Ditches

Ditches

Ditch networks are common on arable farms, performing vital drainage functions that help to create favourable soil conditions. Small adaptations in managing ditches can provide major benefits for wildlife.

What

Wildlife-friendly ditch management works on managing banks and ditches in rotation without compromising drainage function. Create structurally diverse bank vegetation, including areas of mature habitat. Aquatic wildlife will benefit from extending the period between clearing out ditches and where possible, retaining some undisturbed areas.

Buffer strips along the banks also provide permanent vegetation cover and help to reduce the pollution risk of the watercourse.

 

A grass-fringed drainage ditch, just inside the outer seawall. Frampton Marsh RSPB reserve, Lincolnshire, England. January 2008.

Why

Ditches can support a great deal of aquatic wildlife, particularly wetland plants and insects such as water beetles, dragonflies and hoverflies. Larger ditches can also be valuable for wading birds (where they are shallow), amphibians and small mammals. Bank vegetation can provide valuable wildflower-rich grassland. The best ditches have varied bank, marginal and emergent vegetation developed on shallow slopes.

In arable landscapes, ditches can be the only wet habitats making them increasingly important wildlife corridors. Ditches that hold water all year round will attract different species to those which are prone to drying out. Both are valuable habitats.

Aquatic wildlife in ditches benefits greatly from an extended period between clearances. The retention of undisturbed areas prevents cleared ditches from becoming sterile and allows quicker re-colonisation by aquatic species.

Introducing wildlife-friendly bank management can create structurally diverse vegetation along its length, ranging from recently cleared short, sunny and open grassland, through to more established undisturbed habitats. Maintaining 6m buffer strips from the top of the bank provides permanent vegetation cover for wildlife, and can help to fulfil Local Environmental Risk Assessment for Pesticides (LERAP) requirements, reducing the risk of polluting the watercourse.

buffer next to watercourse 2 R Winspear

How

Over time, drainage channels undergo natural succession from recently cleaned to ditches that have become choked with silt and vegetation. Each phase has its characteristic wildlife. Try to maintain a variety of ditch habitats around the farm by cleaning ditches on a rotation.

To make the best decisions on how to manage your ditches, it is important to know how wildlife is currently making use of them. Ditch clearance is usually best undertaken in the autumn and winter months, as this will limit the impact on wildlife. The frequency of clearance will depend on the drainage function and the speed with which the ditch silts up.

It is generally best to not clear entire ditch lengths in a single year, and instead manage them on a rotation to allow wildlife to re-colonise newly cleared areas quickly. In large drainage systems, a range of dredging rotations may be appropriate. The most important drainage channels could be dredged on a more regular basis than those that have less of a drainage function. Managing alternate halves in wide ditches each time within a rotation allows rapid re-colonisation of the excavated area. For some species however, this partial clearance is not appropriate. It is important to look at the species using the ditches before making management decisions. Consult an expert for advice if you are unsure how to proceed.

Weed cutting buckets enable excessive vegetation to be removed while retaining many aquatic plants, so that the gap between full clearance operations can be extended.

It is important to avoid steepening ditch slopes while clearing vegetation. A slope angle of 30-40o is ideal. Avoiding the disturbance of any shallow shelves which can be valuable for freshwater invertebrates is very important. If significant bank works are being undertaken, consider including a range of slope angles. Plenty of shallow slopes on south-facing banks should be included where possible, to maximise wildlife value.

Ditch bank vegetation should ideally be managed on a rotation of 2-5 years, with no more than half of the ditches managed in any one year. Try to restrict cutting of bank vegetation to the autumn and winter months and where possible, alternate cuts along short sections to create a varied age structure of vegetation along the length of a ditch.

Ditches are not isolated features, so consideration should be given to surrounding features when developing management plans. Maintaining existing margins and/or extending buffer strips to at least 6m will not only enhance connectivity to the wider landscape, but will also help to stabilise ditch banks and protect the watercourse from pollution from farm inputs and run–off.

Open and sunny ditches are often the most wildlife-rich so avoid planting new hedges or trees too close to them, particularly on the southern side, as shading will impact on their value. However, allowing isolated trees or patches of scrub to develop in discrete areas can add some habitat variety locally.

Leaving piles of cut vegetation, including reeds or grass clippings from your ditch management can provide important egg laying heaps for grass snakes. A lack of quality egg-laying sites can limit the success of grass snakes, and the heat of the decomposing vegetation incubates the eggs.

It is important to be aware of invasive species in ditches, which if left unchecked can choke out native vegetation and significantly reduce their wildlife value.

letton ditch

More information

For further information, on the conservation value of ditches, visit the Freshwater Habitats site.

For help identifying and managing invasive species which may appear along your ditches, the following may be useful sources of information and advice:

Non-Native Species

Centre for Ecology and Hydrology

In practice

Here are some useful case studies and articles about how farmers are putting Farm Wildlife into practice on their farms

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