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Large wood restoration in boulder dominated streams
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)
Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Science SE-901 83 Umeå, Sweden.
(English)Article in journal (Other academic) Submitted
Abstract [en]

1. An important aim of many restoration activities is to improve ecological structures and processes that have a central role for ecosystem functioning.  Large wood (LW) is such a component, affecting hydraulics, channel morphology, floodplain dynamics, and ecological communities.

2. We studied the effect of in-stream wood restoration, evaluating the difference before and after wood addition using boulder restored sites as controls. We investigated channel dynamics, movement and recruitment of large wood, retention of propagules and fish communities.

3. One of three streams experienced a reduced current velocity after LW placement. The width of the channel and the reduced velocity were probably the reasons why this stream trapped most naturally drifting wood. LW sites experienced increased retention of organic matter compared to control sites, but LW proved to be unimportant in controlling brown trout density and biomass.

4. Restoring habitat heterogeneity has been widely used to enhance ecological functioning, but during the last years its potential to restore streams and rivers has been questioned. In streams affected by multiple stressors, increased habitat heterogeneity is less important. Our result demonstrates that restoration with wood can enhance the restoration made with only boulders, and as a consequence advance ecological functioning.

Keyword [en]
large wood, boulders, timber floating, river restoration, propagule retention, fish
URN: urn:nbn:se:umu:diva-37826OAI: diva2:370243
Available from: 2010-11-16 Created: 2010-11-16 Last updated: 2010-11-25Bibliographically 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.
riparian zone, timber floating, river restoration, cut-off side channels, hydrochory, large wood, anchor ice, fish
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)
Available from: 2010-11-25 Created: 2010-11-16 Last updated: 2010-12-08Bibliographically approved

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