Flow variability maintains the structure and composition of in-channel riparian vegetation
Article first published online: 25 AUG 2011
© 2011 Blackwell Publishing Ltd
Volume 56, Issue 12, pages 2514–2528, December 2011
How to Cite
GREET, J., WEBB, J. A. and DOWNES, B. J. (2011), Flow variability maintains the structure and composition of in-channel riparian vegetation. Freshwater Biology, 56: 2514–2528. doi: 10.1111/j.1365-2427.2011.02676.x
- Issue published online: 13 OCT 2011
- Article first published online: 25 AUG 2011
- (Manuscript accepted 21 July 2011)
- exotic invasion;
- flow variability;
- natural flow regime;
- plant species diversity;
1. Naturally variable river flows are considered to be important for structuring riparian vegetation. However, while the importance of floods for the ecology of riparian vegetation is well recognised, much less is known about the importance of small fluctuations in river flows.
2. We investigated the effect of water supply diversion weirs on the riparian vegetation of upland streams. These weirs remove within-channel fluctuations in flow but do not prevent large floods downstream. We surveyed the in-channel and banktop vegetation of five streams, three of which were regulated by weirs and two of which acted as controls.
3. Unexpectedly, we observed greater species richness within the channel downstream of the weirs. This was because of increased numbers of exotic and terrestrial (‘dry’) plant species. Grass cover was also greater downstream of the weirs. There were no significant differences in the banktop vegetation between the upstream and downstream sites of the regulated streams.
4. Our results highlight the role of within-channel flow variability in maintaining the composition of vegetation within the stream channel. We suggest that greater species richness does not necessarily indicate a less-disturbed environment. Rather, a greater number of ‘dry’ species is indicative of the impacts of flow regulation.
5. Small fluctuations in river flows are probably necessary to protect the ecosystem structure and function of regulated streams. It is recommended that variable within-channel flows be provided in regulated streams.