Effects of stream restoration and management on plant communities in lowland streams

Published source details Pedersen T.C.M., Baattrup-Pedersen A. & Madsen T.V. (2006) Effects of stream restoration and management on plant communities in lowland streams. Freshwater Biology, 51, 161-179.
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Summary

Action: Restore/create river channel (multiple interventions)

A replicated, site comparison study in 2002 of 30 lowland streams in Denmark (Pedersen et al. 2006) found that restored streams had similar macrophyte communities, cover, richness and diversity to natural meandering streams. The overall macrophyte community composition was similar in restored and natural streams (data reported as a graphical analysis; statistical significance not assessed). The most abundant species included water crowfoot Ranunculus sp. and broad-leaved pondweed Potamogeton natans (data reported as abundance scores). Restored and natural streams had statistically similar overall macrophyte cover (restored: 85%; natural: 89%), species richness (restored: 30 species/reach, 2.2 species/0.06 m²; natural: 33 species/reach, 2.4 species/0.06 m²) and diversity (data reported as a diversity index). The same was true for submerged and emergent macrophytes separately (see original paper for data). Additionally, the metrics were typically higher (and otherwise statistically similar) in restored streams compared to streams that remained channelized. However, these comparisons were confounded by much higher cutting pressure in the channelized streams. Methods: In July 2002, aquatic and emergent macrophytes were surveyed in one 100-m-long reach in each of 30 lowland streams (≥10 bank-to-bank transects and approximately 250 quadrats/reach). Ten streams were historically channelized but had been restored 3–12 years previously (remeandered, banks made less steep, bed raised, stones and gravel added). Ten streams were natural. Ten streams remained channelized.

Action: Reduce frequency of cutting/mowing

Action: Reduce intensity of cutting/mowing

A replicated, site comparison study in 2002 of 30 lowland streams in Denmark (Pedersen et al. 2006) reported that cutting pressure (a combination of frequency and intensity) was an important determinant of overall macrophyte community composition. Individual species whose abundance was significantly related to cutting pressure were water crowfoot Ranunculus sp., lesser waterparsnip Berula erecta and water starwort Callitriche sp. (greater abundance under lower cutting pressure) and bur-reed Sparganium emersum (greater abundance under higher cutting pressure). All results were based on graphical analyses. Statistical significance of the overall result was not assessed. Methods: In July 2002, aquatic and emergent macrophytes was surveyed in 30 lowland streams (one 100-m-long reach/stream; ≥10 bank-to-bank transects/reach). Macrophyte cutting pressure – a combination of frequency (0, 1 or 2 times/year) and intensity (0%, 66% or 100% of the channel width cut) – varied between streams. Ten streams were natural, 10 were channelized and 10 were historically channelized but had recently been restored. Cutting pressure was significantly higher in the channelized streams than the natural or restored streams, so the study does not completely distinguish between the effects of cutting pressure and channelization.