Air spade machines help expose the root flare of a tree so any girdling roots can be located and addressed, and while it will remove mulch in the process, it's typically not used for that (the focus is more on removing soil, so it doesn't have to be dug away in a way that injures roots). It should be fine to remove excess mulch at any point. Roots that may have grown into a mulch mound are likely adventitious roots and therefore not as critical to long-term tree health or stability as roots comprising the flare itself. Using a stiff metal rake (handheld or otherwise) should help, but if the area is a tangle of fine roots, it will be difficult no matter what method is used. Thin adventitious roots can be cut off the trunk, as their loss won't hurt the tree. Thicker roots should be evaluated by a certified arborist or licensed tree expert who can determine what's safe to cut and what is riskier to remove. It's probably best to assess on a case-by-case basis, and we don't have more detailed guidance about when to remove or keep certain diameter roots in that situation.

Miri