During World War II, food shortages lead the government to incentivise hedgerow removal to increase food production. This practice continued for several decades due to agricultural intensification; with the size of farm machinery increasing, hedgerows were grubbed out to create larger fields to accommodate these machines and maximise productivity. This intensification has also lead to more soil compaction from large machinery and high densities of livestock. The result is that hundreds of km of hedgerow, in Sussex alone, are now missing from the landscape and our fields are more susceptible to surface run-off and erosion. Thankfully, existing hedgerows now have more legal protection and many farmers see the benefits of planting new ones to help protect valuable soil and water resources, and to provide forage and shelter for livestock in an unpredictable climate with more extreme drought and storm events. In the Ouse catchment, with the help of funders and volunteers we’re supporting landowners to plant hedges in the right places.
Although we know that hedgerows interact with water and can help to slow overland flow, exactly how much, which tree/shrub species are most effective, and at what scale hedgerows need to be restored to begin to reduce flood risk downstream, is still uncertain. What research has shown, is that infiltration rates can be up to 60 times greater in fenced woodlands/shelterbelts1, compared to adjacent pasture, but we don’t know how transferable this is to hedgerows.
Research is now underway at Bangor University, where PhD student Bid Webb is investigating how trees and hedgerows influence infiltration rates compared to adjacent pasture. They are also investigating whether tree age and species play a role. So far, the group’s results suggest that Fraxinus excelsior (Common Ash) has the greatest potential (of the seven species being studies; Alder, Ash, Beech, Birch, Chestnut, Oak and Sycamore) to increase soil infiltration, due to it having the highest fine root biomass, with over 50% of this biomass in the top 10 cm of soil, and the greatest proportion of large pore sizes in the soil. The large pores enable water to quickly infiltrate into the soil, reducing overland flows. The findings suggest that loss of Common Ash from the landscape due to the spread of Ash dieback (a fungus called Hymenoscyphus fraxineus), may have implications for our landscapes’ flood resilience.
1. Carroll, Z.L., Bird, S.B., Emmett, B.A., Reynolds, B. and Sinclair, F.L. (2004). Can tree shelterbelts on agricultural land reduce flood risk? Soil Use and Management, 20, 357-359.