Riparian woodland and water protection

 

Riparian woodlands are those found in association with streams, rivers and lakes. They occupy a variable area along these water bodies, depending on slope and the size of the water body. This position means that they can exert a strong influence on the nature of the water environment and help to protect or buffer it from activities on the adjacent land.

Benefits of riparian woodland

• The roots of bankside trees and associated vegetation help to bind and strengthen stream banks, reducing the risk of bank collapse, erosion and siltation. Underwater roots also provide shelter and homes for freshwater life.
• The woodland canopy casts shade over the water surface, which helps to reduce extremes of water temperature that can be damaging to freshwater life. Shading also helps to reduce excessive weed growth that can choke watercourses.
• Falling twigs, leaves and insects provide an important source of food for freshwater life, while fallen logs and branches can form woody dams and pools that help to enrich freshwater habitats and slow down flood flows.
• The trees, ground vegetation and surface roots can trap sediment and remove nutrient and other pollutants in water draining from the adjacent land on route to the watercourse.

Riparian woodlands also tend to be ecologically rich due to the variety of habitats that they support. They often form important refuges for wildlife and help to assist migration by linking other woodland and related habitats in the wider landscape. Unfortunately, riparian woodlands are very scarce and fragmented in the UK, existing mainly as small patches of wet woodland. The value of this habitat is recognised under the UK Biodiversity Action Plan, which has set targets for achieving both extension and restoration work.

Another benefit of riparian woodlands is their attractiveness to people, being valued both in terms of recreation and landscape views.

Adverse effects of riparian woodland

Despite the many benefits that riparian woodlands can provide, they can also have a number of negative impacts on the water environment. These include:

• Some woodland species, particularly conifers, can cast too much shade. This can significantly reduce water temperatures resulting in reduced growth of fish, especially in colder parts of the country.
• Excessive shading can lead to bare river banks that are more susceptible to erosion, causing siltation and shallower watercourses.
• The entry of too much fine woody debris can restrict fish movement, divert streams and lead to the blockage of culverts and bridges during high flows, with implications for flooding.
• Some woodland species such as willow and poplar can use a lot of water, which may reduce stream water levels and water supplies during dry summer periods.

Objectives of the riparian woodland and water protection project

Forest management has an important role to play in minimising any negative impacts and securing the many benefits that riparian woodlands can provide. The objectives of this research project are to improve our understanding of how riparian woodland influences the water environment and to develop and guide best management practice.

There are five topics of study:

• The effect of riparian woodland management on the freshwater environment
• The impact of conifer clearance from the banks of upland streams
• The role of riparian shade in controlling stream water temperature in a changing climate
• Guidance on the management of riparian buffer areas within commercial forests
• Indicators of ecological quality in rivers: RIVFUNCTION (EU sponsored research).