How do you decide where a species belongs in a food forest?

I've hit an interesting design snag in my food forest planning, and I'm curious how others think through these kinds of questions.

One thing I've been wrestling with is where a particular species actually "fits" within the overall design. It's easy enough to know what conditions the plant likes, but that's only part of the puzzle. I'm finding myself asking questions like:

Is this species primarily a productive crop, or is it more valuable as a support species?
Does it belong close to high-value fruit trees, or is it better on the margins?
Should I be thinking about its role over the next 5 years, or where it will fit in 20 years as the system matures?
How much should its ecological function outweigh its yield?

I keep coming back to the idea that in a food forest, every plant can fill multiple roles, but that almost makes the design decisions harder, not easier.

I'm interested in how other designers approach this. Do you start by defining the function you need in a particular space and then find a species to match? Or do you start with a species you really want to include and then build its guild and surrounding system around it?

I'd love to hear how others think through these kinds of design decisions, especially when a plant seems like it could fit in several different places.

My thought process has always been vertical.  What finished form will the plant have.  Where will it fit "geometrically".  Then I decide how much I value its contribution to the system/guild.  (Will it shade or crowd out a higher value/more needed species).  Those priorities do change as the system matures, so looking forward 10 to 20 years, what are my priorities and what trade offs am I willing to make.  

Keeping in mind the 7 layers of a food forest, first ask what layer is its best fit.  Then is this the best species available for that layer given my priorities.  After that it is preference for what it brings to the system.  (fruit, soil health, pollintors, etc...  This is my approach.  Interested to see what other approaches.  

Jack mentioned the Seven Layers of a Food Forest which reminds me of planting by height.

Also when planting by height remember to keep in mind the direction of the sun's path so that shorter plants don't get shaded out.

Also, group like plants together.  Berries with berries, brassicas with other brassicas, etc.

I think the real answer is just time. You can read all the companion planting charts and plan everything on paper, but you won't actually know how things interact until they've had a couple of seasons together. I started mine by grouping things roughly by water needs and sun exposure, then moved stuff around as I noticed what was thriving and what was getting bullied. The species that ended up being most useful in my system weren't even the ones I planned for, they just found their spot.

I find that the ecosystem does 80% of the selection. I plant lots of stuff and the ecosystem decides if it thrives or perishes.

Joseph Lofthouse wrote:I find that the ecosystem does 80% of the selection. I plant lots of stuff and the ecosystem decides if it thrives or perishes.

So true... nature gives the ultimate feedback, showing us through what thrives and what fades away that the ecosystem is often the best judge.

I usually start with something I want to include and how I fit it in depends on whether it is easy/cheap to source and grow, or likely to be difficult. Survival of the fittest is all very well if it's a £5 pack of seeds, but not so good if you're talking about a $50 tree... although I have started a lot of things from seed too! So generally I will try and fit something where I think it will like it, and go for an overall diversity rather than trying to get a complete guild. I rely on my local flora to fill in the niches and chop/drop what gets too much of a good thing (usually grasses and docken for me).
I'd really like more useful groundcover plants and am thinking of propagating more of my perennial kale, but I do have quite a diverse mix of Brassica seed at the moment, so maybe I'll just go wild with that next spring!

I'm with Joe Lofthouse.  

When I got started growing & planting in high- & dry-lands, I had come from thinning & pruning in humid upland forest, reconning backcountry traces across Southwest North America + subsistence mountain valleys & desert oases of Central Asia, + learning from tree specialists (& JR Smith 1929), + collectors like Gabriel Howearth + breeders like Alan Kapuler in person.  

Rule of thumb was 80% survival but regional observations & early efforts inverted that, not to mention Nature likes the final say on each one.  

I started with filling niches & zones, on small sites crowding-in, always overplanting, easier to get something out than in & up, & as I came to better understand population & breeding genetics, putting in or around the widest possible diversity within adapted species & selections.  Starting from seed & with volunteers, descendants can become new varieties, chop & drop, be grafted over, or just eaten.  The food forest becomes repository + source.  

RMore recently right here I learned about the Greeks just seeding waste dryland with discard apricot & olive pits to let them grow & self-thin + -select, plus elsewhere about the Miyawaki method.  It's missed opportunities to simply put everything into a single individual selection & placement then for it to fail.

It depends on so many things. Your climate, you micro climates, age of and how many people you are growing food for, if food production is  important to you.
I live in a warm climate, where I can grow food all year round. Because of that one of my criteria, is that all of my fruits and berries. Can’t be ready at the same time, because it creates bottlenecks in food preservation. Mine are paced out over the whole year. This means that we have fresh fruits and vegetables year round. The advantage of that, is also that your family will eat more fresh. Fresh makes for a healthier diet, and you don’t end up burned out, because you have preserved food until 4am.
I also look at growing conditions and how large and fast, their canopy develops. Some trees also have special needs, so that you have to start developing the ecosystem before you plant them. So you have to add these things into your design.
I am growing raspberries in a microclimate, in the corner of my food forest garden. I grow gooseberries and currants underneath a large pecan tree we have. That tree creates one of the largest micro climate zones in the garden. The soils and air temperature are 17F degrees lower, underneath that tree, which creates conditions where I can grow things we normally would not be able to.
The last thing I recommend is, that if you are growing fruit, you have your family taste it, before you buy the trees producing it. You don’t want to end up with a tree, that no one likes.
I have been playing around this “diagram”. It’s not completely ready yet, but it might give you something to help you decide.