Is it as simple as planting trees to reduce flood risk?

By Sam Buckland

Sussex Flow Initiative Project Officer

In 2019, and into 2020, we have seen widespread calls for increased tree planting, primarily in tackling climate change. UK tree coverage is 13%, below the EU average of 35%, Friends of the Earth are campaigning for the UK to double its coverage by 2045. There is no doubt that trees offer huge benefits for flood risk reduction through slowing, storing and filtering water, as well as offering a multitude of social, environmental and cultural benefits, highlighted in Trees for flood resilience. 

So why aren’t we planting trees everywhere? The Woodland Trust’s #RightTreeRightPlace captures the main issue that has arisen with well intentioned wide scale tree planting. Across the UK, and particularly within Sussex we are incredibly fortunate to have a huge diversity of habitats of national and international importance, each of which delivers a variety of ecosystem services. Each of these habitats, restored and functioning delivers carbon storage and flood risk reduction, these are outlined in Sussex Local Nature Partnership’s natural capital Strategy. Therefore, there can be potential for tree planting to damage a habitat of greater importance.  
 
President of Sussex Wildlife Trust, Dr Tony Whitbread has written a fantastic series of blogs on the complexities around tree planting. In his words “simple answers to complex problems are always wrong”. In his blog Tony mentions whether ‘to plant or not plant, that is the question’ is another one of the main potential issues, whilst Fran Southgate explains some of the present barriers to natural ‘Tree Regeneration’ rather than tree planting. 

Since 2014, the Sussex Flow Initiative has planted over 60,000 trees with support and funding from the Woodland Trust. We know that these trees have come from UK seed, and that they are UK grown. Certain suppliers of trees may import from abroad, increasing the likelihood of introducing a new pests and diseases.
 
How does Sussex Flow Initiative choose where and what they plant?
 
The tree planting process that SFI follows is the same as that outlined in Tony’s blog. 

In addition, we use historic maps, replanting lost trees and hedges where possible, and identifying opportunities to connect fragmented habitats, encouraging wildlife to move through the landscape. Planting hedges and shelterbelts also offers livestock shelter, food and medication, as highlighted in Fran’s blog.
 
Projects such as Pontren have demonstrated how woodlands can increase soil infiltration by up to 60 times compared to neighbouring unplanted pastures. Infiltration rates will vary depending on the soils and tree species, but trees also act as a physical barrier to overland water flows during heavy rainstorms. Planting shelterbelts and hedges across a hill slope, and expanses of riparian woodland slows down the flow, contributing to flood risk reduction downstream. 

We have also been working with the Sussex Black Poplar Partnership to conserve the black poplar (spp. betulifolia) through planting over 450 of these rare wetland trees. Once a staple within the British landscape, growing to 30m and living 200 years, they were reduced to only 38 trees in Sussex by the mid-90s. Supporting 100 specialist insects the Black Poplar is just one tool which helps us demonstrate how tree planting done correctly or natural regeneration has huge value for biodiversity, as well as flood risk reduction.