The use of large wood in stream restoration: experiences from 50 projects in Germany and Austria

Published source details Kail J., Hering D., Muhar S., Gerhard M. & Preis S. (2007) The use of large wood in stream restoration: experiences from 50 projects in Germany and Austria. Journal of Applied Ecology, 44, 1145-1155.
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Summary

Over the last two decades, restoration of degraded streams rivers has become an objective in some regions, especially Europe and North America. Wood may be incorporated in attempts to improve hydromorphological and hence ecological status of water courses. However, despite growing use of such management interventions, only a few of these projects are described in the available literature. To aid practitioners, a survey was conducted to summarize and evaluate the experiences gained in three central European countries by those involved in projects in which large wood has been used in restoration attempts.

Questionnaire and data collection: The survey entailed consultation with 165 local and regional authorities, stream managers and stream ecologists in central Europe to identify restoration projects in which wood had been used. In total, 72 project managers, who planned and implemented a total of 83 restoration projects, participated and provided data on 50 projects.

A mail survey containing 33 questions was developed according to standard survey techniques. Almost all restoration projects were located in Germany and Austria, with one in Liechtenstein. Each respondent rated the general project objectives and the objectives of wood placement on a Likert scale ranging from 1 (unimportant) to 5 (very important). From this, an average score was calculated (for the 50 projects).

For each project, land-use intensity was assessed by calculating a score based on the percentage of floodplain area covered by different land uses as detailed by the respondents, grouped as: (i) forest and natural non-woody vegetation; (ii) grassland, pasture and fallow land; (iii) cropland and (iv) urban areas. The percentage of floodplain area covered by these four categories was multiplied by four different factors (0, 0.3, 0.6 and 1, respectively). The score was calculated by summing these four values and generating ranges from 0 (low land-use pressure, 100% of floodplain covered by natural vegetation) to 100 (high land-use pressure, 100% of floodplain covered by urban areas).

The volume of single logs and single trees was calculated using the diameter and length given by the respondents and the volume of wood accumulations was also calculated. Problems that occurred during planning and implementation, the wood structures, costs, monitoring techniques and risks, were detailed.

Results indicated the potential for improvement from an ecological point of view, as the number and total wood volume, and the median volume of single wood structures placed in the streams per project, were low compared with the potential natural state. Many wood structures were placed nearly parallel to the water flow, thus reducing their beneficial effect on stream flow and morphology.

Monitoring (of variying quality and duration) to assess restoration success had been undertaken in only 58% of projects. General conclusions drawn included: the potential effects of wood placement must be evaluated on a large scale (i.e. a watershed and reach-scale context); wood addition is most successful if tmimicking natural wood; effects of wood structures on stream morphology are strongly dependent on conditions such as stream size and hydrology; wood placement has positive effects on several fish species; most projects revealed a rapid improvement of hydromorphological status.

Most of the wood structures were fixed (‘hard engineering’). However, soft engineering methods (use of non-fixed wood structures) are resulted in more natural channel features and are significantly more cost-effective.

Conclusions: This study illustrates that installation of large wood has been used successfully in several projects, predominantly to increase the general structural complexity. The authors recommend the use of less costly soft engineering techniques (i.e. non-fixed wood structures), installation of higher amounts of wood, larger wood structures and improved monitoring of impacts (both hydrological and ecological) of future restoration projects.

Note: The compilation and addition of this summary was funded by the Journal of Applied Ecology (BES). If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.blackwell-synergy.com/doi/full/10.1111/j.1365-2664.2007.01401.x