Howdy,
Mattock is a below ground digging tool(heavy), one edge will chop roots, Pick is easy way to loosen soil, Pulaski is firefighting tool, axe head above ground cutting and root cutting hoe(also used to expose roots and cut with axe head), Trenching shovel, straight edge cuts roots, Tree plant, also helps cut roots.
I find the mattock to be a useful tool and maybe you could find a used one. It takes the same handle as a pick. Digging a trench around the trunk, narrow 4"wide or so, gives you room to work. You could be 3-4ft from the trunk if you wanted. You would be able to plant berries in the trench. I cannot kill blackberries and have to herd them around my place. I would keep my eyes open for tree sprouts between the trench and the tree trunk. A sawzall with metal/wood blade can also be used to cut roots and also to girdle, although because of the narrow blade, I would make more than one cut, 3-5, one above the other, 1 inch or so apart.
https://www.powells.com/book/mycelium-running-how-mushrooms-can-help-save-the-world-9781580085793 Find this book used
https://www.powells.com/book/farming-the-woods-9781603585071, this book also, used
https://fungi.com/
You can now buy chainsaw bar oil that has mushroom spore in it. It may also be a non petroleum natural oil.
Inmate, Natures Asylum, Siskiyou Ward
"Live Simply, So Others may SIMPLY LIVE"