In a literal way they are in charge of providing food, which could be a job attributable to a steward. But more they are the leaders of the land, the most involved, thus usually the most caring, informed, and concerned. They often aim to protect the land because they in a much more real sense than most of us know what is happening by first hand experience. They know if you abuse land or any of your resources they will not be there to support you. The strategy of abuse is a short term one, and this is an area in which a short term sentiment will not suffice. That's why I think they are often referred to as some of the most important stewards of the land.