparian communities, are affected by (1) restoration of channelized reaches by boulder replacement, (2) ice formation, and (3) restoration of in-stream wood abundance in the stream channel. Objective (1) was assessed by quantifying the retention of plant propagules in channelized and restored stream reaches and by evaluating effects on riparian plant and bryophyte communities in disconnected and re-opened side channels. Retention of plant propagule mimics was highest at low flows and in sites where boulders and large wood had been replaced into the channel. Propagules are however unlikely to establish unless they can be further dispersed during subsequent spring high flows to higher riparian elevations suitable for establishment. Thus, immigration to new suitable sites may occur stepwise. Our study demonstrates that restoration of channel complexity through replacement of boulders and wood can enhance retention of plant propagules, but also highlights the importance of understanding how restoration effects vary with flow. We detected no differences in riparian diversity between re-opened and disconnected side channels, but we did observe significant differences in species composition of both vascular plant and bryophyte communities. Disconnected sites had more floodplain species, whereas restored sites had more species characteristic of upland forest. This suggests that the reopening of side channels resulted in increased water levels, resulting in new riparian zones developing in former upland areas, but that the characteristic floodplain communities have not had time to develop in response to the restored fluvial regime. Objective (2) was approached by evaluating the effect of both natural anchor ice formation and experimentally created ice in the riparian zone. Riparian plant species richness and evenness proved to be higher in plots affected by anchor ice. Plants with their over-wintering organs above the ice sheet suffered from the treatment but the overall species richness increased in ice-treated plots. Objective (3) was evaluated by studying wood recruitment and movement, channel hydraulics, propagule retention and fish abundance in streams restored with large wood. Only one stream experienced reduced velocities after large wood addition. The large size and reduced velocity were probably also the reasons why this stream proved to be the best one in trapping natural, drifting wood. Increased retention and decreased mechanical fragmentation in large wood sites will lead to decreased loss of detritus from the site and therefore higher availability of coarse particulate organic matter which can result in more species rich shredder communities. Our study did not show that the occurrence of large wood had an important role in controlling density or biomass of brown trout.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2010. 30 p.
Keyword
riparian zone, timber floating, river restoration, cut-off side channels, hydrochory, large wood, anchor ice, fish
Identifiers
urn:nbn:se:umu:diva-37827 (URN)978-91-7459-083-8 (ISBN)
Public defence
2010-12-16, Älgsalen, Uminova Science Park, Tvistevägen 48, Umeå, 13:00 (English)
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Available from: 2010-11-25 Created: 2010-11-16 Last updated: 2010-12-08Bibliographically approved

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