Well, thinking it probably was gophers, if your soil was full of air and you had to tamp it down, chezron. I would take a stake and start poking around in a circular manner, around the plant. See if you can find the tunnel emanating outward. I just use a very long screwdriver. If if is a little hard to push down, then it slips down easily, you know you've found your gopher tunnel. Set a couple of traps, facing back to back from each other, and you'll catch the culprit.

Patty S.

They're sneaky. They will tunnel in, come up from under a plant, eat the roots, and retreat back down into their tunnels. If you get a good spade and dig down and out, you'll find the tunnel. Good luck.
Renee

I wonder Tabebuia rosea is kind of a legume?

No, not a legume. It is a Bignoniaceae.