The tithes of Israel were allocated to the Levites as an inheritance and in exchange for their service in the temple:
Numbers 18:21The reasons for which the Levites received tithes play a role in the discussion of whether tithe was limited to agricultural products only. As the above scripture shows, they received tithe for two purposes: as an inheritance and in return for the work of the Tabernacle. If tithe was only required on food items as some claim, then this would mean that the Levites were both given an inheritance and paid for their work in food.
Behold, I have given the children of Levi all the tithes in Israel as an inheritance in return for the work which they perform, the work of the Tabernacle of Meeting.