I am i a similar situation with an old field that is on degraded farmland. It has been sitting fallow for probably close to 8 years and has had nitrogen fixing shrubs like autumn olive and trees like black locust colonizing. My biggest problem was the amount of bush honeysuckle which had come in. Bush honeysuckle is in invasive here in Ohio and is pushing out the native understory. It is a relatively useless plant for permaculture, though it provides good habitat for birds. I have been slowly removing it from the understory of the 10 acre wood lot at the bottom of the field and trying to establish an understory with plants like spice bush and Paw Paw. It has been a very slow process.
As for the field. I finally had someone come in and bush hog the whole thing (though I had them avoid all the black locust and autumn olive, blackberry hedges, etc. The tractor tore up the ground a bit more than I would have liked, and I now have some bare patches. This is mostly because the ground has been so wet. I am planning to seed clover over all of the bare patches and might try to broadcast it through out the top 3 acres of the field. The grass is not well established and the most common weed seems to be poison ivy. I am hoping that the clover and the grass will out compete the poison ivy if I mow. Meanwhile I am slowly turning the field into an orchard and sheet mulching pieces of it. I have a small vegetable garden down and about 15 fruit and nut trees. I have also started to put in berry bushes. I plan to plant comfrey (and some other edible perennials like horseradish) around the trees and will experiment with nitrogen fixing shrubs (autumn olive is already doing quite well here).
If anyone has any thoughts on this plan, I'd love the advice.
