The Influence of Hedgerow Planting on the Hydrological Functioning of Two Agricultural Soil Reference Groups

Woody features can regulate the hydraulic properties of a landscape by influencing water flow paths during rainfall events and reducing runoff, and hedgerow planting is often included in modelling studies as a natural flood management solution. However, very little empirical evidence exists on the effect of hedgerows on soil hydrological properties, particularly when considering different soil groups. This study quantifies the soil physical and hydrological properties that may affect the flood risk mitigation potential of hedges, such as bulk density, porosity, saturated hydraulic conductivity, proportion of flow through different soil pore classes, and water-stable aggregates. We investigated 32 hedges of different age classes (new, 10 year old and old) in the River Eden catchment in north-west England, comparing them to adjacent predominantly grassland fields. We assessed how soil properties varied under hedges on two widespread reference soil groups and examined the orientation of hedges in respect to slope across the entire Eden catchment area. The soil group affected hydrological properties, but, overall, soil under hedges had a larger proportion of smaller soil pores and a better soil structure, with increased soil organic matter and larger soil aggregates, increased soil porosity and improved infiltration rates compared to grassland soils. Soil porosity under hedges was ∼17% greater than in grasslands in both soil groups but remained significant at 0–30 cm depth on cambisols and at 0–50 cm only on stagnosols. Ksat under hedges was 52 times greater than in adjacent grass fields on cambisols and 45 times on stagnosols, and changes in Ksat under hedges on stagnosols occurred over a longer timeframe. Our results show that, in the catchment, hedge orientation of existing hedges is not associated with slope. Our results show that hedge planting has the potential to contribute to flood risk alleviation, but we found that the magnitude is larger and quicker on well-draining soils than on poorly draining soils. These results will aid future natural flood mitigation modelling.