Hello Katy

We recommend consulting a certified arborist for large trees, valuable trees, or for any root larger than 1.5 inches diameter. These professionals have taken training in care, diseases, pests and passed certification tests. He/she will come on site, properly cut the root, and give a complete diagnosis and a plant care plan, as well. Find certified arborists by zip code here—-

www.treesaregood.org

Some roots should not be removed completely and the arborist will know how to deal with these. Removal does stress the tree so, monitor rainfall received following root removal and provide water equivalent to one inch per week through the growing season, including into fall until the ground has frozen.

Your picture appears to show that the tree was planted too deeply, because there is no root flare showing. This could be why you are seeing suckers appear at the base of the plant. Suckers are also a sign of stressed trees. Your arborist has the special tools to expose the flare and regrade the soil safely, if this is possible.

Here is detailed information on girdling roots. If done incorrectly, there is a risk of the tree falling or dying.

https://hort.ifas.ufl.edu/woody/remove-circling.shtml

This article addresses the root flare, aka root collar-

https://njaes.rutgers.edu/fs099/

I hope this helps!