Final answer:
Shelter belts plant trees to slow soil erosion by acting as a windbreak, which protects the topsoil from being carried away by wind and rain.
Step-by-step explanation:
Shelter belts are designed to plant trees to slow soil erosion. When trees are planted in rows, often perpendicular to the prevailing wind direction, they serve as a barrier that can protect the soil from the direct impact of wind and rain. This helps to reduce the speed at which wind removes the soil's top layer, which can contain vital nutrients for agriculture and ecosystem health. Shelter belts can also be beneficial in combatting other environmental issues, but they are primarily established for the purpose of reducing soil erosion.