One of the key ingredients of a good sustainable garden is to guide the garden into duplicating natural patterns while also getting it to provide food, fuel, and building materials. While there are many things that need to be understood to accomplish this, one of the most important is to understand the natural progression of vegetation.
While I'm not going into extreme detail, it is important to have the picture of the plant life in a temperate 'juvenile' area to be annuals, new perennials, and very young woody plants. As the years progress the dominant plants are 'climax' woody plants with an assortment of shorter plants making the most of life underneath the climax plants. How tall the climax plants are depends a great deal on how much water is available as well as many other growing conditions.
For instance, in spots in California, the climax trees are giant red woods. In places in Utah, the best we can do is medium sized sagebrush.
In a traditional garden the climax plant is often an annual that will be cut down at the end of the growing season. In a forest garden it is often a large fruit or nut tree that produces food for many years.
Because of this long term food production, there are many who think this is the ultimate in gardening and that they are fully obeying nature's laws.
I myself would have to disagree with this conclusion.
Even now I hear the cries of "burn the heretic!" But please, consider that the food forests that the American Indians maintained were in fact maintained. That is, they were burned to eliminate undesirable plants and cut out competition from younger plants that might cut down on production.
This is in fact not a climax condition anymore that a tilled garden is. (Please remember that I am not a fan of tilling!) It is an artificially maintained condition that nature is fighting against.
So if what I am saying is correct, why am I saying it? Because real sustainable gardening is about choosing the best option for what your conditions, resources, and production needs are. It is about letting your garden progress to the level it needs to be, then starting the cycle over again.
This start may be taking the orchard to the ground and planting vegetables. Or it may be replacing a worn out tree by planting the new one in part of the annual patch and planting vegetables where the old tree was.
Or whatever. It really depends on conditions, resources, and productions needs coupled with what you have observed works.