Managing riparian buffer areas

Photo of riparian woodlandThe following management recommendations are based on a review of the international literature:


Prepare catchment management plan

Management of riparian woodland should be based on a consideration of site sensitivity, intrinsic value and potential. Identify which functions of the riparian buffer area are most relevant to the location and prepare a plan that is appropriate for the entire forest or water catchment. New woodland should not be planted on key wetland habitats, and the potential for priority species such as water vole and otter should be considered. Early consultation with local stakeholders is recommended.

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Width

The riparian buffer should reflect stream size and the natural dimensions of the riparian zone. Minimum widths for either side of the stream channel are:

  • 5 m for streams <1 m wide
  • 10 m for streams 1 – 2 m wide
  • 20 m for streams >2 m wide.

Where the natural riparian zone exceeds these widths, the dimensions of the buffer area should be increased, up to twice the minimum recommended width.

Greater widths should be considered where there is scope to restore native floodplain woodland. However, buffer widths greater than 20 m on either side of a watercourse are unlikely to result in further significant benefit to the aquatic zone.

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Canopy structure

Establish and maintain an open woodland canopy with half the watercourse open to sunlight and the remainder under dappled shade.
This is best achieved by creating an irregular mix of five vegetation structural habitats:

  • Open ground
  • Occasional large trees
  • Trees with open glades
  • Scrub thicket
  • Closed woodland canopy.

The distribution and management of the taller vegetation elements should reflect the stream orientation, to ensure that sufficient light reaches the stream and banks to support the development of a vigorous cover of ground and marginal vegetation.

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Species choice

The vegetation established within the riparian buffer should be native and appropriate to the location and soil water regime, preferably from a local source. Use an Ecological Site Classification to identify the preferred woodland type and determine the component tree, shrub and herbaceous species using the national vegetation classification system.

Alternatively, an assessment of the shading requirements of the existing ground flora would provide an indication of which tree and shrub species are most appropriate. A shade tolerant vegetation community should be replaced by areas of scrub woodland (willow and alder), while a shade intolerant one by high canopy woodland (aspen, birch, bird cherry, gean, rowan or oak). This will ensure some continuity in the existing physical conditions at the site. The use of alder should be limited in acid sensitive catchments and areas at risk from Phytophthora disease.

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Establishment method

Natural regeneration is the best method of establishing native tree and shrub species where an appropriate seed source exists, if conifer regeneration can be controlled. This will only be possible where grazing pressure is light. Fencing will not be practicable on most sites and should be avoided in flood prone areas where it could interfere with flood control and access. Slow growing, large seeded trees such as oak may need assistance to thrive where the sward is dominated by bracken and vigorous grasses such as Deschampsia and Holcus. Seedlings should be transplanted and protected using tree guards.

Where natural regeneration is unsuitable locally sourced plant material should be used in any planting scheme. Planting sites should be prepared by mounding, either by hand or using a lightweight excavator to minimise trafficking. No drainage is permitted within the riparian buffer and very wet sites should be left unplanted. Planting should favour light-foliaged species in irregular small groups to replicate the vegetation structure of a secondary forest.

On wind firm sites that lack broadleaf trees and shrubs, a few conifer trees from the first rotation should be retained to create areas of light/moderate shade and provide coarse woody debris until the new riparian woodland becomes established.

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Use of chemicals

Great care must be exercised when applying any fertiliser or herbicides in close proximity to watercourses. Applications should be limited to spot treatments using chemicals that are approved for use in or near water.

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Maintenance thinning and felling

Riparian buffer areas should be inspected regularly (e.g. every 5 years) to check on woodland condition and progress when establishing new sites.

The level of shade and the structure of the woodland should be assessed to determine the need for additional work such as beating up, thinning or the control of regeneration by undesirable conifer species. Areas of dense shade may require selective thinning, pollarding or coppicing. Dense shrub thickets of willow or alder over 200 m long are particularly suited to coppicing where grazing is not an issue. Willow should be pollarded or coppiced in a 20 to 25 year rotation and alder a shorter 15 to 20 year rotation.

Consider phasing the cutting of adjacent stretches (e.g. in 50 m to 100 m sections) to provide as diverse a range of scrub habitats as possible. It may be appropriate to adopt a different management regime on each stream bank, depending on stream size, orientation and site sensitivity. For example: a 15-year rotation on the north bank would allow a mature shrub community to become established, guaranteeing a seed source for future natural regeneration; while a 5-year rotation would be more appropriate on the south bank to prevent the development of heavy shade.

Cutting should be carried out between August and March to avoid disturbing nesting birds.

Coppicing is unsuitable where grazing by deer or farm livestock threatens the regrowth and continued life of the tree. In areas of high grazing pressure pollarding is a more suitable method of reducing shade. Removing the top of the stem above the reach of livestock protects the new growth. The retained pollard stems form a refuge for bryophytes and lichens that may be absent in a coppice stand, which would lack mature stems and therefore prevent the development of a late successional lichen flora.

Thinning or group felling operations within the riparian buffer should be carefully planned to avoid trafficking by heavy machinery and minimise site disturbance. Such operations may need to coincide with those on the adjacent land to facilitate extraction. However, the riparian buffer may benefit from felling some trees to waste, to provide a source of deadwood and coarse woody debris. Operations should be carried out during late summer when the soils are driest and there is least risk of disturbing nesting birds. Where there is a need to fell bankside trees, these should be felled away from the stream to prevent damage to the stream banks.

Grazing can provide a useful management tool for maintaining a herbaceous sward and controlling shrub and tree species. However, the need for good access and stock proof fencing, the risk of increased bank erosion and the potential contamination of water supplies by pathogens such as Cryptosporidium, will make most sites unsuitable.

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Dead wood and veteran trees

Dead wood such as upturned root plates, large diameter logs and standing trees forms an important habitat for many invertebrates, bryophytes, lichens and fungi, particularly in the shaded and moist conditions of riparian woodland. Notable trees should be identified, mapped and retained where they pose no threat to personal safety. These include seed bearing, over-mature, forked, cavity, damaged, dead, wind blown and undermined bankside trees, which add structural diversity and character to the area.

Debris dams are natural features of wooded streams and greatly enhance the aquatic habitat; they should not be removed unless downstream sites are at risk of flooding from debris blockage or they form a significant barrier to migratory fish.

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Structural engineering

In severely eroded streams, consideration should be given to reinforcing stream banks through the use of gabions or timber groynes. These will reduce hydraulic scouring of the banks creating deeper stream channels and facilitate the establishment of marginal vegetation. Advice should be sought from the local water regulatory authority and fisheries trusts when planning this type of work.

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Forest operations within the riparian zone

The riparian buffer must not be used to store equipment, fuel, oil or chemicals due to the high risk of leakage polluting adjacent watercourses.

During harvesting operations on the adjacent land, care should be taken to avoid brash being deposited within the riparian buffer area. Stream crossings should be avoided and temporary culverts created when this is not possible.
The drainage system on restock sites should be redesigned so that drains terminate at the edge of the riparian buffer.

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