Forest grazing counteracts the effectiveness of trees to reduce flood risk

Planting trees can reduce flood risk, but a high intensity forest land use, such as grazing, can counteract the positive effect of the trees, a recently published study suggests. As the frequency and severity of flooding becomes an increasing problem, land managers are turning to natural flood management measures, such as tree planting, to reduce the risk. When rainfall exceeds the rate at which water can enter the soil it flows rapidly over the land's surface into streams and rivers. Trees can help to reduce the risk of surface runoff by increasing the number of large pores in the soil through which water can drain more easily. Land use, such as grazing, also affects the soil's ability to absorb water; however, while the effect of land use on surface runoff has been well studied in grasslands, little is known about the effect of land use in forests. The study, undertaken by Lancaster University and the Centre for Ecology and Hydrology and published in the journal Geoderma , investigated the rate that water infiltrated the soil under trees at an experimental agroforestry site in Scotland. Researchers found that infiltration rates were between ten and a hundred times higher under trees, when the forested area remained relatively undisturbed, compared with adjacent pasture.