[malfist]

Grafting generally only works within families. I.e. you can't graft a chestnut onto an apple tree.

I doubt many (if any) shade trees would support a fruit.

That said, families can be surprisingly large. Most citrus all come from the same four parent plants and you can mix most of them. Apples and plums are also closely related

[13of40]

Where I live there are a lot of non-fruiting cherry and plum trees planted for shade, so I can imagine people grafting on a fruit bearing branch here and there.

[malfist]

I didn't consider that, thank you for your perspective

[pvaldes]

My bet would be on japanese crabapple