Any kind of wood can be used to make wall-mounted shelves: particle board, reclaimed wood, hardwoods, softwoods or plywood. Options also depend on the budget for the shelving; whether the shelving needs staining, finishing, sanding or painting; and the heaviness of the objects occupying it.
Hardwoods or a double layer of 3/4-inch plywood carry heavy weights well. Softwoods are best used outdoors because any type of softwood must acclimatize to its environment. Hardwoods and reclaimed wood are ideal for indoor wall-mounted shelves and can be sanded, stained, painted and finished if desired. The wood that best suits the purpose of the shelving and fits the decor are key deciding factors.