I've been watching the local tree of heaven, and finally, it has put leaves out. It is one of the latest trees to do this, so the second week of May is about right. A nice tree, but unfortunately, it has two bad habits - it secrets toxins from the roots, thus killing plants nearby. And it suckers, meaning that you not only get two for one, you get ten for one. And they are big.
Somebody just told me that they survived Hiroshima, not sure how true this is.
The last thing to emerge are Jerusalem artichokes, still not up yet.