Well let's see… the variables that impact that kind of decision include scale, budget, and intensity of management. I'm starting to see the outlines of a pattern language for forest garden establishment and management, here are a few thoughts.
First, take care of rainwater harvesting, your occasion, earthworks, wildlife or livestock exclusion fencing, and other infrastructure needs.
At a backyard scale you can do an “instant succession” where you sheet mulch heavily and plant out everything at once in its final location. Of
course, you need to wait to plant things that require shade until it is present. This is how I did most of my backyard, which is only 1/10 of an acre. When you have that little
land and you want 200 species or more on it, and you want a heavy emphasis on the herbaceous understory diversity and productivity, this is an excellent strategy.
Larger-scale plantings often start with the woody species and add the understory later. Martin Crawford has done this with great success, rolling out landscape fabric to kill the grass under the trees once they are ready to go, and then planting heavily with herbaceous species that he propagated in his nursery. Geoff likes to plant a lot of the initial understory from seed which I think is a great idea also.
Lately what gets me excited is thinking about planting out the trees and shrubs on contour or keyline
water harvesting layout and then planting in strips between those rows using prairie restoration techniques. Books like A Practical Guide to Prairie Reconstruction by Carl Kurtz lay out the techniques for using tractor–drawn seeders to plant a diversity of prairie species. You could use prairie
natives as there are many excellent useful ones, or you could experiment with mass–planting food forest understory species from seed. Some but not very many are available in the kind of quantity of seed you would want. Examples might include perennial sylvetta arugula, chicory, clovers, sorrells, and more. Some species you might need to grow out your own seed to get to that kind of scale.
You can also think about successional issues. For example, there is a couple of years where there will be full sun in the understory and that is a great time to capture that light and convert it into annual crops, perennial scallions, strawberries, and other short–lived sun–loving crops. You also might use Lawton's lovely technique of planting out vast amounts of nitrogen fixing species for chop and drop, between fruit nuts and other cropping trees planted on their long–term spacing. I'd love to meet someone who has done this in cold climates, please post!. I think one of the most promising woody plants for this technique in the US would be false indigo (Amorpha fruticosa), which is widely adapted, native almost everywhere in the US, and easily grown from seed.
In terms of spacing long–term productive trees, I typically want to see them spaced such that their canopy edges will just touch when they are mature, or preferably half again as far apart. Martin Crawford recommends that wider spacing to allow sufficient sunlight. In high and dry areas like Colorado more shade is desirable, do you would want them closer together. Depends what you want to grow underneath and how much light it wants (ginseng, ramps, and
mushrooms full shade, while gooseberries, Turkish rocket and hazels part shade).
My thoughts about spacing are based in part on my
experience being smaller–scale. I like to plant grafted varieties which tend to be fairly expensive, so I want to baby them. If you are growing seedlings, cheap wholesale bareroots, or mass–grafting your own, you might put them closer together figuring a fair amount will die. Certainly some of my pampered babies die as well, but I often try to replace them with something of the same mature canopy width.
I'm afraid I'm terrible with design software though I've seen people do excellent work with several programs. Could some other people chime in on that? I do all my work on paper.
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