Afforestation to ‘Slow the Flow’

There is growing recognition amongst policy-makers and land managers that poor land stewardship can exacerbate the risks of floods and droughts, with the need to ‘work with natural processes’ in order to both increase resilience to climate change and deliver positive conservation outcomes. Such ‘win-wins’ resulting from the integrated management of land and water are the focus of a joint statement from the Society for the Environment and collaborating organisations, which was released to mark World Environment Day on the 5th of June this year.

In particular, the statement, Forestry and water management – integration for multiple benefit’, makes the case for increased rates of afforestation and the ongoing management of trees and vegetation, to ‘slow the flow’ of water through catchments. The contribution of trees to the management of surface water run-off varies by species, by maturity and density but generally, the tree canopy intercepts water before it hits the ground; tree roots aid the penetration of water into the soil, both contributing to the slower movement of water through the catchment and re-charging depleted groundwater reserves; whilst tree root systems stabilise the soil and prevent soil erosion and sediment run-off into water courses. Afforestation then has the potential to provide multiple benefits for flood and drought management, water quality and biodiversity.

The relative lack of evidence for the benefits of afforestation and vegetation management, compared to that for more traditional, ‘hard’ engineering’ approaches to flood-risk management, makes it challenging however, the statement suggests, to justify widespread deployment of ‘natural flood management’ measures. There is evidence for the benefits of natural flood management at small scales, including through the work of geographers, but more research is required to demonstrate how the effectiveness of afforestation varies with different parameters, such as location, geology, slope, aspect, native vegetation, climate and land use.  In the meantime, the organisations recommend, afforestation rates should increase, as a ‘low regrets’ measure for water management in the upper parts of catchments.

The statement cautions that tree-planting should not be viewed as a ‘universal panacea’, presumably by those wishing to argue for conservation measures on the basis of flood and drought-risk benefits. The statement acknowledges that during the most extreme rainfall events, trees may do little to slow the flow of water over saturated ground from the upper to lower part of catchments, where settlements are generally located. The organisations stress that ‘in working with natural processes, every case is different’. As the evidence-base evolves it will be important to capture these differences to ensure that good practice guidance for flood-risk management incorporates the emerging benefits of tree-planting for flood-risk management, ecology, biodiversity and soil health in a range of contexts.

Natural Flood Management will be discussed as part of the RGS-IBG’s forthcoming 21st Century Challenges: Policy Forum on ‘Achieving Sustainable Flood-Risk Management in the UK’, taking place on 8th November. Chartered Environmentalists (CEnv) – a professional accreditation awarded by the Society for the Environment – benefit from a discount for tickets for this event. Find out more and book your place.  

Image: Forest, Loren Kerns. Flickr.

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