Weird questions!

[N/A N/A]

Who owns above the physical land?
- Example: say I have a tree that is rooted in my yard and I hang a birdhouse off a limb that hangs right over my neighbor's property line. Is the birdhouse considered on his property?

Who owns below the land surface?
- Example: if I dig a tunnel that starts on my land but goes under the property line and under my neighbors property (even if it doesn't exit on their property) is the tunnel considered their property?