I'm in the planning stages for a 6.5 acre polyculture orchard. Going to have 9 16' berm/swale structures of varying length with the berm portion being the the planting area. The idea is to leave 45' wide alleys for mob grazing/annual cropping. Going off of an average traditional recommended spacing of most of our cultivars being 20' that gives us somewhere around 220 trees. Now I'm trying to figure out how Farmer/Helper tree fit in to this spacing scheme. Part of me really wants to shove 1 or 2 leguminous trees/shrubs in the space between the 20 foot spacing of the cultivars at 10' or 5', but I'm worried about crowding. Any advice/ideas/input that anyone has to offer would be very much appreciated. I am particularly interested if anyone knows what the Mark Shepard Restoration Ag approach is. I've been able to find a lot of information on Mark's way of doing things, but haven't really found much on spacing or farmers trees.
You might want to check Geoff Lawton's recent Permaculture for Profit video, where he visited with Mark. They throw around some numbers for how many trees Mark has planted on his 106 (?) acres. It's a pretty huge number, I don't think he worries about crowding when he is planting
Later, when trees are getting underway, he definitely culls for the best performing trees.
Guiding the growth of other species? A common approach is to interplant with a "nurse" tree, such as European black alder or white pine, to help promote better stem form on the walnuts.
If you are looking for nitrogen fixing, the only species that Shepard mentions in his book is Siberian Pea:
A later speaker then mentioned some current problems with agroforestry in Saskatchewan, one of which was the horrible, mean and nasty “invasive” Siberian peashrub! Siberian peashrub not only survives in Saskatchewan, but it kicks butt. One of the biggest problems with this plant is that it “invades” canola fields and was rapidly developing herbicide resistance. Well, hold the phone folks. A perennial shrub that produces its own nitrogen fertilizer, has large yields of highoil and high-protein beans, produces wood that can be coppiced and burned as a biomass feedstock, can be harvested mechanically with a straddle harvester, is actually invading fields of an annual crop that also produces oil and protein but requires annual inputs of tillage, planting, herbicide, fertilizer while increasing wind and water erosion? Um, what’s the problem here?
At the conference I quickly rearranged my presentation on permaculture to include Siberian peashrub as a major industrial component of a staple food-producing, permanent crop. One year later I was informed that research has begun at the University in Regina dealing with this plant, Caragana arborescens, as a harvestable protein and biomass crop.
But I think that you'd be far better looking at Michael Phillips' The Holistic Orchard. He focuses on the soil:
Simply having a good OM score indicates that sufficient carbon and nitrogen reserves are on hand. Organic matter at 5 percent provides a potential of 120 pounds per acre of nitrogen yearly.
The majority of nitrogen in any soil needs to be converted from locked organic nitrogen to mineral nitrogen that can be used by the plants. The protein forms of this element in organic matter must first be ammonified, and then a portion of this might indeed be nitrified in order to be taken up by the feeder roots. Fungi and bacteria drive these processes. The available levels of ammonium and nitrates constantly bounce back and forth between immobilization and mineralization as the soil food web in its entirety cycles nutrients.
A fungally dominated soil delivers the right nitrogen to fruit trees and berries, which in turn allows these plants to better resist disease.
What he's saying is that if you build the soil around your trees with hardwood dominated ramial wood chips, you'll have what you need. He does use nitrogen fixing plants when he's thinking about plant allies, in particular comfrey:
The marvel of comfrey from a fruit tree perspective begins with its deep-reaching root system, which effectively mines potassium, calcium, and other untapped minerals. Its leaves and stalks are flush with nutrient wealth, producing a lush plant that blossoms just after petal fall on apple trees in a cascading series of delightful pale purple-pink umbel florets. Bumblebees delight in this subsequent nectar source. As comfrey starts to set seed, it becomes carbon-heavy—and thus top-heavy—and soon falls in every random direction as living mulch, thereby suppressing grass growth and preventing it from becoming the dominant ground cover. A new round of herbal shoots from comfrey’s insistent roots responds to this sunlight opportunity, repeating this same cycle at least two times more in a given year. The circumference of a comfrey circle grows as the mother plant expands outward. The soil here becomes deep brown, even black, brimming with life force. Fruit tree feeder roots find this an irresistible invitation, totally unlike the reception provided by a dense sod where high carbon dioxide levels produced by fine grasses (in the process of root transpiration) proves disagreeable. Comfrey leaves room in the humus for trees to find full mycorrhizal connection. And to think—all you had to do was plant comfrey starts (root crowns) around the anticipated dripline of the tree to launch this self-renewing orchard plan.
A broad mix of species belongs under and within the vicinity of fruit trees. You can make deliberate choices here to reflect a certain look, or you can trust serendipity (enhanced by introduced species left to go to seed) to bring a diverse understory to the fore. Red clover has nitrogen-fixing capability, being a legume, which ties in nicely to comfrey’s need for high nitrogen . . . which in turn will be made available to fruit tree roots in the form of ammonium by the action of soil life. Legumes are noted as well for raising available phosphorus levels. The humble dandelion is especially adept at drawing potassium up. Chicory’s specialty is twofold: This plant accumulates zinc, and, when it dies, the hole left by the decaying root is an act of soil aeration in itself. Other plants like nettle, yarrow, and horsetail contribute similarly to this crescendo of specific nutrients. Are we tuning in to how a diverse understory contributes homegrown fertility to the orchard through organic matter cycled through the soil food web? Minerals are being mined and brought to the surface by this array of taprooted plants, and this will go on for a long, long time.
The emphasis is mine.