Mulch vs plants under trees?

OK I'm confused.  Is planting plants under trees better than mulch - or is this more about not having to replenish the mulch every few years?  I can understand the concept of plants providing living fertilizer as they die - but how does one distinguish between a "weed" plant that competes with the tree versus a beneficial plant - I mean, they are both feeding from the same soil right? 

Plants both feed from the soil and feed the soil.  When plants grow the soil improves.  Maintaining empty mulch at any scale is very labor and energy intensive.  Industrial ag turns to annual application of poisons... so we just pick our weeds.

So what to grow under a tree?  Something with functions....
fruit tree guilds
When to assemble an apple tree guild

Yes plants could compete with each other.  But compete for what, where and when--light, nutrients, water, spring, summer, at what distance?  Plants growing in proximity can also both thrive.  Then again you can always chop the top off a plant that is starting to compete? voila! problem becomes solution.

Some competition is going to be ok since the overall fertility will probably be improved by understory plants.  To determine good combinations, Paul has mentioned some things to look out for.  You can also look at the root system of the trees and plants.  I believe many trees have a good amount of surface roots, which is why grass (which will take up the surface with its roots) is usually not a good companion.

For example comfrey is a very popular forest garden plant because of its deep taproot and the fact that it accumulates nutrients in its leaves and therefore makes a nice mulch too.

I would think: if you wanted to establish a tree, you want to give it a good head start in its environment. So any competition should be controlled.
Mulch could be a safe praxis at the start of the the tree's establishment. Then you efficiently suppress competitors.

A tree nurser here has a nut plantage on a loan. He uses the loan clippings directly for mulch around the tress, to prevent the grasses from taking over. But then he keeps cats and has a falcon, both that catch the mice that in seasons hide under the mulch and eat the bark of his trees.
So, mulch can also be a place for rodents.

An accumulator plant like comfrey sounds like a very good idea. That would certainly bring nutrients into circulation and make them available also to the tree. But if you then used the comfrey for mulch other places, then you would probably over time remove important mineral nutrients from the spot.

Maybe one should start with a lot of comfrey and other accumulators, and then successively to thin it out replacing it by other plants from seed or planted directly.

Generally, both a decaying mulch and a living mulch are going to positively benefit a productive tree.

The living mulch (plants) can serve many functions: shade the soil to reduce water evaporation, build soil with roots, fix nitrogen (legumes), produce biomass to later be used as dry mulch, bring up nutrients from subsoil (dynamic accumulators), fill up niche space (depending on the type of tree the rhizosphere will have open zones that can be tapped into), attract beneficial insects and pollinators, fumigate the soil of nematodes, provide habitat/shelter for invertebrate species, block out unwanted species, and more...

The decaying mulch (wood chips, leaves, etc.) will also serve many functions, especially in the short term: conserve moisture in soil, keep soil warm in winter, block out unwanted species, add organic matter to soil and build soil life, and more...

In the early stages of setting up a polyculture dominated by a productive tree it is worthwhile to bring in available dry mulch to get the system started. Ideally, once the polyculture is established you can just chop and drop mulch, always maintaining both living and decaying mulch.

Elan

i prefer both.

HI, I'm new to the forum.
We have got an old apple tree and I wonder what I could plant underneath,.
I put in some new trees apples plums and the like and I planted them in a zig zag pattern and put gooseberries, josta and currants in between. I put in comfrey root cuttings as well, but they didn't come up so far ( maybe 2 weeks).
I think the trees profits if the plants underneath are not too dominant, however harvesting or pruning is more difficult.