I find that thinking and working in patches is the best approach to any kind of site with an established wild ecosystem in place, even at relatively early stages of succession I learned the hard way on multiple sites that "tucking in" isolated new plants here and there in an existing forest of any age, or thicket, or meadow; is usually a prescription for failure. The
root networks of the surrounding wild vegetation will be attracted to the disturbed, enriched, and probably irrigated spots where the new plants are. I've even found after a few months that plants I was watering regularly were drying out FASTER than those going without! So it proved better, to me, to design my new plantings in groups...patches large
enough to create sizeable gaps in the root network (and overhead
canopy as well) to give the new plants a chance to establish. Such groups make watering and fencing easier too, since you are doing these things to the whole cluster and not individual plants.
A very good way to use succession in forest garden patches is to start them out as annual gardens, with your useful
trees and perennials planted right in there too. Or, to see it another way....you lay out your planting with the trees, etc. at their mature spacings, and then you have all this space available between them, which the plants will eventually fill in and shade....why not fill that space with something useful in the meantime. So stick your vegetables, corn, wheat, whatever in there in the meantime. The additional attention,
water, soil amendments, etc. that you will be providing for the short-term benefit of the annuals will also hugely benefit the trees and perennials. When the patch begins to fill in....move the "garden" to the next patch and continue!