pick up a ph test kit for soil....
check the results from multiple points around the tree, and at various distances from it...
ammend the soil prior to buying seed.... this is coming from a fellow Buckeye bud.
and a serious plant person, and also, from my wife, who was a propagation manager at the largest ohio nursery...
removing the debris, and aerating the soil, and doing "some" trimming, may help, but its ohio, and we had a soggy freaking year....
I gotta go mow..
careful what seed ya buy, a lot of it is junk.... sold for big $$, and is all relatige to the ph of the soil, moreso than the sun/shade thing.
oh, don't over trim the tree.... we have 17 year locusts hatching this year, soooooo.... they are gonna do some damage, maybe the larvea has had the effect already, and that's the cause for your dead circle... they are rising, and eating all the lush shoots and roots... just tossing this out...
17 years ago, the year after I met my wife, her nursury in Perry Ohio was extremely hit by the hatch, its all good, because it is a natural progression, and tree growth is stimulated by this all, as bad as it sounds... but I recall walking around there, and the Holden Arboretum, and seeing the critters, and various stages of hatch, and damage.. truely interesting.
http://www.cicadamania.com/cicadas/brood-v-17-year-cicadas-due-in-spring-of-2016/now my wife is insisting Grubs.... do you see skunks rooting around there recently...
I kind of agree with her on that also, grubs like those spots, as they really have a "desired" soil content, with exacting moisture conditions... and below a pinoak, man, they would like that for sure...
so, she says for you to send me pictures, and she will tell ya what's wrong...
I think its bugs.. so does she...
I'll add, she says they eat roots, specifically deeper than gras roots live, but I think as they rise, they eat sumpin, maybe a snack, and that would be the early ones eating soft grass roots... meh
https://en.m.wikipedia.org/wiki/Periodical_cicadasmore reading..
ride safe, and happy arbor day...