Living wind I know you know a lot about
permaculture so i am using your question to say what might be important to new comers. You are only asking about a certain area and that absolutely surounnded by trees so what i say here is crazy but then it seems so important to say that
permaculture is about planting a mixture in case any nwewby should get mixed up about the whole system that i am going to leave it.
The permaculture way is a complete design plan, which means it is not about which plant to plant but which combination of trees and all other plants.
I told my brother in law about permaculture and how you combine trees and other types of plants and fungi and he said, "oh they create a ecosystem". Permaculture is about planting lots of trees which is something you seem to already have in the background so maybe you just need the clearing in the
wood for sunloving plants. The permaculture design is to plant lots of different plants and I bet they innoculate with mushrooms too so not only plants and they include animals taht will tidy up eat bad insects and provide manure. SOo plants fungi and animals.
permaculture concentrates on producing food but as other plants can help with the fertility of the system, they also plant things that dont produce food but help with the fertility of the whole.
One sort of tree they plant with fruit and nut trees is pioneer trees, which is to say trees that are so hardy they will grow in hard pan or the desert or the marsh or whatever the problem of that place is.
Another type of tree they plant is
nitrogen fixing trees which may also be pioneer trees. For a marsh or coolish place this would be
alders for a desert, prosopis, for inbetween hot and cool places,
locust trees.
Pioneer trees that can fix nitrogen because they have nitrogen fixing nodules on their roots would fill both requirements that of living in a difficult place and of making the ground more full of nutrients because they fix nitrogen.
Nitrogen fixing trees can usefull because they will grow where there is a shortage of the sort of nitrogen that plants normally need so they can grow in infertile soils like deserts, unless those deserts became deserts from too many chemical fertilisers that cause salting up of the
land, in which case the desert may have plenty of nitrogen in it, but normally deserts lack nutrients.
There is lots of nitrogen in the air but the nitrogen in the air is of the molecule N2, two nitrogen atoms stuck together and plants cant absorb nitrogen in this sort of partnership or molecule, maybe its not a soluble molecule. Some sorts of bacteria rearrange nitrogen molecules, plants like their nitrogen partnered in this weway NH4+, nitrogen with 4 hydrogen atoms and a + electro magnetic charge to it. NH4+ comes from ammonia NH3+ that comes from rotting organic matter, NH3+ broken down and built up by bacteria and actinomuycetes and fungi becomes the N4+ ammonium salts that plants like.
Plants also like NO3- one nitrogen and 3 oxygen atoms stuck together with a minus or negative electro magnetic charge. NO3- comes from bacteria breaking down and building up the NH4+ molecule, first turning it into NO2- and then into the NO3- that plants like to eat.
Recently scientist have found that plants wil take up amino acids too and these have nitrogen in them and you find more and more bottles of fertilisers that say they contain amino acids for sale in garden centres.
The nitrogen rich leaves of nitrogen fixing plants leave the nitrogen on top of the soil when they fall which benefits surrounding plants. As rain is always washing nutrients down into the soil and off to rivers, you need mechanisms that bring back the nitrogen the rain is washing away and leave it on top of the soil to counteract the work of the rain and plants are the mechanisms that do this and that is one reason that having deep medium and shallow rooted plants is an advantage, they can recover the nutrients from many different depths of soil, and deposit them on th esurfacea again.
Accumulators, plants that draw more nitrogen out of the soil than others do deposite may deposite more of this nitrogen they have retrieved in their leaves, plants such as comfrey, and so like the nitrogen fixing plants are usefull for counteracting the work of the rain.
Comfrey is often used as manure, grown in one spot and its cut top carried to where nuitrients are wanted or thrown in the compost heap. Comfrey is an accumulator i presume, it takes up so much nitrogen that its leaves have more nitrogen in it, according to one chart i read, than manure as manure is just mashed plants maybe that is not suprising.
I suppose Bill Mollisons idea of planting it everywhere instead of just in one patch, of planting it under each tree is good, the rain washes nitrogen into the soil everywhere and so we need the plants that complete the cycle pulling it up into their leaves that then drop on the earth leaving the nitrogen on top again everywhere.
Plants also pick up iron, calcium, potasium, phosforus, and other microelements, all the things that the rain washes out of the soil and leave them on top again. So comfrey is used like the trees with nitrogen fixing nodules in their roots, to put nitrogen on top of the soil where the rain is going to take time to wash it away and save you the expense of buying in fertilisers.
Plants are expensive but they are often not an expense you have to replenish every year as fertilisers are.
You could plant trees that grow very fast like poplars, cotton woods. or pines that are going to put a lot of biomass in your soil with their roots and whose trunks will give you material for huggleculture beds without you having to wait too many decades for this wood. agri rose macaskie.