Woodland belts will probably be used more frequently in the future as buffers or filters for air pollution and acidification, to reduce nutrient leakage, or as general protection. Tree planting alongside traffic routes and around dwellings is often recommended today for environmental benefit. The importance of such planting is illustrated by an investigation of the environment in western Scania in Sweden (SOU 1990:93), which found that road traffic is responsible for 80% of nitric oxide emissions and 60% of hydrocarbons. Following this, it is estimated that, in Sweden alone, 20,000 people are constantly exposed to harmful levels of nitrogen dioxide and carbon dioxide. Considerably more people are exposed to air pollution that can give rise to cancer, allergies and asthma. About 300,000 people in Scania live in areas where noise levels are troublesome. A series of different measures is therefore required to improve the situation.