Continental walker Matt Green of I'm Just Walkin' graciously provided us with the content of this post: the photograph above and observations below about the trees seen along his walk across the U.S. Thank you Matt.
The only big thing I've noticed in terms of numbers of trees is that there tend to be more trees where it's hillier, but that's because the flatter areas tend to be farmed, and where there are fields, there's not much room for trees. So Pennsylvania had a lot more trees than Ohio and Indiana along my route.
I saw a lot of flowering trees in western PA and Ohio. Fewer here in Indiana, but there are some nice dogwoods blooming now.
I don't have any particular recollections of trees in people's yards. I think there's a whole mix of tree types and sizes.
I've seen a few good treehouses, but other than that there haven't been many visible signs of tree use by people.
I noticed more birds in farm land, but I think that's just because they were more visible there without trees obscuring them, and my brain just records bird calls as background noise. But today I paid a little more attention and noticed lots of audible birds in the areas with more trees, so I'm sure that's been the case throughout.