Trees and hedgerows mean less run-off and erosion, reducing flooding and siltation downstream. Photo: Coed Cymru - coedcymru.org.uk/ .
Woods and trees are functioning parts of a living landscape
6th March 2014
Trees, woodlands and hedgerows do much more than enhance the appearance of Britain's rural landscapes, writes Mike Townsend. They diminish flooding, reduce erosion, assist water infiltration, enhance biodiversity - and we need more of them!
By reducing grazing and allowing taller vegetation and tree planting more water will be retained in boggy areas and percolate deep into the soil.
Recent flooding has highlighted the importance of land use in either contributing to or mitigating flood risk. In particular the suggestion that trees might play an important role in helping reduce flood risk.
Reports from the Woodland Trust on water and farming and water in towns provide a review of the evidence for the role of trees. Forest Research has also undertaken a significant amount of work looking at the role of trees in delivering better water quality as well as modelling the impacts of increased tree cover on flood risk.
These show that trees can make an important contribution both to mitigating flooding and improving water quality.
Lessons from Pontbren
In 2012 The Woodland Trust and Coed Cymru, on behalf of the Pontbren Farmers, commissioned a review of the scientific evidence and the story of how, over the last 15 years, Pontbren farmers have transformed their farms, and key lessons have emerged:
- The hedgerow restoration, new hedgerows and shelter belts have created a financially and biologically more sustainable farmed landscape.
- The trees have provided shelter for the sheep, helped in excluding areas prone to the ever increasing menace of liver fluke, and reduced surface water runoff from fields which carried with it nutrients and soil.
- Studies at Pontbren showed that planting tree belts across the slopes led to increased infiltration of water into the soil - more than 60 times that of neighbouring sheep grazed pasture without tree belts. This is as a result of the improved soil structure and effect of tree roots.
- When this effect was modelled across the catchment the result was a potential reduction in peak stream flows of as much as 40%. This is clear evidence that integrating trees into our upland farms will play a part in reducing flood risk downstream.
- This farmer led initiative also showed the importance of an intimate knowledge of the land in designing and siting tree belts. The farmers knew where shelter was needed, but they also knew where runoff was a problem, where land lay wet for much of the year and those areas prone to erosion.
More resilient, sustainable, biodiverse ...
They have managed simultaneously to improve the resilience and sustainability of their farms whilst delivering public benefits of improved water quality and flood mitigation.
In addition, the new planting and restored hedgerows and woodland have delivered biodiversity benefits and helped store carbon.
There are undoubtedly opportunities in the uplands for more extensive areas of new woodland, but the answer is not to remove farmers. Farmers in the uplands are a crucial element to the survival of communities in these areas.
In Wales 80% of farmland is classed as upland - that's most of Wales. These farms are not massive agribusinesses, they are generally small family farms. They are central to the survival of communities and an essential element of Welsh culture and language.
But with more trees and hedges on them, these farms can also be a part of the nation's flood defences.
Cooperation in Cumbria
In Cumbria the Woodland Trust has been working with Natural England and the Rivers Trust to bring together people and resources to look at how to manage trees and woodlands in the uplands to benefit rivers.
A particular feature of Cumbria is over 112,000 ha of common land - land that is generally privately owned but managed by several (or many) others who enjoy common rights to the land, for example to graze animals, gather firewood or dig turf.
On Tebay Common, over 1,000ha at the western end of the Howgills north of Kendal, the Trust has been working with Natural England, the Tebay Common Grazing Association and the landowner.
The intensity of past grazing has given Howgills an almost treeless landscape. Over the next two winters around 65,000 trees and shrubs will be planted on 110ha (270 acres). The trees will be planted to create an open habitat suitable for future wood pasture grazing and perfect for threatened species such as the linnet, lesser redpoll and tree pippit.
Retaining water in boggy areas
The negotiations have taken three years and involved many parties - the Tebay Grazing Association alone has over 20 farmers with rights to graze the common. Many others have an interest including local residents, the Open Spaces Society, archaeologists and others concerned with landscape and ecology.
By reducing grazing and allowing taller vegetation and tree planting more water will be retained in boggy areas and percolate deep into the soil. This will mean slower run off and less sediment.
The trees should also help river shading which will moderate water temperature, important in successful spawning of fish and for other river wildlife.
Modeling undertaken by Forest Research show that woodland strategically located on floodplains can mitigate large flood events by absorbing and delaying the release of flood flows.
Research based on the River Cary in south-west England suggested that a 2.2km reach of floodplain woodland could increase flood storage by as much as 71%, delaying the flood peak progressing downstream.
Further work at Pickering as part of a project called Slowing the Flow has shown how tree planting and other natural measures can help reduce flooding.
This suggests there are opportunities for creating strategically placed floodplain woodland to alleviate downstream flooding, particularly the increased risk associated with climate change.
Water management is undoubtedly an important 'ecosystem service' of upland areas. But the UK National Ecosystem Assessment recognises four categories of ecosystem service; supporting, regulating, provisioning and cultural.
It is essential that the cultural value of upland farming is not lost in the response to recent flooding. Pontbren shows that a balance can be met for maintaining farming in upland landscapes with the wider needs of society.
A compelling option
Planting trees and woodland will not stop all flooding. Engineered flood defences will continue to be needed to prevent inundation of many places.
But it is clear that strategically located trees and woodland can play an important part in reducing flood risk, whilst also improving water quality, contributing to biodiversity conservation, storing carbon and helping support more sustainable farming practices.
It is these multiple benefits which make it such a compelling option - for farmers as well as Government, its agencies and the many communities impacted by flooding.
Trees and other aspects of land management have a critical role to play in protecting property and farmland. It is vital the government responds positively to this opportunity by putting in place support for creation and management of trees and woodland - and ensure that their full role in flood defence is realised.
Mike Townsend is Principal Advisor to the Woodland Trust.
This article was originally published by the Woodland Trust under the title 'Trees and Flooding'.
Woodland Trust reports
- Planting trees to protect water - RBC Bluewater Farming Report (PDF, 800KB)
- Trees in our towns (PDF, 1.2MB)
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