[1]https://www.motherearthnews.com/organic-gardening/root-devel...
Unfortunately the original publication is not available. And even if it's back, I'm not sure I'd spend $1.9k to check... https://www.amazon.com/Mitteleuropaeischer-Gruelandpflanzen-...
As these diagrams illustrate, a typical tree has roots reaching out at least 3x the radius of the 'root line' myth common among landscapers and construction workers. The truth seems to be more that any damage within that circle affects a pie slice of roots that are doing the real work. Cut a hole that's 18° wide and you can kill up to 5% of the roots.
The trees support the fungi (sugars) and the fungi enable exchange of nutrients and tree-to-tree hormonal signaling of environmental health state. This is useful in enabling speedier responses to pathogens and insects infestation and sharing nutrients across trees (“altruism”). Usually this sharing and communication network is among members of the same species and often the same kinship. I do not know the primary literature on this area, but this is a good introduction:
The Hidden Life of Trees by Wohlleben, Peter
Some of the shapes may say more about the site than the tree.
