I have a pin oak, grass is thinning around under the tree, not a lot of sun gets to the ground. I'm told oak trees produce tannins that along with the lack of sun make the grass go away. So, I'm thinking of trimming off the branches up to about 20-25 feet and planting a sun/shade mix of grass in the next few weeks. Am I on the right track? This is the backyard and there are other trees, not oaks, nearby, 20-30 feet away that the grass is doing well under, I also have a gigantic oak with trimmed branches that the grass is very thick underneath that's about 40 feet away. The thinning has been coming on for a few years now but more pronounced this spring after a mild winter. Thoughts?

http://www.scotts.com/smg/goprod/turf-builder-dense-shade-grass-seed/prod10280026

Thanks, Steve.  I have a similar problem with lots of trees lining the backyard.

Is this all some kind of weird code for "manscaping"

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_cicadas

more reading..
ride safe, and happy arbor day...

Pin oaks have roots that are very close to the top of the soil and even crest it.  They don't have a deep tap root.  They dry the soil out under them severely once summer gets going.  You can aeriate the soil under it before adding more seed and a light amount of additional topsoil. You need shade tolerant seed and plenty of watering.  You'll find you need to re-seed each year.  And of course, as much tree thinning as possible.  We have a 48" across Pin Oak at my rental house.  When we lived there I fought to keep grass under it.  Now that its a rental, it's pretty much dirt.

Is this all some kind of weird code for "manscaping"

Thanks for all the great info, and yes, just about all what you've said is happening. I am planning on trimming soon, all the branches up to about 25 feet are dead anyhow, we treated for grubs last June and are track to be treated again, I've just reseeded with Scott's sun/shade mix, there was another bag there with what they called a "buckeye mix", supposedly specially formulated by Ohio State University, but it was $$$$$$. I dethatched it somewhat and roughed up the soil which was basically moss with patches of grass from my seeding last fall. We are due for our annual Ohio spring Monsoon that others call may, cool, rain every 3rd day, then during the last week, 90 degrees and no rain for 3 months. Thanks all again, some great ideas I never thought of. Oh, Rich, BTW, my camera is from 1977, if you want pics, you gotta come over or wait a few weeks.