Study

Composition and richness of macrophyte communities in small Danish streams – influence of environmental factors and weed cutting

  • Published source details Baattrup-Pedersen A., Larsen S.E. & Riis T. (2003) Composition and richness of macrophyte communities in small Danish streams – influence of environmental factors and weed cutting. Hydrobiologia, 495, 171-179.

Summary

Action: Use cutting/mowing to control problematic plants

A replicated, site comparison study in 1998 of 33 lowland streams across Denmark (Baattrup-Pedersen et al. 2003) found that cutting submerged plants affected plant community composition and reduced species richness and diversity, but had no significant effect on cover. The overall plant community composition differed between cut and uncut streams (data reported as a graphical analysis; statistical significance not assessed).  Cut streams had lower plant species richness (13.4 species/reach; 2.1 species/quadrat) than uncut streams (18.5 species/reach; 2.5 species/ quadrat). The same was true for plant diversity (data reported as a diversity index). However, total plant cover did not significantly differ between treatments (cut: 69%; uncut: 78%). Methods: In July–August 1998, aquatic and emergent vascular plants were surveyed in 33 small lowland streams (approximately 1.9 m wide, 20 cm deep, 0.13 m/s flow). In 25 streams, submerged plants had been cut between 1993 and 1998 (at least once/year). Cutting covered either the whole stream width or the central two-thirds, and was carried out with a scythe, boat-mounted knives or an excavator. The other eight streams had not been cut. Plant species and cover were recorded in 150 contiguous quadrats/stream (each 25 x 25 cm).

 

Action: Reduce frequency of cutting/mowing

A replicated, site comparison study in 1998 of lowland streams across Denmark (Baattrup-Pedersen et al. 2003) found that reducing cutting frequency affected the plant community composition. The overall plant community composition in 1998 was significantly affected by the cutting intensity in both 1993 and earlier in 1998 – but in different ways. Streams cut at lower frequencies in 1993 tended to be dominated by submerged plants and tall emergent plants in 1998. However, streams cut at lower frequencies early in 1998 tended to be dominated by shorter emergent plants in summer 1998. All results were based on a graphical analysis. Data for different frequencies were not reported. Methods: In summer 1998, aquatic and emergent vascular plants were surveyed in ≤small lowland streams (150 contiguous 25 x 25 cm quadrats/stream). Some streams had data on the frequency of cutting that occurred in 1993 and/or 1998. Frequency was classified as once/year, twice/year or more than twice/year. Cutting covered at least the central two-thirds of each stream. The study does not report the precise number of streams with frequency data or in each frequency class.

 

Action: Reduce intensity of cutting/mowing

A replicated, site comparison study in 1998 of lowland streams across Denmark (Baattrup-Pedersen et al. 2003) found that reducing cutting intensity affected the plant community composition. The overall plant community composition in 1998 was significantly affected by the cutting intensity in both 1993 and earlier in 1998. Streams cut at lower intensity tended to be dominated by small emergent plants. Streams cut at higher intensity tended to be dominated by submerged plants and tall emergent plants. All results were based on a graphical analysis. Data for different frequencies were not reported. Methods: In summer 1998, aquatic and emergent vascular plants were surveyed in ≥67 different lowland streams (150 contiguous 25 x 25 cm quadrats/stream). These included 36 streams with data on cutting intensity in 1993 and 67 streams with data on cutting intensity in 1998. In each year, submerged plants had either been left uncut, cut and removed from the central two-thirds of the channel, or cut and removed from the whole width of the channel (precise number of streams for each intensity not reported). Cutting occurred at least once/year.

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