Ground cover under fruit trees, beyond the mulching ring, can help to conserve water and regulate temperature, promoting the health of your deciduous food-producing investments.
Ideally, non-organic ground-cover would be used, since it does not compete with the tree for water and helps to maintain a healthy level of moisture in the dirt below it. Pebbles can look very elegant indeed, creating subtle plays of light that change throughout the day and evening, while protecting fallen fruit from pests.