Sheet Mulching over established fruit trees

I have an established Peach tree (about 15' tall) near an old Grape Vine. Both produce fairly well, but I'd like to start planting connected guilds around both.

I live in zone 9b near an old creek bed. My soil is old river-bed: Pretty hard clay with lots of rocks.

I was planning on using Toby Hemmingway's Sheet Mulching method: http://tobyhemenway.com/resources/how-to-the-ultimate-bomb-proof-sheet-mulch/

My concern is that this will choke out the root system of both the peach tree and grape vine.

Does anybody have recommendations on how to begin the guild process without potentially choking out established trees? Is that just too much organic material to stack on top of the roots, or should it be okay?

Also, any recommendations on good guild plants would be welcome

Hi

That is a deep layer it might go anerobic if the soil is wet and you get lots of rain. You might try unschredded leaves mixed with sticks and twigs to block the light without making a layer of slime that cuts the roots off from air exposure. and you could plant the guild with more mature plants that reach above the mulch before you cover the soil. If you don´t have grass growing between them you could just plant the guild plants and pull up the undesireables and lay them on the ground as green mulch i think other than grass most "weeds" are already there benefitting the plant like a polyculture would so just replace them with more usefull similar plants.  

That's good advice, thank you! Unfortunately, there is mainly grass surrounding both. I do have a ton of fallen oak leaves around, so I may try just cardboard, 1-2 inches of compost, and oak leaves as mulch on top.

HI
I live next to a creek too one of my favorite plants is corn flowerd they self mulch (die back to the crown in winter)Produce both early and mid summer flowers on the same plant. They are perennial and indestructable. there are clumps growing in the middle of a meadow and in shade under trees. they smother out any competition even grass. They grow knee high make heaps of biomass in the leaves like comfrey. The flower petals make tasty blue colored tea. Some people consider it medicinal and you can buy it in fancy tea shops here, but i havent looked up its merit.

Done alotta sheet mulching, and never seen it affect an established tree... UNLESS you have a pre-existing water-management issue, or you let the mulch build up against the crown/trunk; then you can get crown-rot and/or adventitious surface roots which can girdle the crown and scaffold roots.

Though I think 8-12" is a little on the thick side.  Of course it depends on the material: hay will be bulkier than arborists' wood chips... Basically the paper/leaves are the primary weed barrier; everything else is either soil amendment or paper-weight.  It will rot down soon enough.

YOu only have to keep away from the tree trunk.