Try cutting the grass close to ground level with a scythe or knife and lay it around the trees, careful not to let anything touch the trunks and then add any other mulch you have; straw, old hay, even stones. Search these forums for fruit tree guilds. They will reward you for your hard work. I'm suggesting pies
We scrap down to the ground with machetes, it takes about 1 minute per tree for us - be we have lots of practice! (more than 150,000 trees)
Cutting the grass and turning it into mulch helps, ideally different ground covers could be introduced to encourage more fungus. Using branches and other woody debris as part of your mulch material will promote the growth of good fungus. Mixing in a little bit (don't need a lot) of forest duff or woody compost will introduce good kinds of fungi to your mulch and eventually (or so the idea goes) soil.
If you have any animals, you can use their grazing to keep the grass down and get some fertilizer at the same time. Just be sure to put guards around the tree (round wire fence cages are commonly used) so that they don't get munched. If you live in an area with deer, that might be a good idea anyway.
Maybe it is a good idea to reduce vegetation at the feet of trees when they are newly planted but to much reduction of the ground cover is not ecological, no ground plants means less organic matter to form soils and less plants to fix carbon . In olive grooves and citrus grooves here, there is such a reduction of grund cover as must do for the soils where these trees are grown and the trees themselves are so prunned as to give very little shade to the earth or leaves to contribute organic matter or a dry leaf mulch that would protect the soil from the suns rays. I think havign total bare soil under olives is new, i think they used t graze animals under the trees before, though they overgrazed and left hhing pretty bare. They certainly fed prunned branches to the sheep it is mentioned as feed o¡in my book on spanish races of sheep. .
sepp holzer sells apple trees with all the plants he can pull up with their roots at their feet. I suppose comfrey some deep rooted plants who know fox gloves gentians, the plants of all those seeds he puts on his land. The tractor carrying the tree carries a has a tree with a good thichk patch of vegetation on the soil pulled up with the roots
The trees i plant live though there is grass at their feet as long as i manage to keep them watered the first summer.
I wonder which is more important the grass covering the ground and stopping surface evaporation if ther is a shower of rain or the water the grass might drink from the soil.
Dry grass would shade the soil reducing th eloss of moisture in summer. you can shade new trees to, i do with branches and shade cloth.
Also vegetation does absorb the wet of rains through their leaves, reducing the loss of water from evaporation. The tree takes it up before it can evaporate off. There was a study done of this with juniper trees.
Other evidence that leaves take up wateris the fact that foliar feeds only get absorbed when the leaves are wet when they are sprayed on or after rains or with dew on the leaf, in ht edays after the spraying, so there is quiet a bit of evidence to prove that wetness gets absorbed by leaves where there is vegetation instead of getting lost through evaporation and grass seems to get so tremendously wet with dew that i wonder if it is not specially good at condensing the humidity in the air, making dew for itself. Any wetness absorbed will be distributed through the plant, that means to the roots that lose water to hot soils, look up hydraulic redistribution trees. So plants will contribute to the humidity in the soil.
Plant roots greatly better the earth, as they die back in it and regrow they leave a lot of organic material in the ground and all plants except the cabbage family have mycorrhyzal fungi that leaves glomalin in the ground that makes soils stick together into crumbs breaking up the heavyness of clays and sticking sands together a bit, so helping with drainage and the amount of air held in soils, air is important to plant roots, also th ebettered soil lets plant roots penetrate the soil better, as well as making the soil easier to work . Google glomalin to read about this.
The clearing of undergrowth in woods means the empoverishment of soils in woods as it reduces the growth that provides organic material, as does the clearing of bushes in woods to reduce fire risk and and the extraction of wood when the trees are cut. If trees lay were they fall their wood would contribute to form soils.
Oaks here in spain are dying of a variety of illnesses collectively called seca, dry, which would point to their defenses having been reduced and hunger is a good reason for a reduction in defenses. Herbicides used without the knowledge of authorities is another.
I think the reduction in health maybe a result of some change in farming, the clearing of undergrowth to reduce competition with the trees from other plants wich maybe was not done so much before. Clearing the undergrowth would mean a great reduction in the amount of organic matter avaliable for soils, so soils with less capacity to absorb and rtetain water and also a reduction of nitrogen in the soil, from the break down of organic matter in the soil.
Spanish evergreen oaks die if they have too much water or nitrogen, they live on poor soils but maybe there is a too poor even for them.
Another idea for helping the oaks that exists nowdays that might be new, that may prejudice them more than it helps them, is the plouging of the ground at their feet in order to break up any crust that might have formed on the soil and so improve the absorption of rain. If there was undergrowth it would break up the soil as it grew up through the soil and died down again. More important this breaking up of the crust would mean distruction of the superficial roots of the oaks, those roots of trees that run horizontal and paralel to the ground just below the soil, and Heidi Guildmeister says that though it is not what we imagine the more superficial roots are impoartant in a dry coutry, they take up the rain of summer showers, and of dew, breaking them would weaken the trees. agri rose macaskie.
I agree with the others who have replied. Cut the grass as it competes for nutrient and water. But here in Scotland our climate is wet and cardboard would disintegrate, so I have used old carpet made from natural fibres as a mulch mat.
Another person here with a wet climate... I'm in N.Ireland.
I use cardboard (usually a couple of layer) however I don't soak it first, but weight it down with manure or other compostable material instead. The tree doesn't get the benefit of this stuff until the following year when the card breaks down. Then I push the remains back to flatten the area round the tree and add yet more card and manure until the tree is established. Of course this works for the few select trees I have time to tend.
A larger planting here used to just get annual treading of the grass. The trees are now 13 years old and have done grand - though perhaps slower off the mark than the cardboarded ones...
Maybe this is the reason you should bring in fungi from the woods to the trees you plant in the grass then you will have a varied community of tree fungi that will help keep a balance between the fungi's that might attack your trees and so save them.
I looked up micorhyzal fungi trying to find a product i could use to put on the roots of my new apples there is a product called mico grow and found that you get one type of mycorrhyzae to seed on ground cover plants and another packet for trees, i think it wa also aanother packet for bushes but i only remaber the fgrass type ones and the tree type ones, so it seems that there are different mycorrhyzal fungi for different plants we know tha tboletus grow on some trees and truffles on others, so the fungi in you praire is there it is what makes glomalin, it is just a different fungi.
Paul Stamets suggests that cauliflower fungi might be good at stopping honey fungi, and he himself experiments with this idea.
He tried growing two fungi in the same petri dish to find out which fungi out grew the other and has found out some fungi are stronger than say honey fungi when it comes to taking over between fungi, while they are not famouse for killing trees, so maybe the reason you need lots of forest funghi around is that the fungi maintain a battle among each other and keep the balance of fungi in the wood it sounds like an episode of gnomes, so the fungi that do for orchard trees may not win out so easily in the middle of a forest.
If I remeber right and i hope i did because i have been using the idea, an easy experiment for me to make because i have turkey fungi in my garden on the dead wood in the garden, turkey fungi is one of the fungi that have been used as a way of doing for harmfull parasitic fungi on trees. I whizzed up turkey fungi in the liquidizer with a bit of water, and mixed the mixture up with clay and painted it on on my apple trees and the apples liked it so much that the two i have that though they have not died have never grown put out a lot of new shoots though on a more badly cancered tree the change is not noticeable. I did this the autumen before last.
It is only an experiment, a risk, though on cankered trees it is not so big a risk as it would be on healthey trees, Paul stamets mentions it a s somthing one man tried and had a success with, he did not say it was proven and sure treatment. I have to read it again to make sure i read it right i dont like writing about things without double chequing. agri rose macaskie.