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Many parts of the UK are seriously impacted by flooding and the frequency of floods is expected to increase due to climate change.

This is due to a combination of projected sea level rise, heavier rainfall episodes and increased rainfall in winter.

Consequences of flooding

For flood-intolerant tree species, flooding and prolonged waterlogging can:

  • Restrict the supply of oxygen to tree roots, preventing their normal function in absorbing water and nutrients.
  • Restrict rooting depth and increase the risk of windthrow due to reduced tree stability and anchorage.
  • Damage or wash away newly planted trees, before their roots become established.
  • Reduce tree growth.
  • Damage soil health.
  • Increase vulnerability of trees to disease and infection.

Risk factors

Site factors that influence the impact of flooding include:

  • Poorly drained, heavy soils.
  • Lowland and floodplain forests and woodlands.
  • Species sensitive to root damage during waterlogging.
  • Site infrastructure, including culverts, drains, and bridges.
  • Poorly maintained road networks.

Forests and riparian woodland can contribute substantially to reducing downstream flood risk due to their rainfall interception, water uptake, and high surface roughness, slowing both run-off and the peak flow in streams and watercourses. However, these benefits are dependent on healthy woodlands and the trees themselves may be damaged by an increase in soil wetness and flooding.

Adaptation measures

Care in species choice, soil management and drainage, woodland design, placement and management can mitigate these effects. They can also help to secure woodland benefits for reducing downstream flood risk.

How to help mitigate the long-term impact of flooding and reduce flood risk:

Decision Support Tools

There are range of online tools to assist managers in assessing risks to forest and woodlands and selecting appropriate adaption measures.

Find out more

Further resources

UKFS Practice Guide – Designing and managing forests and woodlands to reduce flood risk
https://www.forestresearch.gov.uk/publications/designing-and-managing-forests-and-woodlands-to-reduce-flood-risk/
Forestry and natural flood management 
https://www.forestresearch.gov.uk/research/forestry-and-natural-flood-management/
Revised valuation of flood regulation services of existing forest cover to inform natural capital accounts
https://www.forestresearch.gov.uk/publications/revised-valuation-of-flood-regulation-services-of-existing-forest-cover/
Slowing the flow at Pickering research project
https://www.forestresearch.gov.uk/research/slowing-the-flow-at-pickering/
Can trees and woods help reduce flooding?
https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/flooding/
Natural mitigation of flood risk
https://post.parliament.uk/research-briefings/post-pn-0623/