Approaches to managing riparian vegetation are briefly discussed below with references to guidance and good practise together with details of where these can be found.
Before progressing with a particular maintenance regime, it is important to consider whether riparian vegetation management is necessary. Excessive vegetation growth may be seasonal or temporary, and given time, ‘normal’ vegetation may naturally re-establish. Watercourses that have little or no open water in mid-summer due to aquatic vegetation growth do not necessarily need any management. The water margins and vegetated shallows are a far more valuable habitat than is open water. Where management is deemed necessary, complete removal of a particular species, or clearance of a certain area is rarely possible and often harmful. In nearly all cases, rotational management of different areas over a period of years is more effective than total clearance in creating a balanced environment.
The method employed to control bankside vegetation is important and depends on the management aims and the required outcome. Grazing, mowing and herbicides are common methods used for this purpose, but their impact upon wildlife can be very different. Guidance on these methods is provided in Chapter 14 of the Waterways and Wetlands Handbook (BTCV, 2003) as well as several other important sources including The New Rivers and Wildlife Handbook (RSPB, 2001) and the Riparian Vegetation Management good practice guide (SEPA, 2009).
Buffer strips refer to the vegetated riparian zone between a watercourse and adjacent land. They may consist of trees, wetland, scrub or grassland. Buffer strips protect water quality by trapping sediments and breaking down pollutants before they reach the watercourse. They can easily be created through the establishment of fencing to separate them from adjacent land use, particularly grazing livestock. Section 3.3 of the Riparian Vegetation Management good practice guide (SEPA, 2009) (pp11-15) provides detailed methodology on the design of buffer strips including minimum widths.
Good practise approaches to cutting and mowing
Mowing can have an intense impact upon habitat structure as it involves the rapid removal of all vegetation. It should be used with care and only when appropriate to the management objectives of the site. The key considerations when carrying out mowing are the timing, the pattern of mowing and the correct disposal of cuttings (especially if invasive species are present).
- Timing of mowing – autumn mowing (over summer mowing) is recommended as it avoids the breeding bird season, maintains abundance and diversity of species and provides invertebrates with food and shelter.
- Pattern of mowing - it is important to avoid a ‘blank cut’ of bankside vegetation. Patch cutting on a rotation normally leads to substantial improvements in plant diversity and habitat structure. On riverbanks, leaving an uncut strip from the top of the bank down to the water’s edge enables a representative mix of terrestrial, semi-aquatic and aquatic plants to be retained.
- Disposal of cuttings - if possible, cuttings should be moved from areas of conservation interest and heaped on dry areas of low conservation value they provide hibernation and refuge for animals and invertebrates.
Further details are provided in The New Rivers and Wildlife Handbook (RSPB, 2001) (pp257-258) and the Riparian Vegetation Management Good Practice Guide (SEPA, 2009) (pp26-27).
Grazing (biological control)
Grazing is an environmentally sensitive approach to vegetation control, and is a widespread and valuable tool that benefits wildlife as well as flood defense. Low intensity grazing on grassland with no additional inputs can benefit wildlife and can be cheaper than cutting by machinery or by hand, especially on wet sites.
Guidance on riparian grazing regimes
Timing and intensity of grazing is critical, as is the choice of livestock. If a site requires summer grazing, cattle should be used. Stocking before July is undesirable, especially in sites good for ground nesting birds. Livestock densities must be managed to ensure that overgrazing does not occur. The objective should be to graze at a level that allows banks to be inspected, to reduce the dominance of grasses, and to encourage plant richness and habitat structure for invertebrates and birds. Overstocking will adversely affect the quality and structure of the sward, thereby reducing wildlife interest.
More advice on judicious grazing management is provided in The New Rivers and Wildlife Handbook (RSPB, 2001) (pp256-257) and Section 4.1 of the Riparian Vegetation Management good practice guide (SEPA, 2009) (pp25-26).
Herbicides should not be used without first contacting the appropriate regulatory authority (e.g. SEPA or EA). Their use is restricted and should be considered carefully in consultation with the authority. Spot treatment or preventing a vegetation problem by correct management and early remedial action is preferable to widespread herbicide use to control a problem.
Further advice on their use is contained in The New Rivers and Wildlife Handbook (RSPB, 2001) (pp259) and the Riparian Vegetation Management Good Practice Guide (SEPA, 2009) (pp27). Guidance is also provided in the following documents:
English Nature (2003) The Herbicide Handbook: Guidance on the use of herbicides on nature conservation sites.
Environment Agency (2010) Agreement to use herbicides in or near water. Guidance Notes: AqHerb01.
Trees should be retained where possible as they provide structural support to the riverbank. Where management is required, coppicing or pollarding (cutting to encourage regrowth from the stump) should be considered before complete removal which is always a last resort option. These methods reduce excessive shading without removing the stabilising effect of the stump and roots.
Guidance on tree management options is provided in the Riparian Vegetation Management good practice guide (SEPA, 2009) (pp31-36) and The New Rivers and Wildlife Handbook (RSPB, 2001) (pp274-281). This includes coppicing, pollarding, and thinning. Coppicing and pollarding need to be undertaken within a cycle to maintain growth. Selective tree thinning should be undertaken as part of the management strategy for a watercourse. All tree works should be carried out by trained staff during the winter months to avoid adversely affecting nesting birds.